Science Focus 4 Textbook

>>>

Kerry Whalley Carol Neville Peter Roberson Greg Rickard Geoff Phillips Faye Jeffery Janette Ellis

Sydney, Melbourne, Brisbane, Perth and associated companies around the world

Pearson Education Australia A division of Pearson Australia Group Pty Ltd Level 9, 5 Queens Road Melbourne 3004 Australia www.pearsoned.com.au/schools Offices in Sydney, Brisbane and Perth, and associated companies throughout the world. Copyright © Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2005 First published 2005 All rights reserved. Except under the conditions described in the Copyright Act 1968 of Australia and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner. Designed by Polar Design Edited by Kay Waters Illustrated by Wendy Gorton, Bruce Rankin, Vasja Koman and John Ward Prepress work by The Type Factory Set in Melior 10 pt Produced by Pearson Education Australia Printed in Hong Kong National Library of Australia Cataloguing–in–Publication data: Science focus 4. Includes index. For secondary school students. ISBN 0 1236 0447 8. 1. Science - Textbooks. I. Whalley, Kerry. II. Title. 500

3

considerations

1.3 100% organic 1.4 Maths in chemistry

2

Materials

UNIT

Chapter review

2.1 2.2 2.3 2.4

23

Pure metals and alloys Mining and minerals Corrosion of metals Plastics and fibres Science focus: Nanotechnology 2.5 Soaps Chapter review

24 29 38 43 54 (on CD) 58

Electricity and communications technology

59

3.1 3.2 3.3 3.4

60 68 76 84

Electricity Electromagnetism Waves in communication The communications network Scence focus: Microwaves cook from the inside 3.5 Electronics Chapter review

91 (on CD) 93

4

Genetics

95

UNIT

UNIT

3

10 15 (on CD) 22

4.1 4.2 4.3 4.4

96 106 114 120

Inheritance Human inheritance The molecule of life Controlling inheritance Science focus: Biotechnology and DNA fingerprinting Chapter review

128 133

UNIT

1.1 Writing chemical equations 1.2 More and faster! Rate and yield

5.1 5.2 5.3 5.4 5.5 5.6 5.7

Describing motion Acceleration Newton’s first law Newton’s second law Newton’s third law Gravity Work and energy Chapter review

136 147 153 159 164 169 176 183

6

Health and disease

185

UNIT

2

135

6.1 6.2 6.3 6.4

186 192 196

Health Disease Infectious diseases Transmission and control of infectious diseases 6.5 Non-infectious diseases Chapter review

7

Evolution

UNIT

Chemical reactions

Motion

7.1 7.2 7.3 7.4

The evolution of a theory Evolution unravelled Evidence for evolution Human evolution Scence focus: Putting flesh on old bones: archaeology and Australia today Chapter review

8

Global issues

203 211 221

222 223 232 239 249 255 260

262

UNIT

1

5

8.1 8.2 8.3 8.4

Global warming The ozone layer Nuclear radiation: good or evil? Energy crisis Chapter review

263 272 276 285 293

9

Individual research project

294

UNIT

iv v viii 1

UNIT

Acknowledgements Introduction Syllabus correlation grid Verbs

9.1 Being an individual Science focus: Science can be funny 9.2 My investigation Chapter review

Periodic table Index

295 299 302 308 310 311

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We would like to thank the following for permission to reproduce photographs and text. The following abbreviations are used in this list: t = top, b = bottom, l = left, r = right.

Jim DeLillo: photo by Jim DeLillo, figure 3.4.10.

The Age: figure 2.1.5.

Dr Karl Kruszelnicki: reproduced with kind permission from the author of Great Mythconceptions, HarperCollins, 2004. Article can be found on his website : p. 91.

Andrea Simonato: figure SF 9.1.

NASA: figures 5.5.2, 8.1.1(l), 8.1.1(r), 8.2.6.

Auscape: figures 7.2.1, 7.2.8(l), 7.3.7.

Newspix: Anthony Weate, p. 23; Susan Turner, figure 2.2.4; James Knowler, figure 4.4.7; David Crosling, figure SF 7.7; News Limited, figure 8.4.8.

Australian Associated Press: figure 1.2.1. Australian Nuclear Science and Technology Organisation: figure 8.4.6. Australian Picture Library: figures 4.2.3, 5.2.9; Joel W. Rogers, figure 2.1.3; Sandro Vannini, figure 2.1.4; William Taufic, figure 2.2.9; Penny Tweedie, figures 2.4.4, 2.4.9, 6.1.5, 6.4.5, 7.1.5; Rob Lewine, figure 4.2.1; Nick Rains, figure 6.1.6; Lester V. Bergman, figure 6.3.8; Jonathan Blair, figure 7.3.11; Larry Williams, figure 7.4.9; Pam Gardner, figure SF 7.5; Les Stone, figure 8.1.9; Ric Ergenbright, figure 9.1.3; Jim Sugar, figure 9.2.3. Australian Radiation Protection and Nuclear Safety Agency: figure 8.4.9. Blackmagic Design: figure 3.5.13 Bureau of Meteorology: figure 8.1.7. CSIRO: figures 4.4.11, 8.1.5; ©CSIRO Human Nutrition. Reproduced from 12345+ Food and Nutrition Plan (K. Baghurst et al., 1990) by permission of CSIRO Australia, figure 6.1.3. David Heffernan: figures 3.5.1, 3.5.2, 3.5.5, 3.5.7, 3.5.9. Dorling Kindersley: p. 2, figures 2.2.2, 3.1.8, 3.4.2, 7.3.5.

Pearson Education Australia: Ben Killingsworth, figures 1.3.3, 4.4.4; Tricia Confoy, figure 2.3.1; Elizabeth Anglin, figures 2.4.1, 2.5.2, SF 3.1, 4.4.2, SF 4.3, 6.3.2, 6.5.13, 9.1.4, 9.1.5, SF 9.3; Anna Small, figures 3.4.11, 4.2.11, SF 9.2; Peter Saffin, figures 4.2.4, SF 9.4. Photolibrary.com: figures 1.1.5, 1.2.2, 1.3.12, 1.4.5, 2.2.6, 2.4.12, 2.4.13, 2.5.4, SF 2.2, SF 2.4, SF 2.5, SF 2.6, SF 2.7, p. 59, 3.1.2, 3.2.3, 3.2.12, 3.3.6, 3.3.8, 3.3.10, 3.3.11, 3.4.3, 3.5.14, SF 3.2, p. 95, 4.1.1, 4.1.4, 4.1.6, 4.2.5, 4.3.6, 4.3.7, 4.4.1, 4.4.3, 4.4.9, SF 4.1, SF 4.2, SF 4.7, 5.1.2, 5.1.3, 5.2.1, 5.2.2, 5.3.1, 5.3.2, 5.3.3, 5.3.5, 5.6.3, 5.6.4, p. 185, 6.3.5, 6.3.6, 6.3.7, 6.3.9, 6.3.11, 6.4.1, 6.4.2, 6.4.4, 6.4.7, 6.4.8, 6.4.9, 6.5.1, 6.5.2, 6.5.4, 6.5.7, 6.5.8, 6.5.9, 6.5.10, 6.5.12, 6.5.14, 7.1.2, 7.1.4, 7.1.7, 7.1.9, 7.1.12, 7.1.13, 7.2.2, 7.2.11(b), 7.2.11(t), 7.4.4, 7.4.6, 7.4.7, 7.4.8, 8.3.2, 8.3.8, 8.3.11, 8.4.2, 8.4.7, 8.4.12, p. 294, 9.2.1, 9.2.2. The Picture Source: figure 2.4.10. South Australian Museum: figure 7.3.3. Willandra World Heritage Area Three Traditional Tribal Groups: published with the consent of the indigenous owners, figure SF 7.3(t).

The DW Stock Picture Library: figure 7.1.1. Fairfax Images: figures 5.1.9, 5.7.2. Getty Images: p. 135, figures 5.7.3, 6.1.7, 6.2.2, 6.4.10, p. 222, figures 7.1.3, 7.4.2, 8.3.9. Greg Rickard: figure 2.1.2. Jim Bowler: figures SF 7.2, SF 7.3(b), SF 7.4, SF 7.6.

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Every effort has been made to trace and acknowledge copyright. However, if any infringement has occurred, the publishers tender their apologies and invite copyright owners to contact them.

The Science Focus series has been written for the NSW Science syllabus, stages 4 and 5. It includes material that addresses the learning outcomes in the domains of knowledge, understanding and skills. Each chapter addresses at least one prescribed focus area in detail. The content is presented through many varied contexts to engage students in seeing the relationship between science and their everyday lives. By learning from the Science Focus series students will become confident, creative, responsible and scientifically literate members of society.

Coursebook The coursebook consists of nine chapters with the following features. Chapter opening pages include: • the key prescribed focus area for the chapter • outcomes presented in a way that students can easily understand • pre quiz questions to stimulate interest and test prior knowledge. Chapter units open with a ‘context’ to encourage students to make meaning of science in terms of their everyday experiences. The units also reinforce contextual learning by presenting theory, photos, illustrations and ‘science focus’ segments in a format that is easy to read and follow.

Each PFA has one Science Focus special feature which uses a contextual approach to focus specifically on the outcomes of that PFA. Student activities on these pages allow further investigation and exploration of the material covered.

Each unit ends with a set of questions. These begin with straightforward ‘checkpoint’ questions that build confidence, leading to ‘think’, ‘analyse’ and ‘skills’ questions that require further thought and application. Questions incorporate the syllabus ‘verbs’ so that students can begin to practise answering questions as required in examinations in later years. The extension questions can be set for further exploration and assignment work and include a variety of structured tasks including research, creative writing and internet activities suitable for all students. Extension questions cater for a range of learning styles using the multiple intelligences approach, and may be used for extending more able students.

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Key numeracy and literacy tasks are indicated with icons. Practical activities follow the questions. These are placed at the end of the unit to allow teachers to choose when and how to best incorporate the Prac 1 Unit 1.2 practical work. Cross references to practical activities within DYO the units signal suggested points for practical work. Some practical activities are ‘design-your-own’ (DYO) tasks. Chapter review questions follow the last unit in each chapter. These cover all chapter outcomes in a variety of question styles to provide opportunities for all students to consolidate new knowledge and skills.

The use of the Aboriginal flag in the coursebook denotes material that is included to cover Aboriginal perspectives in science.

Companion Website The Companion Website contains a wealth of support material for students and teachers, which has been written to enhance the content covered in the coursebook.

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Online review questions Auto-correcting chapter review questions can be used as a diagnostic tool or for revision at school or home, and include: • multiple choice • matching • labelling • fill in the blanks.

Destinations A list of reviewed websites is available— these relate directly to chapter content for students to access. Interactive activities These are activities that apply and review concepts covered in the chapters. They are designed for students to work independently, and include: • interactive animations to develop key skills and knowledge in a stimulating, visual and engaging way • drag-and-drop activities to improve basic understandings in a fun and engaging way • QuickTime videos to enhance the learning of content in a visual way.

Homework Book The Homework Book provides a structured program to complement the coursebook. These homework activities: • cover various skills required in the syllabus • offer consolidation of key content and interesting extension activities • provide revision activities for each chapter, including the construction of a glossary • cater for a multiple intelligences approach through varied activities • have ‘Worksheet’ icons in the coursebook to denote when a homework activity is available.

Teacher resource centre A wealth of teacher support material is provided and is password protected and includes: • a chapter test for each chapter, in MS Word to allow editing by the teacher • Coursebook answers • Homework Book answers • Teaching programs.

Worksheet 2.4 Metal experiments

Teacher resource pack Material in the teacher resource pack consists of a printout and electronic copy on CD. It includes: • curriculum correlation grids mapped in detail to the NSW syllabus • chapter-based teaching programs • contextual teaching programs • Coursebook answers • chapter tests in MS Word • Homework Book answers.

Worksheet 4.3 Pedigree analysis

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Science Focus 4

Stage 5 Syllabus Correlation

A fully mapped and detailed correlation of the stage 5 curriculum outcomes is available in the Science Focus 4 Teacher Resource Pack.

chapter

1 23456789

outcomes

Chemical reactions 5.1

Materials

Electricity and communications technology

Genetics

Motion

Health and disease

Evolution

Global issues

Individual research project

▲

▲

5.2

▲ ▲

5.3

▲

▲

5.4

▲

▲

▲

5.5

•

5.6

•

•

5.7

•

5.8

•

•

5.9

• •

5.10 5.11

• • • • • • •

• • • • • • • •

•

• •

5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22

• • • • • • • • • • •

5.23 5.24

•

5.25

•

5.26 5.27 Note:

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• • • • • • • • • • • •

• •

•

• • • • • • • • • •

• •

▲ indicates the Key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Areas.

• • • • • • • • • • • • • •

• • • • • • • • • • • • •

• • • • • • • • • •

• • • • • • •

•

•

• • •

•

Verbs Science Focus 4 uses the following verbs in the student activities. Explain

identify components and the relationships among them; draw out and relate implications

relate cause and effect; make the relationships between things evident; provide the ‘why’ and/or ‘how’

Extrapolate

infer from what is known

Gather

collect items from different sources

Apply

use, utilise, employ in a particular situation

Identify

recognise and name

Appreciate

make a judgement about the value of

Interpret

draw meaning from

Assess

make a judgement of value, quality, outcomes, results or size

Investigate

plan, inquire into and draw conclusions

Justify

support an argument or conclusion

Calculate

determine from given facts, figures or information

List

write down phrases only, without further explanation

Clarify

make clear or plain

Modify

change in form or amount in some way

Classify

arrange or include in classes/categories

Outline

Compare

show how things are similar or different

sketch in general terms; indicate the main features of

Construct

make; build; put together items or arguments

Predict

Contrast

show how things are different or opposite

suggest what may happen based on available information

Critically add a degree or level of accuracy, depth, (analyse/evaluate) knowledge and understanding, logic, questioning, reflection or quality to (analysis/evaluation)

Present

provide information for consideration

Propose

put forward (e.g. a point of view, idea, argument, suggestion) for consideration or action

Deduce

draw conclusions

Recall

Define

state meaning and identify essential qualities

present remembered ideas, facts or experiences

Demonstrate

show by example

Recommend

provide reasons in favour of

Describe

provide characteristics and features

Record

Discuss

identify issues and provide points for and/or against

store information and observations for later

Recount

retell a series of events

Account

account for: state reasons for; report on give an account of: narrate a series of events or transactions

Analyse

Distinguish

recognise or note/indicate as being distinct or different from; note differences between

Research

investigate through literature or practical investigation

Evaluate

make a judgement based on criteria; determine the value of

State

provide information without further explanation

Examine

inquire into

Summarise

express concisely the relevant details

1

Chemical reactions Key focus area:

5.2, 5.7.3

Outcomes

>>> The nature and practice of science By the end of this chapter you should be able to: write the formulas for some common chemicals construct word equations for simple chemical reactions explain why the equations for chemical reactions need to be balanced construct balanced formula equations for chemical reactions identify some compounds that use covalent bonding and others that use ionic bonding

Pre quiz

identify the characteristics of some families of organic compounds.

1 List two states that you are in right now.

2 Write chemical formulas for water, carbon dioxide and hydrochloric acid.

3 What is dephlogisticated air? 4 Can matter be created or destroyed? If so, how?

5 How can you get two flames from a Bunsen burner?

6 Can ethanol be dangerous to your health?

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1

3.1 UNIT

UNIT

context

1.1 Chemical reactions occur around us all the time. A colour change or release of heat are signs that a chemical change is probably taking place. Chemical reactions can be very simple or highly complex. It is easy to record

going any further. It is essential that you can write correct chemical formulas, or none of your equations will be correct. Here are a few facts you may have forgotten:

Equations and formulas Chemical equations take the form: reactants

→ products

The substances present at the start of a reaction are called the reactants, and the new substances formed are called the products. Chemical equations can be written as either word equations or balanced formula equations. For example, the reaction between magnesium and hydrochloric acid may be represented as the word equation: magnesium + hydrochloric acid

→ magnesium + hydrogen chloride

or as a balanced formula equation: Mg + 2HCl

→ MgCl2 + H2

Whichever way we write it, the reaction probably looks something like that shown in Figure 1.1.1. By now you should be able to write the symbols for many elements and the chemical formulas of many common compounds. If you are not yet sure how to do this, refer to Science Focus 3, Chapters 1 and 2, before

H

Cl Cl-

Mg

H H +

+

Mg2+ Cl-

H

Cl

The reaction between magnesium and hydrochloric acid

our observations of chemical reactions, but we also need to be able to represent what is going on at a chemical level. The easiest way to represent reactions is to use chemical equations.

Fig 1.1.1

General: • An element consists of only one type of atom, e.g. Fe, O2 and S6. • A compound consists of two or more different atoms, chemically bonded together, e.g. H2O, H2SO4 and CO2. • Ions are charged particles. Positive ions are formed when metal atoms lose electrons, e.g. Na+, Mg2+ and Al3+. Negative ions are formed when nonmetal atoms gain electrons, e.g. Cl–, S2– and N3–. • A polyatomic ion or radical is a charged particle made up of more than one type of atom, e.g. NH4+, SO42– and CO32–. Pure metals: • The bonding within metals (e.g. iron (Fe), gold (Au) and calcium (Ca)) is called metallic bonding. • All metals are solid at 25°C, except mercury (Hg), which is liquid. Covalent bonding: • Covalent bonding is the sharing of electrons and occurs only between non-metals and other nonmetals, like carbon (C) and oxygen (O), sulfur (S) and hydrogen (H), nitrogen (N) and fluorine (F). • A molecule is composed of non-metals and is the smallest number of atoms that exist bonded together in a stable form. Atoms of the noble gases (Group VIII) exist by themselves and are called monatomic. For carbon dioxide (CO2), a molecule consists of one carbon atom and two oxygen atoms covalently bonded together. This molecular formula represents the number and type of atoms in the compound.

3

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Writing chemical equations • A diatomic molecule consists of two non-metal atoms covalently bonded together. Elements that exist as diatomic molecules are the gases hydrogen (H2), oxygen (O2), nitrogen (N2), fluorine (F2) and chlorine (Cl2), the liquid bromine (Br2), and solid iodine (I2).

The bends When we breathe, oxygen (O2) in the air is absorbed and dissolved into our blood and used for respiration. Nitrogen (N2) is also absorbed and dissolved, but is not used. If a diver who is breathing compressed air rises from the deep too fast, the nitrogen forms bubbles in the diver’s blood. Crippling pain and paralysis (the ‘bends’) often result. Divers often use a mix of compressed oxygen (O2) and helium (He), to remove much of the problem of nitrogen bubbles. It allows a diver to come to the surface twenty times faster than with compressed air.

Ionic bonding: • Ionic bonding almost always involves metals combined with non-metals. Ionic compounds are crystalline solids, unless dissolved in water as an aqueous solution. • The formula of an ionic compound is not a molecular formula, since ionic compounds form large crystal lattices, not molecules. Instead the formula shows the ratio of ions in the crystal. For example, the ionic compound magnesium oxide has the formula MgO. This doesn’t mean that one atom of magnesium and one atom of oxygen move around together; it just means that in any sample of magnesium oxide, the ratio of magnesium ions Mg2+ to oxide ions O2– is 1:1. A small crystal may contain a thousand magnesium ions and a thousand oxide ions, while a larger crystal may contain a million magnesium ions and a million oxide ions. Either way, the formula is simply MgO. Fig 1.1.2

Two different ways of representing the structure of the ionic crystal caesium chloride

Cs+ ion Cs+ ion

4

Cl– ion

Cl– ion

Sometimes more than one of a polyatomic ion is needed in a formula. This is when brackets are used, for example Fe2(SO4)3, Ca(OH)2, (NH4)2CO3. Worksheet 1.1 Writing formulas

Balancing chemical equations Let’s take another look at the reaction between magnesium and hydrochloric acid. Mg + 2HCl

→ MgCl2 + H2

In this equation there are a lot of twos! But does each 2 mean the same thing? The small numbers (like the ‘2’ in H2) are called subscript numbers. These show how many of that type of atom or ion are in the formula. If there is no subscript number after an atom or ion, it means there is only one of that atom or ion in the formula. Brackets with more subscript numbers simply multiply everything inside. Take these examples: • H2O has 2 hydrogen (H) atoms and 1 oxygen (O) atom. • MgCl2 has 1 magnesium ion (Mg2+) and 2 chloride ions (Cl–). • Ca(OH)2 has 1 calcium ion (Ca2+) and 2 hydroxide ions (OH–). The brackets indicate that overall there are 2 hydrogen (H) atoms and 2 oxygen (O) atoms. • Fe2(SO4)3 has 2 iron (Fe3+) ions and 3 sulfate ions (SO42–). The brackets indicate overall that there are 3 sulfur (S) atoms and 12 oxygen (O) atoms. You cannot fiddle with or change subscript numbers. These numbers are determined by the place of each element in the periodic table. If you change subscript numbers then you are actually inventing new chemicals! Water (H2O), for example, is the safe liquid we drink and wash in. H2O2 is also a clear and colourless liquid but is a very strong corrosive bleach called hydrogen peroxide. See what happens if you fiddle Prac 1 p. 9 with subscript numbers? The larger numbers in front of formulas indicate how much of each chemical is being used and how much is being produced in the reaction. These are the numbers we can fiddle with to balance an equation. The Law of Conservation of Matter states that ‘matter can be neither created nor destroyed; it can only be changed from one form to another’. This means that there must be the same number of each type of atom on each side of the equation. The atoms

UNIT

1.1 The easiest way to balance equations is to The hydrogen–oxygen fuel follow steps. To show space o Apoll cells used in the this we will use another missions produced pure water as a by-product. The astronauts example. then used this for drinking. The Sodium carbonate is: on reacti equation for this is added to nitric acid, 2H2 + O2 → 2H2O producing sodium nitrate, water and carbon dioxide. • Step 1: Write the word equation for this reaction. Fuel cells

Putting a ‘2’ in front of a formula means two of that species e.g. 2HCl means

Cl

H

Cl

H

The smaller subscript numbers are different. They show how many of each type of atom are present. H2O represents

O H

H H

CH4 represents

C

H

sodium + nitric carbonate acid

H

H

Fig 1.1.3

Sodium carbonate is Na2CO3 and nitric acid is HNO3.

are simply being rearranged by the reaction. The unbalanced equation for the above reaction is:

Sodium nitrate is NaNO3, water is H2O and carbon dioxide is CO2.

→ MgCl2 + H2

There is one magnesium on each side of the equation, so they are already balanced. However, while there is only one hydrogen atom on the left, there are two on the right. These can be balanced by doubling the amount of HCl we use. A large ‘2’ is added in front of the HCl, giving us two hydrogen atoms on both sides. Mg + 2HCl

sodium + water + carbon nitrate dioxide

• Step 2: Find the formula for each substance in the word equation.

What do the numbers in chemical equations mean?

Mg + HCl

→

→ MgCl2 + H2

This also balances the chlorines. When an equation is balanced, the mass of the products is equal to the mass of the reactants. Nothing has been destroyed and nothing new has been created. All the atoms have just been rearranged. This is known as the Law of Conservation of Mass, and is another way of stating the Law Prac 2 of Conservation of Matter. p. 9

• Step 3: Use these formulas to write an unbalanced formula equation. Na2CO3 + HNO3

• Step 4: Balance each element, one by one, until there are the same numbers of each type of atom on both sides. Sodium (Na): Two on the left, but only one on the right. Put a big ‘2’ in front of the formula for sodium nitrate (NaNO3): Na2CO3 + HNO3

Oxygen (O): Six on the left, but nine on the right. Placing a big ‘2’ in front of the formula for nitric acid (HNO3) solves the problem:

+

O

H

O O

H H

H

H

2H2

+

O2

A balanced equation has the same number and types of atoms on each side of the equation.

→ 2NaNO3 + H2O + CO2

The other way to balance for oxygen would have been to put a ‘2’ in front of the formula for sodium carbonate. This would have solved the oxygen problem, but it would have unbalanced the numbers of sodium and carbon.

O H H

→ 2NaNO3 + H2O + CO2

Carbon (C): One on each side. No balancing required.

Na2CO3 + 2HNO3

H

→ NaNO3 + H2O + CO2

2H2O

Fig 1.1.4

Hydrogen (H): There are now two on each side, so no more balancing is required. • Step 5: Double check the numbers of atoms on each side to make sure your final equation is correct. Na2CO3 + 2HNO3

→ 2NaNO3 + H2O + CO2 5

>>>

Writing chemical equations Reactant side: 2 Na, 1 C, 9 O, 2 H, 2 N Product side: 2 Na, 1 C, 9 O, 2 H, 2 N Problem solved! Sometimes a bit of trial and error is required before you successfully balance an equation. Following the steps above, you should find that Al2O3 + C

→ CO + Al

becomes the balanced equation Al2O3 + 3C

→ 3CO + 2Al

Which state are we in? The reaction between calcium and oxygen, forming calcium oxide, may be represented as: 2Ca + O2 → 2CaO

But what form is each chemical in? Are they solid or liquid, a gas or dissolved in water? In order to complete the picture of the reaction, we use more subscripts to indicate the physical states of the reactants and products. These were briefly introduced in Chapter 2 of Science Focus 3. The subscripts used are: • (s) for a solid substance • (g) for a gas • (l) for a pure liquid Fig 1.1.5

Lights, action! Calcium oxide (quicklime) produces an intense white light when it is burnt and so was used as an early spotlight in theatres. The performers on stage were ‘in the limelight’, a term that is still used for a person who is the centre of attention.

• (aq) to show that a substance is in aqueous solution (i.e. dissolved in water). Including states, the above reaction would look like this: 2Ca(s) + O2(g) → 2CaO(s)

All the details of the reaction are now clear. Two atoms of solid calcium react with one molecule of gaseous oxygen, producing two solid calcium oxide ion clusters. This gives a lot more information than before. From this point on, try to write all your chemical equations The fall of Rome including state subscripts. Lead poisoning probably played a significant part Unless told otherwise, you in the fall of the Roman should always write the states of Empire. Infertility was reactants and products as they caused by drinking wine from leaden vessels. Lead occur at Standard Laboratory was also used as a cure Conditions (25°C and ‘normal’ for diarrhoea. Cosmetics 1 atmosphere pressure). used by ancient peoples For example, at Standard included white lead on the face, mercury sulfide Laboratory Conditions, mercury as lipstick, and arsenic (Hg) is a liquid and sulfur (S) sulfide as eyeshadow; the a yellow solid. They react to ultimate self-poisoner’s make-up kit! form mercury sulfide (HgS), the reaction being: Hg(l) + S(s)

Normally we think of nitrogen as a gas but it can also be cooled down to make it into a liquid.

→ HgS(s)

+

liquid mercury

Hg(l)

Fig 1.1.6

+

solid sulfur

solid mercury (II) sulfide

S(s)

HgS(s)

Compounds have very different physical properties from the elements that made them.

Worksheet 1.2 Writing and balancing chemical equations Worksheet 1.3 Revising chemical equations

6

UNIT

1.1

UNIT

1.1 [ Questions ]

Checkpoint Equations and formulas 1 Chemical equations have three main parts. State the name of each part. 2 State what ‘+’ and ‘→’ mean in chemical equations. 3 List the three main types of chemical bonding.

Balancing chemical equations 4 State the Law of Conservation of Matter. 5 Explain how the Law of Conservation of Matter applies to chemical equations.

Which state are we in? 6 State the symbols and name used to show the state of matter of chemicals in chemical equations. 7 State the Standard Laboratory Conditions of temperature and pressure.

Think 8 Compare the Law of Conservation of Mass with the Law of Conservation of Matter. 9 Compare the use of subscript numbers in chemical equations with the use of larger-sized numbers. 10 Contrast NaCl(s) with NaCl(aq). 11 Identify the molecules in the list below. a CO2 b H2O c NaCl d Li2CO3 e N2 f CaO g Ar 12 Calcium forms the ion Ca2+ and chlorine forms the chloride ion, Cl–. Identify the correct ionic formula for calcium chloride. A CaCl B Ca2Cl C CaCl2 D Ca2Cl 13 Explain why Na2SO4 is not a molecular formula, but H2O is. 14 Identify the equation that is correctly balanced. A HNO3 + MgO → Mg(NO3)2 + H2O B 2HNO3 + MgO → Mg(NO3)2 + H2O C 2HNO3 + 2MgO → 2Mg(NO3)2 + H2O D 2HNO3 + 3MgO → Mg(NO3)2 + H2O

15 Identify the equation that is not balanced. A C5H12 + 8O2 → CO2 + 6H2O B Mg + 2HCl → MgCl2 + H2 C 2Zn + O2 → 2ZnO D 4Al + 3O2 → 2Al2O3

Skills 16 At Standard Laboratory Conditions (SLC), oxygen exists as O2(g). Construct the formula for each of these substances at SLC, including the appropriate state: (aq), (l), (s), (g). a water b carbon dioxide c dilute sulfuric acid d calcium chloride e neon f hydrogen g magnesium carbonate crystals h dilute nitric acid 17 For each of the following substances, state: i the chemical formula ii the type of bonding as metallic, ionic or covalent a magnesium b strontium sulfate c oxygen gas d carbon monoxide e calcium chloride f sulfur dioxide g sodium h argon 18 Modify the following equations so that they are balanced. a P4 + O2 → P2O5 b KClO3 → KCl + O2 c BaO + HNO3 → Ba(NO3)2 + H2O d Pb3O4 → PbO + O2 e Pb(NO3)2 → PbO + NO2 + O2 19 Modify these equations so that they are balanced. Include any missing states. a H2(g) + O2(g) → H2O b Na + Cl2 → NaCl(s) c CaCO3(s) → CaO(s) + O2 d CH4 + O2 → CO2 + H2O(g) e HNO3 + Ca(s) → Ca (NO3)2(aq) + H2 20 Jessica heated some bright blue copper(II) nitrate crystals in a test tube. She noticed brown nitrogen

7

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Writing chemical equations

dioxide gas being produced. A glowing splint held at the top of the test tube re-lit, proving that oxygen gas was also produced. A fine black solid, copper(II) oxide, was left in the test tube. a In this reaction state the reactants and the products. b Construct the word equation for this reaction. c Construct the balanced chemical equation, including states.

Analyse 22 David added some dilute hydrochloric acid to some solid limestone (calcium carbonate) in a beaker. When he weighed the products after the bubbling had stopped, he noticed that there had been a reduction in mass. Explain why his results did not seem to agree with the Law of Conservation of Mass. 23 Solid sodium reacts with oxygen to produce solid sodium oxide. The following experimental data were obtained for the reaction between sodium and oxygen, producing sodium oxide:

21 For each of the following reactions, construct: i the word equation ii the balanced formula equation, including states a Dilute hydrochloric acid reacts with grains of sodium hydroxide. Water and sodium Mass of sodium Mass of oxygen Mass of sodium oxide chloride are the products. reacting (grams) reacting (grams) produced (grams) b Ammonia (NH3) gas is produced when 2.00 0.70 2.70 nitrogen gas is added to hydrogen gas. 3.00 1.04 4.04 c Carbon monoxide gas combines with oxygen to form carbon dioxide gas. 4.00 1.39 5.39 d Solid iron combines with chlorine gas to produce solid iron(III) chloride. a Construct a word equation for this reaction. e Dilute sodium hydroxide solution is added b Construct an unbalanced chemical equation for the to dilute sulfuric acid. Sodium sulfate and reaction, then balance it. water are produced. c Modify the equation to include the states of the f Ammonium nitrate dissolves in water to produce reactants and products. ammonium and nitrate ions. d Explain how the above results prove the Law of g Hydrochloric acid reacts with calcium metal. A Conservation of Mass. solution of calcium chloride is produced, through which rise bubbles of hydrogen.

[ Extension ] Complete the following activities by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 1 and clicking on the destinations button. 1 Investigate green chemistry. a Describe what is meant by ‘green chemistry’. b Outline some examples of what is being done in the study of green chemistry. c Present your information as a poster to convince the general public that green chemistry is important for society and the environment.

8

2 Connect to the CSIRO double helix website and locate the ‘Cool Experiments’ page. a Identify an experiment that involves a DYO chemical reaction and can safely be done at home. b Perform the experiment and present a scientific report on your findings. 3

Complete the tutorial on balancing chemical equations. This may mean spending some time each day over about two weeks working through the tutorial. Record your self-assessment in a log during this time.

UNIT

1.1 Prac 1 Unit 1.1

UNIT

1.1 [ Practical activities ] Studying a reaction

Conservation of mass

Aim To make quantitative observations of the reaction of magnesium metal and an acid

Aim To investigate conservation of mass in a

Equipment Magnesium strips, 1 M sulfuric acid, large beaker, small filter funnel, 100 mL measuring cylinder, cling wrap, gloves, lab coat, safety glasses

Prac 2 Unit 1.1

chemical reaction

Equipment Solid calcium carbonate, 0.5 M hydrochloric acid, 200 mL conical flask, balloon, spatula, 100 mL measuring cylinder, lab coat, safety glasses, access to an electronic balance Fig 1.1.8

inverted measuring cylinder of acid balloon large beaker

water

cling wrap

conical flask

filter funnel

30 mL acid magnesium calcium carbonate

Fig 1.1.7

Method 1 Cut a 4 cm long strip of magnesium. Place it under the filter funnel in the beaker.

Method

2 Fill the beaker with water until it covers the filter funnel.

1 Measure out approximately 0.2 g of calcium carbonate in the conical flask.

3 Fill the measuring cylinder with acid and cover it in cling wrap.

2 Measure out 30 mL of hydrochloric acid into the measuring cylinder.

4 Carefully invert the measuring cylinder on top of the filter funnel. Let the neck of the filter funnel pierce the cling wrap.

3 Place the conical flask, measuring cylinder and balloon on the balance and record their total weight.

5 After the bubbling seems to have stopped, measure the volume of gas collected in the measuring cylinder.

4 Pour the acid into the conical flask and quickly place the balloon on top. 5 When the reaction is complete, re-weigh the flask (with balloon attached) and empty measuring cylinder.

Questions 1 Construct a word equation and the balanced formula equation for this reaction. The products are hydrogen H2 and magnesium chloride MgCl2. 2 Calculate the volume of hydrogen gas that you would expect to have been produced if you had used instead: a an 8 cm strip of magnesium b a 1 cm strip of magnesium

Questions 1 Construct a word equation and balanced formula equation for this reaction. 2 Assess whether your results agree with the Law of Conservation of Mass. 3 If your results do not agree with the Law, propose reasons why.

9

UNIT

1. 2

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context

Some reactions are slow. Others are fast. When we take an antacid, we hope its reaction with the acids in our stomach will be a quick one, since it will relieve our indigestion. Some reactions are so fast, however, that they explode! When solid potassium is added to water, large volumes of explosive hydrogen gas are rapidly The Hindenburg disaster produced, the energy released by On 6 May 1937, the hydrogen-filled the reaction setting the hydrogen Hindenburg airship burst into flame alight. Other reactions like the while landing in New Jersey, USA. The hydrogen was viewed as the culprit rusting of iron, or milk turning for many years. Extensive recent sour, are very slow. How quickly research has, however, discovered For a long time, hydrogen was Fig 1.2.1 a reaction happens can make the that hydrogen did not cause the initial blamed for the Hindenburg disaster. high fire. The actual cause was the difference between it being safe or flammability of the fabric cover. It was dangerous. The speed of a reaction If, for various reasons, only 5 g was made of a cotton substrate with an aluminised cellulose acetate butyrate obtained then the yield was 5/11.3 × 100 = is also important in industry. covering. The observations at the 44%. When producing chemicals a slow scene were consistent with a huge d ignite So how are a fast reaction rate and a good reaction may be unprofitable. aluminium fire. The fabric was e. spher atmo the in ty activi yield achieved? by electrical Speeding up industrial reactions is The hydrogen only exploded once the a very important area of chemistry. fire had burnt through the covering. The electrolytic refinement of copper An especially important Australian produces copper bars like these. Fig 1.2.2 example of this is the production of sulfuric acid.

Industrial reactions For a reaction to be carried out profitably in industry it must occur fairly quickly, and it must give a good yield. The yield is the amount of product obtained, and can be expressed as the percentage of the expected product that is obtained. For example, if 6 g of aluminium reacts according to the equation: 4Al(s) + 3O2(g) → 2Al2O3(s)

we could expect to obtain 11.3 g of Al2O3.

10

Methods commonly used to improve yield include: • carrying out the reaction at a reasonably high temperature. The higher the temperature, the greater the energy of the reactants, making the reaction more likely to occur. • using a catalyst. Catalyst are substances that are not consumed in a reaction, but help the reaction to proceed more quickly. • removing the products as they are formed. • constantly adding reactants to replace Prac 1 p. 13 those used up. Specific reactions may have particular conditions associated with them. Prac 2 DYO p. 14

Sulfuric acid, H2SO4 As an example of an industrial process, we will look at the production of sulfuric acid, a chemical very important to our everyday lives. Sulfuric acid production dates back to the early alchemists. At one stage, concentrated sulfuric acid was called ‘oil of vitriol’ because it was prepared by distilling hydrated ferrous sulfate, FeSO4.7H2O, otherwise known as iron vitriol. Sulfuric acid is the cheapest bulk acid, and is sometimes referred to as the ‘king of chemicals’ because it is produced in such huge quantities worldwide. A country’s sulfuric acid production is considered an excellent indicator of its industrial well-being.

Uses of sulfuric acid In the nineteenth century, the German chemist Baron Justus von Liebig discovered that when sulfuric acid was added to soil, it increased the amount of phosphorus in the soil for plants to use. The current largest single use of sulfuric acid is in making fertilisers, both superphosphate and ammonium sulfate. It is also used to make many organic compounds, including ether, nitroglycerine and dyes. It is important in refining petroleum, making paints and pigments, processing metals and making rayon. It is found in car batteries Prac 3 and used in the superconductor industry for p. 14 cleaning.

Some properties of sulfuric acid • • • • •

Strong acid Corrosive Colourless liquid Density 1.85 g/cm3 Melting point 10.4°C

Fig 1.2.3

UNIT

1.2 Some products made using sulfuric acid superconductors nitroglycerine

car battery dyes rayon

• Boiling point 340°C • Very soluble in water • Dissolving the concentrated acid in water releases a lot of heat (highly exothermic). • Is a dessicant (absorbs water from surroundings) • Can cause severe ‘burns’ to skin • Can cause blindness if it gets in eyes.

Production of sulfuric acid The contact process is the most commonly used method for producing sulfuric acid.

air

Sulfur burner

SO2

Deduster

SO2 + air

molten sulfur Diluter

Converter

Drying tower SO2 + air

SO3 Water

Storage tanks

Heat exchanger Absorption tower Conc. H2SO4

The contact process for the production of sulfuric acid

SO3

Fig 1.2.4

Step 1 Molten sulfur is burned in air to produce sulfur dioxide gas. S(l) + O2(g)

→ SO2(g) 11

More and faster! Rate and yield considerations The O2 comes from air which has been dried with 96% H2SO4 and then had dust particles removed. The yield is increased by making sure that plenty of oxygen is available. Step 2 In the converter, the reaction rate is increased by heating the sulfur dioxide in oxygen. The catalyst vanadium oxide turns it into sulfur trioxide. This is a reversible reaction—it can occur in both directions.

>>> The gases are passed over several catalyst beds, rather than just one, to give them more chance of reacting, thus increasing the yield further. Step 3 In the absorber, oleum (H2S2O7) is produced. Like the other reactions involved in sulfuric acid manufacture, this is exothermic. The energy released can be used to make electricity, which helps maintain the cheap price of sulfuric acid.

2SO2(g) + O2(g) → 2SO3(g)

Fig 1.2.5

SO3(g) + H2SO4(l)

Step 4 Oleum is hydrated to form sulfuric acid.

The converter used for sulfuric acid production

feed gas

420°C reaction bed 1

H2S2O7(l) + H2O(l)

10% SO2 11% O2

heat exchangers

600°C 63% conversion 450°C reaction bed 2 510°C 84% conversion 450°C reaction bed 3 475°C 93% conversion 420°C reaction bed 4 535°C 99.5% conversion

UNIT

1.2

to oleum or intermediate absorber from intermediate absorber to final absorber

→ 2H2SO4(l)

You can see that to make this series of reactions occur faster and with high yield, they are maintained at a reasonably high temperature and a catalyst is used. Products are removed as they are formed, and fresh reactants are injected. This combination gives the industrial process for sulfuric acid production a 99% yield.

Who was the False Geber? The man who discovered sulfuric acid around 1300 did not write under his real name. Instead, he borrowed the name of Geber from a long-dead Arabic alchemist. His real name was never revealed, so this great chemist has always been known as the False Geber.

Worksheet 1.4 Rates of reaction

6 Describe two ways to obtain a faster reaction rate.

Sulfuric acid 7 Sulfuric acid is known as ‘the king of chemicals’. Explain why.

[ Questions ]

8 State three major uses of sulfuric acid. 9 State five properties of concentrated sulfuric acid. 10 Identify the catalyst used in the contact process.

Checkpoint Industrial reactions 1 State an example of: a a fast reaction b a slow reaction 2 Clarify what is meant by the ‘yield’ of a reaction. 3 Clarify what is meant by the ‘rate’ of a reaction.

12

→ H2S2O7(l)

11 State the formula for the following substances: a sulfuric acid b sulfur dioxide c sulfur trioxide d oleum

Think

4 State what the ‘ideal’ yield of a reaction would be.

12 Several catalyst beds are used in the contact process. Explain why.

5 A fast reaction rate and a good yield are particularly desirable for industrial reactions. Explain why.

13 Propose a reason why it is called the contact process.

UNIT

1.2 Skills

14 Explain what happens in the converter, including how the rate and yield are maximised.

18 Identify the elements that make up sulfuric acid. 19 It was expected that 2 tonnes of aluminium was to be obtained from 4 tonnes of ore, but only 1.65 tonnes was obtained. Calculate the percentage yield.

15 Construct balanced equations for each step in the production of sulfuric acid by the contact process. 16 Draw a simplified flow chart to demonstrate the four steps in the contact process. 17 Evaluate the importance of considering the rate and yield in an industrial reaction.

[ Extension ]

2 The airbag in a car works because of a very fast chemical reaction. a Investigate how an airbag works. b Present your findings in a brochure that explains this clearly to car owners.

Investigate 1 Research a chemical reaction of industrial importance. This may include one of the following: • the Haber process for producing ammonia • the Ostwald process for producing nitric acid • the production of margarine • the catalytic converter in car engines and power plants • the Solvay process for producing sodium hydrogen carbonate • the production of superphosphate a Construct a labelled diagram or flow chart outlining the chemical process. b Describe how the reaction conditions are controlled to obtain: i the maximum yield of product ii a fast reaction rate c Outline three significant uses for the product obtained in the industrial process researched. d Present your information in a form that is suitable for display at a science fair.

UNIT

1.2

3

Sulfuric acid and sulfur dioxide can cause problems in the environment. Research what these problems may be and produce a web page or PowerPoint presentation that outlines your information.

Surf 4

[ Practical activities ]

Find out more about the Hindenburg disaster by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 1 and clicking on the destinations button. Write a newspaper article to assess the true chemical nature of the Hindenburg disaster.

acid + Mg

ice water

Rates of reactions 1 Prac 1 Unit 1.2

acid

Aim To investigate the variables that affect reaction rates 1 Time the reaction from the moment the magnesium is dropped into the acid, until there is no magnesium left.

Equipment

Lab coat, safety glasses, gloves, magnesium strips, ice, 1 M HCl, hydrogen peroxide solution, solid manganese dioxide, stopwatch, spatula, 4 test tubes, test-tube rack, 10 mL measuring cylinder, 2 ×100 mL beakers

>>

2 For the second experiment, cool the acid before adding the magnesium.

Fig 1.2.6

13

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More and faster! rate and yield considerations

Method 1 Add a 2 cm strip of magnesium to a test tube. 2 Add 5 mL of acid and time how long it takes for the reaction to finish. The reaction is Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) 3 Place 5 mL of acid in the second test tube and sit it in a beaker of ice water.

7 Add 5 mL of hydrogen peroxide solution to each of two beakers. Hydrogen peroxide gradually breaks down according to the equation 2H2O2(aq) → 2H2O(l) + O2(g) 8 To one beaker, add a very small amount of manganese dioxide. 9 Compare the two beakers and record your observations.

4 Once again, add a 2 cm strip of magnesium and time how long it takes for the reaction to finish.

Questions

5 Add 2 mL of acid and 3 mL of water to a third test tube.

1 Identify factors that made the reactions proceed faster or slower.

6 Add a 2 cm strip of magnesium and time how long it takes for the reaction to finish.

2 Predict the effect of heating the reactions. 3 Identify the role of the manganese dioxide in the hydrogen peroxide reaction.

Rates of reactions 2 Prac 2 Unit 1.2

DYO

Aim To investigate how the surface area affects reaction rate Equipment Lab coat, safety glasses, gloves, marble chips (large and small), powdered calcium carbonate, dilute hydrochloric acid, stopwatch, spatula, 4 test tubes, test-tube rack, 10 mL measuring cylinder, electronic balance

Method 1 Using the equipment listed, design and perform an experiment to test the effect of surface area on the rate of reaction. 2 Construct a graph to display your results.

Questions 1 Use your results to deduce how surface area affects the rate of reacton. 2 Propose how your experiment could be improved.

TEACHER DEMONSTRATION Dehydrating action of sulfuric acid Prac 3 Unit 1.2

Note: This experiment should be performed in a fume cupboard.

Aim To observe the dehydration action of concentrated sulfuric acid Equipment Lab coat, safety glasses, gloves, conc. H2SO4, blue copper(II) sulfate crystals, glucose or sucrose, 2 × 100 mL beakers, 2 spatulas

Method 1 Add 2–3 spatulas of blue copper(II) sulfate crystals to a beaker. 2 Carefully pour about 10 mL of conc. H2SO4 over the crystals.

14

3 Leave for a few minutes. 4 Add 2–3 spatulas of glucose or sucrose to another beaker. 5 Carefully add about 15 mL of conc. H2SO4. 6 Leave for several minutes.

Questions 1 Describe your observations for each experiment. 2 Construct an equation for each reaction.

UNIT

context

. 13 It is common nowadays to see organically grown produce in shops, and see labels that say ‘100% organic’ or ‘made from organic ingredients’. This means the food has been grown by natural methods, avoiding the use of synthetic chemicals such as insecticides. In chemistry, the term ‘organic’ refers to the Organic water chemistry of substances in One brand of mineral water is

currently being marketed as ‘100% organic’. Does this mean that the water was ‘grown’ by natural methods or does it mean that it is full of both living and dead organisms? Marketing campaigns frequently misuse terminology and should be treated with care—for example, a brand of marshmallows is currently being labelled as ‘fat free’. Marshmallows have always been fat free, but are full of sugars, which will be converted to fat if you eat too many!

Organic chemistry Organic chemistry is the chemistry of carbon compounds. Carbon has four outer-shell (or valence) electrons and can covalently bond with up to four other atoms, usually other carbon atoms, hydrogen or oxygen. In this way, carbon is unique

My necklace was once my grandmother! Humans are built from organic substances and are therefore a good source of carbon. Diamonds are one of the forms pure carbon takes. A company in the United States, LifeGem Memorials, is developing a process to exploit these two facts: they intend to convert cremated human remains into diamonds, which can then be worn as jewellery by grieving relatives!

Fig 1.3.1

This person contains many organic compounds, including proteins, lipids and carbohydrates.

which carbon is the main element. Organic substances also contain other elements such as hydrogen, oxygen and nitrogen, but carbon is always the ‘backbone’. Organic substances are the basis of all living things, and of everything that was once living. Deadly rhubarb

in that it is able to form millions of different stable compounds. Compounds like carbon monoxide (CO) and carbon dioxide (CO2) are inorganic compounds, as are methane (CH4) and vinegar (acetic acid, CH3COOH).

Multiple bonds

Rhubarb contains high levels of a deadly organic compound, oxalic acid. Although the edible stalks contain a very low level of oxalic acid, the level in the leaves is high, so high that during World War I, people died from eating them as a vegetable. Beetroot and peanuts also contain significant amounts of oxalic acid, but you would have to eat a lot to overdose. Oxalic acid kills by lowering our blood calcium below the critical level.

Before we go any further, it is important that you understand the difference between single bonds, double bonds and triple bonds. Some information to help you understand the bonds: • A single bond is one pair of electrons being shared between two atoms. • A double bond is two pairs of electrons being shared between two atoms. • A triple bond is—you guessed it—three pairs of electrons being shared between two atoms. Carbon has atomic number 6, which means it contains six protons and six electrons. It has two electrons in the first shell, and four electrons in its outer (valence) shell, giving it an electronic configuration of 2.4. Its four valence electrons place it in Group IV of the Periodic Table. To achieve a stable eight valence electrons, carbon needs to gain four more electrons. It does so by forming four covalent bonds. These can be: • four single bonds, or • two double bonds, or • a single and a triple bond, or • one double bond and two single bonds.

15

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100% organic Fig 1.3.2

Multiple bonds Single bond

Double bond

C C

C

C

O shared pair of electrons

T o shared pairs of electrons

H

H

H

H C

C

H

C

H

H

H

H

Ethane contains only single bonds

H

C

Th shared pairs of electrons

C

C

then the number of hydrogen atoms in the molecule is 2n + 2 = (2 × 2) + 2 = 6

Triple bond

H

n=2

C

Ethene contains one carbon-carbon double bond and four carbon-hydrogen single bonds

C

where n is the number of carbon atoms. Put simply, the number of hydrogen atoms equals double the number of carbon atoms plus two. For example, if the compound contains two carbon atoms,

The molecular formula is therefore C2H6. The alkanes form a related series of molecules called a homologous series. Each molecule in the series is a little bigger than the previous one: each subsequent molecule has an additional –CH2 unit added to it. The first two members in the homologous series of alkanes are methane, CH4, and ethane, C2H6.

H

Ethyne contains one carbon-carbon triple bond and two carbon-hydrogen single bonds

Fig 1.3.4

Methane and ethane

H

Hydrocarbons

H

The simplest organic compounds are hydrocarbons. These are compounds that consist only of carbon and hydrogen. Hydrocarbon compounds are important in our everyday lives. Cars run on hydrocarbon fuels and other hydrocarbons lubricate their engines. The many plastics we use are derived from hydrocarbons.

Fig 1.3.3

These items are all hydrocarbon-based.

Alkanes Alkanes are hydrocarbons that contain only single bonds. They have the general formula CnH2n + 2

16

C

H

H

H H

H methane CH4

H

C

C

H

H

H

C H

H

H H

The first part of the name indicates how many carbon atoms are in the compound. The prefixes used for naming are listed in the table. The second part of the name indicates what type of compound it is. For alkanes, the name ends in –ane. For example, the alkane containing four carbons is called butane. It has the formula C4H10.

H

H C

C

H

H H

ethane C2H6

Prefix

Number of carbon atoms

Meth

1

Eth

2

Prop

3

But

4

Pent

5

Hex

6

Hept

7

Oct

8

Non

9

Dec

10

Crude oil is formed from the remains of plants and animals that lived millions of years ago, and is composed mostly of alkanes. The crude oil is refined (separated into its components) by fractional

UNIT

1. 3 distillation. This means that the crude oil is heated and passed into a column where the components are separated according to their boiling points into the different fractions. Some of the fractions are used as is, while others are cracked to produce shorter-chain alkanes and some new chemicals, alkenes. Cracking involves heating the large molecules in the presence of a catalyst. An example of one of these cracking reactions is shown in Figure 1.3.7. Fig 1.3.7

A cracking reaction

H C

H H

C

H

H

H H C

C H

H

H H C

C H

H C

heat

H H

H heptane H

H

H C

+

C H

H

H H

C

H

H C

C H

H C

H H

H pentane

ethene

Fig 1.3.5

C

H

H

Crude oil forms from the remains of dead animal and plants under the Earth’s crust. Oil rigs are used to extract the oil.

Alkenes cool (25°C)

crude oil in

very hot (400°C)

Fig 1.3.6

Name of fraction

How many carbons in chain?

What is it used for?

Gas

1–4

Fuel

Petrol

4–10

Fuel for cars

Kero

10–16

Fuel for jets

Diesel oil

16–20

Fuel for central heating. Can also be cracked to make smaller molecules

Lubricating oil

20–30

Oil for machines like cars. Can be cracked

Fuel oil

30–40

Fuel for ships and power stations

Paraffin wax 40–50

Waxy papers, candles, polishing

Bitumen

Roads

50 and over

Alkenes contain a double bond and have the general formula CnH2n

This means the number of hydrogen atoms in the molecule is exactly double the number of carbon atoms. The two smallest alkenes are ethene and propene. Alkenes are named in the same way as alkanes, except that their names end in –ene. The major use for alkenes is in making plastics such as polyethene, the material used to make shopping bags. The double bond can break, and the molecules can join end-on-end to form long polymer chains. You will learn more about this in Chapter 2, Materials.

Fractional distillation of crude oil

17

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100% organic Fig 1.3.8

Alkenes

H

H C

C

H

H

H

H

H C

H

C

C

H C H

H H

H

C

H

H

H H

C

Alkynes Alkynes contain triple bonds and have the general formula C2H2n – 2

The number of hydrogen atoms in an alkyne molecule is equal to double the number of carbon atoms minus two. Two alkynes are shown in Figure 1.3.11.

C

H

ethene

propene

C2H4

C3H6

Fig 1.3.11

Alkynes C

H H

H H

C

C

H

CC

H

C

C

H

H

C2H4

Checking out

heat catalyst

H

H

H

C

C

ethyne

propyne

H

H

C2H2

C3H4

Twenty million Australians Part of a polyethene polymer looks like: use nearly seven billion plastic check-out bags every H H H year! Organic chemicals have H H changed the way we live and C C C the resources we use. But ly careful think C C also we must H H H about how we use them. als chemic organic Many H H are not biodegradable. This means they do not break The formation of Fig 1.3.9 down naturally, but instead polyethene for ment environ the stay in hundreds and sometimes thousands of years. Plastic bags in the ocean are a great Plastic bags kill thousands of sea birds and marine cause of concern as they animals every year. Fig 1.3.10 are mistaken for jellyfish by turtles, whales, sea birds and other animals that eat them. Once in the gut the bags slowly and painfully kill the animal. The bag is then released back into the ocean, to kill again when the animal’s body decomposes. Do you use alternatives to plastic bags when shopping?

H

C

C

H

H

C

C

C

H H

The simplest alkyne is ethyne, commonly called acetylene. It is highly reactive due to the presence of a triple bond. If acetylene is burned in a stream of oxygen, very high temperatures (almost 3000°C) are reached. This is why the oxyacetylene torch is used in welding. Other alkynes are used in many manufacturing processes.

Welders use an oxyacetylene torch that reaches temperatures of up to 3000°C.

Fig 1.3.12

Alcohols Alcohols contain the hydroxy group, –OH. The hydroxy group is known as a functional group. A functional group is an atom, or group of atoms, that affects the properties of a compound.

18

The biological molecule cholesterol is an alcohol and an important component of our bodies.

H O

H H

C

C

H

H

H

H

H C

H H H

C

H C

C

H

H H

O

C

H

O C

H

H H May be called 1-propanol or 1-hydroxypropane. The hydroxy group is attached to the first carbon.

May be called ethanol or hydroxyethane.

H

C

H

H H

May be called 2-butanol or 2-hydroxybutane. The hydroxy group is attached to the second carbon.

Combustion of hydrocarbons and alcohols When hydrocarbons or alcohols burn in lots of oxygen, carbon dioxide and water are produced. This is called complete combustion. These reactions also produce heat energy, which may be harnessed, for example in coal-fired power stations, to produce electricity. In complete combustion: ethane + oxygen

2C2H6(g) + 7O2(g)

H

Fig 1.3.13

How to name alcohols

Ethanol is the alcohol in beer, wine and spirits and is the best known of the alcohols. Ethanol has many other uses, however: it is an excellent solvent, is found in many glues, paints and inks, and is used as a reactant to make rubbers and flavourings. One way to produce ethanol is by fermentation of fruit or vegetable matter. This reaction may be represented as: glucose C6H12O6(aq)

→ ethanol + carbon dioxide → 2C2H5OH(aq) + 2CO2(g)

The catalyst for this reaction is yeast. Another widely used alcohol is 1,2ethanediol, better known as antifreeze. The addition of this molecule to radiator fluid lowers the melting point of the liquid so that it won’t freeze in cold weather. Methanol is the main component of methylated spirits. Propanol is used as rubbing alcohol. 1,2,3-propanetriol, known as glycerine or glycerol, is a component of many moisturisers.

UNIT

1. 3

→ carbon dioxide + water → 4CO2(g) + 6H2O(g)

Sometimes, if the supply of oxygen is limited, incomplete combustion may occur. This is usually characterised by a black, smoky flame. In incomplete combustion, two reactions tend to occur simultaneously: ethane + oxygen

2C2H6(g) + 5O2(g) ethane + oxygen

2C2H6(g) + 3O2(g)

→ carbon monoxide + water → 4CO(g) + 6H2O(g) → carbon + water → 4C(s) + 6H2O(g)

Incomplete combustion produces less heat energy than complete combustion and can also produce a deadly pollutant, carbon monoxide gas.

Zero limit for L and P platers Since May 2004 the legal blood alcohol content in New South Wales for all learner and provisional licence holders has been zero. The reason for this limit is that a little bit of ethanol has a huge effect on your body. Low doses affect the reticular system—the primitive part of the brain that maintains consciousness and responsible behaviour. The initial effect you feel depends on how much sensory input you are getting, as this determines which brain pathways are affected. In quiet settings, you may become drowsy. In a social setting, you are more likely to feel stimulated. This is the result of the alcohol affecting the pathways dealing with inhibition. Ethanol is not a stimulant—it is a central nervous system depressant. Even in very small amounts, it slows your reflexes and impairs your judgement.

Incomplete combustion in car engines produces carbon, carbon monoxide and other chemicals that contribute to photochemical smog and air pollution.

Worksheet 1.5 Organic chemistry

Fig 1.3.14

Prac 1 p. 21

19

>>>

100% organic

UNIT

1. 3

[ Questions ]

Checkpoint Organic chemistry 1 Clarify what is meant by ‘organic chemistry’. 2 List the main elements in organic compounds. 3 Explain what is meant by a ‘hydrocarbon’.

15 Complete the table by identifying the molecule or its formula. Molecule name

Molecular formula

Pentane C4H8

Multiple bonds

C10H18

4 Contrast single, double and triple bonds.

Hydrocarbons 5 List two examples of hydrocarbons that have: a single bonds only b a double bond c a triple bond

Hexene Octane C3H8 Propyne

6 List five important hydrocarbon products. 7 Explain what is meant by a ‘homologous series’.

Alkanes, alkenes and alkynes

16 Fractional distillation separates the alkane fractions in crude oil. Outline how this is achieved.

8 Identify the three homologues series of hydrocarbons.

17 State the name of the alcohol we drink.

9 State the name and formula for the: a first three alkanes b fourth alkene c first alkyne d polymer made from ethene

18 State another name for: a antifreeze b acetylene c methylated spirits 19 Identify the products formed from:

10 State the purpose of: a fractional distillation b cracking alkanes

Alcohols 11 Identify the special functional group that alcohols contain.

Combustion of hydrocarbons and alcohols 12 Distinguish between complete and incomplete combustion.

Think 13 Identify one carbon-based compound that is not an organic compound. 14 It is not possible for the molecules methene and methyne to exist. Account for this fact.

a the complete combustion of methane b the incomplete combustion of methane 20 Compared with the blue flame of a Bunsen burner, the yellow flame is relatively cool and very dirty, leaving a layer of black carbon on anything heated in it. Propose reasons why two flames can be so different when they burn the same gas.

Analyse 21 a Identify the reactants and the products in the fermentation equation. b State two uses for fermentation. 22 Explain the meaning of the statement: ‘Fermentation is catalysed by yeast’. 23 Evaluate complete and incomplete combustion in terms of their efficiency in releasing the energy in fuel, and their effect on the environment. 24 Discuss the importance of organic chemistry for society.

20

UNIT

1. 3 [ Extension ] Investigate 1 Carbon compounds play an important role in our everyday life. Research information on ten useful carbon compounds. For each compound: a State the correct chemical name and common name. b Construct a model. c Describe one significant use.

UNIT

1. 3

ACTIVITY Making molecules Use a molecular model building kit to construct models of some alkanes, alkenes, alkynes and alcohols. Draw and name the models you make.

[ Practical activity ] Complete and incomplete combustion

Prac 1 Unit 1.3

Aim To examine the products of complete and incomplete combustion Equipment

Ethanol, Pasteur pipette, kerosene with wick, lab coat, safety glasses, heat mat, watch-glass, candle

Method 1 Light the candle and note things like the colour of the flame and any sign of soot. 2 Put a few drops of ethanol on a watch-glass and light it carefully. Observe the flame. 3 Light the kerosene burner and observe the flame.

Questions

ethanol

kerosene

1 Describe any evidence observed for: a complete combustion b incomplete combustion 2 The molecular formula of ethanol is C2H5OH. Kerosene is a mixture of hydrocarbons with an average formula of C12H26. Explain the difference in the way these compounds burned, in terms of their formulas.

Fig 1.3.15

3 Is the burning of petrol in cars an example of complete combustion or incomplete combustion? Justify your answer.

21

UNIT

>>>

context

1. 4 In any reaction billions of atoms, ions and molecules are colliding with each other and rearranging each other. A single drop of water, for example, contains billions of water molecules and a beaker of water has many, many more. When chemists run an experiment, they deal with very large numbers of atoms, ions and molecules and not just single atoms or small groups of them. The numbers involved are

The mole If you were asked how many eggs are in a dozen, you would of course say 12. We use a dozen instead of counting individual eggs, so three dozen is 36 eggs, 10 dozen is 120 eggs and so on. The mole also stands for a group of things, although a mole has many more things in it than a dozen. The mole in chemistry has nothing to do with small, furry, burrowing animals but instead stands for a huge number, called Avogadro’s number. This number is an incredibly large 6.02 × 1023, or 602 000 000 000 000 000 000 000 or 602 thousand billion billion! There would be 6.02 × 1023 eggs in a mole of eggs, and a mole of people means 6.02 × 1023 people. This is well over a thousand billion times the current world population! In chemistry, a mole of carbon atoms would contain 6.02 × 1023 carbon atoms and a mole of water would have 6.02 × 1023 water molecules in it. The mole is useful in chemistry because it gives us a number of atoms or molecules that we can actually see and measure out. A single atom or molecule is far too small to work with.

so huge that a new way of counting is needed. This is where the mole comes in. The maths involved in chemistry is tricky at first, but very useful once you get the hang of it!

mole of carbon atoms must be 12 grams. The mass of one mole of oxygen atoms is 16 grams. Likewise, if we weighed out 127.6 g of tellurium (Te) then we would have a mole of tellurium atoms.

Fig 1.4.1

Typical information from the periodic table. Some periodic tables may be arranged slightly differently.

atomic number

atomic mass (the mass in grams) of 1 mole of these atoms

element symbol element name

Weighing a mole The periodic table on page 310 of the Science Focus 4 coursebook includes all the details of each element. It also includes the atomic mass (sometimes called the atomic weight) of the element. The atomic mass is the mass in grams of a mole of those atoms. For example, the atomic mass of carbon C is 12, so the mass of one CD2

How big is a mole? A mole of cane toads would cover an area the size of Queensland with a layer of amphibians many kilometres thick! Maybe we should call it a ‘toad’ instead!

Fig 1.4.2

Masses in a reaction

mercury + sulfur

→ mercury sulfide

→ 1 mole HgS(s)

or, using the atomic masses from the periodic table on page 310 of the coursebook: 200.6g Hg(l) + 32g S(s)

→ 232.6g HgS(s)

In words, this means that 200.6 g of mercury will react with 32 g of sulfur to produce 232.6 g of mercury sulfide. Let’s look at another reaction, this time between gallium and oxygen. Its word equation is: gallium + oxygen

e.g. calculate the formula mass of C2H6O2 This is made up of: 2 carbons 6 hydrogens 2 oxygens

2 carbons

2 oxygens

6 hydrogens

The formula mass is then:

= (2 × 12 g/mol) + (6 × 1 g/mol) + (2 × 16 g/mol) = 62 g/mol

→ HgS(s)

This tells us that one atom of mercury reacts with one atom of sulfur to form one ion cluster of mercury sulfide. It also tells us that one mole of mercury atoms would react with one mole of sulfur atoms to produce one mole of mercury sulfide. So: 1 mole Hg(l) + 1 mole S(s)

CALCULATING FORMULA MASSES

(2 × atomic mass of carbon) + (6 × atomic mass of hydrogen) + (2 × atomic mass of oxygen)

This formula equation is already balanced: Hg(l) + S(s)

Fig 1.4.3

Calculating formula masses

The mole is useful because it allows us to use the periodic table and balanced chemical equations. We can calculate exactly what mass of a reactant is required for a reaction and how much product the reaction will produce. As an example, let’s look at the reaction of liquid mercury with sulfur powder to form mercury sulfide. The word equation is:

UNIT

1.4

→ gallium oxide

The mass of 1 mole of a compound is called the formula mass. To calculate formula mass, simply break the substance down into its elements. For example, ammonium carbonate has the formula: (NH4)2CO3. This is made from 2 nitrogen atoms, 8 hydrogen atoms, 1 carbon atom and 3 oxygen atoms. From the periodic table, the atomic masses of these elements are:

Did Lecoq crow? For a scientist to name a new discovery after himself is simply not done. The element gallium was discovered and named in 1874 by Frenchman Paul Emile Lecoq de Boisbaudran. The name ‘gallium’ came from Gallia, the Latin name for France. But gallus is rooster in Latin, while ‘le coq’ is French for rooster. A coincidence, or was this Frenchman cleverly putting his personal stamp on his find?

The balanced chemical equation is: 4Ga(s) + 3O2(g) → 2Ga2O3(s)

In other words, four gallium atoms react with three molecules of oxygen gas to produce two ion clusters of gallium oxide. It also tells us that: 4 moles Ga(s) + 3 moles O2(g)

→ 2 moles Ga2O3(s)

Unlike the example above, here we need to do some calculations for masses: 4Ga(s) (69.7 g × 4) 278.8 g

+

3O2(g) (16 g × 6) 96 g

→

2Ga2O3(s) (69.7 g × 4) + (16 g × 6) 374.8 g

This means that 278.8 g of gallium reacts with 96 g of oxygen to give 374.8 g of gallium oxide, or: 278.8g Ga(s) + 96g O2(g)

→ 374.8g Ga2O3(s)

Element

Symbol

Atomic mass (grams)

Nitrogen

N

14

Hydrogen

H

1

Carbon

C

12

Oxygen

O

16

Hence, the formula mass = (14 g × 2) + (1 g × 8) + (12 g × 1) + (16 g × 3) = 96 g This means that one mole of (NH4)2CO3 has a mass of 96 grams.

Taking it a step further … Let’s look at the combustion of methane. CH4(g) + 2O2(g)

Prac 1 p. CD7

→ CO2(g) + 2H2O(l)

Formula mass of methane (CH4) = (12 g × 1) + (1 g × 4) = 16 g CD3

>>>

Maths in chemistry!

Dephlogisticated air

Formula mass of oxygen (O2) = 16 g × 2 = 32 g Formula mass of carbon dioxide (CO2) = (12 g × 1) + (16 g × 2) = 44 g Formula mass of water (H2O) = (1 g × 2) + (16 g × 1) = 18 g Fig 1.4.4

The combustion of methane

O H

H O

H H

C H

H

O O

+

H

H O

+

O O

C

O

This equation shows that 1 mole of methane molecules (16 g) reacts with 2 moles of oxygen molecules (2 × 32 g = 64 g), producing 1 mole of carbon dioxide molecules (44 g) and 2 moles of water molecules (2 × 18 g = 36 g). Another way this could be written is: 16g CH4(g) + 64g O2(g)

→ 44g CO2(g) + 36g H2O(l)

The mass of reactants is 80 g and so is the mass of products: the Law of Conservation of Mass is obeyed. Let’s say that we only have 8 grams of methane, and not 16 g as assumed in the equation above. The formula mass of methane is 16 g so this is equal to 8/16 or half of a mole. Half a mole of methane will only need half the oxygen and will obviously only produce half the amount of carbon dioxide and water, i.e.: Mass of oxygen used = 1/2 × 64 g = 32 g Mass of carbon dioxide produced = 1/2 × 44 g = 22 g Mass of water produced = 1/2 × 36 g = 18 g Getting the hang of it? Let’s try another example to make sure. Hydrogen sulfide reacts with chlorine gas to give hydrogen chloride gas and solid sulfur. The balanced chemical equation for this reaction is: H2S(g) + Cl2(g)

CD4

→ 2HCl(g) + S(s)

Fig 1.4.5

A portrait of Joseph Priestley

Joseph Priestley first isolated oxygen in the eighteenth century, calling it ‘dephlogisticated air’. Priestley was an English clergyman and was dubbed ‘Dr Phlogiston’ by newspaper reporters of the day. He was delighted with the effects of breathing his pure oxygen, dephlogisticated air. He wrote that ‘my breast felt peculiarly light and easy for some time afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it’. Unfortunately, the mice died soon after in Priestley’s experiments. As predicted by Priestley, breathing pure oxygen became fashionable for a short time in the early 2000s, particularly in California, USA. Patrons of ‘oxygen bars’ would be hooked up to breathe bottled oxygen.

Using the atomic masses from the periodic table, the formula masses are found to be: H2S = 34 g Cl2 = 71 g HCl = 36.5 g S = 32 g In terms of masses we have: H2S(g) 32 g

+

Cl2(g) 71 g

→

2HCl(g) + S(s) 2 × 36.5 g 32 g

Another way of writing this could be: 32g H2S(g) + 71g Cl2(g)

→ 73g HCl(g) + 32g S(s)

But what if we don’t want 32 g of sulfur, but only want to produce, say, 4.5 g? How much of each reactant will we need to mix? Mass of one mole of sulfur = 32 g We don’t need one mole of sulfur, but need only a fraction of a mole. The fraction of sulfur produced = 4.5/32 mole. So we only need this mass of hydrogen sulfide reacting: = 4.5/32 × 34 g = 4.8 g The mass of chlorine reacting needs to be: = 4.5/32 × 71 g = 10 g

Breaking down formulas If you take a look at the formula for carbon dioxide, you can see that 12 g of its formula mass comes from

carbon, and the rest comes from oxygen. Calculated as a percentage of the total mass of 44 g we get: Percentage of carbon in carbon dioxide = 12/44 × 100 = 27% Percentage of oxygen in carbon dioxide = 32/44 × 100 = 73% Carbon dioxide can be formed in many ways. For example: C(s) + O2(g)

or

→ CO2(g)

2CO(g) + O2(g) → 2CO2(g)

Whichever way carbon dioxide is formed, it will always contain the same proportions of carbon and oxygen. This is called the Law of Constant

UNIT

1. 4 Proportions: this simply states that a compound will always have the same proportions of each element, regardless of how it was made.

10 Iron reacts with sulfur, producing iron(II) sulfide. a Given that iron(II) is Fe2+ and sulfide is S2–, construct the formula for the compound iron(II) sulfide. b Construct a balanced chemical equation for this reaction. c 55.9 g of iron completely reacts with sulfur. Calculate the mass of sulfur needed and the mass of iron(II) sulfide that will be produced.

Skills 11 Using the following equation:

UNIT

1. 4

2H2(g) + O2(g) → 2H2O(l)

[ Questions ]

Checkpoint The mole 1 Clarify what is meant by the term ‘mole’ in chemistry. 2 Outline why the ‘mole’ is used instead of individual atoms in chemistry.

Masses in a reaction 3 The large numbers that appear in front of compounds are the only ones we can alter to balance a chemical equation. Explain how these numbers relate to the number of moles of each chemical taking part in the reaction. 4 The formula mass of water is 18 g. Explain how this was calculated.

Taking it a step further 5 Explain how the mole ratios of reactants and products can be used practically in chemistry. 6 The Law of Conservation of Mass is obeyed in chemical reactions. State how the mole can be used to show this.

calculate a the number of moles of each reactant required b the number of moles of water produced c the masses of each reactant required and the expected mass of the product 12 Use the information from the periodic table on page 310 of the coursebook to calculate the formula mass of: a glucose, C6H12O6 b calcium nitrate, Ca(NO3)2 c hydrogen peroxide, H2O2 d sodium phosphate, Na3PO4 13 Given that the formula of lead oxide is PbO2 calculate the masses missing in the table below. Mass of lead reacting (g)

Mass of oxygen reacting (g)

Mass of lead oxide produced (g)

2.00 4.00 6.00 8.00

Breaking down formulas 7 Outline how the percentage of carbon in carbon dioxide can be calculated. 8 Clarify what is meant by the ‘Law of Constant Proportions’.

Think 9 Calculate the number of each in the following examples: a socks in a pair of socks b eggs in a dozen eggs c gold atoms in a mole of gold d H2O molecules in a mole of water e dozens of eggs in a mole of eggs f pairs of socks in a mole of socks

14 Calculate the percentage by mass of each element in potassium hydrogen carbonate, KHCO3.

Analyse 15 Consider these two reactions: Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) In a flask, 2.5 g of calcium reacted with sufficient hydrochloric acid. In another flask, 2.5 g of magnesium reacted with sufficient hydrochloric acid. a Identify the common product from both reactions.

CD5

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Maths in chemistry!

b Which flask would produce more gas? Justify your answer. (Hint: Think about how many moles of each metal there are at the start.) 16 Copper(II) carbonate (CuCO3) decomposes when heated, producing copper(II) oxide (CuO) and carbon dioxide (CO2). a Construct a formula equation for this reaction and balance it. b If 6 g of copper(II) oxide is produced, calculate the mass of copper(II) carbonate that must have reacted. 17 When methane gas (CH4) burns in oxygen (O2), carbon dioxide and water vapour are formed. a Construct a balanced formula equation for this reaction. b Calculate the minimum mass of oxygen needed for 4 g of methane to completely burn.

18 Nitrogen forms many different compounds with oxygen. One of these was found to contain 28 g of nitrogen for every 64 g of oxygen. a Calculate how many moles of nitrogen and of oxygen this is equivalent to. b Identify the probable formula of this compound. 19 Is it cheaper to buy sodium carbonate (washing soda) as the anhydrous (waterless) salt Na2CO3 at $2.00 per kilogram, or as the decahydrate salt, Na2CO3·10H2O, at $1.00 per kilogram? Justify your answer. 20 A student produced a compound that he believed was Al2O3. He found that his compound was 45% aluminium and 55% oxygen. Is it Al2O3? Justify your answer. 21 Sarah conducted an experiment where she burned 0.3 g of magnesium in oxygen. From her results she calculated that 0.7 g of magnesium oxide was produced. Her prac partner, Stephen, said that was impossible. Decide which of them is correct, and justify your answer.

[ Extension ] Investigate 1 Research information to discover how scientists have contributed to the understanding of maths in chemistry. a Describe how Amadeo Avogadro came to have a very important number named after him.

b Antoine Lavoisier deduced the Law of Constant Proportions. Explain how he did this. c Outline the contribution of one other chemist in this area. 2 Estimate how many people are alive in the world today. Is this equal to, more than, or less than a mole of people?

ACTIVITY Reacting ratios The following table shows the results of an experiment in which various masses of the fictional metallic element mysterium, symbol M, were reacted with sulfur, producing mysterium sulfide: xM(s) + yS(s) → MxSy(s) 1 List the reacting masses of sulfur in the table. 2 Construct a line graph of the mass of mysterium reacting (vertical axis) against the mass of sulfur reacting (horizontal axis). 3 Justify whether this graph proves the Law of Constant Proportions. 4 Explain why logically the graph should pass through the origin. 5 Use rise/run to calculate the slope or gradient of the graph. 6 Construct an equation for the straight line in the graph.

CD6

Mass of mysterium reacted (g)

Mass of sulfur reacted (g)

1.00

1.41

2.00

2.82

3.00

4.23

4.00

5.64

5.00

7.05

6.00

8.46

7.00

9.87

Mass of mysterium sulfide produced (g)

UNIT

1. 4 Prac 1 Unit 1.4

UNIT

1. 4 [ Practical activity ] Method

TEACHER DEMONSTRATION Reacting amounts

1 Clean the magnesium strip with the sandpaper. 2 Curl the magnesium strip and place in the crucible. Place the lid on, and weigh it.

Aim To calculate the mass of the product that should be obtained from reacting magnesium in air and compare with experimental data Equipment 5 cm magnesium strip, crucible with lid, tripod, Bunsen burner, pipe clay triangle, electronic balance, heat-proof mat, tongs, sandpaper, gloves, safety glasses, lab coat

3 Place the crucible on the pipe clay triangle over the Bunsen burner. DO NOT LOOK AT THE BURNING MAGNESIUM DIRECTLY OR ALLOW STUDENTS TO VIEW DIRECTLY. 4 Heat it until combustion starts. If necessary, lift the lid slightly from time to time to keep the combustion going. 5 When the combustion is complete, let the crucible cool, then reweigh it.

crucible, with lid, containing magnesium

Bunsen burner

Questions

pipe-clay triangle tripod

1 Constuct a balanced equation for the reaction of magnesium with oxygen, O2, producing magnesium oxide, MgO. 2 Record the mass of magnesium that reacted, and the mass of magnesium oxide produced. 3 Calculate the mass of magnesium oxide that you should have obtained from this amount of magnesium.

heat mat

4 Compare the theoretical mass with the actual mass. 5 Propose reasons why the theoretical and actual mass are probably close, but not exactly the same.

Fig 1.4.6

CD7

>>> Chapter review [ Summary questions ] 1 Clarify what the Law of Conservation of Mass means with regard to reactants and products. 2 Explain the purpose of using a chemical equation. 3 List the possible states in which chemicals may exist and list the symbols used for them in an equation. 4 Write a chemical equation demonstrating the following features: reactants and products, states of each substance, correctly written formulas, and numbers balancing the equation. 5 Define the term ‘SLC’. 6 State one thing that could make a reaction go faster, besides using a catalyst. 7 State the percentage yield obtained in the manufacture of sulfuric acid. 8 Summarise the four steps in the production of sulfuric acid. 9 Using equations, outline how the yield and rate are controlled in the contact process. 10 List three properties and uses of sulfuric acid. 11 Use an example to help define the term ‘homologous series’. 12 List five important uses for organic compounds.

[ Thinking questions ] 13 Assess whether a fast reaction rate guarantees a good yield. 14 Evaluate the need to consider rate and yield in industrial reactions. 15 Which of the following two formulas is a molecular formula? SO2 or Na2SO4 Justify your answer. 16 Modify the following chemical equations so that they are balanced. a Al(OH)3 + HNO3 → H2O + Al(NO3)3 b H2O + K → H2 + KOH 17 Describe organic chemistry.

22

18 Draw diagrams to demonstrate the molecular structure of ethane, ethene and ethyne. 19 An organic molecule has five carbon atoms. State its name if it is an alkane, alkene or alkyne. 20 Describe how a polymer is made from ethene.

[ Interpreting questions ] 21 Extrapolate in order to complete this word equation: magnesium + hydrochloric acid → 22 Describe in words what these equations are showing: a 2Na + 2H2O → H2 + 2NaOH b CuO + 2HNO3 → Cu(NO3)2 + H2O 23 Solid lithium carbonate reacts with dilute hydrochloric acid to produce a salt, water and carbon dioxide. a Identify the likely salt produced. b Construct a word equation for the reaction. c Construct a balanced formula equation for it, with subscripts indicating the states of each chemical. 24 For each of the reactions below, construct: i the word equation ii the balanced formula equation, including states a Dilute hydrochloric acid reacts with a lump of potassium hydroxide to produce water containing dissolved potassium chloride. b Sulfur dioxide is added to oxygen, producing sulfur trioxide gas. c Solid magnesium combines with chlorine gas to produce solid magnesium chloride. d Silver nitrate solution is added to sodium chloride solution, producing sodium nitrate solution and a precipitate of silver chloride. 25 Contrast complete and incomplete combustion. 26 Write the word and formula equations for the complete combustion of propane. 27 a Outline the process of fermentation. b Discuss the importance of fermentation as a chemical reaction. Worksheet 1.6 Chemical reactions crossword Worksheet 1.7 Sci-words

>>>

2

Materials Key focus area

>>> The implications of science for society and the environment

relate the uses of substances to their properties explain how materials such as metals and plastics have changed our world construct word equations for the rusting of iron and the corrosion of aluminium

Outcomes

relate the properties of substances to their structures

5.4, 5.7.3, 5.11.1, 5.11.2, 5.12

By the end of this chapter you should be able to:

balance formula equations for the rusting of iron, the smelting of iron, and the electrolysis of sodium chloride explain how metals can be protected from corrosion discuss the impact of mining on Australian society and the environment explain why conservation and recycling of materials are important to our continued well-being.

nugget but sodium can’t?

2 What is slag and what has it got to do with iron?

3 Why do plastic objects often have a ‘bump’ or seam?

4 Why do we feel wet and clammy on hot days if we wear nylon but not if we wear cotton?

5 How does Thorpie’s Speedo swimsuit help him go faster?

Pre quiz

1 Why is it that gold can be found as a

>>>

UNIT

context

2.1 The metals gold and silver have been much prized since primitive times. Copper, its alloy bronze, and later iron and its alloy steel, replaced the stone spearheads and axes of primitive humans, improving their chances when hunting and waging tribal fights. Each newly extracted metal allowed technology to change. And society changed with them.

Properties of metals Most metals are very dense, because metal atoms pack tightly together when they combine. Metal atoms also have low electronegativity, meaning that they have very little control over their outer-shell electrons. These electrons move freely throughout the metal without being bound to any one atom. This provides

free electrons, not bound to any single atom

Very few metals can be used as pure elements because they are generally too soft to be made into anything useful. Copper and aluminium are two of only a handful of metals that can be used in their pure form.

multidirectional bonding

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

Electrons can carry current.

−

+

+

+

+

+

+

+

+

+

+ Electrons rapidly transfer heat.

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

lattice (arrangement) of metal ions

24

Pure metals

Metal atoms lose control of their outer-shell electrons, which are free to wander.

Fig 2.1.1

bonding will not break even if layers shift

multidirectional bonding between the atoms and accounts for the following properties of metals: • They are malleable—the bonding allows them to stay together and not break apart when hammered or bent. • They are ductile—this is the ability to be drawn or stretched into wires. • They are electrical conductors—the free outer-shell electrons enable them to carry electrical currents. • They are heat conductors—these same electrons rapidly transfer heat, making metals excellent thermal conductors.

+

+

+

+

+

+

+

+

+

+

Pure metal

Element symbol

Uses

Properties that make it particularly suited to its use

Aluminium

Al

Overhead electricity cables, saucepans and cans, Alfoil

Excellent conductor of heat and electricity, extremely light, non-toxic

Copper

Cu

Electrical wiring

Excellent electrical conductor Easily drawn into wires

Sodium

Na

Nuclear reactor coolant

Conducts heat well Melts at 98°C, allowing molten sodium to flow along pipes in the reactor

Zinc

Zn

Coating for iron (galvanised iron)

Protects iron from rusting

Tin

Sn

Coating for steel cans for food, liquid, etc.

Stops steel from rusting, non-toxic, unreactive

Mercury

Hg

Thermometers

Liquid at room temperature, expands rapidly when heated, leaves tubes clean once it retreats, leaving no traces

Lead

Pb

Flashing around windows and rooftops to stop water entry

Very soft and easily bent, resists corrosion

UNIT

2.1

Alloys An alloy consists of a metal combined with one or more other elements. An alloy has properties that are different from those of its components. These new properties are usually an improvement over those of the main or base metal in the alloy. For example, brass is more durable than its base metal, copper. Pure iron is extremely soft, but if small amounts of carbon are added, its strength increases dramatically. The alloy formed is steel. Mild steel has 0.5% carbon, while tool steel has about 1%. If the carbon content increases to between 2.4% and 4.5%, cast iron

Fig 2.1.2

Cast iron lace … very beautiful, very hard, but very brittle

is formed. This is strong but brittle and shatters easily if hit or dropped. Stainless steel has chromium (20%) and nickel (10%) added to stop rusting.

Jewellery used for body piercings is usually rust-resistant surgical-grade stainless steel but infection may still occur.

Fig 2.1.3

25

>>>

Pure metals and alloys Pure gold jewellery would break if it was used for normal everyday wear. Instead, it is alloyed with silver or copper to increase its strength. The carat scale measures the amount of pure gold in jewellery, with pure gold rated as 24 carat. Jewellery is often 18 carat, meaning that it is 18/24 (threequarters or 75%) gold. Some alloys and their composition and uses are listed in the table.

UNIT

Gold cheaper than iron!

Damascus steel was used in the ancient world to manufacture swords of extreme strength. The exact technology was lost about 200 years ago but one recipe calls for ‘normal’ steel to be heated, then cooled in two stages. The final cooling was supposedly achieved by thrusting the sword into the body of a ‘muscular slave’. The strength of the slave apparently transferred on his death into the metal!

When the Egyptian Pharaoh Tutankhamen was buried 3400 years ago, two daggers were buried with him. One dagger had a blade of gold, the other iron. Because of its rarity at that time, the iron dagger was far more valuable than the gold one!

Fig 2.1.4

Tutankhamen’s dagger, with an iron blade and gold scabbard

Alloy

Composition

Uses

Advantages

Brass

70% Cu, 30% Zn

Household and nautical fittings, musical instruments

Appearance, limited corrosion, harder than pure copper

Bronze

95% Cu, 5% Sn

Statues, ornaments, bells

Appearance, little corrosion, harder than brass, sonorous (rings well when struck)

Duralumin

96% Al, 4% Cu, traces of Mg and Mn

Aircraft frames

Strong, light

Solder

60 to 70% Sn, 40 to 30% Pb

Joining metals together, electrical connections, low-friction bearings

Low melting point

Cupronickel

75% Cu, 25% Ni

‘Silver’ coins

Hard wearing, looks like silver, attractive

EPNS (electroplated nickel silver)

Cu, Ni, Ag

Plated onto cutlery, plates and bowls

Looks like silver, cheaper, resists corrosion

Alnico

Al, Ni, Co

Magnets

Aluminium is light, nickel and cobalt can be magnetised

Dental amalgam

Hg, Sn, Ag, Zn, Cu

Tooth fillings

Hardens slowly after being mixed

2.1

26

Wanted: muscular slave for short job!

[ Questions ]

Money, money, money! Australian ‘gold’ $1 and $2 coins contain 92% copper, 6% aluminium, 2% nickel and no gold. The ‘silver’ coins are 25% nickel, 75% copper and no silver. Metal was first used as money in about 2000 BC, but ‘coins’ were not invented until 600 BC in Lydia, Anatolia. They were crude beads of electrum, a naturally occurring alloy of silver and gold.

Worksheet 2.1 Toothache! Worksheet 2.2 Media analysis: Fry me to the moon

Checkpoint Properties of metals 1 State whether the following are true or false. a Metal atoms pack tightly together, giving metals high density. b Metal atoms have high electronegativity. c Free electrons in metals make the metals good conductors.

2 List the properties that all metals exhibit. 3 Explain whether metal atoms have high or low electronegativity.

Pure metals 4 Outline a factor that limits the use of pure metals. 5 List two metals that can be used in their pure form.

Prac 1 p. 28

UNIT

2.1 a State the breaking stress of: i a 50/50 alloy of copper/zinc ii an alloy of 20% Cu and 80% Zn iii an alloy containing 60% zinc iv pure copper v pure zinc b Identify the proportions of copper that make the alloy stronger than pure copper. c Identify the proportions of zinc that make it weaker than pure zinc. d Identify the strongest copper/zinc alloy. e Identify the composition of three alloys that all break at a strain of 25 x 106 N/m2.

Alloys 6 Define the term ‘alloy’. 7 Alloys have advantages over their parent metals. Clarify this statement using an example.

Think 8 Explain whether metals would be good or poor electrical conductors if they had a tight hold on their outer-shell electrons. 9 Are coins pure metals or alloys? Justify your answer. 10 List two properties of metals that make them ideal for electrical wiring. 11 Aluminium is used for overhead electrical cables, while copper is used for home wiring. Propose a reason why.

[ Extension ]

12 List three reasons why mercury is ideal for thermometers.

Investigate Analyse

1 Lead and mercury are described as cumulative poisons. a Explain what this means. b Describe how these metals get into the environment and into the bodies of animals. c Summarise the main effects of these metals on the human body. d Present your information as a newspaper article explaining the dangers of these metals to society and the environment.

13 State the base metal in a ferrous alloy. (Use element symbols to help you.) 14 List the different types of steel, in order from the lowest carbon content to the highest. 15 Use the table on page 26 to state which metal(s): a is most abundant in Australian ‘gold’ and ‘silver’ coins b is the only metal that is a liquid at normal room temperatures c is the main component of steel d is common to both the alloys brass and bronze e is added to iron to make stainless steel

2 Schools generally use red or green alcohol thermometers. a Investigate which metal was used in thermometers before alcohol. b Explain why this metal is no longer used. c Account for the use of alcohol thermometers.

16 Use the information on page 26 to state what fraction and percentage of pure gold is in: a a 12-carat gold ring b a 9-carat gold nose stud c a 22-carat gold chain

3 Some dentists are concerned about using dental amalgam as fillings in teeth. a Justify their concerns. b Outline some alternatives to using amalgam. 4 a Research the Bronze and Iron Ages. b Propose ways in which the discovery of copper/ bronze and iron/steel would have changed the way of life of people at that time. c Present your information as a poster or a creative story showing what life was like then.

Skills 17 The table below shows the stress that different alloys of copper and zinc can take before breaking. Construct a graph of stress (vertical axis) against the percentage of copper (horizontal axis). Analyse your graph to answer the following questions.

% Cu

0

10

20

30

40

50

60

70

80

90

100

Stress (N/m2 × 106 )

19

16

12

8

5

32

58

40

23

21

33

27

>>>

Pure metals and alloys

UNIT

2.1

[ Practical activity ] How much is it worth? 3 Convert any prices per tonne into prices per gram by dividing by 1 000 000. For example, if aluminium is A$2781.40 per tonne, the price per gram is 2781.40 × 1 000 000 = A$0.00278 or 0.278 cents per gram.

Aim To calculate the value of metal in Australian Prac 1 Unit 2.1

coins

Equipment

$2, $1, 50 cent, 20 cent, 10 cent and 5 cent coins, the business section from a recent newspaper (not Monday), access to an electronic scale

4 Convert any prices per ounce into prices per gram by dividing by 28.35 5 Write a complete list of the prices in Australian dollars per gram.

Fig 2.1.5

6 Use an electronic balance to find the masses of a $1 and a $2 coin. 7 Copy and complete this calculation for each gold coin: Mass of coin = _____ g [put mass of coin here] Mass of copper in coin

= 92% of _____ = _____ g

Mass of aluminium in coin = 6% of Mass of nickel in coin

_____ = _____ g

= 2% of _____ = _____ g [put price per gram here]

[put mass of metals here] Cost of copper

= _____ × _____ = A$ _____

Cost of aluminium

= _____ × _____ = A$ _____

Cost of nickel

= _____ × _____ = A$ _____

8

Add the answers to find the total cost of the coin.

9

What percentage is this of its face value?

10 Use a similar method to calculate the value of the silver coins.

Questions

Method 1 Find the following values and copy them into your workbook: • the US to Australian dollar exchange rate • the prices of aluminium, copper and nickel 2 Convert any US dollar prices into Australian dollars by dividing by the exchange rate. For example, if A$1 = US$0.5064 and the price of aluminium was US$1408.50 per tonne, then its price in Australian dollars was 1408.50 × 0.5064 = A$2781.40 per tonne.

28

1

Deduce whether any of the coins are worth more than their face value.

2

Fifty-cent coins originally had silver in them, but now don’t. Explain why.

3

Use the prices of gold and silver to calculate the cost of each coin if they were really gold or silver.

UNIT

context

2.2 Metals have been used for thousands of years, the first to be used being the native metals such as gold. Unlike gold, most metals are not found as pure elements, but as compounds of oxygen. They need to be ‘released’ from their oxygen before they can be used. Over the centuries, metallurgists (scientists who specialise in metals) have developed a variety

Metals in the crust Metals make up only a quarter of the Earth’s crust. Oxygen and silicon make up the rest. The oxygen does not exist as a gas, but is chemically combined with metal atoms as solid oxides.

potassium 2.2% sodium 2.8%

of efficient and inexpensive ways of doing this. At first they used heat. The discovery of electricity, however, allowed for the extraction of many more metals, particularly aluminium. Imagine your life without metals! Gold, gold, gold!

as either a nugget or a vein of the metal trapped in another rock such as quartz. They just need a little cleaning or the surrounding rock removed. Native elements are so stable and unreactive that they have survived without reacting with the chemicals of the air, dirt or water. A vein of pure gold trapped in quartz

magnesium 2.2%

The earliest recorded discovery of gold in Australia was in 1823 at Bathurst, New South Wales by James McBrien, a Department of Lands surveyor. At the time McBrien was surveying a road along the Fish River, between Rydal and Bathurst. The first gold rush had begun!

Fig 2.2.2

all the other metals and non-metals 1.2%

calcium 3.6% iron 5% aluminium 8.1%

silicon 27.8%

Fig 2.2.1

oxygen 46.7%

The percentage abundance of elements in the Earth’s crust. Oxygen is by far the most abundant, being combined with metals as oxides or with silicon as silicon dioxide in sand or silicates.

Metals ready to go: native elements Native elements can be either non-metals, like carbon and sulphur, or metals, like silver, platinum, copper and gold. The metals can be found as pure elements,

29

>>>

Mining and metals Metals that need work: minerals and ores All other metals are found combined with other elements as compounds. Minerals are rocks containing large amounts of a particular metal. If there is sufficient metal to make it worth mining, it is called an ore.

Is it worth mining?

Ore

Chemical composition

Metal extracted

Bauxite

Aluminium oxide, Al2O3

Aluminium, Al

Chalcopyrite

Copper iron sulfide, CuFeS2

Copper, Cu

Galena

Lead sulfide, PbS

Lead, Pb

Haematite

Iron oxide, Fe2O3

Iron, Fe

Pitchblende

Uranium oxide, U3O8

Uranium, U

Rutile

Titanium oxide, TiO2

Titanium, Ti

Sphalerite

Zinc sulfide, ZnS

Zinc, Zn

Mining produces valuable metals and creates jobs. Sometimes, however, mining is not worth its expense or the negative effects on society and the environment. Major ore deposits in Australia Legend Aluminium (bauxite) Copper (chalcopyrite) Gold Iron (haematite) Lead (galena) Uranium (pitchblende) Silver Titanium (rutile) Zinc (sphalerite)

Able Echo Island Darwin BaroteNabarlek Woodcutters Jabiluka Ranger Browns Koongarra Union Reefs Coronation Hill Mitchell Plateau Mt Todd Bulman Sorby HillsSandy Creek

Nabalco

Weipa Aurukun

Pera Head

Palmer River

McArthur River

Robe River-Deepdale Kintyre Mt Tom Price Rhodes Ridge Jimblebar Paraburdoo Channar Newman WESTERN AUSTRALIA Abra Marymia Fortnum Plutonic Peak Hill Bronzewing Reedys Weld Range Yeelirrie Cue Agnew-Lawlers Group Mt Magnet Mt Morgans Geraldton Youanmi Scuddles Mulga Rock Mt Gibson Koolyanobbing Kalgoorlie Group Copperhead Kambalda-St Ives Coolgardie Higginsville Jarrahdale Perth Norseman Bounty Pinjarra Del Park Wagerup Worsley Manyingee

Westmoreland Cairns Red Dome Constance Range NORTHERN TERRITORY Century Kidston Balcooma Tanami Gecko Lady Loretta Orlando Ben Lomond Gunpowder White Devil Woolgar Callie Charters Towers Area Peko Hilton Thalanga The Granites Mt Isa Wirralie Selwyn Bigrlyi Tick Hill Mt Coolon Plenty River Cannington Lucky Break Osborne Angela Arltunga Gladstone QUEENSLAND Cracow Mt Rawdon Dawson Valley Pandanus Creek

Admiral Bay

800

1200

1600

Gympie

SOUTH AUSTRALIA

Brisbane

Tarcoola

Olympic Dam

Beverly Beltana Honeymoon

Drake NEW SOUTH WALES

2000

Port Latta Rosebery Savage River

Kilometres

Bell Bay Beaconsfield TASMANIA

Henty

Hellyer

Hobart

Mt Lyell Risdon

30

Bingara

Elura Comet Valley Mt Gunson CSA Hillgrove Menninnie Dam Nillinghoo Radium Hill Mt Grainger Mineral Hill Whyalla Tomago Port Pirie Broken Hill Northparkes Lake Cowal Burra Kurri Kurri Newcastle West Wyalong Temora Adelaide Sydney VICTORIA Woodlawn Port Kembla Wedderburn Kangaroo Island Canberra Bendigo Stawell Benambra Ballarat Woods Point Portland Geelong Melbourne

N

400

Horn Island Wenlock River

Wollogorang (Redbank)

Blendevale Goongewa Cadjebut

Yarrie Bamboo Creek Marble Bar Nifty Telfer Nullagine

0

Fig 2.2.3

UNIT

2.2 The mining process Underground mines are used for the mining of deep ores but water penetration, possible collapse, venting of poisonous and explosive gases and the provision of fresh air for the miners are problems that must be managed. If the ore is close to the surface, open-cut mining is easier. An overburden of soil is removed and the ore is dredged out, creating benches, or steps that spiral into the hole. These are also used as access roads to haul the ore to the surface by truck. Open-cut mines cause problems including unsightliness, pollution of surrounding areas with dust, pooling of water, destruction of land above the ore, and the need to repair the land after mining ceases. Pollution and environmental degradation can be severe around mines and processing sites. This photo shows the effect of the Ok Tedi mine in Papua New Guinea.

Before mining begins, many important questions need to be asked: • How much ore is there and how concentrated is it? • How deep is the ore? What type of mine is needed? • Is the site close to existing ports and rail lines? • Is there a population centre nearby from which workers can be employed? • Who owns or controls the land? If they live there, will they be happy to shift? What compensation is appropriate? • What water and air pollution will it cause? • What damage will be done to the environment and how can it be minimised? • What will be the cost of building the mine and the processing plants, and repairing the environmental damage? • What is the current and expected future price of the metal? • What profit is expected?

Fig 2.2.4 Structure of an underground mine

Fig 2.2.5

mill and treatment plant

head frame

winder house ore conveyor

two-compartment shaft

cage or skip

ladder No. 1 level

drive (along the ore body)

pump line compressor

overhead stope

No. 2 level ORE BODY No. 3 level

underhand stope No. 4 level cross-cut

well

31

>>>

Mining and metals Fig 2.2.6

An open-cut mine showing benches and environmental degradation

The activity series When metals react, they lose electrons to form positive ions. Some metals lose their electrons more easily than others. These metals are reactive and are harder to extract. Different extraction techniques are required, depending on the metal’s position in the activity series. As we move up the activity series: • the chance of metals reacting with chemicals becomes greater • the metals become less stable • there is less chance of finding the metals in their natural state • the compounds of the metals become more stable and more difficult to break down • the extraction process becomes more difficult and more expensive.

Concentration of the ore

Extraction by electrolysis

Impurities and waste called gangue are mined with the ore. The mined material is crushed by rollers or by large steel balls that fill a large rotating drum called a ball mill. Gravity and sieves separate some of the gangue, with the remainder then separated by froth-flotation. This is a technique pioneered in Broken Hill, New South Wales, in which the crushed ore floats away on a frothy emulsion of oil and water, leaving the gangue behind. The ore is now ready for extraction.

Electrolysis is such a powerful method that it could be used to extract any metal from its ore. It uses a huge amount of electricity, however, and is used only when there is no cheaper method available. A voltage is applied to a molten sample or solution of the ore and the positive metal ions move to the negative electrode. When it gets there, the ion is forced to take back its outer-shell electrons to form metal atoms that then plate the electrode.

Zn

Heating with C or CO

Fe Ni Sn Pb Cu

Roasting in air

Ag

Occurs naturally

Au

32

More expensive extraction

Al

Method of extraction needs to be more powerful

Mg

Ores more difficult to decompose

Ca

Compounds of the metal are more stable

Na

Metals become more reactive

Electrolysis

Electronegativity increases

K

Extraction method

Metals more likely to be found as native metals

Metal

Fig 2.2.7

UNIT

2.2 The extraction of sodium from molten rock salt by electrolysis

chlorine gas Cl2

CleNa+

Na+ ions take back electrons to form Na metal

iron ore limestone coke exhaust gas iron forms and trickles down (400°C)

ecarbon monoxide forms and rises (800°C) ee-

carbon dioxide forms and rises (1400°C)

hot air blast

Molten Na+Cl-

molten slag

molten iron

Sodium is made by electrolysis of sea water or, more commonly, rock salt. The salt is melted to break the salt crystals into its ions, then converted into pure elements by electrolysis. At the negative electrode: Na+ + e–

molten steel

→ Na

and at the positive electrode: 2Cl–

→ Cl2 +

2NaCl(l)

→ 2Na(l) + Cl2(g)

Prac 1 p. 37

Extraction by heat Heat is sometimes sufficient to extract the pure metal. Aluminium, more This is called smelting. The valuable than gold more reactive metals such is Aluminium cookware as lead, iron and zinc need d ate reported to have origin or per Em carbon or carbon monoxide nch when the Fre the ved ser III n leo po Na (CO) to help the conversion -day King of Siam (modern along. et qu Thailand) at a state ban and To extract iron, coke (a tes pla e in 1867. Th de ma re we d use y source of carbon), limestone ler cut s of aluminium, with les (CaCO3) and iron ore important guests eating (Fe2O3) are heated in a ld. go re pu of from plates d to har so s wa blast furnace. m niu mi Alu y, very extract that it was ver expensive at the time.

metal solidifies as it is drawn out by the rollers

2e –

Overall,

water-cooled mould

continuous sheet is cut into slabs water sprayed on hot metal

Smelting iron in a blast furnace and rolling it into shape

Fig 2.2.8

Smelting of iron occurs as a series of chemical reactions. First the coke reacts to form carbon dioxide: C(s) + O2(g)

→ CO2(g)

Limestone then decomposes, forming calcium oxide and more carbon dioxide: CaCO3(s)

→ CaO(s) + CO2(g) 33

>>>

Mining and metals Carbon dioxide reacts with more coke, forming carbon monoxide: CO2(g) + C(s)

→ 2CO(g)

This reacts with the iron ore to form molten iron, which then runs to the bottom of the furnace: Fe2O3(s) + 3CO(g)

Luckily, iron is relatively common, since iron consumption is currently nine times that of all the other metals put together. Metals are non-renewable resources and all will eventually run out.

→ 2Fe(l) + 3CO2(g)

Waste calcium oxide reacts with sand in the iron ore, forming calcium silicate: CaO(s) + SiO2(s)

→ CaSiO3(l)

Calcium silicate is called slag and floats on the molten iron. Fig 2.2.9

Steel-making in action

Fig 2.2.10

More stable metals only need roasting in air. Most copper is extracted by roasting copper(I) sulfide, found in an ore called copper pyrites: Cu2S(s) + O2(g)

→ 2Cu(l) + SO2(g)

Recycling versus mining Metals that make up less than 0.1% of the Earth’s crust are considered to be scarce. Silver (abundance 0.000 01%) and gold (0.000 000 5%) are scarce and therefore expensive, but some of our most commonly used metals are considered scarce too: copper (0.007%), mercury (0.000 05%), zinc (0.013%), lead (0.0016%) and tin (0.004%).

34

More than 50% of all aluminium cans in Australia are collected and reprocessed.

Metal

Element symbol

Amount used per year (millions of tonnes)

Estimated year at which known reserves of the metal will run out

Iron

Fe

800

2110

Aluminium

Al

12

2350

Copper

Cu

8

2040

Zinc

Zn

4.5

2060

Lead

Pb

4

2020

Tin

Sn

0.25

2015

Eating gold In many cultures, it has been traditional to decorate food with pieces of gold leaf (fine layers of hammered gold). Many of Australia’s top restaurants are now using it too, on top of dishes such as risotto and even in cocktails. The gold leaf is eaten but has no taste, smell or texture. Injections of gold have been used for many years as relief from arthritis, so maybe this will help justify the cost of eating it!

Recycling of aluminium is common, because the production cost of new aluminium is twenty times more than the cost of recycling it. Recycling of many metals is often too expensive to make it worthwhile. The difficulty of separating the iron from tin in food cans makes it far too expensive to recycle iron at the moment, despite millions of cans being thrown out every year. Worksheet 2.3 Extraction of metals

UNIT

2.2

UNIT

2.2 [ Questions ]

Checkpoint Metals ready to go: native elements 1 Clarify what is meant by a ‘native element’. 2 List four examples of native elements. 3 State two forms in which native elements may be found.

Metals that need work: minerals and ores 4 Modify the following statements to make them correct. a Metals that are not native elements are found as alloys. b Rocks containing large amounts of ores are known as minerals. c A mineral contains sufficient metal to mine. 5 Use the table on page 30 to list three ores and the main metal they contain.

Is it worth mining? 6 A mining company decides not to mine a particular metal. State three factors that might have led to this decision. 7 State two features of a commercially successful mine.

The mining process 8 List the problems of an underground mine. 9 Construct a diagram showing the structure of an underground mine.

Concentration of the ore 10 From the following list of words, identify the correct terms to fill in the spaces below. extraction, froth flotation, ball mill, gangue, crushed Mined material is _________ by rollers or steel balls within a _________. Impurities known as _________ are separated by __________. The remaining ore is now ready for _________.

The activity series 11 Define the term ‘activity series’. 12 State the reason why some metals are more reactive than others. 13 Metals are extracted from their ores depending on their position in the activity series. List the extraction methods needed, in order from the least to the most active metals.

Extraction by electrolysis 14 List three metals that can only be extracted by electrolysis. 15 Use a diagram to explain how sodium is extracted from sodium chloride by electrolysis.

16 State a disadvantage of using electrolysis for extraction of metals.

Extraction by heat 17 List three metals that can be extracted by heat. 18 Construct a diagram of a blast furnace and label the important parts. 19 State the chemical formula for slag. 20 Construct the chemical equations for the smelting of iron ore.

Recycling versus mining 21 State whether the following statements are true or false. a Metals are known as renewable resources. b Iron is the most common metal in the Earth’s crust. c Metals that make up less than 0.1% of the Earth’s crust are scarce. 22 State one disadvantage and one advantage of recycling metals.

Think 23 Explain why a reactive metal atom like sodium (Na) has a very stable metal ion, Na+. 24 State which metal(s): a are extracted by electrolysis b are extracted in a blast furnace c are extracted by roasting in air d are native 25 Contrast the following: a slag and gangue b mineral and ore c overburden and ore d electrolysis and smelting e stable and reactive 26 Explain why metals higher up the activity series are more likely to be found as ores than as native elements. 27 Platinum is a native element. Explain where it should appear in the activity series. 28 Mining companies regularly take out mining leases on any land that may contain valuable mineral ores. This may even include the land on which you live. If the mining company holds the lease, it has the legal right to buy the land. Do you consider this acceptable? Justify your answer. 29 Contrast a shaft, a drive and a stope.

>>

35

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Mining and metals

Analyse 30 List three sites where each of the major ores listed in the table on page 30 are mined. 31 Use the words below to complete the flow chart in Figure 2.2.11 summarising the process of mining an ore and extracting the metal it contains. exploration, electrolysis, gangue, froth flotation, crushing, native-metal, roasting slag, blast furnace, open-cut, underground Fig 2.2.11

32 Use the activity series to predict whether these metal ions and metal atoms would swap electrons: a Na and Au+ b Na+ and Au c Mg and Cu2+ d Pb2+ and Al e Ca2+ and Cu

Skills 33 Construct a bar graph showing the elemental composition of the Earth’s crust. 34 The years for the first successful extraction of different metals are shown in the table.

overburden

Aluminium

1890 AD

Zinc

1500 AD

Iron

1400 BC

Lead

2000 BC

Copper

8000 BC

a Construct a time line showing these discoveries. b Use the activity series to explain why different metals were discovered at different times in history. extraction

b Use a map to summarise where it is processed and extracted. c Describe the transport facilities that probably had to be built to mine and shift the ore, giving consideration to whether it is near a large town. Al

Fe

Cu

Au

[ Extension ] Investigate 1 Research how car bodies can be recycled for their metals. Construct a poster aimed at convincing the public that recycling car bodies is a useful idea.

36

4 Underground miners used to carry canaries with them. Research why and use a cartoon to summarise your research. 5 The mobile phone revolution has brought with it a problem of recycling unwanted phones and batteries. Research what metals are used in making mobile phone batteries and the difficulties they produce if not recycled responsibly. Construct a brochure that could be used to inform the public.

Action

2 Research how to pan for gold and design an instruction sheet.

6 a Record the number of cans and types of cans your household throws out in a week. b Estimate how many cans are thrown out per year.

3 Locate a current mining town in Australia. a Describe the ore mined there.

7 a Construct a bar chart of current prices of metals listed in the commodity prices of the newspapers.

b Compare the current buy-back price of aluminium cans with the price for new aluminium from commodity prices in newspapers.

Creative writing Gold rush!

Surf 8 Complete the activity called ‘Start a Mine’ by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button. Construct a poster showing how your mine progressed from start to finish.

UNIT

2.2 Prac 1 Unit 2.2

UNIT

2.2 A rich gold deposit has been discovered 100 metres under Richville, a very wealthy suburb in your area. A multinational mining company is deciding whether it should mine there. Prepare two letters to a newspaper, one supporting a mine and one against. Imagine that the gold had been discovered instead in a remote area of the outback inhabited by its traditional indigenous owners. What will you do now? Are your reasons for and against the same as before? Prepare another two new letters, one in favour of a mine and one against.

[ Practical activity ] Electrolysis of copper

2 Add a small spatula of black copper oxide.

Aim To extract solid copper from a solution

3 Carefully warm over a yellow Bunsen burner flame. Stir with the glass rod until all the copper oxide is dissolved and the solution is blue. Do not boil.

Equipment 1 M sulfuric acid, black copper oxide, spatula, 50 mL beaker, glass stirring rod, Bunsen burner, tripod, gauze mat, bench mat and matches, 12 V power pack, globe, electrodes and connecting leads, filter paper/paper towel

Method

4 Remove the beaker from the tripod and place on the bench mat. 5 Connect up the circuit as shown in Figure 2.2.12. Set the power pack on 6 V DC and allow it to run for a couple of minutes.

1 Pour approximately 20 mL of 1M sulfuric acid into the beaker.

6 Draw a diagram of the set-up. Mark the electrode being copper plated. What is happening at the other electrode and to the colour of the solution?

Fig 2.2.12

7 Turn off the power and remove the electrodes. Carefully remove any pure copper onto filter paper/paper towel.

Questions 1 Explain whether copper formed at the positive or negative electrode. 2 Explain what happened to the blue colour of the solution. 3 In this experiment, copper ions in the solution are taking back electrons to form copper atoms. Describe the evidence for this. 4 Construct a balanced chemical equation for what is happening to the copper ions. 5 Propose a reason why electrolysis is never used commercially to produce copper. 6 Aluminium can only be extracted by electrolysis. Propose a reason why copper and not aluminium was used in this experiment.

37

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UNIT

context

2. 3 The steel body of a car eventually bubbles and rusts away, but aluminium cans and gold jewellery stay ‘good’ forever. Why? They are all metals aren’t they? Some metals are more reactive than others. Reactive metals corrode when exposed to water, air or other chemicals, usually forming metallic oxides. Pure sodium and potassium react with just about

Corrosion of iron and steel Iron is common and cheap. Its alloy, steel, is extremely strong, making it the most commonly used metal on Earth—car bodies, skyscraper frames, concrete reinforcing, pins and needles are all made from various grades of steel. Unfortunately, most steels rust—they react with air and water to form a red coating of iron(III) oxide, Fe2O3. Rust is flaky and easy to dislodge, allowing the rusting process to continue into the next layer. The iron or steel gets thinner, loses its strength and gradually returns to the compound that it was extracted from. Although an extremely complex reaction, it can be summarised as: 4Fe(s) + 3O2(g)

Fig 2.3.1

38

→ 2Fe2O3(s)

Rusted corrugated iron—a common sight around Australia

anything—their corrosion is very quick and often explosive! In contrast, iron corrodes very slowly, while gold is extremely stable and corrosion is rare.

Fig 2.3.2

Rust is flaky and allows the rest of the iron to rust away too.

Breaks between the rust flakes allow water and oxygen to enter into deeper layers. Rusting causes iron(III) oxide (rust) iron to thin.

For rusting of iron to take place, both oxygen and water must be present as either liquid or vapour. The rusting process can be accelerated by salts or heat.

Corrosion protection Stainless steel is an alloy that resists rusting and is used for surgical apparatus, body piercings and equipment in conditions of high heat and salt, such as in kitchens and on boats. Other types of steel can

A stainless steel toaster

Fig 2.3.3

Method of protection

Uses

Advantages

UNIT

2.3 Disadvantages

Painting

Car bodies, cast iron lace

Cheap, easy, attractive

Chips and scratches easily

Layer of grease or oil

Tools, machine parts

Cheap, easy, lubricates parts

Messy, needs to be reapplied regularly

Plastic coating

Dishracks, outdoor furniture

Cheap, attractive

Cracks allow water to enter, plastic deteriorates with age

Tin plating

Food cans

Does not react with food, non-toxic, less reactive than iron/steel

Needs electrolysis to plate steel, expensive, scratches will rust

Chromium plating

Car parts

Attractive

Needs electrolysis to plate steel, expensive, scratches will rust

be protected by coatings that stop air and water from reaching the surface. A scratch or crack in the coating, however, allows rusting to start again. Another method is to coat the surface or attach another more reactive metal. Galvanised iron is iron dipped in molten zinc. Zinc is more reactive than iron and will react instead of it. This is called sacrificial protection. Scratches and chips will not rust, as long as some zinc is close by. Nails and roofing materials are commonly made from galvanised iron. Reactive magnesium blocks are often bolted onto steel structures such as piers and deepwater gas rigs and oil rigs at sea. Prac 1 The magnesium sacrifices itself to protect p. 41 the structure.

protective treatment. Anodising is a technique where the layer of aluminium oxide is deliberately built up using electrolysis. Colours may be added as the layers are deposited. Saucepans and window frames are often made from anodised aluminium. Prac 2 p. 42

Worksheet 2.4 Metal experiments

oxygen

water aluminium oxide layer

Zinc sacrifices itself to protect the iron it plates.

Fig 2.3.4

Aluminium oxide tightly binds to the metal.

Water and oxygen corrode zinc instead of iron.

Fig 2.3.5

Fe

Zn Fe

Fe scratch

Aluminium: reactive but it doesn’t corrode! Aluminium is a very reactive metal and the surface reacts almost immediately with the air to form a fine layer of dull grey aluminium oxide, Al2O3. Unlike rust, this layer does not flake and acts like a tightly bound layer of paint. Aluminium needs no further

2.3 UNIT

Zn

Aluminium oxide does not flake.

Aluminium oxide acts like the perfect paint layer—hard to scratch and non-flaky.

[ Questions ]

Checkpoint Corrosion of iron and steel 1 List three substances required for iron to rust. 2 State two things that speed up the rate at which iron rusts. 3 Construct the equation for the conversion of iron into rust.

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39

Corrosion of metals

Corrosion protection 4 List three ways in which iron and steel can be protected from corrosion. 5 Describe what is meant by ‘sacrificial protection’.

Aluminium: reactive but it doesn’t corrode! 6 State the name of the corrosion-resistant coating formed on aluminium. 7 Clarify what is meant by the term ‘anodising’.

Think 8 Use the equation from Question 3 to help you construct a balanced equation for the corrosion of aluminium (Al) in oxygen (O2) to form aluminium oxide (Al2O3). 9 Use the activity series to predict which metals would show little or no corrosion. 10 Zinc doesn’t rust but it does corrode. Explain. 11 The paint around a scratch on a car door will eventually bubble. Use your knowledge of the flaky nature of rust to explain why. 12 a Explain why the insides of cans of food are coated in tin or a thin layer of plastic. b You should never buy cans of food that are dented or scratched. Explain why. 13 Use the activity series to identify metals that would provide sacrificial protection to iron. 14 Galvanising gives better protection than painting an iron surface. Explain why.

>>> 15 Explain why iron rusts and crumbles, but aluminium just dulls. 16 Describe how you can tell whether an aluminium window frame has been anodised. 17 The magnesium blocks attached to piers dissolve away over time. Outline what needs to happen when they dissolve.

Analyse 18 You need to protect a zinc structure from corrosion. Predict which metals you could bolt onto the zinc to protect it. 19 ‘Iron is the most valuable metal on Earth.’ Justify this statement. 20 Three sheets of iron are each coated in a different metal: copper, magnesium and tin. Predict what will happen to each sheet if the coating is scratched. 21 Steel window frames would be a silly choice near the sea. Explain why. 22 The jewellery used in body piercing is surgical-grade stainless steel, platinum or gold. Explain why these metals, and not cheaper ones, are used.

Project Which metal is that? Find which metals or alloys are used for these purposes:

[ Extension ] Investigate 1

Research the following information and write a report, using illustrations where appropriate. a Explain why roof decking is corrugated or ‘ribbed’. b Outline what is meant by ‘Colorbond roofing’. c Outline the advantages and disadvantages of various metal roofing materials.

Action 2

40

Rust is red-orange. Red-orange rocks often have high iron content. Find photos of rocks or landscapes that are ‘rusty’. Construct a collage showing the pictures collected.

1 The filament in light bulbs 2 Hot and cold water pipes 3 Turns black when exposed to light and is used as film coating 4 Used in fireworks and single-use flash bulbs to give brilliant light 5 Part of haemoglobin, the part of our blood that carries oxygen 6 Added to ‘super’ petrol to avoid ‘knocking’ 7 Makes up the metal plates of a car battery 8 Is in the catalytic converters of car exhaust systems to remove pollutants 9 Used in smoke alarms as a radioactive source 10 A radioactive element used in atomic bombs 11 The metal that is used in many street lamps, giving an orange colouring

UNIT

2.3

UNIT

2.3 [ Practical activities ] Corrosion of iron Prac 1 Unit 2.3

Aim To investigate factors affecting the corrosion of iron Equipment 5 iron nails (not galvanised), copper wire, magnesium ribbon, distilled water, salt (sodium chloride) solution, fine sandpaper or steel wool, 4 test tubes, test-tube rack, Bunsen burner, bench mat and matches, 250 mL beaker, peg or tongs, marking pen

5 Put both into test tubes containing salt water. 6 Put another two nails in the other two test tubes, marking which contains fresh water. 7 Leave for three or four days. 8 Draw each nail, showing the location of any reddish rust and any white corrosion on the magnesium or blue/green corrosion on the copper.

Questions 1 Deduce which factors encourage rusting.

Method 1 Polish each nail with sandpaper or steel wool.

2 Describe the effect of heat on the rate of rusting.

2 Fill the 250 mL beaker with cold water.

3 List all the metals used, in order from most to least reactive.

3 Heat a nail in a blue Bunsen flame until red hot. Use the peg to drop it into the water. Record what happens. 4 Tightly wind the magnesium ribbon around a nail, and the copper wire around another nail.

4 Which test demonstrated sacrificial protection? Justify your answer. 5 Explain why one metal sacrificed itself and not the other. Fig 2.3.6

copper

peg 1

2

3

magnesium 4

red-hot nail

250 ml beaker

cold water water

salt solution

41

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Corrosion of metals

Anodised aluminium Aim To anodise a piece of aluminium Prac 2 Unit 2.3

Equipment Piece of aluminium, aluminium foil, 2 M sulfuric acid, detergent, fabric dye solution, safety glasses, 2 x 250 mL beakers, tongs, tissues, 12 V power pack with wires and alligator clips, retort stand, bosshead and clamp, Bunsen burner, tripod, gauze mat, bench mat and matches or hot plate

Method

4 Set on the lowest voltage, then gradually increase until it reaches 12 V. Leave for 15 minutes, then wash the piece of aluminium in water. 5 In the other beaker, heat the prepared solution of fabric dye, then place the aluminium piece in it. Leave for 10 minutes. 6 Rinse in fresh water and cool. 7 To seal the anodised surface, boil the piece in fresh water for a further 10 minutes.

1 Line one beaker with aluminium foil, then three-quarters fill it with sulfuric acid.

Questions

2 Scrub the piece of aluminium in warm water and detergent and dry well. Do not touch the aluminium with bare hands—use tongs.

1 Explain why the aluminium piece must be handled only with tongs after cleaning.

3 Place as shown in the diagram and connect to the power pack.

2 Aluminium is highly reactive but doesn’t seem to corrode as badly as iron. Explain why. 3 Describe what anodising produced. 4 Explain why anodising would not work with iron.

power pack

aluminium dilute sulfuric acid

Fig 2.3.7

42

aluminium foil

UNIT

context

2.4 Nowadays we take plastics for granted, but before 1950 plastics were almost unheard of. Think of all the things that you wouldn’t have if plastics had not been invented. Like metals before them, plastics changed technology and the way we build and use our world.

H H H

Carbon is a Group IV element and each carbon atom can bond with up to four other atoms. This gives carbon the ability to form continuous lattices (e.g. diamond and graphite) and an amazing variety of molecules. Most molecules found in living organisms, fossil fuels, drugs, plastics and fibres contain atoms of carbon. This puts them into the same category—they are all organic compounds.

Plastics are everywhere. Most packaging and many fibres are plastic.

Fig 2.4.1

methane H

Elephants on the billiard table! By 1868 elephants had been slaughtered in such huge numbers that the supply of ivory could not meet demand. The Phelan and Collender Company offered a US$10 000 award to anyone who could find a replacement for the ivory used in their production of billiard balls. In response, brothers John and Isaiah Hyatt developed a natural polymer, celluloid nitrate or celluloid. Although used for billiard balls, it found more use as photographic film. It was also used for dolls and false teeth, a worrying fact since celluloid is highly flammable!

H

H

H

Plastic: carbon-based compounds

C

H

H

H

C

C

H

H

H

H

H

O

C

C

C

C

H

H

O

ethanol (the alcohol H in beer, wine, spirits, etc.)

H

H

C C

C

C

C C

H

H benzene

H

H O

C

H

methyl butanoate (artificial rum flavouring)

H

Fig 2.4.2

Some organic molecules made of carbon

The properties of plastics make them extremely useful for a wide variety of applications. Plastics: • are good thermal and electrical insulators, having no free electrons to conduct electricity or heat • are strong and light and can be moulded into different shapes • do not react with water or oxygen, making them weather- and rot-resistant. This is both a good and a bad property—outdoor furniture will not rot, but plastic packaging won’t decompose when thrown out; plastics are not biodegradable. • become brittle over time if exposed to sunlight. Chemicals can be added, however, to make them more resistant. • can have other chemicals added to colour and reinforce them (e.g. glass fibres are added to a plastic resin to make fibreglass) • sometimes react with or dissolve in other organic substances (e.g. turpentine, methylated spirits, petrol) • can sometimes burn very easily, producing noxious fumes when they do—PVC produces hydrochloric acid fumes when it burns!

43

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Plastics and fibres

Plastic

Other names

Polythene

Polyethene

Uses Milk crates, rubbish bins, buckets, plastic bags, cling wrap, soft squeeze bottles

Acrylic PVC

Safety glasses, plastic screens Polyvinyl chloride, polychloroethene

Waterproof clothing, guttering, pipes

Nylon

Brush bristles, fabrics, rope, carpets

Polystyrene

Without bubbles (unexpanded): yoghurt and margarine containers; with bubbles (expanded): insulation, Eskies, cups, packaging

Melamine

Unbreakable dishes

Urea formaldehyde

Electric switches and plugs

Phenol formaldehyde

Door handles, saucepan handles

Monomers and polymers

Thermoplastic and thermosetting plastic

Plastics start with small molecules derived from the oil industry. A process called polymerisation combines them into larger molecules that make up plastic. The small molecules are called monomers and the big ones polymers. Poly is a Greek word that means ‘many’. Polyurethane is made from many urethane molecules, and polyethene is ‘many ethenes’. Imagine a monomer as a single ‘paperclip’. Noxious aircraft! The polymer Plastics and synthetic ‘polypaperclip’ fibres are used in the e becaus would be a string of interiors of aircraft they are light and can be connected paperclips. Prac 1 moulded into the shapes required. The toxic fumes and smoke they produce on burning have been the primary cause of death in otherwise survivable accidents. A fire started in a luggage compartment of a Saudi Arabian Airlines Lockheed Tristar soon after take-off from Riyadh in 1980, filling the cabin with toxic smoke. The plane returned to the airport and landed safely. Instead of evacuating as quickly as possible, the captain taxied and then ran the engines for a total of 6 minutes. All 301 people on board died, including the captain.

When lightly heated, many plastics soften and can be remoulded into new shapes. When cool, they reset. These materials are called thermoplastic, examples being PVC, polythene and acrylic. These polymers arrange themselves into long parallel chains, which slide over each other, allowing flexibility and stretch. If heated they It’s only natural! Many natural polymers retain their basic structure but can exist, too. Wood is made slip over each other to fill whatever from the organic polymers moulds they are poured into. cellulose, lignin and resin. Natural rubber, amber, Thermoplastics are manufactured gum, asphalt and pitch as powder, pellets or granules for are all natural organic shipping to other factories to be polymers. Asbestos is an heated and moulded. example of an inorganic

p. 51

(no carbon) polymer.

Worksheet 2.5 Shape-shifter of modern medical science

H

H

H

H

H

H

H

H

H

C

C

C

C

C

polymerisation C

C

H

C H

C

H

H

H

ethene monomers

Cl

H C

H

Cl

C

H C

H

polymerisation

C

H

H

chloroethene monomers

H H H H polyethene polymer

Cl

H

Cl

H

Cl

C

C

C

C

C

H H H H H polychloroethene (PVC) polymer

Many identical monomers join to make a polymer.

44

Fig 2.4.3

Fig 2.4.4

UNIT

2. 4 Resin has been added to the hooked end of this spear thrower and is being heated to make it sticky.

The first use of thermoplastics? Australian Aborigines have been using resins for thousands of years. Resins from certain plants become soft when heated and very hard when cooled—that is, they are thermoplastic. Resins are obtained from both Porcupine Grass (Triodia species) and Grass Trees (Xanthorrhea species). If a fire goes through an area of grass trees, the resin oozes out and forms bubbles in the sand around the base of the tree. The resin is collected and crushed to a powder. The end of a spear is dabbed in the crushed resin, and heated until the resin becomes sticky. This is repeated many times until there is enough resin to adhere a spearhead. The soft resin is also used to attach stone blades to the wooden handles of tools or weapons using a process called ‘hafting’.

Thermoplastics are recyclable as they can be heated, individual strands cannot move— re-melted and re-moulded many times. Recycling is an thermosetting plastics will char (burn at the important way of managing plastics as it keeps them edges) but will not soften. They therefore out of the environment. Plastics are not biodegradable need to be manufactured and moulded at Prac 2 p. 52 so they stay in tips and the environment for hundreds, the same time. Bakelite is an example of a even thousands, of years. Plastic bags are a major thermosetting plastic. concern for birds, animals and sea life since these creatures can become Thermosetting and thermoplastic Fig 2.4.5 tangled in them or try to feed on them, with the bag subsequently blocking Thermoplastic the animal’s digestive add heat tract. Because plastic bags do not decay, they are released once more into the environment when the long polymer chains animal’s carcass decays. Chains slip over each other and Thermosetting plastics the plastic melts. Thermosetting cannot be remoulded. The polymers have strong cross-linking bonds locking them into a giant molecular structure. Individual add heat strands cannot be shifted without breaking part of the structure. This makes thermosetting plastics hard (scratch resistant), Bonds break and the plastic brittle (will shatter if decomposes (chars). dropped) and rigid (not able to be bent). When

45

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Plastics and fibres Working with plastic Thermoplastics can be moulded into new shapes in a number of different ways.

Extrusion moulding Extrusion moulding is used to make many common items such as pipes, hoses, plastic straws, curtain tracks, rods and fibres.

Blow moulding Bottles are commonly made by blow moulding. A sign of blow moulding is the seam where the two halves of the mould met. Fig 2.4.6

This is the most common method of production. A knob of plastic where the plastic injection took place is left behind. Toys, bottle caps and outdoor furniture are commonly made by injection moulding.

heaters

screw

Ring-shaped die produces a continuous pipe.

mould in open position

plastic pipe

molten plastic

softened thermoplastic

nozzle Slit die produces a continuous strip.

Mould is closed.

46

Plastic expands to fill mould, leaving seam.

metal tube compressed air

Fig 2.4.7

Shellac is a common natural furniture varnish and wax, and is made from the excretions of tiny Tachardia lacca bugs. In 1907, Belgian chemist Leo Baekeland was working in the United States to make an artificial substitute for it. His equipment became clogged when he mixed phenol and formaldehyde. The new material could not be dissolved and was a superb thermal and electrical insulator. The plastic, bakelite, had been invented and found immediate and widespread use as electrical fittings and saucepan handles.

The nozzle creates the shape in extrusion moulding.

pellets of solid thermoplastic

motor

Bugs inspire the first synthetic plastic!

Injection moulding

metal tube

Molten plastic is expanded by compressed air to fill the mould in blow moulding.

Mould opens.

UNIT

2. 4 pellets of solid thermoplastic mould (two parts)

Injection site is left as a ‘bump’.

Are you stringing me along? ram

heating cylinder

molten plastic

Molten plastic is squeezed into a two-part mould to fill it.

Fig 2.4.8

Fibres were not just used as serious tools in Aboriginal life, they were used for fun! String games are common in indigenous cultures both in Australia and around the world. In these games, string figure designs were made that resembled objects used in everyday life, such as dilly bags and baskets. Designs also showed animals and people, or ideas such as the forces of nature. String games were used for learning and to help tell stories.

Natural and synthetic fibres A fibre is any substance that can be woven or knitted into a fabric. There are two main types—natural and synthetic.

Natural fibres Wool, mohair, silk, cotton, linen (flax), hair, fur and coir (the hairy covering of a coconut) are all natural fibres. They have had many uses for thousands of years. In many Aboriginal societies, making objects from plant fibres was an important activity. Items needed for hunting as well as for carrying and collecting food were made along with ritual objects for use in religious ceremonies. The parts of many plants provide fibre to make string, bags, rope, baskets, fishing nets or baskets, clothing and mats. Fibres come from the following plant parts: • underground stems (rhizomes) of plants such as the bulrush • leaves and stems of grass-like plants such as the mat-rush • bark of trees and shrubs such as some species of Acacia and native hibiscus. After the plant parts have been collected, the fibrous material is extracted and separated. Some materials are soaked in water until the nonfibrous tissue rots away. Chewing or scraping with a sharp rock or shell then flattens and softens the remaining fibres.

Fig 2.4.9

An Aboriginal woman using natural fibre to make a basket

On some trees, such as the paperbark, little preparation is needed. The bark is simply peeled from the trees and used to make water containers, mats and liners for babies’ baskets.

Synthetic fibres Synthetic fibres are made entirely from chemicals and are usually stronger than natural fibres. Nylon, Terylene, Lycra, Kevlar, Spandex, Elastane, polyesters and acrylics are all synthetic fibres. Synthetic fibres are produced by the extrusion of a polymer though a multi-holed head called a spinneret. Some use natural fibres as their building block. Wood and paper (a wood product) contain the natural

47

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Plastics and fibres

New, improved Concorde

Softened thermoplastic is squeezed out of a multi-holed nozzle called a spinneret. A synthetic fibre is formed.

Fig 2.4.10

polymer cellulose. If wood pulp is soaked in solutions of caustic soda (sodium hydroxide, NaOH), a sticky cellulose gum forms. When extruded, the gum forms a new fibre—viscose, acetate, tri-acetate and rayon all come from wood pulp.

Length and strength

Prac 3 p. 53

The molecules in a synthetic fibre are aligned along the thread, making them stronger than the plastics they came from. The fibre will be particularly strong if its molecules are long—the longer the molecule,

Fig 2.4.11

Longer molecules produce stronger fibres than shorter ones. The strongest are monofilaments. a pair of molecules

As molecules get longer the force of attraction between them increases.

the greater its attraction to In 2000 an Air France others that lie next to it, and the Concorde took off from Charles De Gaulle Airport stronger it will be. The fibre can in Paris. A tyre burst, still tear, though, since the end of sending fragments into each molecule represents a weak the wing, puncturing the fuel tanks. The spilled fuel spot. ignited and spelt the end Monofilaments are made for the plane. Concordes from molecules that are the same once again took to the sky in 2001, this time length as the fibre. There are no fuel tanks lined with with ends and therefore no weak spots. Kevlar. However, they never Fishing lines are monofilaments regained the patronage of of nylon. Monofilament materials before the catastrophe and were finally removed from are extremely strong and flexible, service in 2003. making them ideal for uses where a tear or puncture would be catastrophic: Kevlar is a monofilament that is five times stronger than steel, but half the density of fibreglass. It is used in bulletproof vests, the sails of ocean-going yachts and the fuel tanks (actually fuel-bags) of Formula 1 racing cars. Ropes, fibre-optic cables, automotive hoses, belts and gaskets are often made of Kevlar. Goalie masks in hockey use a fibreglass/Kevlar mix.

Other properties

The rough surfaces of natural fibres give them a large surface area that can absorb and hold water and dirt. In contrast, the surfaces of synthetic fibres are smooth, making them stain-resistant, water-repellent and ideal for clothing. Drip-dry or wash-and-wear fabrics are synthetic. Synthetics are uncomfortable in hot weather, however, as they do not absorb sweat. Instead, it stays on our skin, making us wet and clammy. Natural fibres absorb sweat and keep our skin dry. Synthetic fibres a monofilament are thermoplastic and will melt if heated: ironing must be done with care and tumbledrying is usually not Each recommended. Molecules separate at their ends.

Force

Prac 4 p. 53

molecule is the same length as the monofilament.

Length DYO

48

Prac 5 p. 53

Other fibres If synthetic fibres are heated strongly with no air present, they do not burn but char until all that is left is a fibre of pure carbon. Carbon fibre is extremely strong and when mixed with resins can be used for making lightweight and flexible structures ideal for bike frames and tennis racquets. Glass fibre is produced by running molten glass into a perforated steel bowl (like the barrel of a washing machine). When spun fast, glass threads fly out and then cool in the air. When mixed with resins, fibreglass is produced.

UNIT

2. 4 Swimming in shoes! Australians have always loved the beach but ht. until 1900 it was illegal to bathe in daylig ugh altho ed, allow was ng bathi 1902 From men and women had to swim separately and fully clothed—men wore neck-to-knee woollen bathers and women wore huge ! bathing dresses, caps, stockings and shoes g makin , heavy very Wool holds water and gets the In easy. ning drow and ult diffic ming swim 1930s Jantzen’s ‘Topper’ swimwear allowed es, men to zip off their top at secluded beach ss tople go to ed allow and in 1938 men were on the beaches of Perth. The bikini was launched in 1952, but the newly developed ers ‘lastex’ fabric needed bone or metal stiffen is wear swim rn Mode to prevent it slipping off! Lycra or ne Elasta , nylon from made only comm blends. Swimmers once again are wearing neck-to-knee bathers, to protect children from UV radiation and to allow competitive a swimmers to reduce drag. Adidas makes from made suit swim competitive full body suits Teflon-coated Lycra, while Speedo makes lled mode e textur a has from ‘Fastskin’, which on shark skin.

Shark skin has scales or ‘dermal teeth’ that reduce drag as the shark swims.

Fig 2.4.12

Speedo’s Fastskin material directs water flow in a similar way to that over a shark’s skin.

Fig 2.4.13

Worksheet 2.6 Recycling

UNIT

2. 4

[ Questions ]

Checkpoint Plastic: carbon-based compounds 1 State what is meant by an ‘organic compound’. 2 List three examples of organic compounds. 3 List these facts about carbon (C): a its group number b its period c the number of electrons in its outer shell d the maximum number of bonds it can form e two continuous lattices that it forms

Monomers and polymers 4 Identify the correct terms in the following list to fill in the spaces below. polymer, polymerisation, monomer, plastics A small molecule capable of joining together in a long chain is called a ________. When small molecules join together they form a ________. Small molecules join together in a process known as _______ and result in the production of ________.

Thermoplastic and thermosetting plastic 5 Define the term ‘thermoplastic’.

6 List three forms in which thermoplastics are manufactured. 7 Define the term ‘thermosetting’. 8 List three properties of plastics made by thermosetting.

Working with plastic 9 Use a diagram to demonstrate how extrusion moulding is achieved. 10 State the type of moulding used to make bottles. 11 List three plastic items made by injection moulding.

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49

Plastics and fibres

Natural and synthetic fibres 12 State whether the following are true or false: a A fibre is any substance that can be woven or knitted into a fabric. b Nylon, cotton and linen are all examples of natural fibres. c Natural fibres are produced using a spinneret. 13 a State the name of the method used to produce fibres. b State the name of the ‘nozzle’ used to produce fibres.

>>> 24 Explain how the length of a molecule affects the strength of a fibre. 25 Where do fibres tend to break? 26 Explain why care must be taken when drying and pressing synthetic fibres. 27 Explain how cross-links stop thermosetting plastics from melting. 28 Use Figure 2.4.3 to construct a general equation for the polymerisation reaction. 29 Evaluate the use of plastics in terms of their effect on society and the environment.

Length and strength 14 Use Figure 2.4.11 to outline what is meant by a monofilament. 15 Use an example to demonstrate the usefulness of a monofilament.

Other properties

Investigate

16 Outline three desirable and three undesirable properties of plastics.

1 Materials such as polystyrene are called foams. Research how plastic foams are made. In your answer, include the chemical equations involved.

17 Explain why natural fibres are able to absorb and hold water.

Other fibres 18 List three examples each of natural fibres, synthetic fibres made from plastics and synthetic fibres made from wood products.

Think 19 Contrast: a the surface of a natural fibre with that of a synthetic fibre b a monomer with a polymer c thermoplastic with thermosetting plastics d injection moulding with blow moulding 20 List examples of: a five synthetic polymers b three natural polymers c one inorganic polymer d three thermoplastic polymers e one thermosetting polymer f one monofilament 21 A train could be considered a polymer. State what the monomer would be. 22 Explain how thermoplastics can melt and then reset on cooling.

Analyse 23 Would the production of thermosetting plastic powder be a good idea? Justify your answer.

50

[ Extension ]

Action 2 Use a paperclip to represent a monomer. Link them together to construct models of a polymer, a thermoplastic and a thermosetting plastic. 3 Inspect ten plastic items around your home for seams or ‘bumps’. List the items as made by extrusion, blow or injection moulding. Present your findings in a table. 4 Inspect the washing/drying/ironing instructions on six different pieces of clothing. Present the information in a table showing the fibre composition of each. List any recommended washing instructions, noting whether ‘no heat’ is stated. 5 Gather information by counting how many plastic bags are collected in one week in your home from shopping. Discuss your results and include comments on whether alternatives could have been used.

Surf 6 Find out more about how plastics are recycled by connecting to the Science Focus 4 Companion Website at www.pearsoned.com. au/schools, selecting chapter 4 and clicking on the destinations button. a Construct a graph showing the amount of plastic used in Australia in each State. b Produce a report which outlines how plastics are recycled. c Justify the need to recycle plastics.

UNIT

2. 4

[ Practical activities ] Identifying plastics

2 Describe the appearance—is it transparent, translucent or opaque?

Aim To identify properties of some common Prac 1 Unit 2.4

UNIT

2. 4

plastics

3 Describe its flexibility—does it bend or is it stiff?

Equipment

4 Does it feel ‘waxy’?

Labelled pieces (each about 2 x 1 cm) of polythene, polystyrene, PVC, perspex, nylon, ‘mystery’ plastics, dissection board/bench mat, scissors, turpentine, nail polish remover, dilute hydrochloric acid (HCl), detergent, 250 mL beaker, tongs, access to meths burner set-up in fume hood Fig 2.4.14

turpentine

6 How hard is it to cut with scissors? 7 Are the cut edges smooth or jagged? Does the cut show bubbles or cells? 8 Add two drops of detergent to a 250 mL beaker of cold water. Add a plastic—does it float or sink? 9 Place a drop each of turpentine, HCl and nail polish remover onto three small squares of each plastic. Leave for five minutes and record whether each piece dissolved, went soft or remained hard. 10 Break each plastic into smaller pieces and use tongs to hold a piece in a meths burner flame.

HCl

2 drops of detergent

5 Does your fingernail or the scissors scratch it?

WARNING: The meths burner must be in a fume hood. If no fume hood is available, do not do any burning tests. Do not smell any fumes or smoke.

nail polish remover

11 Did the burning produce smoke? If so, what colour was the smoke? What colour was the flame? Did molten plastic drop from it? Did the drops burn as they fell?

This must be in a fume hood 250 mL beaker

12 Run tests to determine what each of the mystery plastics is.

meths burner

Questions 1 Identify each plastic as either thermoplastic or thermosetting. 2 Identify the mystery plastics.

Method 1 Copy the table below into your workbook. Your teacher may split you into groups to run all tests on one plastic only or to run one test on all the plastics. Polythene Appearance Flexibility Feel Ease of scratching Ease of cutting Description of cut Does it float? Effect of flame What dissolves it?

Polystyrene foam

PVC

3 Explain why the burning must be done in the fume hood and not in the lab.

Perspex

Nylon

4 Explain what is produced from PVC when it is burnt. 5 Deduce whether any plastics sink in, or react with, water. 6 A sample of plastic kept burning once it was lit. Its flame was blue with a yellow tip. Identify the plastic.

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Plastics and fibres

Making casein plastic Prac 2 Unit 2.4

Aim To make a polymer called casein from milk. Casein was an early plastic that is still used for buttons and some wood glues. It is hardened industrially with formalin.

8 After a couple of days, remove the mould and polish with the sandpaper. 9 Use tongs to hold a small amount of the dry casein in a Bunsen flame. Does it melt, burn or char?

Equipment

Extension

Full cream milk, vinegar, Bunsen burner, bench mat, tripod, gauze mat and matches, 100 mL measuring cylinder, 2 x 250 mL beakers, thermometer, glass stirring rod, elastic band, coarse cloth for straining, paper towel/filter paper, assorted moulds (bottle caps, moulded chocolate trays etc.), fine sandpaper, tongs

10 Chip off a piece of casein and find its mass. 11 For every 50 g of casein you chip off, measure out 20 g of borax and 40 mL of water. 12 Add the borax and water to a conical flask and swirl until dissolved. 13 Crumble the casein into the borax solution and shake until creamy glue is formed.

Method 1 Set up the Bunsen burner and tripod.

14 Use it to glue two chips of wood together. Use the clamp or elastic bands to hold the pieces together. Leave it overnight to ‘cure’, then try to separate the pieces of wood.

2 Place 100 mL of milk in one of the 250 mL beakers. Warm gently until it reaches 50°C. Do not overheat. 3 Add 10 mL vinegar and stir with the stirring rod. 4 The milk should curdle to form white lumps of curds (casein) and yellowish liquid called whey.

Questions 1 Deduce whether the casein plastic produced was thermosetting or thermoplastic.

5 Use the elastic band to secure the piece of cloth tightly over the other 250 mL beaker. Strain through the curds and whey.

2 State the purpose of the final test.

6 Carefully remove the cloth and squeeze to remove as much liquid as you can.

3 Identify a use of the casein.

7 Empty onto the paper towel/filter paper. Pat dry, then firmly press into moulds. Leave the casein to dry in the sun.

5 Little Miss Muffet ate her curds and whey. Explain whether you would.

4 Outline how casein is hardened industrially.

Fig 2.4.15

100

110

thermometer 90

10 mL vinegar

curds

50°C

elastic band

30

40

50

60

70

80

250 mL beaker

0

10

20

100 mL milk

curds

cloth whey

curds mould

filter paper

52

UNIT

2. 4 TEACHER DEMONSTRATION Making nylon Prac 3 Unit 2.4

This demonstration must be done in a fume hood.

4

Aim To make a sample of nylon Equipment

Use tweezers to lift part of the layer of nylon formed between the solutions. Drape it over the glass stirring rod and wind the fibre out.

Questions

Fume hood, 1,6-diaminohexane, anhydrous sodium carbonate, sebacoyl chloride or adipoyl chloride, cyclohexane, 2 x 250 mL beakers, tweezers, glass stirring rod

1

Construct a three-frame cartoon or diagram to show how the nylon was made.

Method

2

Predict what would have formed if the two solutions had been allowed to mix.

3

The nylon fibre formed is not very useful. Explain why.

1

Dissolve 2.2 g of 1,6-diaminohexane and 5 g of anhydrous sodium carbonate in 50 mL of water.

2

In another beaker, mix 2 mL of sebacoyl chloride or adipoyl chloride in 50 mL of cyclohexane.

3

Gently pour the 1,6-diaminohexane solution down the side of the beaker and onto the top of the cyclohexane solution. The two solutions must not mix but must form layers.

Identifying fibres Aim To compare and contrast natural and Prac 4 Unit 2.4

synthetic fibres

Equipment

Labelled samples of fabrics (wool, cotton, linen, rayon, nylon, polyester), microscope, microscope slide and coverslip, pins or tweezers, metal tongs, matches, bench mat

Method 1 Remove an individual thread, about 2 cm long, from each fabric sample.

3 Explain why synthetic fibres have smoother surfaces than natural ones.

wool

4 List the fabrics in order from the safest near a flame to the most dangerous.

silk

cotton

5 Clothing fires are more common among children than adults and more common among girls than boys. Propose reasons why. 6 Recommend which fibres should be used for clothing for babies and young children.

linen

nylon

Fig 2.4.16

Fibres under the microscope

2 Place it on the microscope slide and use the tweezers or pins to tease the fibres apart.

Natural versus synthetic

3 Place a coverslip on top and inspect the fibres under the microscope. 4 In your workbook, sketch and label each fibre, taking note of its surface.

Prac 5 Unit 2.4

Plan and run an experiment to determine the amount of water different fabrics can hold.

5 Cut/tear a strip about 2 × 1 cm from each fabric. 6 Use tongs to hold a strip over the bench mat. Hold a lit match under the strip. Record your observations for each fabric. Did it catch fire, melt or char? What colour were the flame and smoke? What was left?

Questions 1 Match your samples with the diagrams in Figure 2.4.16.

Questions DYO

1 Construct a flow chart showing how you conducted your experiment. 2 List the fibres tested in order from those that held the least water to those that held the most. 3 Identify which of the fibres were synthetic.

2 Deduce which fibres were natural and which were synthetic.

53

Science focus: Nanotechnology Prescribed focus area: The implications of science for society and the environment Michael Crichton’s novel Prey tells the story of research going horribly wrong. In this future world, self-replicating nanoscale robots take on their own existence and start to cooperate with each other. They prey on living creatures, including the research scientists who created them, to gain the building blocks they require to reproduce themselves. This book caused a very strong response in some people who saw nanotechnology as being far too dangerous and thought that the book predicted the future. At present, however, nanotechnology is still evolving and there is little risk. There is also very strong support within the scientific and medical communities for the development of nanotechnologies because of the huge benefits that might be gained. In the future it is unlikely that nanoscale robots could gain such independence, but they will certainly be developed and become highly useful to society for many reasons.

How small is a nanometre? Nanotechnology involves making and manipulating incredibly tiny objects. The size of the objects dealt with in nanotechnology is in the order of 10’s to 100’s of nanometres. One nanometre is equal to just one thousand millionth (one billionth) of a metre. A single atom has a diameter of about 0.10 to 0.3 nanometres, which gives you an idea of just how tiny the nanometre is.

A different approach Multidisciplined Working with incredibly small objects requires cooperation between scientists from various disciplines. Nanotechnology draws on chemistry, physics, electrical engineering, molecular biology, quantum physics and materials science. It offers a

How small is a nanometre? As you move from left to right across the diagram, each step is ten times smaller. Domain of nanotechnology Limit of human vision

Fig SF 2.1 The future?

Limit of light microscope Rhinovirus (common cold) ~30 nm

Note: There are 1000 millimetres (mm) in 1.0 metre (m). There are 1000 micrometres (µm) in 1.0 millimetre (mm). There are 1000 nanometres (nm) in 1.0 micrometre (µm).

54

10 –

10 nm m =

Diameter of atoms ~0.10 to 0.30 nm

10

Carbon nanotubes ~1 nm

0.

Width of DNA molecule ~2 nm

10 – 9 1. 00 m nm =

.0

10 –

8 m nm =

Nanowire chemical detector wires are ~10 nm

10

Mitochondrion from human cell ~500 to 700 nm 10 – 7 0. 1 = 0 m 10 µ = 0 m nm

00

10 – 5 = = 0.0 m 10 1 µm0 m m

4 m = m m

10 –

10

0.

10 – 3 1. 00 m m = m

0.10 mm = 50 to 100 µm

10 – 6 m µm =

Human red blood cell ~6.0 µm

Human hair

~0.05 to

1.

Small fly 5.0 mm

huge range of possibilities, with applications already being explored in medicine, computing, electronics, engineering and lithography.

Top down Until recently the manufacture of the smallest of objects was a ‘top down’ approach. This means the substance would be engineered to reduce it down to the desired size, like sculpting a small statue from a large block of stone. This approach is suitable for micro-sized objects such as silicon chips and micro machines, which often use an etching process to make small components out of a larger piece of substance.

Fig SF 2.2

brick by brick. With STEM it is possible to manipulate single atoms on the surface of a material and to lay down incredibly thin surface layers on a substrate. Figure SF2.3 shows how a STEM operates. The STEM and sample are contained in a region which has had the air evacuated using a vacuum pump. The STEM piezotube probe is then moved over the surface of the sample, maintaining a fixed distance by ensuring the tunnelling current between the probe and sample does not change. Through computer analysis of the data collected, an image of the surface features of the sample can be produced. Using a STEM, individual atoms can be identified. With a secondary voltage applied between the tip of the probe and the surface, the chemical bonds holding a surface atom in position can be broken and the single surface atom moved. This ability to manipulate individual atoms has made bottom-up engineering of nanoscale objects a reality—it is now becoming possible to assemble something by moving individual atoms into position. Figure SF2.4 shows a STEM image of a surface that uses single atoms to represent data. The individual atoms hold data just like pits on a CD. Such data can be written and read using a STEM. Data storage at this scale means that 300 copies of a 300-page book could be stored on the cross section of a human hair.

These micromechanics components were created using a top-down approach to etch them out of silicon. For scale, a fly’s leg can be seen.

Bottom up The development of the scanning tunnelling electron microscope (STM or STEM) finally made it possible to produce images of an atom. It was quickly realised that with some modifications the STEM would be the perfect tool to directly manipulate the surface of a material on the atomic scale. This provided the opportunity to try and create structures from the bottom up. This means assembling a structure atom by atom, like building a house

The basic features of a scanning tunnelling electron microscope (STEM)

Distance control for piezotube to sample and scanning unit

Applied control voltage for piezotube containing electrodes

Fig SF 2.3

Piezotube generates a flow of electrons that is focused at the sample

Sample being studied Tunnelling current amplifier Data processing and display of images

Tunnelling electron current

Tunnelling voltage

55

Red gold

Fig SF 2.4

Individual silicon atoms (yellow) sit on this surface and represent data, like pits on a CD.

With the nanoscale so incredibly small, objects do not behave in the way expected at larger scales. ‘Quantum’ effects begin to act at the atomic level and this produces some very interesting results. For example, the metal gold is gold in colour when we look at a sample large enough to see with the human eye. But when gold atoms are arranged to produce tiny crystals of gold on the nanoscale, the gold appears red. These curious results show that we have a lot to learn about how substances behave at the nanoscale.

The future of nanotechnology A large amount of investment is going into nanotechnology research and development to produce innovative new products for the future. The possibilities are endless. Below are described some of the most promising areas where nanotechnology will be applied in the future.

Surfaces The ability to lay down incredibly thin layers of a substance onto the surface of other material can improve the properties of a substance and offers many advantages in chemistry and engineering. For example, laying down an incredibly thin protective coat on solar cells could improve transmission of light into the cells, and thereby improve their efficiency. Also, surfaces could be made self-cleaning by applying a coating that repels dirt. Manipulating the surface of materials can also make it possible to store vast amounts of information in very small spaces. A scanning beam interference lithography machine can be used to create gratings or grids with structures on the scale of a few nanometres. The structures created are used in astronomical devices such as space telescopes and satellites. A laser is used to create the pattern on the target surface. In the future this machine could be used to produce nanotechnology components for computers and machines.

56

A scanning beam interference lithography machine creates nanoscale grids and grates for space technology.

Fig SF 2.5

Medical An application of nanotechnology being explored is the creation of nanobots (nanoscale robots) to be placed in humans. Nanobots could monitor the internal conditions of the body, such as blood sugar levels, temperature, nervous activity or production of hormones by endocrine glands. Nanobots could be designed to seek out and destroy viruses and bacteria in the bloodstream. They could also be engineered

Fig SF 2.6

This nanobot is injecting a drug to kill cancerous cells in a human body. Could this be how we treat disease in the future?

to target certain cells in the body, identifying the cell and delivering a product to it. For example, a nanobot could be designed to detect cancerous cells. Drugs could be packaged inside the nanobots to be injected directly into the cancer cells with no damage to the normal cells of the patient.

This image of carbon nanotubes was created using a STEM. Carbon nanotubes have the potential to be used in electrical devices and have unusual properties. Much research is being done with carbon nanotubes, and their applications are likely to be diverse.

Fig SF 2.7

Computing Nanotechnology offers the potential to manufacture new, smaller, faster and more efficient integrated circuits for computing. It has made quantum computing possible, with incredible processing speeds far beyond the ability of present silicon-based microprocessors. Quantum computers would store and process information at an atomic level. A solid-state quantum computer element can be made by positioning phosphorus atoms 20 nanometres apart in very pure silicon. The phosphorus atoms behave as an incredibly tiny and extremely fast microprocessor. Promising research into quantum computing is being conducted at the University of New South Wales.

[ Student activities ] 1 Development of a quantum computer is being pursued energetically in a number of countries. The University of New South Wales (UNSW) has purchased a very expensive STEM to assist in its research. a Research the work being done on quantum computers at UNSW. b Summarise the work being done and any progress made to this point. c Compare this research with that being done in another location. 2 As a molecular biologist and nanoengineer, you have been given the task of designing a nanobot to help solve an important medical problem. a Identify a medical problem you would like to solve using nanobots, e.g. diabetes, cancer, HIV, haemophilia or another of your choice. b Construct a poster or model of a nanobot that could help solve this medical problem. Include labels or a key to show the features of your nanobot, and an explanation of how the nanobot will tackle the medical problem. 3 Tests on carbon nanotubes show that they have extraordinary, unexpected properties.

a Research carbon nanotubes to find out: i what they are ii what special properties they have iii their possible applications and uses iv why it would be important to conduct further research into carbon nanotubes b You are a research scientist and you want to work with carbon nanotubes but you need funding for your project. There is $1 000 000 in funding for nanotechnology available, but you have to appear to be at the forefront of research to get this. Using the information you have about carbon nanotubes, construct an application that will get the funding you need for your research. Include the possible outcomes and products you will create, and how they will benefit society. 4 Produce a poster, display or other presentation to teach the general public about nanotechnology, and what it may offer society in the future. You will need to conduct research to include information about: a examples of current and future research and products b public safety and any social issues c the importance of continuing to invest in this area of research

57

>>>

UNIT

context

2.5 We always seem to be getting dirty or getting covered in oils and grease. Dirt, oils and grease are made from organic compounds that normally dissolve only in other organic substances. Although there are obvious problems in washing ourselves in turpentine,

methylated spirits or nail-polish remover, dry-cleaners use similar organic solvents to dissolve and remove grease from clothes. At home you need to use soap and water to get clean, but how does this work?

Making grease soluble Surfactants are molecules that assist water in dissolving dirt and grease.

Water Australians are too clean!

At home, water is our main washing liquid. It is a polar molecule, having small electrical charges on each of its atoms. Water will dissolve other polar molecules, like sugar, and ionic substances such as salt or sodium chloride (Na+Cl–), which have positive and negative ions. Water by itself will not dissolve grease.

Fig 2.5.1

Detergents, shampoos and soaps are surfactants.

Fig 2.5.2

Many babies suffer from eczema, or skin hypersensitivity. It seems that we are all using too much soap, bubble bath and shampoo, since all remove essential oils from the skin. This causes dryness and makes us susceptible to eczema. Dermatologists recommend using soap-free cleansers instead. For babies all that is generally needed is some bath oil or moisturiser.

Water is a polar molecule and can use its slight charges to dissolve ionic substances.

δ+ δ– H O

–

δ+ H

a water molecule

H H

δ+ δ+

+

–

– +

–

+

–

Water weakens the forces holding salt chemicals together.

H

δ+

O O

O

H

H H

δ–

δ–

δ–

δ+

δ+

δ+

H H

δ+ δ+

means slight negative charge

O

δ–

+

–

means slight positive charge

H H

δ+ δ+

O

δ–

CD8

Once separated, they are unlikely to rejoin.

Soap, shampoos and detergents are surfactants and have both organic and ionic parts. Surfactant molecules are similar to those of plastics in that they are long and have an organic carbon backbone. This will dissolve grease nicely. Unlike most molecules, however, they have a charged or ionic end. This is then joined to a metal ion (usually the sodium ion, Na+). This end will dissolve in water nicely. We now have the perfect molecule for dissolving grease—one end dissolves the grease, while the other end dissolves in water. Once the grease is dislodged, surfactant molecules surround it and keep it from re-depositing back onto the surface. These tiny dissolved liquid

What gorgeous hair! The molecules of most hair conditioners tend to have positively charged ends that are attracted to the weak negative charge of the hair. They stay there even when the hair dries. (Fabric softeners work in the same way.) Shampoos and conditioners are normally sold in separate bottles because their opposite charges interfere with each other if they are mixed. In combined shampoo-conditioners, the conditioner molecules are trapped in crystalline shells. When lathering hair, the shampoo works, but there is insufficient water to break down the conditioner crystals. These only break down on rinsing, when more water is present.

grease patches and the water form a mixture called an emulsion. The water can now wash away the grease. Hot water and agitation (vigorous movement) also help loosen the grease from the surface and keep it from re-depositing on it. Lather (bubbles) will also assist in keeping grease from dropping back and is particularly useful in situations where little water is used (e.g. shaving, washing cars, hair shampoo). Many fibres (including hair) take on a weak negative charge when wet. Once dissolved and carrying their load of grease, the soap or shampoo molecules also carry a negative charge and are thus less likely to re-deposit the grease back onto the fibre. Prac 1 Prac 2 p. CD11

and magnesium precipitates. These are left behind as a dirty grey substance called scum, which deposits as a dirty ring around basins and baths, or as scale in pipes and kettles. Soft water has less dissolved salts and soap produces less scum. Soap lathers better, feels smoother and more slippery in soft water, and less of it is required to get clean. Prac 3 p. CD12

UNIT

2.5 Scum-free and bubbles galore! Many New South Wales cities have excellent soft water: it lathers well and leaves very little scum. In other areas, ‘water softener’ systems are attached to each home’s water supply. Beads of zeolite replace the offending calcium and magnesium ions with sodium. Soap doesn’t react with sodium.

p. CD11

water

hydrophilic head (ionic end dissolves in water)

hydrophobic tail (organic end dissolves in grease) surfactant molecule

grease

Surfactant (soap, detergent) molecules have a hydrophobic end that hates water but loves grease. The other end is hydrophilic—it loves water.

Fig 2.5.4

Fig 2.5.3

Hard and soft water Tap water contains many impurities. If it has a lot of calcium and magnesium salts dissolved in it, then it is hard. Soap reacts with these salts to produce calcium

Lather (bubbles) keeps the dirt and grease from re-depositing on the hair.

Soap is made when natural fatty acids found in materials like vegetable oils and animal fats react with an alkaline (basic) solution such as sodium hydroxide. The process is called saponification and is summarised by the reaction: fat + alkaline solution

→ soap + glycerol

Skin soap

soda Bases such as caustic and ) ide rox (sodium hyd s are their alkaline solution they if s ou extremely danger The n. ski h wit t tac con in come its as y per slip skin becomes ation ific on sap go der un fats and form soap!

CD9

>>>

Soaps

Whale soap?

Detergents are produced from chemicals in crude oil. The big advantage of detergents is that they don’t produce scum.

UNIT

2 .5

In the past, whale blubber was commonly the fat from which soap was made. Whales are now prote cted, however, and the fat used in soap manufactur e comes mostly from cows slaughtered for their meat. Just about any fat or oil can be used and many soaps are now made with vegetable or plant oils. Palmolive soap is named because it is made with palm oil and olive oil.

[ Questions ]

Checkpoint Water 1 Modify the following statements to make them correct: a Water is a non-polar molecule. b Sodium chloride is a polar molecule. c Water is able to dissolve grease. 2 State the types of substances that normally dissolve in water.

Making grease soluble 3 Identify the type of compound that grease is made of. 4 Some liquids are able to dissolve grease. List three such liquids. 5 List three ways in which grease is prevented from re-depositing on a surface. 6 State the reactants in saponification.

Hard and soft water

Think 10 Explain how soap is able to dissolve both in water and in grease. 11 Identify as many factors as you can that will affect the cleaning of a piece of fabric. 12 If lather doesn’t help to dissolve grease, explain how it helps to remove grease from a fabric. 13 If shaving cream did not lather, state where the cut whiskers would end up. 14 Identify three vegetable oils that could be used for the production of soap. 15 If animal fat is needed to produce soap, propose some sources of the fat.

Skills 16 Contrast detergent with soap. 17 Compare soap molecules with: a plastics b ionic compounds

7 Lathering results in ‘scum’ forming when water is hard. List the chemicals that cause water to be hard.

18 Construct a word equation for the production of soap.

8 Clarify what is meant by ‘soft water’.

19 Construct a diagram showing how soap helps grease to dissolve in water.

9 State the advantages of soft water.

Create

[ Extension ] Investigate 1 a Use a dictionary to define the term ‘phobia’ and include some examples. b One end of a surfactant molecule is hydrophobic and the other end is hydrophilic. Clarify the meaning of these terms and identify which end is which. 2 Conduct research on the Internet to answer the following questions: a List what is in a soap-free cleanser like Dove. b Scotch, 3M and ENJO all make cloths that clean without the use of chemicals. Describe how they do this.

CD10

20 Construct a three- to four-frame cartoon/diagram showing how shampoo-conditioners work.

c Research the dry-cleaning process. Describe how it cleans clothes, making reference to the chemistry involved. If necessary, use diagrams to assist your explanation. d Explain why soap films are often coloured. e Describe the machine that can make three-storeyhigh soap bubbles.

Action 3 Design a survey of soaps. Record your results in a table showing the first six ingredients of at least three different brands of soap, hair shampoos and shower gels. Identify and discuss any trends you find.

UNIT

2 .5

UNIT

2.5 [ Practical activities ] Fig 2.5.5

Make soap! Prac 1 Unit 2.5

WARNING: The soap made here uses and contains very corrosive sodium hydroxide. Do not get any sodium hydroxide on your skin or in your eyes. Do not use the soap produced.

250 mL beaker

5 mL oil water

Aim To produce a sample of soap Equipment Olive oil or coconut oil, 1 M sodium hydroxide solution, saturated solution of sodium chloride, kerosene, 3 test tubes, rubber stopper, 400 mL beaker, 100 mL beaker, 250 mL beaker, hot plate (preferably) or a Bunsen burner, bench mat, tripod, gauze mat, matches, filter paper or paper towel

Method 1 Pour about 5 mL of oil into a test tube.

test tube

yellow flame

10 mL sodium hydroxide solution

bench mat

2 Carefully add 10 mL of sodium hydroxide solution. 3 Place the test tube in a boiling water bath for 30 minutes. Shake the tube every few minutes to mix the contents. 4 Place 50 mL of the sodium chloride solution in the 100 mL beaker, then pour the hot oil mix in. The soap formed should float to the top.

9 Fill a fresh test tube with water, then add 3 or 4 drops of kerosene. This will be our ‘grease’. Stopper and shake. 10 Add some soap, then shake again. Compare with what you saw before.

5 Scoop up the soap and place it in the 250 mL beaker. Rinse a few times with a little water.

Questions

6 Let the soap dry on filter paper/paper towel.

1 Draw a cartoon explaining how soap was made here.

7 Two-thirds fill the other test tube with water and add a little soap.

2 Describe what happens to the kerosene in water alone.

8 Stopper and shake. Does it lather?

4 Construct a word equation for the reaction.

3 Describe the effect that the soap had on it.

How good is it? Prac 2 Unit 2.5

Aim To design and run an experiment that compares liquid and powder laundry detergents Equipment Powder and liquid laundry detergents

Method DYO

1 Identify all the variables or factors that would influence the effectiveness of laundry detergent in removing grease.

2 Choose one factor that you think would have a big effect.

3 Design and run an experiment that would test it. 4 Write a report on the effect of the variable you chose and why you think you obtained the result you did.

Questions 1 Draw a conclusion about the variable you tested. 2 Gather conclusions from other groups who tested different variables. Assess which variables had an effect and which didn’t.

CD11

>>>

Soaps

How hard is it? Aim To test water hardness Prac 2 Unit 5.2

Equipment Distilled water, dilute magnesium sulfate solution, solution of calcium hydrogen carbonate, suspension of calcium carbonate in water, small chips of bath soap, shampoo, detergent, 5 test tubes, rubber stoppers to fit test tubes

6 Repeat the experiment but use a few drops of shampoo. 7 Repeat again with a few drops of detergent.

Questions 1 Describe what soap does in hard water.

Method 1 Put about 2 cm of distilled water and 2 cm of tap water into two separate test tubes.

2 Identify the solution that was the hardest. Justify your answer.

2 Put about 2 cm of each solution into the other test tubes.

3 Deduce whether the water showed any hardness when it contained shampoo or detergent.

3 Add a small chip of soap to all five tubes and stopper lightly.

4 Outline the advantage of detergent over soap.

4 Shake the tubes vigorously and watch for any lather that forms.

stopper Look for lather.

solution of different salts

Hold stopper and shake.

small chip of soap

Fig 2.5.6

CD12

5 Record your results in order from the solution that produced the most lather (the softest) to the one that produced the least lather (the hardest).

Is the water hard or soft?

5 Design a test to see if temperature has an effect on water hardness.

>>> Chapter review [ Summary questions ] 1 State an example of an alloy and its base metal. 2 State whether the additives in alloys are usually metals or non-metals. 3 List the carbon content of: a cast iron b tool steel

c mild steel

4 State how many carats are in pure gold. 5 If gold is 18-carat, state the percentage of gold present. 6 State a use for each of these materials: a aluminium d Duralumin b zinc e bronze c cast iron f haematite 7 State one example each of: a an alloy of copper b an alloy of iron c an impurity commonly added to iron d a commonly used pure metal e a non-metal abundant in the Earth’s crust f a scarce metal g a metal that is cheaper to recycle than to produce

g bauxite h celluloid i Kevlar

h i j k

an ore a native metal a natural fibre a synthetic fibre made from wood products l a monofilament fibre m a surfactant n an organic solvent

8 Identify a metal that is extracted by: a electrolysis b smelting

c roasting

9 List the ingredients for a blast furnace. 10 State the special name given to the corrosion of iron. 11 Outline what is meant by ‘anodised aluminium’. 12 List four properties of a thermosetting plastic.

[ Thinking questions ] 13 Rose-gold is a pink-gold colour. Propose a metal that could be added to the base metal to create this colour. 14 It is thought that iron simply oozed out of the rocks used to surround the cooking pits of ancient hunters. Compare these conditions with those of a blast furnace.

58

17 Explain why stainless steel is ideal for use as replacement bone (hips, tooth implants, knees). 18 Corrugated iron (steel) is galvanised and is commonly used for roofing. a Explain what will happen after all the zinc coating has corroded away. b Explain whether the zinc can be replaced. 19 If car bodies are galvanised, propose reasons why they are also painted. 20 Identify problems associated with using plastic shopping bags. 21 An optic fibre is transparent fibre that carries light unbroken from one end to the other. Explain whether an optic fibre needs to be a monofilament. 22 Explain why natural fibres cannot drip-dry.

[ Interpreting questions ] 23 Use a diagram to describe the bonding in metals that allows: a conduction of electricity b conduction of heat 24 Use the data in the table on page 34 to construct the following graphs: a a pie chart showing the amount of metals used each year b a bar graph showing when each metal is estimated to run out 25 Construct a diagram showing what happens in the electrolysis of copper chloride. Label the diagram and use chemical equations to show the chemical reactions at each electrode. 26 Aluminium metal is high on the activity series, yet is a commonly used metal. Use Figure 2.3.5 to explain why it does not rust. 27 Phenylethene is an ethene molecule with one hydrogen replaced by benzene, C6H6. a Construct a diagram of a phenylethene molecule. b Polystyrene foam uses phenylethene as its monomer. Construct a diagram showing ten phenylethene monomers joined to form the polymer polystyrene.

15 Primitive prospectors found gold and silver before any other metal. Explain why.

Worksheet 2.7 Materials crossword

16 Salt is often used in Europe and North America to help melt ice on roads. Their cars also rust more quickly than ours. Explain why.

Worksheet 2.8 Sci-words

>>>

3

Electricity and communications technology Key focus area:

>>> The applications and uses of science

compare series and parallel circuits and describe everyday applications of each describe the relationship between voltage, resistance and current, and use Ohm’s law to calculate values of each

Outcomes

use an analogy to describe voltage, current and resistance

5.3, 5.6.1, 5.6.3, 5.12

By the end of this chapter you should be able to:

contrast AC with DC electricity describe how some electromagnetic devices operate describe the main components needed for efficient transmission of electricity explain how waves transmit energy list and describe the different forms of electromagnetic radiation contrast analogue with digital signals and their use in communication explain how communication signals can be transmitted

electricity that comes from our power points?

3 How do mobile phones find each other? 4 Describe an appliance that uses electromagnetism.

5 Who invented the telephone? 6 What is a digital message made up of?

Pre quiz

1 What do AM and FM on the radio dial stand for? 2 What are the voltage and frequency of the AC

>>>

UNIT

context

3.1 We live in an ‘electrical’ society. Every day you use a wide variety of appliances that need electrical energy to run. Discmans, iPods, toasters, televisions, microwave ovens, computers and even the family car all need electricity. You might not appreciate how much you rely on electricity until you have A major blackout to go without.

A simple circuit A circuit is a path from one side of a power source (e.g. a cell, battery or power pack) to the other. The four basic parts of a simple circuit are: • an energy source, such as a cell or battery. A cell or battery can be thought of as a charge pump. • a conducting path (wires) for the electricity to flow through Fig 3.1.1

On 14 August 2003 an electrical failure suddenly hit the United States and Canada. About 50 million people in cities from New York to Toronto had no power. People were trapped in subway trains and elevators for hours. The loss related to the blackout was estimated at $6 billion. One month later, Italy’s 57 million people also were affected by a blackout. Luckily it occurred on a weekend so its initial impact was less dramatic and caused less economic damage. Some developing countries have regular ‘brownouts’ because their need for electricity exceeds their ability to generate it. Electricity supply must be ‘rationed’, and so suburbs and towns have times each day when no electricity is available.

Fig 3.1.2

Imagine this scene without electricity. What problems would it cause?

• an energy user or load, such as a globe, motor, buzzer, heating element or resistor • a switch to turn the current on and off.

A simple circuit and its equivalent circuit diagram circuit

circuit diagram

cell 1.5 V

1.5 V cell

+ –

switch

connecting wire

60

globe

Fig 3.1.4

The water pump and electrical circuits Conductor/lead

Cell

Unit

3.1 current (I) switch Globe

Battery

resistance

high voltage +

A

Closed switch

Fixed resistor

Open switch

Variable resistor

Ammeter

Leads connected

battery

low voltage – ground

valve V

Voltmeter

Common components in simple circuits

high pressure

Leads crossing

Fig 3.1.3

Inside a circuit There are three very important values in circuits that we can measure and calculate. • Whenever charge moves, we have a current. In most circuits the moving charges are electrons and current is defined as the rate of flow of those electrons. Current is measured in amperes (A) or amps for short. Sometimes in a circuit there will be more than one path that the current can take. More current will flow down the easier path and less down the harder one. In mathematical formulas, current is given the symbol I. • Depending on what part of the circuit we are talking about, voltage is a measure of how much energy: – is available from the battery or power pack to push current through the circuit. It may be thought of as the size of the ‘push’. – is used when current passes through a load. Voltage is measured in volts (V) and is sometimes referred to as potential difference. Voltage is given the symbol V in mathematical formulas. • Resistance is a measure of how much a load (e.g. globe, motor, resistor) restricts and reduces the flow of current. Resistance is measured in ohms, or Ω for short. In mathematical formulas, resistance is given the symbol R. To help you understand these terms we will use the analogy of a water pump circuit. In a water circuit, the pressure supplied by the pump (P) drives the water around the closed loop of a pipe at a certain flow rate (F). The waterwheel (W)

water wheel

pump low pressure water reservoir

restricts the flow, slowing down the water, using up its energy. The valve turns the flow of water on and off. In an electrical circuit, the energy or voltage (V) supplied by the battery drives the electrons around the circuit, causing an electric current (I). The resistance (R) slows the electrons, using up their energy. A switch turns the flow of electricity on and off.

Water in pipe

Units

Electricity in wire

Units



Pressure (P)

Pascals

Voltage (V)

Volts



Flow rate (F)

Litres/second

Current (I)

Amps

Resistance to flow (W)

Newtons

Resistance (R)

Ohms

Voltage A battery or power pack is the ‘pump’ of an electrical circuit. A water pump takes in water at low pressure, supplies energy to it and ejects it at high pressure. A battery or power pack takes in charge at low voltage, adds energy to it and ejects it at a higher voltage.

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Electricity

Resistance high voltage + low voltage

high pressure

–

low pressure

valve

A switch has voltage behind it, but no current if not switched on.

Fig 3.1.5

If closed, pressure is behind valve but no flow of water.

A waterwheel restricts the flow of water, slowing the water down and taking away its energy. Light globes, buzzers, motors, heating elements and resistors are loads that restrict the flow of current and remove energy from the electrons. These loads change the electrical energy into other forms such as sound, light, heat and kinetic (moving) energy. The filament of a light globe is a very thin wire. As the current tries to squeeze through, it encounters resistance and uses up some of its energy. In a thick wire, electrons move more freely and with little resistance. Little energy is lost. Increasing the resistance of the circuit will cause a decrease in the current, and results in more energy being used up by the load. Resistance in a circuit can be compared to a water wheel.

Fig 3.1.7

Voltage can be compared to the pressure of water in a pipe.

Current When current flows through a wire it moves freely, losing almost no Fatal currents energy. This is just like water in a A current as small as 0.1 to pipe where there is little resistance 0.2 amps can kill! Most deaths to slow the water down. A higher associated with electric shock icity electr the current means more electrons flow happen because interrupts the heartbeat, which past a point in a circuit every is controlled by small electrical second. currents in your body. High erous A current of 1 ampere means dang voltages are more than low ones because they can that 1 coulomb of charge passes drive a higher current through by a point in the circuit each your body. The 240 volts in our second. A coulomb is an amazing easily is lies home power supp 6 250 000 000 000 000 000 electronenough to drive a deadly current through your body. sized charges! Current can be compared to the rate of flow of water through a pipe.

Thick wire offers little resistance to flow of electrons.

A resistor acts as a load, converting electrical energy to heat and light.

A water wheel is like a load in the circuit. It converts kinetic energy of water to movement of the wheel.

Fig 3.1.6

A large pipe offers little resistance to flow of water.

Heat energy being released in a glowing resistor of an electric bar heater

62

Fig 3.1.8

Types of circuits

Ohm’s law

There are two basic types of circuits—series and parallel.

Ohm’s law describes the relationship between the current, voltage and resistance in a circuit. Typical results from this experiment may be:

Series circuits If you arrange two globes one after the other in a line with the battery, the globes are said to be in series. The voltage supplied is split between the two globes, but the current passing through each is the same. The two globes glow more dimly than a circuit with only one globe. If a globe in this circuit is removed or ‘blows’, the circuit is broken, so the other globe will not work either.

6V

6V

no current

bulb goes out 1A 3V

1A 3V

Current, I (amps)

A

0

0

B

3

1

C

6

2

D

9

3

E

12

4

V Resistor

bulb removed

E D C B A

A

Ohm’s law can be found using a circuit where the resistance is changed.

Fig 3.1.9

A series circuit with two globes

1A

Voltage, V (volts)

UNIT

3 .1

Variable resistor to alter current

Fig 3.1.11

Graphing these results shows that the electric current is directly proportional to the voltage (V α I). This means if the voltage is doubled, so is the current. A graph of Ohm’s law is therefore a straight line passing through the origin. The slope or gradient of the graph gives us the resistance. It can also be calculated by dividing the voltage by the current, R = V/I.

Parallel circuits R =

Ohm’s law

Slope =

V = slope I vertical rise horizontal run

= 62 = 3 12

∴R

=

3Ω

10 6

8 Voltage (V)

If you arrange the globes next to each other but on separate branches you have built a parallel circuit. The voltage used by each globe is the same, but the current is split between each branch. Each globe glows with equal brightness. If a globe in this circuit is removed or blows, the other globe will remain lit as there is still a circuit through which current Prac 1 Prac 2 p. 66 p. 66 may flow.

6 2 4

4A

6V

2A

2A

6V

2A

6V

current divides

4A

2A

2

6V 6V

no current

2A

1

2 3 Current (A)

Ohm’s law is shown by this graph.

4

5

Fig 3.1.12

Ohm’s law is stated as: Fig 3.1.10

A parallel circuit with two globes

Voltage = Current × Resistance V =IR

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Electricity

Fig 3.1.13

Using Ohm’s law

2ESISTANCE #URRENT

6

2

! )

)

2

!MMETER

4OUSETHETRIANGLESIMPLYUSEAFINGER TOCOVERWHATYOUWISHTOFIND 4HEREAREONLYTHREECOMBINATIONS  &INDTHEVOLTAGEUSEDWHENARESISTOR OF7HASACURRENTOF!FLOWING THROUGHIT

 &INDTHECURRENTFLOWINGTHROUGHA RESISTOROF7IFTHEVOLTAGESUPPLIED IS6

2

6 )

2   

You may find the triangle in Figure 3.1.13 helpful when calculating V, I and R. Worksheet 3.1 Ohm’s law Prac 3 p. 67

AC/DC

64

The difference between AC and DC is in the way the electrons move in the wire. In direct current (DC) the electrons flow in one direction only. A battery or DC power pack provides a source of electrons and the potential difference or voltage between the terminals causes them to move from the negative

6 2

)

!

The electric eel (Electrophorus electricus) is an unusual species of fish that is capable of generating powerful electrical shocks. It can grow up to 2.5 metres in length and 20 kg in mass, and can produce 500 volts and 1 ampere of direct current. This is enough to kill a human!

 &INDTHERESISTANCEOFACIRCUITOFA 6BATTERYTHATDRAWSACURRENTOF!

6

6)2 s VOLTS

Animal electricity

6OLTAGE

6OLTMETER

6 )

6

) 2

2 6 )   7

(–) towards the positive (+) terminal. The flow of electrons through a wire can be thought of as similar to water in a hose: it only goes one way. Remember that conventional current flows in the opposite direction to the flow of electrons. That is, current (I) flows from the positive (+) towards the negative (–) terminal. In alternating current (AC) the electrons shuttle back and forth in the wires. This occurs because the voltage at the power point or the AC power pack constantly changes from positive to negative to positive and so on. The back and forth voltage change is measured in hertz, one change or cycle per second being 1 Hz. In Australia the AC electricity that we use at home has a voltage of 240 V and moves back and forth 50 times every second or 50 Hz. Imagine the water in a pipe constantly changing its direction of flow.

UNIT

3 .1

UNIT

3 .1 [ Questions ]

Checkpoint

Think 15 Explain what an electrical appliance marked with 240 V, 50 Hz means.

A simple circuit 1 Clarify what is meant by a ‘circuit’.

16 A series circuit and a parallel circuit each have two globes in them. Describe what would happen in each if one of the globes was to blow.

2 List the four parts of a simple circuit.

Inside a circuit 3 Define the terms ‘voltage’, ‘current’ and ‘resistance’. 4 State the units for voltage, current and resistance. 5 Complete the following table to compare an electrical circuit with a water pump circuit. Electrical circuit

Water pump circuit

Battery Pipe Voltage or energy Switch Water flowing through pipe Water wheel

6 Draw diagrams to demonstrate all of the components in both the water pump and electric circuits. Label each component. 7 Describe how a waterwheel causes resistance.

17 Propose reasons why the lights in a home are wired in a parallel circuit. 18 Construct diagrams for the following circuits: a two lights and a switch in series b two lights in parallel and a switch to turn both lights off at once c three lights in parallel, each of which can be turned off individually d two lights in series, parallel to a single light. One switch should turn off all lights at once, and another switch should turn off the single light only.

Skills 19 Use Ohm’s law to calculate the missing values in the table.

Current (amps)

Voltage (volts)

3

15

5

8 List three examples of a load that could be included in a circuit.

Types of circuits 9 Outline how components in a circuit are connected: a in series b in parallel 10 A series circuit and a parallel circuit were set up, each with two globes. Compare the brightness of the globes in each case.

Ohm’s law 11 State Ohm’s law in both words and symbols. 12 Sketch a graph to demonstrate the relationship of voltage, current and resistance in Ohm’s law.

6 240

10

Resistance (ohms)

18

240

0.5

14 12

1.5

20 A circuit has a 12 volt battery connected to a 50 ohm resistor. Calculate the current in the circuit. 21 Ming constructed a series circuit with a 75 ohm resistor. He connected the circuit to an 8 volt battery. a Draw a diagram to demonstrate the circuit. b Calculate the current in the circuit.

AC/DC 13 Contrast direct current with alternating current. 14 Identify the type of electricity used: a in your home b in a battery-operated appliance

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Electricity

[ Extension ] Action 1 Use an interactive program such as ‘Crocodile Clips’ to construct circuits that can be used in different situations, including: a a doorbell that can make a buzzer operate b a doorbell for the hearing impaired that has a light as well as a buzzer c a circuit for a light that can be switched on or off at the top or bottom of stairs d a circuit for a refrigerator door to turn the light on and off e light circuits for home

UNIT

3 .1

2 Construct an electrical circuit for a simple appliance or game that runs on batteries. You could, for example, build a model lighthouse, a bedside lamp or torch, a car with motor and lights, or a game like ‘The Nervy’, where you have to manoeuvre a loop of wire along a bent coat hanger without the loop touching the wire and setting off the buzzer and light.

Surf 3 Research Ohm’s law and complete interactive tutorials about it by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.

[ Practical activities ] Simple series and parallel circuits Aim To compare the brightness of globes in

Prac 1 Unit 3.1

series and parallel circuits

Equipment Three globes, connecting wires, switch, power pack

Method

Questions 1 Draw circuit diagrams to demonstrate the three series and parallel circuits. 2 Construct a table showing the number of globes and brightness in each.

1 Connect a series circuit containing one globe and observe its brightness.

3 Compare the brightness of globes in series with that of a single globe.

2 Modify the circuit by inserting a second globe and then a third globe in series. Note the brightness of each globe.

4 Compare the brightness of globes in parallel with that of a single globe.

3 Investigate the effect of removing each globe one at a time, by gently unscrewing them a little.

5 State the effect of removing a globe when they are: a in series b in parallel

4 Repeat all the steps but use a parallel circuit instead.

Measuring voltage and current in circuits Prac 2 Unit 3.1

Aim To compare current and voltage in series

Method

and parallel circuits

For each of the circuits listed below:

Equipment Three globes, connecting wires, switch, power pack, ammeter, voltmeter Warning: Before completing this activity you will need to know how to correctly connect a voltmeter and ammeter into a circuit. Incorrect connection of meters can damage them. Check with your teacher before starting.

66

1 Use an ammeter to measure the current on each side of the battery, and in each branch of the circuit (or between each globe in the series circuits). 2 Use a voltmeter to measure the potential difference across each globe, and across the battery.

UNIT

3 .1 Questions

3 Draw each circuit and record your results on the circuit as you go.

1 Describe how the current changes in different parts of: a a series circuit b a parallel circuit

Circuit 1: a single globe in series Circuit 2: two globes in series Circuit 3: three globes in series Circuit 4: two globes in parallel

2 Describe how the voltage is split between globes in a series circuit.

Circuit 5: three globes in parallel

3 Compare the voltages of globes in a parallel circuit.

Ohm’s law 1

0 –1

A

2

0.4 0.6

Prac 3 Unit 3.1

0.2

0 .2

–0

3

Aim To investigate Ohm’s law Equipment

voltmeter 6

4 2

0 .2

Two resistors of known (but different) resistance value, connecting wires, switch, 12 volt power pack, ammeter, voltmeter

0

.4 .6 .8

V

8 10 1.0

ammeter

switch

Method 1 Assemble the circuit shown in Figure 3.1.14.

+

2 Set the power pack to 4 V, close the switch and record the current displayed on the ammeter and voltage on the voltmeter.

power pack

3 Repeat step 2 but increase the voltage by 2 V.

Fig 3.1.14

4 Continue to increase the voltage in 2 V steps up to 12 V. Record the current and voltage readings. 5 Enter the results in a table like the one below and use Ohm’s law to calculate the resistance at each voltage setting. 6 Repeat steps 2 to 5 using the other resistor. 7 Calculate the average resistance for each resistor. 8 Construct a graph of voltage versus current for each resistor on the same set of axes.

Resistor 1 Voltage (V)

Current (A)

resistor

–

Resistance (ohm)

9 Calculate the slope of the graph for each resistor. The slope of the graph is the resistance value. Compare this to the known values of the resistors.

Questions 1 Compare the average resistance calculated using Ohm’s law with the actual resistance from the slope of the graph. Suggest reasons for any differences. 2 Describe the shape of the graphs and use it to predict what would occur if:

Resistor 2 Current (A)

a the voltage was doubled b the resistance was doubled

Resistance (ohm)

4 6 8 10 12

67

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UNIT

context

3.2 You use electricity every day in many different ways. Although magnets are less common, you will also have used them. They are the basis of all compasses and are used to hold notes on our fridge and to keep cupboard doors shut. There is an important connection between electricity and magnets: electricity can make magnetic fields and magnetic fields can make

An electric current causes a magnetic field In 1820, Danish physics professor Hans Oersted was carrying out experiments with electric circuits when he noticed that the needle of a compass on his desk moved whenever an electric current flowed nearby. Oersted was able to move a compass needle without touching it, as if by magic. The compass was doing what compasses do—it was reacting to a magnetic field. In this case, the

electricity! This connection is responsible for most of the appliances you use—everything from speakers to televisions, trains to vending machines.

magnetic field was produced by the electric current. Oersted had discovered that electricity could cause magnetism. Later in this unit we will see that the reverse is also true—that magnetism can cause electricity. This connection between two quite different phenomena is known as electromagnetism. The magnetic field produced around a straight, current-carrying wire is circular. If the wire is looped, several circular magnetic fields combine to produce a stronger field down the centre of the loop. If a wire is coiled so that several loops are placed together, the magnetic field is stronger again and we have what is called a solenoid. An electromagnet is a solenoid with an iron core that further concentrates the field down its centre. Unlike permanent magnets, electroPrac 1 p. 74 magnets can easily be switched on and off.

a

current

< new AW Corbis CB066635>

field

current

b

compasses N

S

c iron core

thumb points to N pole card

The magnetic field around a straight, currentcarrying wire. The ‘right-hand grip rule’ can be used to determine the direction of the field, which is the way a small compass needle would point.

68

N

iron filings

Fig 3.2.1

S

fingers indicate current direction

Fig 3.2.2

The magnetic fields from several loops are combined and concentrated in an electromagnet.

Electric bell

Uses for electromagnets There are many applications for electromagnets that are essential to our everyday life. Many are not easily noticed and range from large industrial electromagnets to the tiny speakers in your mobile phone.

Industrial electromagnet

You hear it every day—the school bell. How does it work? switch

spring

electromagnet

Industrial electromagnets are used extensively in metal scrap yards and allow the movement of large amounts of steel. The ability to switch magnetism on and off is extremely useful in industry.

UNIT

3 .2

Fig 3.2.3

contacts electromagnet attracts striker

bell

Fig 3.2.5

circuit breaks

An electric bell

When the switch is pressed, the electromagnet effect begins and attracts the striker, causing it to sound the bell and simultaneously break the circuit by moving the contacts apart. With the contacts apart, current no longer flows and the electromagnet is turned off. This allows the striker to return to its ‘rest’ position where the contacts touch once more, causing current to flow again, and the cycle repeats, resulting in the familiar bell-ringing sound.

Relay

Door latch Door latches are usually found in high-security areas. To open a door a button is pressed, resulting in a current flowing to a coil. The resulting magnetic field attracts the latch out of the door recess, opening the door.

Electromagnetic relays are found in cars and industrial machinery. The starter motor in a car allows a small current within a thin wire to control a much larger current within a larger cable, thereby reducing the cost of connecting wires and increasing safety.

heavy duty cable ignition switch

An electromagnetically operated door latch

Fig 3.2.4

starter motor light duty cable

electromagnet door latch

coil

spring attached (1) to latch (2) to recess

battery

door recess door frame

contacts

turning ignition key activates electromagnet, which attracts contacts and closes the starter motor circuit

A car relay

Fig 3.2.6

Speakers switch

Loudspeakers are an essential part of a teenager’s life, being part of nearly everything that makes noise. Mobile phones, answering machines, stereos,

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Electromagnetism televisions and surround-sound systems all have speakers of some sort. A speaker receives varying electrical current that flows through a coil, causing it to become an electromagnet. The speaker also contains a permanent magnet which interacts with the electromagnet. The two magnets attract when the current fed into the speaker flows one way and repel when the current flows the other way, producing vibrations in the cone. These vibrate molecules in the air to create sound waves. A typical loudspeaker

Fig 3.2.7

Superconductors

are cooled to –270°C they lose When metals like tin and lead with allow large currents to flow so and ce, all electrical resistan cool to lot a ts cos t —i blem pro e is a little loss of energy. But ther h‘hig ed call sodevelopment are the metals this far. A more recent h as suc l eria mat mic cera of e s mad temperature’ superconductor cooled to Ceramics like this need to be yttrium barium copper oxide. nductors. erco sup ious prev to d compare ‘only’ –200°C, a huge saving maglev ude incl s ture superconductor Applications of high-tempera c fields neti mag tiny ct dete can that trains (see below) and devices the brain. such as those produced by

coil

Trains cone

permanent magnet

Television Electromagnets control which pixels (coloured spots or rectangles) are illuminated on a television screen. Although the actual electron beams are not coloured, they are shown coloured in Figure 3.2.8 to show that there is one beam for each colour pixel in a section of screen.

Japan’s experimental maglev (short for magnetic levitation) train uses superconducting electromagnets to lift it 10 centimetres above the track, position it correctly and propel it at speeds of over 500 kilometres per hour. Such high speeds are possible because of the train’s streamlined shape, and the lack of friction between the train and track. The maglev train ‘floats’ due to the repulsion between electromagnets, providing a frictionless track.

electromagnet for deflecting electron beams

beam of electrons

electron beam sweeps across screen

shadow mask keeps electron beam aligned

Fig 3.2.8

70

How a television works

Worksheet 3.2 Inside MLX01

Fig 3.2.9

A magnetic field causes an electric current In 1831, English scientist Michael Faraday demonstrated that if a magnet is moved into a coil of wire, a current was produced in the coil. If the magnet stopped, so did the current. If the magnet was removed, a current was produced but in the opposite direction. By continually moving the magnet in and out of the coil, he produced a continuous but alternating current (AC). Faraday had found that by changing the magnetic field inside a coil, he could generate an electric current. He had Prac 2 Prac 3 p. 74 p. 75 produced a simple generator. Fig 3.2.10

a magnet in and out of the coil in Faraday’s experiment. More than a dynamo is needed to power a city, however. To generate sufficient electrical power, massive turbines are spun by water or steam. The principle is the same though: the turbines are attached to magnets that then spin in a coil to produce AC electricity.

UNIT

3 .2

A bicycle dynamo

Fig 3.2.11

A current is produced if the coil of wire moves relative to the magnetic field.

magnet and coil move closer together S

N

V

Fig 3.2.12

Compare the size of the person in this photo with the steam-driven turbine used to generate electricity.

moving wire

Microphone S

N V

induced current

A moving coil-type microphone contains a diaphragm which vibrates a coil in response to sound waves, generating a current which varies with the strength and frequency of the vibrations. This current can be fed into an amplifier and converted into a louder sound by attaching speakers. A moving coil-type microphone coil

Fig 3.2.13 magnet

Applications of generators Apart from battery-powered devices, most of the electricity we use is AC and comes from electrical generators. These can be small (as on a bike) or huge, feeding the power grid of a city. Bikes often have a small AC electric generator called a dynamo attached to their wheel rim. A rotating magnet inside the dynamo produces alternating current similar to that produced by moving

diaphragm

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Electromagnetism Traffic light magic

Vending machines

How do traffic lights ‘know’ there is a car waiting at them? Pads under the road have a coil in them that carries a current. The electromagnetic field it produces induces a current in the car, which in turn interferes with the current in the road. When this interference is detected, the lights ‘know’ that they should change to let the car through.

It’s not just coils that have currents induced in them by magnetic fields. A solid coin passing through an electromagnet in a vending machine creates swirling currents within it. These currents in turn create magnetic fields, and interact with the electromagnet to slow the coin down. Coins that are not the correct weight or made from a non-metal are not slowed the right amount, and are rejected. The operation of a vending machine

For efficiency reasons the best voltage for long-distance transmission of electricity is between 220 000 and 500 000 V, whereas the electricity is generated at a much lower voltage. In all these cases a transformer is needed. Transformers use solenoids and the magnetic fields they produce to either increase (step up) voltage or reduce (step down) voltage to the value required. Transformers use electromagnetism to step up or step down voltages. This is a step-up transformer.

Fig 3.2.15

iron core primary coil

Fig 3.2.14

secondary coil input voltage output voltage Upper plate

EP

R LU

IBUS UNUM

S

ER ICA

Coins of the wrong metal slow down and fall into the reject chute.

U

FI NT NI TE VE CE AM D STATES OF

Non-metallic objects are not slowed down, hit the upper plate and fall into the reject chute.

Coins of correct metal slow just enough to pass over the reject chute into the vending machine.

Transformers Sometimes the voltage provided is either too much or too small for the intended use. For example, laptop computers only need 16 V and mobile phones need only 5.7 V to recharge. The 240 V available from the power point would damage both if used directly.

Power transmission Power stations use energy from burning coal, flowing water or other sources to spin turbines in large generators, and transmit power through an extensive network of overhead and underground power lines. Because high-voltage transmission is more efficient, a transformer is needed close to the power station. These high voltages would be far too dangerous, however, if fed directly into your suburb or home, and so a series of transformers are used to reduce the voltage to the final (but still deadly) 240 V we use. How electricity reaches our homes from the power station

Fig 3.2.16

transmission lines 220 kV–500 kV 66 kV

consumer

11 kV step-down transformer

power station 16.5 kV

72

step-up transformer

step-down transformer

step-down transformer/sub-station

240 V underground cable to home (or overhead lines)

UNIT

3.2

[ Electromagnetism ]

Checkpoint An electric current causes a magnetic field 1 State the year when Oersted discovered that a current produced a magnetic field. 2 Construct a diagram showing the shape of the magnetic field around a straight wire. 3 Outline the difference between a solenoid and an electromagnet. 4 State the key advantage of an electromagnet over a conventional magnet.

Uses for electromagnets 5 a List three devices that use electromagnets. b State the job done by the electromagnet in each case.

A magnetic field causes an electric current 6 Use Figure 3.2.10 to outline the result of: a placing the magnet in the coil of wire b removing the magnet from the coil of wire c continually moving the magnet in and out of the coil of wire 7 List two devices that contain a simple generator.

Transformers 8 State what a transformer is used for. 9 Use Figure 3.2.16 to state the main stages in electricity transmission. 10 List the two main types of transformer. 11 State what type of transformer would be needed: a for a laptop computer b for long-distance transmission c at a substation on the outskirts of a town d to recharge a mobile phone 12 Count the number of primary and secondary coils in Figure 3.2.15 and propose a way of deciding whether the transformer is step-up or step-down.

Think 13 Use an example to explain how an electromagnetic device operates. 14 Propose a way in which a soft drink machine might ‘know’ when an incorrect coin has been inserted. 15 From the following, identify those situations in which an electric current is generated. a b c d

UNIT

3 .2

A magnet enters a wire coil. A magnet sits still inside a wire coil. A magnet is removed from a wire coil. A wire coil moves towards a magnet.

e A wire coil moves away from a magnet. f A current is turned on in a wire coil facing another wire coil. 16 Compare the voltages of transmission lines with that used at home. 17 Explain why power companies bother increasing the voltage of power lines if it is only going to be reduced again before reaching homes. 18 Propose a reason why high-voltage power lines are always kept well above the ground by tall pylons.

Skills 19 Design and sketch a circuit that uses electromagnets to release a trapdoor when a person steps on a certain section of floor.

[ Extension ] Investigate 1 Research how electromagnetism is used to record and erase magnetic audio or video tapes. Use a diagram to explain your information. 2 Research some of the discoveries made by Joseph Henry (1797–1878) in the area of electromagnetism and give a one-minute oral presentation on one discovery. Use props to assist you in your explanation. 3 Use an example to explain how ‘Fleming’s left-hand rule’ gives the direction of the force on a current in a magnetic field. 4 a Research whether it is dangerous to live near high-voltage power lines. b Write a letter to the government outlining the potential dangers of electromagnetic radiation. Be sure to support your ideas with evidence. c In your letter, recommend what should be done to reduce the risk of electromagnetic radiation to the community. d Conduct a class debate on this issue.

Surf 5 Find out more about electromagnetics and Japan’s maglev train by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button. Select one example of a device that uses electromagnetism and present your information in the form of an advertisement.

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Electromagnetism

UNIT

3.2

[ Practical activities ] Fig 3.2.18

Oersted’s experiment and the electromagnet Prac 1 Unit 3.2

2V

power pack

+–0

Aim To investigate the magnetic field around a current-carrying wire

VOLTS

Equipment Power supply, switch, insulated copper wire (1 m), tape, switch, small compass, cardboard tube, large iron nail

switch tape

+–

2V 0

compass just inside tube

power pack VOLTS

tape

1 m section of connecting wire

Questions 1 Explain what happens to the strength of a magnetic field as you move further from a wire. 2 Explain whether a larger current produces a stronger or weaker magnetic field.

switch

compass

Fig 3.2.17

Method 1 Assemble the apparatus as shown in Figure 3.2.17. Ensure the power supply is set to 2 volts.

3 Would several coils cancel each other’s magnetic fields or reinforce them? Justify your answer. 4 Explain whether an electromagnet is stronger or weaker with an iron core. 5 Describe how the magnetic fields differ at each end of the nail.

2 Hold the switch down and note any effect on the compass needle.

A simple generator

3 Investigate the effect of moving the compass further away from the wire. 4 What happens if the voltage is turned down (and the current reduces)? 5 Now wind the wire around the cardboard tube as shown in Figure 3.2.18. Use tape to secure the coils to the tube. 6 Compare the strength of the magnetic field inside the tube with that produced in step 2. 7 Now wind the wire around the nail instead of the cardboard tube. Use tape to secure the coils if required. 8 Hold the pointed end near the compass while holding the switch down. 9 Hold the head of the nail (the non-pointy end) near the compass while holding the switch down.

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Prac 2 Unit 3.2

Aim To investigate the correlation between magnetism and current electricity Equipment Solenoid, bar magnet, connecting wires, galvanometer or microammeter

Method 1 Connect the circuit as shown in Figure 3.2.19. Note: A galvanometer is like a very sensitive ammeter, and detects small currents. In each step below, observe the reading on the galvanometer as you carry out the step. 2 Move the north end of the magnet into the solenoid. 3 Leave the magnet resting in the end of the solenoid for several seconds. 4 Withdraw the magnet from the solenoid.

UNIT

3 .2 5 Repeat steps 1 to 4, but move the magnet more quickly. 6 Repeat steps 1 to 5, but move the south end of the magnet into the solenoid.

galvanometer

Questions

G

1 Explain why a globe was not used to detect current. 2 Explain whether a magnet in a solenoid always produces a current. S

N

3 Describe the effect of varying the speed of the magnet.

solenoid

Fig 3.2.19

4 Contrast the effect of the magnet when it is withdrawn with its effect when it enters the solenoid. 5 Describe whether changing the pole (north or south) that approaches the solenoid has an effect. 6 Predict the effect a stronger magnet would have.

A simple electric motor Aim To construct a simple electric motor Prac 3 Unit 3.2

Equipment 1.5 volt battery (‘D’ size), Blu-Tack, 2 rubber bands, 2 paperclips, 1.5 metres of enamelled copper wire, a small but strong disc magnet or a bar magnet, emery paper, pliers (optional)

Method 1 Wind the enamelled copper wire around the battery to make a solenoid. 2 Remove the wire from the battery and straighten 5 cm or so at each end. 3 Wind a centimetre or two of the ends around the loops of wire to keep them together. 4 Using emery paper, scrape the underside of each straight end to expose the copper (see magnified view of straight ends in Figure 3.2.20). 5 Use fingers or pliers to shape the two paperclips as shown. 6 Use the rubber bands to attach the paperclips to the battery. 7 Place the magnet so it sticks to the top of the battery (see Figure 3.2.20). Alternatively, hold a bar magnet near the coil. 8 Stabilise the battery using Blu-Tack. 9 Add the loops to complete the motor and check that measurements and positioning match the figure.

10 Give the loops a nudge (you may need to try spinning the coil both ways) to start the motor. You may need to experiment with the position of the magnet.

Questions 1 Explain why several loops are better than a single one. 2 Predict what would happen if the entire wire (loops included) was not insulated. 3 Explain how scraping half the coating from the straight ends of the wire helps. Predict what might happen if you didn’t do this. 4 Identify possible improvements to your model motor. 5 Take apart a small electric motor (e.g. from a broken toy) and compare the parts with your model.

View from above enamelled copper wire

coil magnet

less than 1 cm

Ensure part of coil is directly above magnet

less than 1 cm when coil is vertical

paper clip strong magnet rubber band

battery (1.5 volts)

Blu-Tack enamelled/insulated copper wire exposed copper

Fig 3.2.20

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UNIT

context

3.3 Visible light is only one section of a wide variety of waves known as the electromagnetic spectrum. While visible light allows us to see, other invisible forms such as X-rays enable us to see into the body without invasive surgery. Other invisible forms give us the radiant heat of sunlight and the basis of most communication, from radio to TV to mobile phones. It’s fairly easy

Two kinds of waves There are several different types of waves, but the main two are transverse and longitudinal (sometimes called compression) waves. These are illustrated in Figure 3.3.1 using a slinky. Fig 3.3.1

Two kinds of waves

4RANSVERSEWAVE

PARTICLE MOVEMENT

WAVEDIRECTION

! " PARTICLE MOVEMENT

,ONGITUDINALWAVE !

WAVEDIRECTION

to visualise ocean waves or ripples caused by a stone dropped in a pond, or even those in a slinky, but what exactly are the waves that make up light and the electromagnetic spectrum?

Rather than moving along with the waves, both simply bob up and down on the spot. If the coils of a slinky or the particles of water did move the full distance from A to B, they would all end up at B, leaving nothing Prac 1 at A—this clearly does not happen! p. 83

Properties of waves Imagine you are shaking a slinky back and forth to generate transverse waves at a steady rate. This rate has another name: frequency. If you are producing two waves every second, the wave frequency is 2 waves per second, or 2 hertz (2 Hz for short). The unit ‘hertz’ is used to describe anything that has regular repetitive behaviour, and can be taken to mean ‘per second’. For example, a wheel that rotates 10 times per second has a frequency of 10 hertz. Likewise, a sound wave that hits your eardrum with 200 compressions per second has a frequency of 200 hertz.

" COMPRESSION

RAREFACTION

Transverse wave

wavelength

amplitude

Breaking waves When an ocean wave reaches shallower water, friction from the sea bed slows the bottom of the wave more than the top, with the result that the top may break away, allowing some particles of water, possibly carrying a surfer, to move with the remains of the wave.

76

One of the special characteristics of waves is their ability to transfer energy from A to B without particles actually moving along the full route. When a transverse wave travels from A to B, the actual particles in the wave merely vibrate up and down. In a longitudinal wave the particles vibrate back and forth. Think of a surfer on a board or a boat floating in the ocean.

‘middle’ position

wavelength wavelength

Longitudinal wave

wavelength wavelength

particle’s middle position

maximum movement amplitude

Amplitude and wavelength for two kinds of waves

Fig 3.3.2

The distance between successive crests or successive troughs in a series of transverse waves is called the wavelength. The height of crests above their normal, middle position is called the amplitude of the wave. In a longitudinal wave, the wavelength is the distance between compressions or rarefactions, and the amplitude is the distance that particles vibrate from their normal, middle position.

UNIT

3 .3 cause a changing electric field, which causes another magnetic field, which causes another electric field and so on and so on. For this reason, we say that light consists of electromagnetic waves that travel at an incredible speed of 300 000 kilometres per second.

electric field

Light waves

magnetic field

Fig 3.3.3

The magnetic and electric fields of light waves are perpendicular to each other.

The range of colours we are able to see is called the visible spectrum. White light is really a mixture of all the colours of the visible spectrum, and consists of waves of different wavelengths and frequencies all travelling at the same speed. The human eye is more sensitive to some colours than to others.

Fig 3.3.4

Sensitivity of the eye

When sound or light travels from A to B, energy is transferred but no particles actually move from A to B. This suggests that these phenomena behave just like the water and slinky waves described above. As discussed in Science Focus 1, sound waves are longitudinal waves requiring particles to pass vibrations from one layer to the next. Hence sound can travel through gases, liquids and solids but cannot travel through a vacuum. But how can light be a wave? Nothing seems to be vibrating back and forth when we shine a torch, though we can see where its beam strikes an object. Also, light can travel through the vacuum of Spirit warning space. Aboriginal tribes used We saw in Unit 3.2 that an a device called a bull electric current causes a magnetic roarer, or kooladoo, using field and that a changing te unica to comm sound waves. The bull magnetic field causes a current. roarer is used by tribes to A mass will only fall if there is a warn women and young gravitational field, and likewise men’s from children away ceremonies, particularly an electric current only flows during initiation. It is made when there is an electric field. from a flat piece of wood, What all this means is that a in etres centim about 30 magnetic field can cause an length and fastened at one end to a string. When electric field and vice versa. swung around in the air Both magnetic fields and electric it produces a whirring or fields are invisible, but can howling sound likened to those of animals or spirits. be detected by the effect they The sound was regarded have—for example, the electric as the voice of a spirit field around a Van de Graaf that comes to take the young boys away. In some generator can make your hair cases bull roarers were stand on end and the magnetic associated with various field of a magnet will move iron objects known as churinga tiated unini or n filings around. which wome men were forbidden to see. Light can be considered a Penalties were severe— series of changing magnetic blinding by fire-stick or . and electric fields where the death even changes in a magnetic field

400

500

600

7400

Wavelength (nanometres) 1

1 nanometre = 1 000 000 000 of a metre

Other types of electromagnetic waves The visible spectrum is only a small part of a wide group of electromagnetic waves. In order from smallest to largest wavelength, these are: gamma rays, X-rays, ultraviolet rays, visible light, infra-red rays,

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Waves in communication

7AVELENGTHINMETRESM n n n n PICO NANO METREPM METRENM GAMMARAYS

8 RAYS

n

ULTRAVIOLETRAYS

   &REQUENCYINHERTZ(Z

Fig 3.3.5

n







n n MICRO METRE±M

nn n MILLIMETRE METRE KILOMETRE MM M KM

INFRAREDRAYS

VISIBLELIGHT



n





MICROWAVES





RADIOWAVES

!-RADIO &-RADIO SHORT WAVE LONG WAVE RADIO RADIO      GIGAHERTZ MEGAHERTZ '(Z -(Z

The electromagnetic spectrum. Although wavelengths and frequency vary, speed is the same (300 000 000 metres per second) for all types of electromagnetic waves.

microwaves and radio waves. These make up the electromagnetic spectrum. Though we cannot see these other types of waves, they can be detected and are used in a variety of applications.

Gamma rays Gamma rays are extremely high-energy waves released in bursts from the nucleus of certain atoms including uranium and plutonium—hence

they are a form of nuclear energy. Substances that release nuclear energy such as gamma rays are said to be radioactive. Gamma rays can be detected using photographic film or a Geiger counter, and can be used to destroy cancer cells, which are more sensitive to radiation than normal cells. Some normal cells are still killed, however, resulting in the unpleasant side effects of radiotherapy.

X-rays X-rays are produced when fast-moving electrons lose energy suddenly, for example when smashing into a metal target. Short-wavelength X-rays can penetrate dense metals such as lead, while long-wavelength X-rays penetrate flesh but not bone, and so may be used to ‘photograph’ inside the body. The term ‘X-ray’ is also used to refer to the actual photograph produced. An X-ray machine electron gun

electron beam

Fig 3.3.7 target

X-rays

Fig 3.3.6

78

Gamma rays are used to produce scans like this one of a human skeleton. A radioactive isotope is injected into the blood vessels supplying the region, and tends to concentrate in tumours and cancerous bone. Variations in emitted gamma ray intensity result in different areas showing up in the image.

UNIT

3 .3 electric field vibrating in one direction

Polarisation

electric field vibrating in several directions

Fig 3.3.9

Polarisation

Prac 2 p. 83

Sunlight consists of waves in all sorts of orientations. Polarising materials allow only waves whose electric fields vibrate in a certain direction to pass, absorbing all other waves. This reduces glare dramatically. Hence polarising materials are often used in the lenses of sunglasses.

Infra-red rays

A coloured X-ray photograph of a woman’s foot in high-heeled shoe

Fig 3.3.8

Ultraviolet radiation Whenever the Sun shines on us, we receive both visible In 1895, Wilhelm Konrad light and invisible ultraviolet Roentgen was passing (‘ultra’ means ‘beyond’) or UV electrons through a gas in arge disch a called radiation. A small amount a device tube when he noticed that a of UV radiation is vital as it card coated with a barium salt helps produce vitamin D. Too nearby began to glow. much, however, causes damage even He noticed that the card ts objec d place he when d to the skin in the form of a glowe between it and the tube. When suntan, sunburn or various he placed his hand in the skin cancers. Some washing a see way he was amazed to s bone hand his powders contain special of ow’ ‘shad on the card! Roentgen had chemicals which absorb discovered X-rays. ultraviolet light and then reemit it as visible light to give the impression of ‘whiterthan-white’ clothes. Ultraviolet light can be used to kill bacteria, and is used in hairdressing salons and air-conditioning systems. A handy discovery

‘Infra’ is Latin for ‘below’ and infra-red (or IR) rays have a frequency below that of red light. They are often associated with heat and are released from vibrating atoms or molecules. All objects contain vibrating atoms and molecules, so all objects emit infra-red radiation. The hotter the object, the more the vibration, and so the more the energy released as infra-red radiation. When high-energy waves are emitted they become visible as red light—hence the expression ‘red hot’. Remote control devices emit infra-red waves which are detected by special components within televisions and sound systems. They are then converted to electrical energy to control functions such as volume and channels. An infra-red image of a person using a mobile phone

Fig 3.3.10

Visible light Visible light includes the colours of the rainbow (ROYGBIV) and various combinations, including white. Though we can see an amazing range of colours, these colours are a very small part of the electromagnetic spectrum.

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Waves in communication Microwaves

>>> The behaviour of different types of radio waves

Sometimes called short-wave radio waves, microwaves are generated by vibrating electrons in electrical devices, and typically have a wavelength of a few centimetres. They are easy to direct, can pass through the Earth’s ionosphere and are used in satellite communication, radar and mobile phones. Water molecules in food vibrate at the same frequency as microwaves. Hence food strongly absorbs microwaves, converting their energy into heat energy in a microwave oven.

Fig 3.3.12

space satellite

short radio waves (microwaves) pass through the ionosphere

ionosphere reflects medium radio waves

microwaves used for line-of-sight links long radio waves diffract round the Earth

(bending around objects like this is called diffraction). Short waves may also travel around the Earth, by reflecting from the ionosphere.

AM and FM

Fig 3.3.11

This dish receives microwave and satellite signals and relays them to Earth-based parts of the communications network.

Radio waves Radio waves are also generated by vibrating or oscillating electrons (e.g. in a transmitting aerial), and Marconi are used in radio and television Italian engineer is i broadcasting. Radio waves have Guglielmo Marcon generally credited with wavelengths of hundreds of inventing radio. In 1895 metres to tens of centimetres he transmitted a signal and are classified into several the 2.4 kilometres in er’s fath his of s und categories. Long radio waves gro property. He patented the are useful for communicating first ‘wireless telegraphy’ around the Earth, as they bend 6. system in 189 to follow the Earth’s surface

80

You are probably aware of the terms AM and FM when referring to radio stations, but what do they really mean? Electromagnetic waves such as radio waves can carry information (e.g. sound or vision) as changes or fluctuations in either frequency or amplitude. Receivers detect these changes and convert them back to sound or vision or some other form. This information first must be converted into a wave, in a process called modulation. Amplitude modulation, or AM, is the process in which information is carried as changes in wave amplitude. Similarly, frequency modulation or FM is the process in which information is carried as changes in wave frequency. Radio stations transmit sound using both AM and FM, while television stations transmit sound using FM, and vision using AM. Australia’s national broadcaster, the ABC, transmits AM carrier waves of frequency 774 kilohertz (1 kilohertz = 1000 hertz), which will be detected by a radio tuned to this frequency. The higher frequencies of FM stations are less affected by interference, and provide a better quality sound than AM, though they have less range.

UNIT

3 .3 Waves cause electrons in radio antenna to vibrate. Sound wave (pressure wave)

Radio antenna Electrical signal

Amplified electrical signal

FM (frequency modulation)

Receiver

Amplifier

Microphone

Oscillator

Electric carrier wave added

AM (amplitude modulation)

Worksheet 3.3 Electromagnetic spectrum

UNIT

3.3

Modulated waves transmitted by radio mast

Electrical signal created and amplified. Carrier wave removed from electrical signal (demodulation).

Modulation is one of many steps in the transmission of sound via radio waves.

Speaker converts electrical signal to sound waves.

Fig 3.3.13

[ Questions ]

Checkpoint Two kinds of waves 1 State the names of the two kinds of waves. 2 Outline the main differences between them.

Light waves 3 Copy and complete the following statement: A light wave is made up of changing ________ and ________ fields that are ________ to each other, and moves at ________ metres per second. 4 State whether the following statements are true or false. a All electromagnetic waves move at the same speed. b Each different colour of light has a different wavelength. c The visible spectrum contains the electromagnetic spectrum. d Waves transfer energy by moving particles along with them.

Other types of electromagnetic waves 5 State one similarity and one difference between the waves of the electromagnetic spectrum. 6 State the speed of light. 7 List the main types of waves in the electromagnetic spectrum in order from shortest to longest wavelength.

AM and FM 8 AM and FM radio have modulated wavelengths. State the full name for ‘AM’ and ‘FM’. 9 Outline the purpose of modulating radio waves. 10 State an advantage of each type of carrier wave.

Think 11 Explain why it does not make sense to talk about the wavelength of white light. 12 Identify which colour of light has the: a greatest wavelength b highest frequency 13 State which colours the human eye is most sensitive to. 14 Infra-red cameras can help find a lost bushwalker. Outline how this is possible. 15 Identify the radio wave that can penetrate the Earth’s atmosphere. 16 State the name of the harmful rays that are released in a nuclear explosion. 17 Is UV radiation good, bad or both? Justify your answer. 18 Explain how a Geiger counter and gamma radiation can be used to measure the thickness of an object.

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Waves in communication

Analyse

Skills

19 State the wavelength of this wave.

24 Construct a diagram of a transverse wave that has: a a wavelength of 3 cm and amplitude of 2 cm b a wavelength of 10 cm and amplitude of 1 cm. 25 Convert: a 600 nanometres to metres b 0.000 000 850 metres to nanometres 26 Construct a table with the following headings and enter information about each type of electromagnetic wave.

Fig 3.3.14 20 A student shakes out 20 waves on a slinky in 10 seconds. Calculate the frequency of the waves.

Type of electromagnetic radiation

21 The time between each wave Visible light passing is called the period. a Identify the period for the waves in Question 20. b If the wave frequency increases, predict what effect this will have on the period: A The period will increase. B The period will stay the same. C The period will decrease. D There is not enough information to answer the question. 22 Identify which type of electromagnetic wave has a wavelength of: a 1m b 1 km

Source

How it is detected

Use/s

1 millionth of a metre

The Sun, very hot objects

Cones in the eye, photographic film

Sight, photography

27 Construct a diagram of: a a frequency-modulated carrier wave b an amplitude-modulated carrier wave 28 Calculate the frequency of carrier waves transmitted by: a 107.5 ZZZ FM b 1278 2AW (an AM station)

[ Extension ]

c 0.5 mm d 1 millionth of a millimetre 23 Explain what you would expect to see if the following polarising filters were placed in front of a light source as shown. Fig 3.3.15

82

Typical wavelength (approx.)

Investigate 1 Outline the contribution to science of one of the following people by writing a brief biography of their life. a Scottish physicist James Clerk Maxwell and his work on electromagnetic wave theory b the development of radio communications by the American engineer Edwin Armstrong c the first transmission of radio waves by Guglielmo Marconi d John Logie Baird’s contribution to the development of television

2 Radio waves include LW, MW, SW, VHF and UHF. a State what these stand for and why the waves are classified like this. b Describe uses for each type of wave in communications.

Action 3 Design an experiment to investigate how ripples in a tank or pond are affected by a change in water.

UNIT

3.3

DYO

UNIT

3 .3 4 Find a design for a simple radio or ‘crystal set’ (e.g. from an electronics shop or the Internet), then construct and test it.

DYO

Surf 5 Complete a tutorial on waves and the electromagnetic spectrum and record the outcome of your tutorial in your notebook. You can find a link by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.

[ Practical activities ] Waves in a slinky Aim Investigate the movement of waves in a

Prac 1 Unit 3.3

slinky

Equipment A slinky, masking tape, stopwatch, floor or corridor space in which to generate waves between points 5 to 10 metres apart

Method 1 With a partner, stretch a slinky to a length of 5 metres or so without permanently deforming it. 2 Use masking tape to mark points along the slinky every metre or two.

3 Describe what happens when waves meet: a on the same side of the slinky b on opposite sides of the slinky

side to side movement

4 If time permits, investigate longitudinal waves produced by bunching up and releasing the coils.

3 Generate a horizontal transverse wave as shown, carefully observing the masking tape labels as the wave passes them.

Fig 3.3.16

4 Generate a small wave and measure the time it takes to get to the other end. Calculate the speed of the wave. 5 Keeping the slinky stretched by the same amount, generate a bigger wave and calculate its speed. 6 Generate waves at a high frequency and calculate their speed. 7 Repeat but for waves of low frequency. 8 Investigate what happens when waves are generated simultaneously from both ends of the slinky: a on the same side b on opposite sides

direction in which wave travels

Polarised! Prac 2 Unit 3.3

Aim To investigate the interaction of two polarising filters Equipment Two polarising filters, window or other light source

Method 1 Look through one of the filters at a nearby window or other light source.

Questions

2 Now hold a second filter in front of the first, and rotate it while keeping the first filter still.

1 Describe the direction in which the masking tape labels move compared with the travelling wave.

Questions

2 Describe whether the wave speed is affected by: a the size of the wave b the frequency of the waves

2 Explain your observations.

1 Describe what you saw in each case.

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UNIT

context

3. 4 The first Europeans who settled at Sydney Cove received all their messages from the outside world by sailing ship. Most communication was with England, messages taking a year to get there and another for the answer to return. Communication is obviously very different now from what it was in 1788 and will continue to develop in the future. Many of these

Communications history

methods might seem to be science fiction right now, but remember that email and the Internet were hardly known ten years ago! There are many possibilities for how we will communicate that we do not even know about yet.

60 kilometres by telegraph. By opening and closing a simple switch (telegraph key), dots or dashes were sent along the telegraph and transferred to a paper tape printout or converted to sounds for translation by a telegraph operator.

The telegraph Communication was once based on drums, smoke signals, mirrors and flags (semaphore). Then the invention of the telegraph (‘tele’ means ‘at a distance’) changed communication forever. It was a system that sent electrical pulses along a wire. The first telegraph was demonstrated in 1835 by Professor Moncke of Heidelberg, Germany. In 1837, Englishman William Cooke demonstrated his own system (developed with Charles Wheatstone), transmitting a signal a distance of 1.6 kilometres. These early telegraphs used the magnetic effect of a current to move small pointers. In 1844, American Samuel Morse used a code involving dots and dashes to send a message

A

J

S

1

B

K

T

2

C

L

U

3

D

M

V

4

E

N

W

5

F

O

X

6

G

P

Y

7

H

Q

Z

8

I

R

FULL STOP

9 0 (zero)

COMMA

Fig 3.4.1

84

In Morse code, the most commonly used letters have the shortest codes.

A telegraph receiver used to print Morse code messages

Fig 3.4.2

The first telegraph cable was laid across the English Channel in 1851, and in 1858 the first cable across the Atlantic Ocean was laid, although it failed after a month—the tiniest hole in a cable’s insulation was enough to provide an alternative path for the current and so destroy the signal. In 1866 the transatlantic cable was successfully re-laid. By 1869, a cable under Bass Straight connected Tasmania to mainland Australia. During 1872, the Overland telegraph line was completed from Adelaide to Darwin, where it was joined to an undersea cable to Java. From Java, the line connected to Europe and England, allowing overseas communication within hours instead of the customary two months by ship. The telegraph was the main form of telecommunication until the emergence of the telephone.

The telephone

Patent problems

In 1874, Scottish inventor Italian inventor Antonio Alexander Graham Bell came Meucci is credited in his up with the idea of converting home town of Florence with inventing the first sound (e.g. speech) into telephone, but was unable varying electrical impulses for to afford the US$250 to transmission along a wire and patent his idea. then converting the impulses back to sound at the other end. On 10 March 1876, in Boston USA, Bell spoke to his assistant, Thomas Watson, in Cambridgeport, 3.2 kilometres away. This was the first ever telephone call. Bell’s words were: ‘Mr Watson, please come here. I want to see you’. Alexander Graham Bell, inventor of the telephone

Fig 3.4.3

A telephone system requires the following main features: transmitters, receivers, exchanges and a The call of the dead! network connecting users. Almon B. Strowger was an Early manual exchanges who American funeral director atic autom first the ted inven required an operator to use telephone exchange. It is a switchboard to physically rumoured that his incentive was connect a wire from the ess to stop the flow of busin The . sition oppo his caller’s telephone to one going to going operator at his local manual to the telephone of the person exchange was apparently being called. This was called to es directing all funeral queri ess! busin a line. As the number of al funer and’s her husb By establishing an automatic calls on a system increased, exchange, his competitor’s wife mechanical exchanges could no longer manipulate calls.

UNIT

3 .4 were developed that were able to find free lines and connect callers automatically. The first fully automatic exchange in Australia came into operation in Endeavour Hills, Victoria, in 1981. Nowadays all Australian exchanges are fully automatic and switching is computerised, resulting in a system that is quick and very reliable, with calls able to be continually rerouted to make best use of available lines.

Today’s communications network—analogue and digital Our current global communication network must handle a huge amount of ‘traffic’ including voice, image and computer data. It copes by transmitting several signals at once in each line. When you talk into a telephone, the initial input is in the form of smoothly varying sound waves. These are converted into smoothly varying Digital codes electrical signals, otherwise known Information can be represented by as an analogue signal. Most homes combinations of the today are connected to the network digits 1 and 0. This via copper wires designed for use makes it much easier to with analogue signals. Different accurately transmit since short pulses of light or signals can be sent simultaneously electricity can represent by using different frequencies. They the 1 and 0 combinations. can then be separated or filtered at For example, any number can be represented as the receiving end. Hence, one way combinations of 1 and 0 of transmitting several calls at once by imagining place value is to use several carrier waves of columns as shown below. Starting from the right, we different frequencies. This is known use 1 or 0 to build up the as frequency division multiplexing, number in digital form. For or FDM. example 5 in digita Fig 3.4.4

l form is 101 (or pulse, no pulse, pulse). Numbers in this form are also called binary numbers. Each 1 and 0 is called a bit, so the binary number 101 is composed of three bits.

The numbers 5 and 13 in digital form 5

only 1 or 0 allowed

4

2

1

1

0

1

a 3-bit binary number 13

only 1 or 0 allowed

8

4

2

1

1

1

0

1

a 4-bit binary number

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The communications network Digital signal is particularly suited to transmission by optical fibres. Each call is sampled 8000 times per second and is converted Digital to analogue into a signal comprising bits (a bit and back again may be considered as a 1 or a 0, or a A modem converts a pulse or no pulse, or ‘on’ and ‘off’). from ls signa l digita computer into analogue Several different calls may be cut waves in a process called into chunks, interspersed, and sent modulation. Most of the in the one ‘data stream’ at a single made is rk netwo telephone frequency, and sorted out again at from copper wires that are only designed to carry the end of the transmission. This is analogue waves. Hence called time division multiplexing or the need for a modem. A TDM. modem can also convert analogue signals received Frequency division multiplexing into digital ones (called (FDM), in which streams of demodulation) for data are sent at different rates processing by a computer. This dual capability is or frequencies, may be used where a modem gets combined with TDM to maximise its name: modulator– the bandwidth, or the amount of demodulator. information that can be carried. Multiplexing

Fig 3.4.5

these and protects the cable from damage. The inner core carries analogue or digital signals, while the outer copper layer protects the signal from interference between tubes in the same cable or from outside sources. The outer layer also reduces attenuation, or loss of signal strength. The first major coaxial cable in Australia opened in 1962, linking Sydney, Canberra and Melbourne.

insulation

electrical signal

copper core copper wire braiding

Fig 3.4.6

tough plastic sheathing

Coaxial cable can carry both analogue and digital electrical signals. Several of these may be packed into one larger cable.

Time division multiplexing

Optical fibres Second signal/call frequency 1

frequency 2

First signal/call

1 0 1 1 0 1 1 1 00 1 0 1 1 0 0 1 0 1 01 1

1 1 0 1 0 1 0 1 11 0 1 1 0 1 0 1 1 0 1 10 10 Second signal/call

data stream 1

data stream 2

First signal/call

While small-scale links in the network are through copper wire, major links are provided by coaxial cable, fibre-optic cable and radio waves (including microwaves), sometimes via satellites. Signals are converted from analogue to digital as required, depending on the section of the network.

Coaxial cable Most coaxial cables contain several tubes, each consisting of an inner copper core and an outer cylindrical copper mesh layer separated by an insulating material. A tough outer sheath surrounds

86

In the 1930s, the inventor of optical fibre patented a method for manufacturing it ‘just in case anyone ever finds a use for it’. Today, optical fibre forms the backbone of the global communications network. An optical fibre is a hair-thin tube or strand of glass surrounded by a protective cladding which traps and conducts light, thanks to a phenomenon known as total internal reflection (see Chapter 4 in Science Focus 3). To use optical fibres for communication of voice, fax or computer data, the original signal first must be converted into an electrical signal, which is in turn converted into pulses of light, the light being provided by a laser. Laser light is coherent—that is, all its waves are of the same frequency and wavelength and are ‘in step’, resulting in a powerful beam that can carry vast amounts of information with little dispersion or spreading out. Lasers can be switched on/off many millions of times every second, making them ideal for transmitting digital data. Sydney and Melbourne are currently linked by over 1.5 million kilometres of optical fibre.

Fig 3.4.7

UNIT

3 .4 Many optical fibres can fit in a single cable.

Teacher demonstration The laser plastic sheath protective layer optical fibre

laser light

outer covering

WARNING: Never look directly at the source of a laser beam, and never direct a laser beam towards anyone’s eyes. Beware of possible reflections that may redirect a beam near people’s eyes.

Your teacher may demonstrate a laser beam by directing a beam into some chalk dust scattered in the air in a darkened room.

steel core

Microwaves

Incoherent light (many wavelengths, not in step)

Fig 3.4.8

Coherent light (one wavelength, waves in step)

A light bulb produces a mixture of light of various wavelengths which we perceive as white light. A laser produces coherent light of only one wavelength.

LASERS s chromium atoms In a ruby laser, energy from a flash tube excite reflects between which light, emit in the ruby. These atoms then s to emit light atom more lating stimu rod, ruby the of the ends allows some end tive reflec lly partia of the same wavelength. The gives laser light its also ruby The . beam laser a as e escap light to acronym that stands for characteristic red colouring. LASER is an sion of Radiation. Emis lated Stimu by on ificati Ampl Light

Microwave links can be used to transmit digital signals through the It’s that clear! air from repeater station to repeater The glass used in optical station. These stations transfer signals fibres is so clear that from one area to another, and boost you would be able to see signals as required. Microwaves travel through a 100 kilometre thick window made of it. in straight lines, so each repeater station must be in sight of the next one in the network. Signals may be modulated to carry pulses of two different frequencies within the wave—one representing 1 or ‘on’, the other representing 0 or ‘off’. Microwaves are used to link satellites for longdistance communication, as well as within the mobile phone network. The first microwave link in Australia was established between Melbourne and Bendigo in 1959. A microwave repeater station

Fig 3.4.10

laser beam

fully reflective mirror

partially reflective mirror (allows some laser light to leave)

How a laser works

Fig 3.4.9

87

>>>

The communications network Mobile phones Mobile phones use microwaves to transmit digital signals within a network of regions called cells. Each cell uses a different set of frequencies, with no adjacent cells using the same frequency. When you turn on a mobile phone, it sends a signal to the network, which registers your location. As you move from place to place, base stations within the network detect signals from your mobile phone, and the base station receiving the strongest signal sends it to the exchange. When a call is made to your mobile phone, the exchange detects where you are and sends the call to the base stations in the cell you are in. All the above methods of transmission require repeater stations every 50 kilometres or so to boost weakened signals. The table opposite shows the different capacities of each type.

/RDINARY PHONE

/PTICALFIBRES TRANSMITTINGDIGITALINFORMATION BYLIGHTPULSESENABLESMANY CALLSTOBESENTDOWNONEFIBRE SIMULTANEOUSLY

&AXMACHINE FAXTRANSMISSIONS ARESENTOVERTHE TELEPHONENETWORK

!NALOGUESIGNAL ANALOGUESIGNALS FROMORDINARY PHONESARE CARRIEDBY COPPERCABLE TOTHELOCAL EXCHANGE

DIGITALSIGNAL

88

Maximum number of two-way conversations

Copper

600

Coaxial cable

2700

Optical fibre

28 720

Microwaves

1920

3ATELLITEUPLINK ENCRYPTEDDIGITAL INFORMATIONIS SENTTOSATELLITES USINGMICROWAVE FREQUENCIES

-OBILE PHONE

-ICROWAVES DIGITALINFORMATION ISSENTFROMMOBILE PHONESTOBASE STATIONUSING MICROWAVE FREQUENCIES

-AINEXCHANGE THEMAINEXCHANGE HANDLES COMMUNICATIONS BETWEENORDINARY PHONESANDTHE MOBILEPHONE NETWORKAND ROUTESLONG DISTANCEAND INTERNATIONALCALLS

"ASESTATION THEBASESTATION RECEIVINGTHE STRONGESTSIGNAL FROMAMOBILE PHONEROUTESTHE CALLTOTHEMOBILE PHONEEXCHANGE

#OMMUNICATIONSSATELLITE ORBITINGSATELLITESAREUSEDTOROUTECALLS BETWEENPLACESNOTLINKEDBYCABLE $IGITALSIGNAL DIGITALINFORMATIONISMULTIPLEXED ALLOWINGMULTIPLESIGNALSTOBE TRANSMITTEDSIMULTANEOUSLY

,ONG DISTANCEOR INTERNATIONAL CONNECTION OPTICALFIBRESARE USEDTOTRANSMIT LONG DISTANCECALLS MANYOPTICAL FIBRE CABLESARELAIDONTHE SEABED

$IGITAL 5RBANCELLS CELLSARESMALLER SIGNAL INURBANAREAS GIVINGTHENETWORK GREATERCAPACITY

Fig 3.4.11

Worksheet 3.4 ADSL: Digital communication

The global communications network

-OBILEPHONEEXCHANGE CALLSAREROUTEDTOTHE MAINEXCHANGEOR ,OCALEXCHANGE DIRECTTOABASESTATION LOCALEXCHANGE BYTHEMOBILE DIGITISESCALLS PHONEEXCHANGE FORLONG DISTANCE TRANSMISSION

#ELL THEMOBILEPHONE NETWORKISDIVIDEDINTO HEXAGONALCELLS EACH WITHABASESTATIONIN THEMIDDLE

Transmission method

A modern, and some would say essential, communication device—the mobile phone

Fig 3.4.12

,INE OF SIGHTMICROWAVELINK DIGITISEDCALLSFROMLOCAL EXCHANGESAREROUTEDTOTHE MAINEXCHANGEVIATERRESTRIAL MICROWAVELINKS

-OBILEPHONEEXCHANGE THEMOBILEPHONEEXCHANGESENDS OUTCONTROLSIGNALSTOLOCATETHE BASESTATIONRECEIVINGTHESTRONGEST SIGNALFROMAMOBILEPHONE

&AXMACHINE

-OBILEPHONENETWORK BASESTATIONSSENDDIGITALINFORMATION TOTHECELLPHONEEXCHANGEOVER OPTICAL FIBREORCOPPERCABLE 7EAKENINGSIGNAL ASTHEMOBILEPHONEMOVES FURTHERAWAYFROMTHEBASE STATION THESIGNALWEAKENS -OVINGMOBILE PHONE MOBILITYISTHE PRIMEASSETOF THECELLPHONE 3EAMLESSRECONNECTION ASTHEMOBILEPHONEMOVESFROMONE CELLTOANOTHER THECALLISREROUTED FROMONEBASESTATIONTOTHENEXT WITHOUTABREAKINTHECONVERSATION

The future It is likely that in the future our homes will be connected to one cable which provides a broad range of services including telephone, fax, Internet connection, video on demand, video conferencing,

UNIT

3. 4

UNIT

3 .4 pay TV, interactive video and games, and on-line shopping, news and medical diagnosis. Known as B-ISDN—short for Broadband Integrated Services Digital Network—such a system is the ‘next step’ in our ever-expanding global communications network.

[ Questions ]

Checkpoint Communications history 1 List some older forms of communication. 2 Outline the origin of the term ‘Morse code’. 3 State the distance over which the first telephone call was made.

Today’s communications network—analogue and digital 4 State whether the telegraph used digital or analogue signals. 5 Many signals on the communications network are not in digital form. Explain why not. 6 a List the two types of multiplexing. b Describe how each type of multiplexing allows several calls on the one phone line.

The future 7 State the name of the network predicted for future use. 8 Outline the main advantage of this system.

18 The world is sometimes referred to as a global village. Explain why. 19 Your behaviour would probably change if you were having a video-phone conversation. Contrast your behaviour on a video-phone with that on a normal phone.

Analyse

Strowger switch

20 Explain why the Strowger switch shown in Figure 3.4.13 is for set connection to a telephone that has the number 33. 21 Explain why repeater towers in the mobile phone network are arranged in a zigzag pattern, as shown in Figure 3.4.14.

return spring

vertical-drive finger

contact arm

rotarydrive finger contacts

Think 9 List some of the communication services/devices available today that were not available 50 years ago.

Fig 3.4.13

Fig 3.4.14

10 Propose a way of remembering the Morse code for the digits 1, 2, 3, … 0. 11 State two advantages of digital signals over analogue ones. 12 The word ‘signal’ is used a lot in this chapter, rather than ‘call’. Explain why. 13 If several single-core copper wires were used instead of coaxial cable to carry phone calls between two cities, predict the effect. 14 Explain why laser light is ideal for use in fibre-optic communication. 15 Mobile phones are sometimes called cell phones. Explain why. 16 Propose the main advantage of having several different communication paths between two cities. 17 B-ISDN will provide many services in the future. List as many as you can.

Skills 22 a Estimate the number of words per minute you could send using a telegraph device and Morse code. b Estimate the number of words per minute you can say at normal conversation pace. 23 Construct your name in Morse code.

>> 89

The communications network

>>>

24 Decode the following and record the message.

Fig 3.4.15

25 Construct a suitable graph showing the different call capacities of the various cables and microwaves. 26 Although Sydney and Melbourne are only 1000 km apart, there is about 1.5 million kilometres of optic fibre between the two cities. Calculate the number of ‘lines’ or individual optic fibres this represents.

[ Extension ] Investigate 1 There is concern about the effects of mobile phone radiation on the user’s brain. a Gather evidence supporting or denying this effect. b Evaluate your evidence and decide whether it is a concern. c Propose ways in which users of mobile phones can reduce the possible risk. d Present your information as an advertisement (radio, print or television) to pass on your findings to others. 2 Research the lives of one of the early telecommunications inventors and write an autobiographical account of their achievements.

90

3 The original Overland telegraph line was a single strand of wire that transmitted signals using pulses of electric current. There must be a complete circuit for electricity to travel. Explain how the Overland telegraph works with just one wire connecting two places. 4 Research the development of the Internet/World Wide Web. Explain the role of routers and servers in this vast network.

Surf 5 Visit the ‘Telstra classroom’ to choose and complete a tutorial kit in an area of communication that interests you. Construct a PowerPoint presentation on advances in the field of your interest. You will find a link to the site by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.

Create 6 Design a home that uses several futuristic communications services and devices, and explain how each is used.

Science focus: Microwaves cook from the inside Prescribed focus area: The applications and uses of science By Karl S. Kruszelnicki 2004 Microwaves are very weird. They will make food hot, but they are not hot themselves! We humans started using fire to heat our food about one million years ago. And for most of that million years, we used variations on that theme—such as baking, boiling, steaming, poaching, roasting, grilling, frying and so on. There was no really new way to cook food until we started using microwaves, about half-a-century ago. Even today, most people don’t really understand microwaves. But whatever the reason, most people wrongly believe that microwaves cook the food from the inside first. The first real “use” of microwaves was in radar units during WW II. Radar gave the British the huge advantage of being able to detect the approaching enemy planes at night, or through thick cloud. Wartime radar began in 1940, when Sir John Randall and Dr. H. A. Boot invented the magnetron, a device to generate microwaves. The magnetron squirted out the microwaves for only a brief instant, and then stopped transmitting. A different part of the radar unit then listened for the echo bouncing back. There would be an echo only if the transmitted radar beam happened to land on a target. Some of the radar beam energy would be bounced off the target back to the radar unit. If the radar unit had to wait for a long time, the incoming planes were far away—but if there was only a short time before the echo arrived, then the planes were very close. During WW II, the British government got the American government to help with the development of radar. The Raytheon Corporation in the USA became involved. Dr. Percy L. Spencer, an engineer with Raytheon, redesigned the radar units, and worked out how to boost the production from 17 units per week, to 13,000! The idea of using microwaves to cook food came accidentally, around 1946. It was the same Dr. Spencer

who hit on the idea. He had been working long and hard, testing a magnetron—and he needed a break. Luckily, he had a stash of chocolate in his pocket—but not so luckily, the chocolate bar had melted, and had ruined his trousers, leaving him still hungry. But why had the chocolate melted? After all, it wasn’t a hot day. He was an engineer with both an appetite, and a good sense of curiosity. So he got a bag of popcorn kernels, and blasted then with microwaves out of his magnetron. Soon, he had delicious popcorn all over the laboratory floor. He also tried cooking raw eggs, but that experiment wasn’t so successful. The pressure inside rose so rapidly that the eggs burst. So the microwaves could cook food—but with varying degrees of success. Raytheon took up his ideas and developed a commercial microwave oven, the Radar Range. It was enormous (as big as a fridge and weighing 300 kg) but with a very small cooking volume (roughly the same as a modern microwave oven). The sales, unsurprisingly, were quite modest.

Blasting popcorn with microwaves led to the development of the microwave oven.

Fig SF 3.1

91

So how did the microwaves cook? The Raytheon engineers soon found out that microwaves pass right through glass, paper, pastry, fats and most china. On the other hand, water absorbs microwaves very well indeed. The microwaves “shake” the water molecules directly. The molecules of water vibrate about 2.45 billion times each second, and as they rub against each other, this friction produces the heat for cooking. This is how microwaves cook.

microwave, the pastry crust won’t get very hot, but the contents inside will. As you bite into the potato or pie, you pass through the cool (low water) pastry crust into the hotter innards—and you burn your mouth. Second, in that original post-War experiment by Spencer, the egg that he exploded did seem to cook from the inside. But that was because it had a shell that was low in water, and an inner core that was high in water. So the egg looked “normal” until the water on the inside turned into steam and exploded the egg apart. In this case, the inside (the water) cooked, and the outside (the shell) did not. So while the invention of radar turned the Art of War upside down, it did not turn the Art of Cooking inside out…

[ Student activities ]

This X-ray of a microwave oven shows the magnetron (purple, lower right). The magnetron is the tube in which electrons are generated. These electrons are affected by magnetic and electric fields to produce microwaves that are directed at the food.

Fig SF 3.2

So what about microwaves cooking from the outside in? Think of the food as being in spherical layers, like an onion. Let’s assume that each layer is a centimetre thick, and that it absorbs 10% of the incoming microwave radiation. After the first centimetre, only 90% of the energy is left. After the second centimetre only 81% is left—and so on. You can see that more of the microwave energy is absorbed in the outside layers, with hardly any getting to the very centre. Food in a microwave oven cooks from the outside to the inside. So how did this myth that microwaves cook from the inside start? There are two possible explanations. First, pastry and other fatty crusts are low in water. So if you heat a baked potato or a meat pie in your

92

1 a Examine the use of microwaves further. This could include one of the following applications: ovens, satellite communications, mobile phones, radar. b Construct an advertisement to sell the microwave technology you have investigated. Think about who you are aiming the advertisement at—the target audience. Include information about the following: i How can the technology be used? ii What are the advantages of this technology over alternatives? 2 Microwave ovens have recently been the target of safety campaigns because a number of children have been badly burnt while using these devices. a Research how a microwave oven can be a risk to children, and what types of injuries are commonly caused by them. b Propose a set of safety guidelines for microwave use to keep children safe. c Synthesise your information into a safety poster to be placed above a microwave oven. 3 a Research the history of microwaves, their discovery and early uses further. This could include researching one of the people discussed in the feature article above. b Give a visual presentation of your information.

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UNIT

context

3.5 Mobile phones and the communications network, security systems, televisions, computers, supermarket barcode scanners, microwave ovens, digital watches, CD and DVD players all involve electronics—the use of electric circuits containing miniature components to control electric current and hence perform a variety of useful tasks.

Resistors Resistors are commonly made as small, banded, cylindrical devices made of compressed carbon, or a glass or ceramic tube coated with a thin film of metal. They are used to control current and voltage in a circuit, converting electrical energy into heat. Compared to ‘normal’ electric circuits like that in a torch or in a house, the miniature components of electronic circuits are designed to work with very small currents. The resistors used must therefore have

Fig 3.5.1

CD14

A circuit board containing several different electronic components

high resistances. The multiplier prefix ‘k’ is used to indicated 1000 ohms (1000 Ω), while ‘M’ is used to indicate 1 000 000 Ω. For example, 8 kΩ = 8000 Ω, and 3 MΩ = 3 000 000 Ω. Variable resistors may be used as volume controls on radios, TVs and sound systems.

The resistor colour code The coloured bands on resistors are not decoration— they are a code representing the resistance in ohms. The digits 0 to 9 are represented by colours as shown in Figures 3.5.2 and 3.5.3. Resistors resist the flow of current, and can be used to control voltages.

Fig 3.5.2

Fig 3.5.3

The resistor colour codes

Digit

Colour

0 1 2 3 4 5 6 7 8 9

black brown red orange yellow green blue violet grey white

first digit

second digit

number of zeros

4 band resistor yellow 4

tolerance (4th band) gold 5% silver 10% no colour 20%

5% tolerance violet red 7 2 zeros (00) = 4700 V

5 band resistor yellow violet 4 7

5% tolerance black brown 0 1 zero (0)

= 4700 V

Thermistors

Prac 1 p. CD20

Capacitors A thermistor is a device whose resistance drops when it is warmed up. This property makes thermistors useful in circuits that need to respond to changes in temperature (e.g. a fire alarm).

Fig 3.5.4

UNIT

3 .5

Heat decreases the resistance of a thermistor. This is the opposite of what happens with most conductors.

Light-dependent resistors A light-dependent resistor (LDR) or photoresistor also has a variable resistance. Its resistance decreases when the intensity of light falling on it increases. LDRs are ideal in circuits that need to respond to changing light conditions (e.g. to control street lights). More light decreases the resistance of an LDR.

Capacitors store small amounts of charge, but not for very long as the charge eventually leaks Off, but still away. The charge is stored on dangerous! Many electronic devices two metal foil sheets separated such as the television by an insulating material called contain capacitors. Because a dielectric. Because the metal of the charge-storing ability sheets are separated, charge can of capacitors, it is still possible to be given an flow into a capacitor for only a electric shock by meddling short time (like the flow of people with circuitry after the getting onto an empty bus) before power is switched off. the plates fill. The larger the metal sheets, the more the charge that can be stored, so the various layers are rolled up like a Swiss roll to allow a larger surface area to fit into a small volume. The charge-storing ability of a capacitor is called capacitance, and is measured in farads (F) or, more usually, microfarads (µF). Capacitors are used in

Fig 3.5.5 metal foil

dielectric

A capacitor is like a Swiss roll—but don’t try to eat one!

Fig 3.5.6

CD15

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Electronics

Fig 3.5.7

Capacitors store charge.

circuits to control the time taken for various actions (e.g. lights flashing), and to block steady currents but allow changing ones Prac 2 to pass. p. CD20

The microphone

sound wave fixed plate

Fig 3.5.9

The band indicates the negative side of a diode.

A condensor microphone contains two plates acting as a capacitor. The first of the plates vibrates back and forth as sound waves strike it, causing the separation of the plates (and hence their charge-storing ability or capacity) to change. Changes in charge-storing ability cause charge to flow on and off the plates—in other words, an alternating current is produced. This signal may then be connected to an amplifier and converted into sound.

A diode may be considered a one-way valve for current. It conducts very well when connected one way (we say it is forward biased), and very little when connected the other way around (we say it is reverse biased).

Fig 3.5.10

Two very different results using the same diode

+

–

9V ammeter current flows

0.4

0.2 0

–

electric signal

5A A

1.0

moveable plate

0.6 0.8

AMPS

1A

battery diode ‘forward biased’

processing circuit

A condensor microphone

Fig 3.5.8

+

Diodes

9V ammeter 0.4

0.2 0

AMPS

–

diode ‘reverse biased’

5A A

1A

0.6

1.0

CD16

no current flows (or very small current flows)

–

0.8

A substance that conducts electricity is called a conductor, while one that doesn’t is called an insulator. A pure semiconductor is an insulator when it is cold, and a conductor (though a poor one) at room temperature. The two most commonly used semiconductors are silicon and germanium. A semiconductor diode is made from two different layers of specially treated semiconductor and has special properties that make it a very useful electronic component.

Prac 3 p. CD21

Diodes may be used to protect circuits from current going the ‘wrong way’ and damaging sections of the circuit, and for converting AC to DC. A special kind of diode is the light-emitting diode (LED), which is used in indicator lights and digital displays.

Transistors The transistor is the most famous electronic component of all and was invented in 1947 by a team from Bell telephone laboratories led by William Shockley. Like the diode, it is made from treated silicon, and is a type of semiconductor. The transistor, however, contains three layers of treated silicon. Transistors come in many shapes and sizes.

LED the light shine LEDs are far more energy efficient than light bulbs, but you need a lot of them to produce the same light. Traffic lights are gradually being changed from single bulbs to banks of LEDs. The main advantage here is that LEDs don’t all ‘blow’ at once … there are always some left to keep the traffic light operating until its next regular servicing.

UNIT

3 .5 The legs or terminals of a transistor connect to these layers and are known as the emitter, base and collector or E, B and C for short. When placed in a circuit with other components, a transistor can behave amazingly. A transistor may act as a switch (with no moving parts apart from electrons!) and a current amplifier. When no current flows through the base, the transistor is ‘off’, and no current flows from collector to emitter either, despite a voltage being applied. When a small current flows through the base, the transmitter is ‘on’ and allows a larger current (an amplified copy of the base current) to flow from collector to emitter.

Integrated circuits Fig 3.5.11

Miniaturisation did not stop with the invention of the transistor. Photographic processes are used to form millions of connected semiconductor components on thin wafers of treated silicon, sometimes called silicon chips. The finished product is called an integrated circuit (IC) or microchip. Microchips are now used in most electrical products, such as burglar alarms, car indicators and computers. Scientists are continually finding ways to pack more components onto a single chip—in fact, the number has roughly doubled each year since 1965. Modern printed circuit boards connect integrated circuits and separate components together in a compact way.

Fig 3.5.13

integrated circuit

resistor

C B E

emitter current integrated circuits basic current capacitors

Fig 3.5.12

Note the position of each leg in this diagram of a transistor.

CD17

>>>

Electronics

ENIAC Prac 4 p. CD21

Prac 5 p. CD22

Prac 6 p. CD22

UNIT

3.5

tal The first fully electronic digi computer, called ENIAC, was e year completed in 1947—the sam . that transistors were invented of res met are squ 170 It took up to floor space—compare this fit can ch whi rs, pute today’s com in your hand!

ENIAC—Electronic Numerical Integrator and Calculator—was the first electronic computer.

[ Questions ]

Checkpoint Resistors 1 Outline the function of a resistor in a circuit. 2 Identify the feature that distinguishes different-sized resistors.

Thermistors 3 Define the term ‘thermistor’. 4 State three potential uses for a thermistor.

Light-dependent resistors 5 Modify the following statements to make them correct. a An LDR has a constant resistance. b More light increases the resistance of an LDR c An LDR cannot be used in changing light conditions.

Capacitors 6 Outline the purpose of a capacitor. 7 A dielectric assists in storing the charge in a capacitor. Use a diagram to demonstrate how this works. 8 Identify the units used to describe capacitance.

Diodes 9 State two uses for a diode. 10 Two elements are often used to make semiconductors. State their names. 11 A diode is considered a one-way valve for current. Outline how this is achieved.

Transistors 12 State the name of the members of the team that developed the first transistor. 13 Construct a diagram explaining how to identify the base, collector and emitter legs of a transistor. 14 Transistors were a major advance in electronics. Explain why.

CD18

Fig 3.5.14

Integrated circuits 15 A microchip is also called an integrated circuit or a silicon chip. Explain how these terms are connected. 16 Microchips are a major breakthrough in electronics. List two uses of microchips.

Think 17 Identify the type of component described in this unit that may be a key part of: a the control of an air conditioner b automatic doors 18 Many bicycle lights involve one or more flashing LEDs. Outline the advantages of having the LEDs flash. 19 a Evaluate whether ENIAC would fit in your bedroom. b If not, calculate how many rooms of that size would be needed. 20 Estimate how many components may be fitted on a silicon chip next year compared to this year.

Analyse 21 Calculate the resistance of each of the following resistors: a blue, grey, brown b brown, green, orange c red, violet, yellow d red, green, green 22 For each of the following resistors identify the colours (in order) of the first three bands: a b c d

560 Ω 3300 Ω 470 000 Ω 1 200 000 Ω

Fig 3.5.15

Skills

Component

23 Complete the table opposite, identifying words from the text for the missing names of electronic components.

Sketch

Use

Symbol

UNIT

3 .5 Resistor

24 Use several small rectangular light-emitting diodes to demonstrate how the digits 0 to 9 on a digital clock display may be constructed. 25 Construct a circuit diagram for the circuit shown here. Fig 3.5.16

+

Detects light

–

9V

330 μF

26 Calculate how many times smaller a transistor is than an old-style valve.

Transistor

[ Extension ] Investigate 1 3K8 is another way of labelling a 3800 Ω resistor. a Explain what 4K9 means. b Explain what 2M5 means. 2 a Clarify what is meant by ‘p’ and ‘n’ type germanium. b Describe how it is used to make diodes. 3 a Explain how diodes can be used to convert alternating current to direct current. b State the name given to such a circuit. 4 a Describe what is meant by ‘logic gates’. b Use diagrams to demonstrate different types of logic gates. 5 Describe what is meant by a ‘microprocessor’.

6 Justify the use of the term ‘Silicon Valley’. 7 Explain what is meant by ‘CSIRAC’.

Surf 8 Complete the tutorials on resistors and resistor colour codes and record the results in a table showing the coloured bands on the resistors and the resistance they correspond to. You will find a link by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.

CD19

>>>

Electronics

UNIT

3.5

[ Practical activities ]

Fig 3.5.17

Note: Depending on experience and equipment, the following circuits may be constructed using a variety of methods, e.g. card/sticky tape, soldering, breadboard, drawing pins/balsa wood, etc. The card/tape method is not recommended for more complex circuits such as those in Pracs 5 and 6. Resistor colours below are based on the four-band system.

The resistor colour code Prac 1 Unit 3.5

Aim To determine the values of resistors using the colour code Equipment

A selection of resistors mounted on small pieces of cardboard (as in Figure 3.5.17) and labelled alphabetically.

Method 1 Draw a larger version of the table shown below. Resistor

Prac 2 Unit 3.5

The capacitor

A

Aim To investigate the properties of a capacitor

B

Equipment

C

Colours (first 3 bands)

Value

A selection of capacitors (e.g. 100 µF, 470 µF, 100 µF) and above, resistor (about 470 kΩ or so), 9 volt battery, 1 LED 2

Method 1 Charge a capacitor as shown, ensuring that the positive terminal on the capacitor touches the positive battery terminal for a couple of seconds. Connecting the wrong way is dangerous and could damage either object. Carry out step 2 as soon as possible.

Complete a row of the table for each resistor.

100μF

+

470 Ω resistor

–

Fig 3.5.18 –

+ –

9V

100␮F

+

LED

Fig 3.5.19

Questions 1 Predict the effect of using a larger capacitor in step 2. 2 Connect the capacitor to an LED and resistor as shown. 3 Repeat steps 1 and 2 for different capacitors, noting any differences in your results.

CD20

2 Explain why it was important not to wait too long after step 1 before performing step 2. 3 a Predict the effect of placing another capacitor side by side with the original one. b You may wish to combine with another group to investigate this effect.

UNIT

3 .5 A diode/resistor circuit Prac 3 Unit 3.5

Aim To investigate a circuit of a capacitor, diode and resistor Equipment

A light-emitting diode (LED), 330 Ω resistor (orange, orange, brown), 470 Ω resistor (yellow, violet, brown), 1 kΩ resistor (brown, black, red), 9 volt battery, battery snap, connecting wire (2 pieces, each 10 cm), a piece of card on which to lay out the circuit, sticky tape or Blu-Tack

Method 1 Assemble the circuit exactly as shown in Figure 3.5.20, otherwise you could damage the components. Fig 3.5.20 Blu-Tack or tape

2 Notice that one of the legs of the LED is longer than the other. Try placing the LED in the circuit both ways around. Note whether the longer leg must be as close to or as far away as possible from the positive terminal of the battery. 3 Try different resistors in the circuit, both ways around.

Questions 1 When an LED lights up, the positive leg is the one that goes closest to the battery. Identify which leg (long or short) is the positive one on an LED. Justify your answer. 2 Predict the effect of a larger resistance on the LED. 3 Discuss whether it matters which way around a resistor goes. 4 Explain why a resistor is used in this prac. 5 Construct a circuit diagram for this prac.

9V Blu-Tack or tape

9V long leg

The transistor

B

Aim To investigate the properties of a Prac 4 Unit 3.5

short leg

C

E

transistor

Equipment

A transistor (type BC548), 1 light-emitting diode (LED), 470 Ω resistor (yellow, violet, brown), 1.5 kΩ resistor (brown, green, red), 9 volt battery, battery snap, connecting wire (2 pieces, each 10 cm), piece of card on which to lay out the circuit, sticky tape or Blu-Tack

Method

Fig 3.5.23 Blu-Tack or tape

Fig 3.5.21

9V

1 Connect and observe the circuit shown in Figure 3.5.22. Note that the transistor terminals can be identified as shown here. 2 Add a 1.5 kΩ resistor and extra LED in series between the transistor base and the positive battery terminal, as shown in Figure 3.5.23.

Fig 3.5.22

long leg

BC548 B E collector

base

C

short leg

emitter

>> CD21

>>>

Electronics Questions

3 Explain why a transistor is sometimes referred to as an electronic switch.

1 Explain how you can tell when current is flowing (or not flowing) in the circuits on page CD21.

4 Construct a circuit diagram for step 2 of this prac.

2 Compare the size of the current going into the base of the transistor with that going into the collector in the second circuit. short leg

A moisture detector

+

–

9V

Aim To construct a circuit that detects Prac 5 Unit 3.5

moisture

long leg

Equipment

A transistor (type BC548), 1 light-emitting diode (LED), 470 Ω resistor (yellow, violet, brown), 100 kΩ resistor (brown, black, yellow), 9 volt battery, battery snap, connecting wire (2 pieces, each 10 cm), piece of card on which to lay out the circuit, sticky tape or Blu-Tack

470Ω E B C

BC548 transistor

probe

Method

probe

1 Assemble the circuit as shown. 2 Touch the probes together to test the circuit. The LED should glow brightly.

Fig 3.5.24

3 Keeping the probes apart by a few millimetres, touch them to a dry object, then a damp one (e.g. lick a finger if it’s clean).

3 Lie detectors work by using circuits similar to but more sensitive than the one in this prac. Explain how such a circuit could detect when a person supposedly tells a lie.

Questions 1 Discuss how this circuit could be used as: a a water detector b a soil moisture content detector 2 Predict the resistance of: a a dry finger b a wet finger

470 Ω

9 volt battery

Flasher

–

470 Ω

100 μF

–

+

+ –

LED BC548

lights

Equipment

A circuit ‘breadboard’, 2 transistors (type BC548), 2 100 µF capacitors, 2 light-emitting diodes (LED), 2 470 Ω resistors (yellow, violet, brown), 2 10 kΩ resistors (brown, black, yellow), 9 volt battery, battery snap, connecting wire (8 pieces, each 10 cm), other capacitors (e.g. 470 µF, 330 µF, 220 µF)

Fig 3.5.25

Questions 1

Deduce what effect the size of a capacitor has on the circuit.

2

Explain your answer to Question 1 in terms of charge movement.

1 Use the circuit diagram in Figure 3.5.25 as a guide to construct a flasher circuit.

3

2 Once the circuit is working, try exchanging one of the capacitors with a different one and note the effect on the circuit.

Predict what else you might change (besides a capacitor) to alter the flashing rate. If you have permission, the time to do so and the equipment, design an experiment to test your prediction.

4

Construct a circuit diagram for this circuit.

Method

CD22

+ – +

10 KΩ

BC548

Aim To construct a circuit containing flashing Prac 6 Unit 3.5

100 μF

LED

10 KΩ

Chapter review [ Summary questions ] 1 State the units used for the following measurements, giving the full name and short version in each case. a voltage b resistance c current 2 Distinguish between a series circuit and a parallel circuit. 3 Match the following terms to their definitions. Term load voltage current conducting path resistance switch

Definition Uses up electrical energy The ability of a substance to reduce the flow of current Wires for the electricity to flow through The flow of charge, usually electrons Turns the current on and off The energy available to push current through a circuit

4 Distinguish between AC and DC. 5 Copy the following and modify any incorrect statements to make them true. a A magnetic field is produced by a coil or coils of wire, not by a straight wire. b Electricity can cause magnetism and magnetism can cause electricity. c Electromagnets can be turned on and off. d A relay is an electromagnetic switch. e A generator produces current when a magnet sits inside or near its coils. f More energy is lost in power transmission lines when the voltage is higher. 6 List two types of wave that are possible in a slinky.

[ Thinking questions ] 12 Construct diagrams of the following circuits: a a series circuit with two lights and a switch b a circuit with three lights in parallel, and switches to turn all lights off separately c a circuit with three lights in parallel, and a single switch to turn all lights off 13 Complete the following table comparing a water circuit to an electrical circuit.

Electrical circuit

Water pump circuit

switch battery resistor voltage or energy current wire

14 a Construct a graph of Ohm’s law using the experimental results listed below. b Identify what the slope of the graph represents. c Calculate the slope of the graph.

Voltage, V (volts)

Current, I (amps)

0

0

2.5

2

5

4

7.5

6

10

8

7 Explain why not all power is transmitted at 240 volts. 8 List five modern electronic devices.

15 Use Ohm’s law to complete the following table:

9 List four categories of electromagnetic waves and state a use for each type. 10 Outline how early telegraphs used electromagnetism.

Current

Voltage

11 State what each of the following people are famous for. a Samuel Morse b Alexander Bell c Almon Strowger d William Shockley

3 amps

15 V

Resistance 6kΩ

10 amps 240 kV

32 Ω

93

>>> 16 Correct the following statements by identifying the correct word in brackets: Series circuits: a The voltage is shared (unequally/equally) between each resistor. b The current is (the same/different) for each resistor. c If any component is removed, the circuit (will/will not) work. Parallel circuits: d The voltage is (the same/different) for each resistor. e The current (divides into/is the same in) each branch of the circuit. f If one branch of the circuit is broken the other branches (will/will not) still work. 17 State which type of transformer is used close to homes, and explain why. 18 Contrast the visible spectrum with the electromagnetic spectrum. 19 State what happens to the wavelength of electromagnetic waves as the frequency increases. 20 Contrast laser light with light from the Sun. 21 State three ways in which messages are sent within today’s global communications network and outline an advantage of each method. 22 Predict what might happen if the same frequency was used for two different calls in a mobile phone cell. 23 Explain why radios were so large and heavy before transistors were invented.

94

[ Interpreting questions ] 24 The following wave was produced in 10 seconds.

Calculate the: a frequency b wavelength c amplitude 25 The following signal consists of two messages sent using time division multiplexing in groups of four characters: MYHO THEP VERC RICE RAFT OFEG ISFU GSHA LLOF SGON EELS EUP! Analyse the signal and record its two messages. 26 Propose how 0s and 1s could be used to send a digital message originally written in words.

Worksheet 3.5 Electricity and communications technology crossword Worksheet 3.6 Sci-words

>>>

4

Genetics Key focus area

>>> Current issues, research and development in science

identify how genetic information is passed to offspring explain how recessive and dominant genetic characteristics are inherited predict the probability of a person being affected by a particular characteristic

Outcomes

explain the terms ‘gene’, ‘chromosomes’ and ‘DNA’

5.5, 5.8.2, 5.12

By the end of this chapter you should be able to:

recall that sex cells have half the chromosomes of body cells explain two different ways in which cells reproduce identify the likely inheritance of genes from a pedigree.

brown-eyed children. True or false?

2 Why are approximately the same number of boys and girls born?

3 Why is colour blindness rare in girls but common in boys?

4 Why can one ear of corn produce kernels of many different colours, as in the picture on the left?

5 What is a clone? 6 What is GM food? 7 Could a dinosaur fossil be used to ‘create’ a live dinosaur?

8 List techniques that forensic scientists use to prove guilt.

9 Jeans for Genes Day is held each August to raise money for gene research. Why is gene research important?

Pre quiz

1 Blue-eyed parents can produce

>>>

UNIT

context

4.1 Have you ever been told that you have your father’s nose, your mother’s eyes or perhaps your grandfather’s ears? Although each of us is unique, we all resemble our parents and grandparents in some way. Two influences make you what you are at this moment: heredity and environment. Heredity is those characteristics you inherited from your parents.

Environment is all the factors that have acted on you throughout your life. Where do hereditary influences end and environmental influences begin? Genetics is the study of heredity and attempts to provide some answers to this question.

True-breeding plants are those that consistently produce offspring the same as the parents for a particular trait. Yellow-pod plants that always produce more yellow-pod plants would be considered truebreeding. Mendel cross-pollinated true-breeding plants with contrasting traits. For example, he took the pollen from a plant with round seeds and placed it on the flower of a plant with wrinkled seeds. He found that all the offspring (called the F1 generation) were like one of their parents. When these offspring were cross-pollinated among themselves, their offspring (the F2 generation) showed both traits. Some of Mendel’s results are shown in Figure 4.1.2.

Mendel: the father of genetics

The story of genetics begins in a monastery in Austria in 1856. Here a monk, Gregor Mendel, taught science, carrying out experiments in his spare time to study how characteristics are inherited. He was not the first to try this, but he was the most successful, and so is known as the father of genetics. Mendel grew garden peas and studied their characteristics, which occurred in two specific forms, called traits. The traits that Mendel examined included: • seeds that were round or wrinkled • seeds that were yellow or green Parental cross • pods that were smooth or constricted • pods that were green or yellow × • stems that were long or short. round

Gregor Mendel—the father of genetics

Fig 4.1.1

F1 generation

wrinkled

round

× yellow

green

yellow

× smooth

constricted

F2 generation 5474 round 1850 wrinkled

3:1

6022 yellow 2001 green

3:1

882 smooth 299 constricted

3:1

smooth 428 green

× green

yellow

152 yellow

green

× long stem

short stem

long stem

787 long 277 short

Results of Mendel’s cross-breeding experiments

96

Probability ratio

3:1

3:1

Fig 4.1.2

UNIT

4 .1 Dominating genetics Mendel studied 28 000 pea plants, Bees or peas? chromosome consistently obtaining similar results. He Before starting work with nucleus found two traits, which he called: peas, Mendel tried to breed a hard-working but • the dominant trait—this is the trait that protein easily managed honey appeared in the first, F1, generation bee. He tried crossing an • the recessive trait—this is the trait that industrious German bee DNA with a gentle Italian bee. was ‘masked’ in the F1 generation and The result was a bee that reappeared in the second, F2, generation. was neither hard working Based on his observations, Mendel nor gentle! He moved his attention to peas, which concluded that pea plants possess two cell were much easier to hereditary factors for each characteristic. handle. These factors separate from each other genes and pass into gametes. Gametes are the reproductive cells, called ova (eggs) in females and sperm in males, that combine to form the first cell of a new organism. Each new organism receives one hereditary factor from each parent. Chromosomes are made of protein and DNA. Fig 4.1.3 The factors do not blend with each other, but act as Each chromosome has many genes along its length. independent units. Mendel published his work in 1866, but it was poorly understood and largely ignored by the Organism Total number of Number of Number of scientific world. It was not until 1900 that his work chromosomes homologous chromosomes was ‘rediscovered’ and its importance appreciated. (diploid number) pairs from each sex Three scientists (H. De Vries in Holland, C. Correns in cell or gamete (haploid number) Germany and E. van Tschermak-Seysenegg in Austria) working independently reached the same conclusions Human 46 23 23 that Mendel had 34 years earlier. Dog 78 39 39

Genes We now call Mendel’s factors ‘genes’. A gene is a hereditary unit that controls a particular characteristic. Many thousands of genes are located in each of the cells of your body. Together, your genes can be thought of as a set of instructions or genetic program that determines your eye colour, body size, skin type and the many other characteristics that make you what you are. Each gene is made of a chemical called deoxyribonucleic acid or DNA for short.

Chromosomes Genes are located on structures called chromosomes. These are found in the nucleus of your body cells. Chromosomes are long, coiled, thread-like structures made of DNA and protein. Each chromosome has many thousands of genes along its length. As shown in the table opposite, each species of organism has a fixed number of chromosomes in the cell nuclei.

Chicken

78

39

39

Cow

60

30

30

Potato

48

24

24

Tomato

24

12

12

Fruit fly

8

4

4

Pairing up Chromosomes exist in pairs in each body cell, the members of each pair being similar in size and shape. One of the pair was inherited from the father, the other from the mother, making what is called a homologous pair. Most cells in your body therefore contain two of each type of chromosome. They are referred to as diploid cells. In contrast, gametes contain only one of each type of chromosome. Hence, half of the chromosomes in a diploid cell come from dad, the other half from mum. Gametes are known as haploid cells.

97

>>>

Inheritance Human chromosomes treated with stain, then arranged and numbered

Fig 4.1.4

The chromosomes in your cells right now are a copy of those that were present in the single fertilised egg cell from which you grew. How does this copying process take place?

Cell reproduction Mitosis When cells such as those in your skin reproduce, they duplicate their chromosomes. When each cell divides, the resulting daughter cells each receive a copy of

Fig 4.1.6

Mitosis—chromosomes separate at opposite ends of the cell.

the parent cell chromosomes. This type of cell division is called mitosis. Mitosis is an organised series of steps that ensures that each daughter cell is an exact copy of the parent cell. The major steps in mitosis are shown in Figure 4.1.5. Mitosis—cell division to produce new cells identical to the parent cell

Prac 1 p. 104

Fig 4.1.5

a skin cell

two skin cells

Two pairs of chromosomes are visible.

98

Chromosomes are doubled but attached at a point called the centromere.

Chromosomes line up along the ‘equator’ of the cell.

Chromosomes separate and move to the ends of the cell.

Membranes form to produce two daughter cells.

Meiosis

r me? Will there ever be anothe

your father’s characteristics and half your mother’s characteristics. A closer look at genes and how they interact is needed to give you an understanding of how this happens.

A different type of cell division, randomly Homologous chromosomes called meiosis, occurs in the cells sion of divi first the separate during two pairs only with cell a ce in the ovaries and testes, which Hen . meiosis different four e duc pro of chromosomes will produce eggs and sperm. Each Figure in wn (sho s type ete gam e possibl gamete contains only one of each omes, mos chro of s pair 4.1.8). For three e. This in sibl pos Worksheet 4.1 are s type of chromosome. When a type ete gam t eigh possible turn means that there are 64 sperm meets an egg, the resulting etes join. combinations when two gam cell will have the correct number mosomes. chro of s pair Humans have 23 binations of com of chromosomes. During meiosis e sibl pos of ber num The the same two the chromosomes are duplicated, as chromosomes in offspring of It is therefore ion! mill ion mill 70 is parents for mitosis. This is followed by two will ever be e ther that extremely unlikely divisions. another you! • In the first division, the individual chromosomes of each homologous pair separate to form two cells, each containing only one copy of each Cell divides by meiosis. kind of chromosome. • In the second division, the duplicated chromosomes separate to produce a total of four daughter cells. The major steps in meiosis are shown in Prac 2 p. 104 Figure 4.1.7. Homologous pair of chromosomes Meiosis, and the subsequent joining of —one inherited gametes, allows for the passing of chromosomes from from each parent two parents to an offspring. In this way you have acquired chromosomes, and therefore genes, from both your parents. But you do not simply have half

Fig 4.1.7

Meiosis—cell division to produce gametes with half the chromosome number of the parent cell

UNIT

4 .1

Cell division

Four types of daughter cells are possible due to the random way in which pairs separate during meiosis.

During meiosis, homologous chromosomes separate randomly to produce different types of gametes.

Fig 4.1.8

an ovary cell

four egg cells (ova)

Two pairs of chromosomes are visible.

Chromosomes are doubled but attached at a point called the centromere.

Homologous chromosomes line up along the ‘equator’ of the cell.

One of each pair of chromosomes moves to the ends of the cell.

Chromosomes line up along the ‘equator’ of each cell.

Chromosomes separate and move to the ends of each cell.

Membranes form to produce four daughter cells.

99

>>>

Inheritance

mother’s cell

father’s cell diploid cells with two pairs of chromosomes

Cells in ovary divide by meiosis.

With these definitions we can explain Mendel’s observations in terms of genes. The diagram shows the inheritance of pod colour in Mendel’s pea plants. Fig 4.1.10

Cells in the testes divide by meiosis.

Inheritance of pod colour in Mendel’s peas

First cross

×

haploid cells with two chromosomes egg cell (ovum)

Prac 3 p. 105

homozygous green pods (GG)

sperm cell

G

parent cells

homozygous yellow pods (gg) g

G

g

Gametes join. Meiosis produces gametes.

G

g

G

g

first cell of new organism

Meiosis and gamete fusion

Fig 4.1.9

Fertilisation produces a zygote.

g

G

Simple inheritance The gene that controls pod colour in pea plants comes in two forms: one codes for green pods, the other for yellow pods. Different forms of the same gene are called alleles. In his experiments, Mendel observed that green pods were more numerous or dominant, suggesting that: • the allele for green pods is a dominant gene. We can represent the allele for green pods as G. A capital letter is used to indicate dominance. • the allele for yellow pods is a recessive gene. The allele for yellow pods can be shown as g. A lower case letter is used to indicate that it is recessive. Each pea plant contains two genes for pod colour, one received from the female, the other from the male. The different combinations of the parents’ genes are known as the genotype of the plant. For pea pods, the possible genotypes are: • GG (called homozygous as both alleles are the same) • Gg (called heterozygous as the two alleles are different) • gg (also homozygous). The appearance produced by a genotype is called the phenotype of the organism. The genotypes GG and Gg would both be green since G is a dominant allele, while gg would be yellow. Hence there are two possible phenotypes: green (GG and Gg) and yellow (gg).

100

F1 generation Gg

Gg Gg (all heterozygous green pods)

Second cross

Gg

× heterozygous green pods (Gg) g

parent cells G

Meiosis produces gametes.

g

G

g

G

G

Fertilisation produces a G zygote (four possibilities).

heterozygous green pods (Gg)

g

G

g

G

g

G

g

g

F2 generation GG (homozygous green pods)

Gg

gG (heterozygous green pods)

gg (homozygous yellow pods)

Punnett squares A much simpler way to represent the inheritance shown in Figure 4.1.10 is to use a Punnett square. Figure 4.1.11 shows the Punnet squares for Mendel’s pea pods.

• 75% of offspring can be expected to be black (either BB or Bb) • 25% can be expected to be brown (bb). These results show the typical 3:1 (75%:25%) ratio seen in Mendel’s experiments. Worksheet 4.2 Heterozygous or homozygous?

parents 1 and 2

P2

UNIT

4 .1

First cross

P1

G

G

g

Gg

Gg

g

Gg

Gg

Squares show possible zygotes formed by union of gametes during fertilisation (all heterozygous green pods).

Second cross

P1

G

G

GG

g

Gg

Fig 4.1.11

Some characteristics are inherited in a simple way with dominant and recessive alleles. In other cases the effects of the two genes may blend in some way.

Codominance

possible gametes from parent 2 (homozygous yellow pods)

P2

Other types of inheritance

g GG, gG, Gg—green pods Probability of 3/4 (75%)

gG

gg—yellow pods Probability of 1/4 (25%)

gg

Punnett squares show the inheritance of pod colour in Mendel’s peas.

Punnett squares can be used to predict the results of reproduction (crossing) between different organisms. In rats, the gene that codes for coat colour occurs as two alleles. The gene for black coat (B) is dominant over the gene for brown coat (b). Using a Punnett square we can predict the coat colours of potential offspring. Consider the cross of two heterozygous black rats (Bb) shown in Figure 4.1.12:

In codominance the phenotype of the heterozygous organism is a combination of the phenotypes of the homozygous organisms. Consider the case of shorthorn cattle. Three genotypes and three phenotypes occur, as shown in Figure 4.1.13.

pure red (RR)

pure white (WW)

roan (RW)

Bb heterozygous black

Bb heterozygous black

P1

B

b

B

BB

bB

b

Bb

bb

P2

Punnett squares to show inheritance of coat colour in rats from a cross of two heterozygous black rats

Fig 4.1.12

Phenotypes and genotypes in shorthorn cattle. Inheritance of coat colour in shorthorn cattle is an example of codominance.

Fig 4.1.13

Using Punnett squares we can predict the results of crosses between these three types of cattle. Crossing two homozygous cows, a red one and a white one, will produce all heterozygous, roan offspring. Crossing two roan cows will produce heterozygous roan offspring (50%), homozygous red offspring (25%) and homozygous white offspring (25%).

101

>>>

Inheritance Punnett squares to show inheritance of colour in shorthorn cattle

Fig 4.1.14

homozygous white (WW) homozygous red (RR)

P1

W

W

R

WR

WR

R

RW

RW

P2

heterozygous roan (RW)

UNIT

4 .1

heterozygous roan (RW)

P1

R

W

R

RR

WR

W

RW

WW

P2

Sometimes the heterozygous offspring may have a phenotype between the phenotypes of the two homozygous organisms. In snapdragons, allele R produces red flowers and allele W produces white flowers. The genotype RW produces pink flowers. This blending of colours is sometimes called incomplete dominance, but many geneticists consider it to be another case of codominance.

Simple? I think not! The study of inheritance would be relatively simple if the ‘one gene for one characteristic’ model studied so far worked for all characteristics. But rarely do single genes control a characteristic. Many characteristics are controlled by a number of gene pairs, producing even more variation in the characteristic. Examples include your height and skin colour.

[ Questions ]

Checkpoint Mendel: The father of genetics 1 a Define the term ‘genetics’. b Explain why Mendel is known as the father of genetics. 2 Mendel’s findings were based on experiments using garden peas. List the traits that he observed. 3 Explain what is meant by a ‘true-breeding plant’. 4 In the study of genetics state what is meant by the F1 and F2 generations. 5 Define the terms ‘dominant trait’ and ‘recessive trait’. 6 State the conclusion Mendel drew from his pea plant observations.

Genes 7 Define the term ‘gene’. 8 State the name of the chemical from which genes are made.

Chromosomes 9 a Clarify what is meant by a ‘chromosome’. b Describe the relationship between genes and chromosomes. 10 State how many chromosomes are contained in a human: a body cell b sperm cell

102

Incomplete dominance

Pairing up 11 Define the term ‘homologous’. 12 With the aid of an example, contrast diploid with haploid cells.

Cell reproduction 13 a Define the terms ‘mitosis’ and ‘meiosis’. b Identify where each occurs. 14 Construct a table to compare mitosis and meiosis. Include comparisons of the number and type of daughter cells produced, and the type of cells where each process occurs.

Simple inheritance 15 Identify the correct description for each term. Term

Description

Alleles

The physical appearance of an organism for a particular characteristic

Phenotype Genotype Homozygous Heterozygous

An organism with different genes for a particular characteristic Alternative forms of the same gene The genes for a particular characteristic present in an organism An organism with the same genes for a particular characteristic

Other types of inheritance

For each of the following examples predict:

16 Use an example to clarify the meaning of the term ‘codominance’.

a b c d

17 Use an example to clarify the meaning of the term ‘incomplete dominance’.

Think 18 Use an example to explain how two organisms can have the same phenotype but different genotypes. 19 State whether the following are examples of complete dominance or codominance. a In snapdragons, red flowers crossed with white flowers produce pink flowers. b In fruit flies, when red-eyed males are crossed with white-eyed females, all the offspring are red-eyed. c When a green watermelon is crossed with a striped watermelon, half the offspring are green, and the other half are striped. 20 Calculate how many different types of gametes could be produced by an individual with the genotype XxYyZz. (Possible gametes include XyZ, xyZ, etc.) 21 Identify which of the options V to Z shown in the list below represents: a a dominant allele b a recessive allele c the genotype of a heterozygous organism d the genotype of a homozygous organism e a phenotype

V gg W green pea pods X G Y Gg Z g

Analyse 22 In fruit flies, there are two alleles that control eye colour, the allele for red eyes (R) being dominant over the allele for white eyes (r). The following questions refer to the cross of two fruit flies as shown in the Punnett square. Punnett square to show inheritance of eye colour in fruit fly

P1

Fig 4.1.15

R

r

r

Rr

rr

r

rR

rr

P2

the eye colour of parent 1 the eye colour of parent 2 which parent is homozygous for eye colour the percentage of offspring expected to have white eyes e the percentage of offspring expected to be heterozygous for eye colour

UNIT

4 .1

23 In Andalusian fowls, black plumage (B) is codominant with white plumage (W). Heterozygous fowls have blue plumage. a State the genotypes of black, white and blue Andalusian fowls. b Predict the chances of each phenotype occurring in the offspring when two blue fowls are crossed. c A poultry farmer wishes to establish a truebreeding strain of blue Andalusian fowl. Explain why this is not possible.

Skills 24 In cats, short hair (H) is dominant over long hair (h). Two cats heterozygous for hair length are crossed. Use a Punnett square to predict the: a genotype of the heterozygous cats b possible genotypes of the offspring c possible phenotypes of the offspring d probable percentages of each phenotype 25 In hogs, the gene that produces a white belt around the animal (W) is dominant over the gene for uniform colour (w). A hog heterozygous for colour is crossed with a hog homozygous for uniform colour. Use a Punnett square to predict the: a possible genotypes of the offspring b percentage expected of each genotype c percentage of offspring that would be expected to have a uniform colour 26 Assume that the genotypes of Mendel’s purebreeding long-and short-stem plants are LL and ll respectively. Long stem is dominant over short stem. a Using a Punnett square, predict the ratio of longand short-stem offspring in the F2 generation. b Does your prediction agree with Mendel’s observations shown in Figure 4.1.2? Justify your answer.

103

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Inheritance

[ Extension ] result of crossing a horse and a donkey. Research such unusual ‘hybrid’ organisms and write a report outlining your findings.

Investigate 1 Research the contribution of each of the following scientists to our understanding of genetics. Summarise the contribution of each: T.H. Morgan, H. de Vries, W.L. Johannsen, W.S. Sutton 2 Different species have different numbers of chromosomes. Cross-breeding between species is unusual, but it does occur. For example, a mule is the

UNIT

4 .1

Surf 3 Find out more about Mendel and his work by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button.

[ Practical activities ] Observing mitosis

Prac 1 Unit 4.1

Aim To observe mitosis in a series of prepared

3 Move to high power. Re-focus if necessary.

slides

4 Draw five cells in different stages of cell division.

Equipment Microscope, prepared microscope slide showing onion root tips

Method 1 Set up the microscope ready for viewing the slide. 2 Observe the slide under low power. Near the central part of the root is a section with cells in various stages of cell division. Focus on cells in this region.

Questions 1 Present the five cells you have drawn in the order in which they would occur during mitosis. 2 Explain how you can be sure that the cells are undergoing mitosis and not meiosis.

Modelling meiosis

Modelling meiosis Aim To construct models to demonstrate the Prac 2 Unit 4.1

process of meiosis

4 Repeat steps 2 and 3 until you have drawn all possible gametes.

Equipment

6 pieces of pipe cleaner to represent 6 chromosomes; 1 short, 1 medium and 1 long piece of pipe cleaner of colour I; 1 short, 1 medium and 1 long piece of pipe cleaner of colour II (colour I represents chromosomes from your mother, colour II from your father); large sheet of paper for sketching cells

Method 1 Draw a circle to represent a parent cell. Place the pipe cleaners in the cell to represent three pairs of homologous chromosomes. Sketch this cell in your book. 2 Draw two smaller circles to represent daughter cells. Move the pipe cleaners into these two cells to represent two gametes formed when the parent cell divides by meiosis. The gametes should each contain three pipe cleaners, one of each length.

104

Fig 4.1.16

3 Sketch the gametes in your book.

Questions 1 Predict how many possible gametes can be produced from a cell with three pairs of chromosomes.

colour I (from your mother)

colour II (from your father)

2 During meiosis, there is a ‘random assortment’ of chromosomes. Explain what the term ‘random assortment’ means. 3 Meiosis is described as a ‘reduction division’. Explain what this means. 4 Describe one feature of meiosis that was not shown in this modelling exercise.

UNIT

4 .1 Modelling inheritance Prac 3 Unit 4.1

Aim To model the random nature of inheritance

5 Replace the counters and shake the bags.

Equipment

6 Repeat the selection process until 20 results have been obtained.

60 counters or beads or buttons (30 each of two different colours), 2 paper bags

Method 1 Place 15 counters of each colour in each bag. 2 Draw up a table for recording results, using two letters to represent the colours of the counters, e.g. R for red, G for green.

RG

RR

GG

7 Record the totals for each genotype. 8 Continue until 100 results have been obtained (or combine results from several groups).

Questions 1 The modelling used represents a cross between two heterozygous individuals. Explain what ‘heterozygous’ means. 2 Predict the pattern for the three genotypes that you would expect to see. 3 State whether the expected pattern was observed after 20 selections. 4 State whether the expected pattern was observed after 100 selections.

3 Take one counter from each bag (without looking in the bags). 4 The counter from one bag represents the gene from a sperm, the counter from the other bag the gene from an egg cell. Record the genotype of the offspring resulting from your first selection of counters by placing a tick in the appropriate column of the results table.

5 Explain how the 60 counters would need to be arranged in bags to represent each of the following crosses: a homozygous x homozygous b homozygous x heterozygous

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UNIT

context

4. 2 Can you roll your tongue? Many people can’t. Although you collected your genes from your mum and dad, you are probably different to them and to any brothers and sisters. You might more closely resemble your grandparents or even an uncle or aunty. Where do all these characteristics come from? Does human inheritance follow special rules or does it follow the same rules as for peas, rats and cows?

Simple human inheritance In humans, some characteristics are under the control of a single gene. Some of these characteristics are fairly trivial ones, such as the ability to roll your tongue. Others like right- or lefthandedness affect your everyday life. Some produce severe conditions such as albinism.

Some characteristics controlled by a single gene in humans are listed in the table. Albinism is the inability to make the pigment melanin, which normally colours our skin. An albino has white hair and pink eyes. Normal colour (A) is dominant and lack of colour (a) is recessive. Suppose two people who are heterozygous for albinism produce offspring. What are the chances that the offspring will be albino? The Punnett square method tells us that the chances are 1 in 4 (25%).

Characteristic

Dominant

Recessive

Tongue rolling

Able to roll tongue

Unable to roll tongue

Right- or left-handedness

Right-handed

Left-handed

Hair colour

Dark or light

Red

Hairline

Widow’s peak present

Straight hairline

Night blindness

No night blindness

Night blindness

Earlobe attached or free

Attached

Free

Albinism

Normal pigment production

No pigment

Punnett square showing the inheritance of albinism

Fig 4.2.2

heterozygous male (Aa)

P2

heterozygous female (Aa)

We inherit our parents’ characteristics, but do not look exactly like them. Why?

106

Fig 4.2.1

P1

A

a

A

AA

aA

a

Aa

aa

Using a Punnett square we can predict the possible genotypes and phenotypes of their offspring. The chances of each of the possible blood groups of a child are: • 25% of having blood type AB • 25% of having blood type A • 25% of having blood type B • 25% of having blood type O.

An often fatal problem Albinos appear in almost every plant and animal species. In plants it is lethal because the plant cannot make food without the pigment chlorophyll. In animals it is often fatal because it makes the animal a more obvious target for predators. The animal also has no protection from the Sun’s ultraviolet rays and is more likely to get skin cancer or eye damage.

P1

IA

IO

IB

IA IB

IB IO

IO

IA IO

IO IO

P2

UNIT

4 .2

Other types of human inheritance While some of your characteristics were inherited in a relatively simple way, the vast majority were not.

Eye colour

Fig 4.2.3

Albinism is a genetic disorder caused by a single recessive gene.

Blood groups Do you know your blood group? You will probably know only your ABO and Rh groupings. The Rh system is controlled by two alleles, one dominant over the other. A person may be homozygous or heterozygous Rh positive, or homozygous Rh negative. The ABO system involves three different alleles, identified as IA, IB and IO. • IA and IB are codominant. • IO is recessive to both IA and IB. Possible genotypes and phenotypes are shown in the table.

In white-skinned people, eye colour is to some extent determined by a single gene. Brown eyes (allele B) are dominant over blue eyes (allele b). • Genotypes BB and Bb therefore produce brown eyes. • Blue-eyed people are homozygous, bb. Green and grey are genetically considered to be forms of blue. Hazel and black are forms of brown. While the basic colour is determined by one pair of alleles, other genes may modify the effects. At present, three gene pairs are known to influence human eye colour. The first gene, on chromosome 15, has a brown and a blue allele. A second gene, on chromosome 19, has a blue and a green allele. A third gene, on chromosome 15, is a brown eye colour gene. Eye colour is inherited, with brown eyes dominant over blue eyes.

Fig 4.2.4

Genotypes and phenotypes for the ABO blood grouping Genotype

I A IA

IA IO

IA IB

I B IB

I B IO

I O IO

Phenotype (blood group)

A

A

AB

B

B

O

Using this information we can determine the possible blood groups of a child, given the blood groups of the parents. Alternatively, if the blood groups of mother and child are known, the possible blood groups of the father may be determined. Example: Consider the following cross: • mother with blood group A, and the genotype IA IO • father with blood group B and the genotype IB IO.

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Human inheritance

male female

Bright sparks

Continuing on

male with the characteristic

Intelligence seems to be partly inherited under the influence of several genes. Environmental influences also affect intelligence. There is a long and ongoing debate about how much of intelligence is inherited (nature) and how much develops (nurture).

Sharply defined characteristics such as left- or right-handedness are described as showing discontinuous variation. The opposite is continuous variation, shown by characteristics such as height or eye colour, where a continuous range of characteristics may occur. People are not simply tall or short, but show a wide range of heights. Tall parents seem to produce Nature or nurture? tall children. Height is partly same the have twins ical Ident genotype. Do they always have inherited, but probably under the same phenotype? Several the influence of several genes. studies of identical twins Environmental factors must also raised together and separately play a part. For example, have been conducted. The IQ scores of identical twins an undernourished child correlate more closely than may not grow as tall as those of non-identical twins, raised ‘genetically expected’. even when they are Prac 1 apart. In one case, identical twins raised separately both developed schizophrenia within two months of their sixteenth birthday. How much is inherited, and how much is environmental?

p. 113

deceased female

identical twin boys

non-identical twin girls mating of a female and a male

generation I

offspring shown in birth order from left to right

generation II 1

2

3

Fig 4.2.6

Symbols used when drawing pedigrees

with rare characteristics. A pedigree is a pictorial family tree where individuals who show a particular disease or characteristic are marked on it. A little detective work follows, to find patterns of inheritance. The symbols used when drawing pedigrees are shown in Figure 4.2.6.

Analysing pedigrees Consider the pedigree shown in Figure 4.2.7, which shows the inheritance of night blindness. In generation III, the parents who partnered both had night blindness, but they had a daughter (2) who was not affected. This suggests that night blindness is a dominant gene. If it was recessive the parents would

I

II 1

Identical twins have the same genotype. Do they have the same phenotype?

Studying human inheritance Using pedigrees Humans take a long time to breed, so we cannot study human inheritance the way Mendel did with his peas. To overcome this problem, pedigrees of families are recorded and analysed, especially those

108

2

3

4

5

Fig 4.2.5 III

IV 1

2

3

This pedigree for night blindness shows a strange pairing. Why are genetic disorders more likely in children born from parents who are closely blood-related (e.g brothers/sisters/cousins)?

Fig 4.2.7

have to be homozygous to show the disease, and all their children would also show night blindness. The generation III parents must have been heterozygous, and by chance produced a daughter who was not affected. This also shows that sometimes a dominant gene can be less common in a community than a recessive gene. Now consider the pedigree in Figure 4.2.8. How can we know whether the characteristic shown is dominant or recessive? Look at generation II. An unaffected male partners an unaffected female (1), to produce an affected child. This indicates that the characteristic is caused by a recessive gene and that the generation II parents are both heterozygous.

I

II 1

2

3

III

Fig 4.2.8

Pedigree showing the inheritance of a disease. Is it recessive or dominant?

Worksheet 4.3 Pedigree analysis

UNIT

4 .2 Without this chemical, even a simple wound can cause severe bleeding. Untreated, the disease is almost always fatal. Notice that in the pedigree all those affected by the disease are male. To understand why, we first need to understand what makes one person male, and another female.

X and Y chromosomes Look back at Figure 4.1.4, which shows the chromosomes of a human. In 22 of these chromosome pairs, the members of each pair are the same size and shape. For pair number 23, however, there is a distinct difference. These are known as the X and Y chromosomes. The X chromosome carries many genes, the Y chromosome carries few. • A male has the genotype XY. • A female has the genotype XX. • All ova contain an X chromosome from the mother. • Sperm have either an X or a Y chromosome from the father. • It is the type of sperm (X or Y) from the father that determines the sex of the offspring.

Prac 2 p. 113

Boys or girls? Since there are an equal number of X- and Ycarrying sperm, there should be an equal number of girls and boys born. However, in most parts of the world there are slightly more boys than girls born. Why is not clear, but it may be that the sperm carrying the Y chromosome are lighter, and therefore they are more likely to reach the ovum first, to produce a male. However, the balance of males and females in the population is later restored, since the mortality rate for boy babies and men is slightly higher than for girl babies and women.

Sex determination in humans

Fig 4.2.10

Sex-linked inheritance Figure 4.2.9 shows a pedigree for the disease haemophilia, sometimes called the ‘bleeder’s disease’. People with this disease have a defective gene and as a result lack a particular blood-clotting chemical.

I

Sperm may contain an X or a Y chromosome.

All ova contain an X chromosome.

X

Y-bearing sperm Y

Y

X

X

X

Y

MALE

Zygote has genotype XY.

II 1

2

3

1

2

Pedigree showing the inheritance of haemophilia. Haemophilia and many other genetic diseases affect far more males than females.

X

X-bearing sperm

III

X

X X

FEMALE

Zygote has genotype XX.

Fig 4.2.9

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Human inheritance X-linked diseases The Y chromosome is small and carries very few genes. The X chromosome A royal disease is longer and has many The gene for haemophilia has genes on it. In males (XY) influenced history. Born in 1819, owing unkn many of the genes on the an was ria Victo n Quee carrier. She gave birth to four X chromosomes do not have boys and five girls, one son being a matching allele on the haemophiliac. Two daughters went Y chromosome. Therefore on to have haemophiliac sons and, a single gene on the through marriage, introduced the gene into the Russian and Spanish X chromosome, regardless royal families. The illness of one of of whether it is recessive or the Russian heirs, Alexis, set off a to d ibute dominant, will control the chain of events that contr the Russian revolution in 1917. The phenotype of the male. Tsarina, mother of Alexis, thought More than 50 Rasputin had magical powers which ia. ophil conditions caused by could cure Alexis’s haem Because of this, she allowed recessive genes on the Rasputin to influence Russia’s X chromosome have been foreign and domestic policies, . identified. They are called ution revol leading in part to the sex-linked or X-linked

conditions and include colour blindness, some forms of haemophilia and one form of muscular dystrophy. These conditions are far more common in males than females. For example, 8% of males are colour blind, compared with only 1% of females. Example: Consider again the pedigree for haemophilia shown in Figure 4.2.9. Haemophilia is a recessive X-linked disease. The genotypes can be worked out by using • XH for a normal gene and • Xh for a recessive gene for haemophilia on an X chromosome. All affected males have the genotype XhY. In generation II, the females 2 and 3 must have an Xh gene inherited from their father. Since they are not haemophiliacs they must have the genotype XH Xh. In generation II, male 1 must have inherited an Xh gene from his mother, and a Y from his father. Female 1 in generation I must therefore have the genotype XH Xh. Females who have a hidden gene for a disease are called carriers of the disease.

Career profile Medical laboratory technician

Medical laboratory technicians carry out routine laboratory tests and other procedures for use in the diagnosis and treatment of diseases and disorders of the human body. Medical laboratory technicians can be involved in: • setting up equipment used in the laboratory and maintaining it in a clean condition • preparing and staining slides of micro-organisms for examination • testing and analysing blood, tissue or other body samples to determine blood types and composition, and to identify diseases • analysing DNA samples to screen for diseases • communicating the results of tests to the medical officers who have requested them.

A medical laboratory technician preparing DNA for analysis

110

Fig 4.2.11

A good medical laboratory technician will be able to: • work as part of a team with doctors, scientists and laboratory assistants • work accurately and with minimal supervision • do repetitive work without losing concentration • keep accurate records and communicate well with others • apply scientific method to problems.

UNIT

4 .2

UNIT

4 .2 [ Questions ]

Checkpoint Simple human inheritance 1 List three human conditions inherited through a single gene. 2 Two ‘normal’ parents produce a child with a recessive genetic characteristic being expressed. Identify whether the parents have homozygous or heterozygous genotypes. 3 State the probability of a recessive characteristic being expressed in the child of parents who are: a both homozygous for that characteristic and are themselves affected by it b both heterozygous for that characteristic

Blood groups 4 Describe the type of inheritance involved when Rh blood groupings are inherited. 5 Outline the type of inheritance for the ABO blood group system. 6 List the alleles of the ABO system. 7 Identify the codominant ABO allele, and the recessive allele of the ABO system.

Other types of human inheritance 8 State the number of gene pairs thought to influence eye colour. 9 Distinguish between continuous and discontinuous variation. 10 List the two influences on intelligence.

Studying human inheritance 11 Studying human inheritance is complex. Identify the main method of gathering information. 12 Draw the symbols used in pedigrees for a female, identical twin boys, non-identical twin girls, and parents.

Sex-linked inheritance 13 Modify the following statements to make them correct. a The X chromosome is responsible for female characteristics only. b Males have the genotype XX. c The Y chromosome carries more genetic coding than the X chromosome. d Sex-linked diseases occur because the Y chromosome has fewer genes than the X. e Diseases like haemophilia are inherited through males in a family. 14 a Clarify what is meant by the term ‘a carrier’ of the disease haemophilia.

b Explain whether a male can be a carrier of haemophilia.

Think 15 Listed here are some characteristics: height, ability to roll the tongue, skin colour, blood group a From the list, identify two examples of characteristics that show discontinuous variation within a population. b From the list, identify two examples of characteristics that show continuous variation within a population. 16 Cystic fibrosis is a disease carried by a single recessive gene. Two unaffected parents have a child who suffers from the disease. Predict whether they will produce a child without the disease. 17 For each of the blood group genotypes listed below, identify the blood group phenotype. a IA IA b IA IO

c IA IB d IB IB

e IB IO f IO IO

18 An albino female and a non-albino male have two children. One is non-albino, one is albino. Using the letters A for the dominant gene and a for the recessive gene, identify the genotypes of each of the children. 19 a If two albino people partner and produce a child, predict whether the child will be albino. b If an albino person partners a person heterozygous for albinism, predict the chances of their children being albino. 20 Explain why approximately half the human population is female. 21 A genetic abnormality occurs where a person has the genotype XXY. Would the person be male or female? Justify your answer. 22 The ability to roll the tongue is a dominant characteristic. Two people who cannot roll their tongue have four children. Predict how many of these children would be likely to be able to roll their tongue. 23 A child has blood group AB. The mother has blood group A. a Identify the possible blood group genotypes of the father. b Identify the possible blood groups of the father.

Analyse 24 ‘Sperm are either male or female’. Analyse this statement, explaining whether the writer is correct, incorrect, or a bit of both, and justifying your answer.

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Human inheritance

25 Identify the meaning that matches the pedigree symbol.

Symbol

Meaning

28 A man with blood group B and a woman with blood group A produce a child. Predict the possible blood groups of the child by constructing a Punnett square.

A

Mating of a male and female

B

Male with the inherited characteristic

C

Identical twin boys

D

Female without the inherited characteristic

E

Deceased male

29 Colour blindness is an X-linked recessive condition. The symbols used to show the relevant genes are Xn for the recessive allele on the X chromosome and XN for the normal gene on the X chromosome.

26 Some people can roll their tongue into a U-shape. Tongue rolling is controlled by a dominant gene (R) and a recessive gene (r). A pedigree for tongue rolling is shown in Figure 4.2.12. Identify the genotypes of each of these individuals. a I male (generation I male) b II 1 c III 1 Pedigree for tongue-rolling ability

Fig 4.2.12

I

a Identify the genotypes of a non-colour-blind female, a colour-blind female, a non-colour-blind male and a colour-blind male. b If a colour-blind female partners a non-colour-blind male, predict the chances of: i their daughters being colour blind ii their sons being colour blind 30 Haemophilia is an X-linked recessive disease. A heterozygous female does not show the disease. Her genotype is XHXh. a Identify the genotype of: i a haemophiliac male ii a non-haemophiliac male b If the heterozygous female partners a nonhaemophiliac male, predict whether their sons will be haemophiliacs.

[ Extension ] Investigate

II 1

2

3

4

III 1

2

IV 1

2

3

Skills 27 Construct a pedigree from the following information. Jim and Jean are partners. They have four children: Scott, James, Natasha and Alan. James has a partner, Kylie.

112

They have two children: Susan and Alison. Susan has a partner, Paul. They have three children: Anne, Emma and Colin. James, Natasha, Susan and Anne are all albino.

1 a Gather information about the pedigree of a champion horse or show dog. b Construct a pedigree for your chosen animal. c Discuss the factors and outcomes that were important when matings were chosen at each stage of the pedigree. 2 a Research the genetics of human blood groups, and the problems raised by blood transfusions. b Present a case study on one problem that has occurred with a transfusion, explaining why the problem arose. 3 a Research some studies that have been conducted concerning twins. b Evaluate the evidence, summarising whether heredity or environment is the major factor responsible for patterns of inheritance.

UNIT

4 .2 Surf 4 Complete the following activities by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button. a Research a human genetic disease such as cystic fibrosis or muscular dystrophy. Contact the relevant society for information.

UNIT

4 .2

b Design a website or pamphlet explaining the cause, occurrence and treatment of the disease. 5 Complete the activity on constructing pedigrees, and give a PowerPoint presentation of your resulting pedigree. The tutorial contains instructions on how to do this.

[ Practical activities ] Variation within a population Aim To analyse continuous variation in humans

Prac 1 Unit 4.2

Equipment 25 people to survey (e.g. the students in your class), graph paper

Method

2 Survey 25 people of about the same age. For each person, record their height (in cm) and the heights of their parents. 3 On the same axes, plot graphs showing the heights of the 25 people surveyed, and the heights of their parents.

1 Draw a table for your results.

Questions Person

Height (cm)

Height of mother (cm)

Height of father (cm)

1 Based on your results explain whether there appears to be any link between height and parental heights. 2 Do your results support the conclusion that height shows continuous variation in a population? Justify your answer.

1

Construct a pedigree Prac 2 Unit 4.2

Aim To analyse your family and construct a pedigree for different characteristics Method

1 Figure 4.2.13 shows four pairs of human characteristics that are inherited. Select one of these pairs. Survey as many members of your family as possible (brothers, sisters, parents, grandparents, uncles, aunts etc.) to determine which characteristic of the chosen pair they have.

Questions 1 Discuss whether your pedigree gives any information about how the characteristic is inherited. For example, does it appear to be a simple dominant/recessive characteristic? 2 Discuss whether your findings agree with how the characteristic is actually inherited. You may have to conduct research to find out.

2 Construct a pedigree for the chosen characteristic for your family.

Widow’s peak or not?

Can roll the tongue or not?

Inherited features

Which thumb is on the top?

Fig 4.2.13

Length of second toe?

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UNIT

context

4.3 A

T

T

A

A

T

G

C

sugar–phosphate chain

We have seen a little of how the genes on chromosomes interact to produce certain inherited characteristics. How does it all work on a chemical or molecular level? Genes are made of DNA. So how does the DNA actually lead to the appearance of a characteristic such as eye colour?

base pair

T

C

A

G

The structure of DNA Imagine getting a ladder and twisting it into a spiral. Well, a twisted ladder is the same shape as a molecule of DNA! The DNA molecule is called a double helix. The uprights are made of a chain of alternating sugar and phosphate units. The ladder rungs are pairs of molecules containing nitrogen (called nitrogen bases) which form cross-bridges. There are four different nitrogen base molecules, represented by the letters: • A—adenine • T—thymine • C—cytosine • G—guanine. Khan you get a Because of their free meal? chemical structure, each In 2004, Shish, a restaurant in London base can pair only with in the United Kingdom, one other. The only offered its customers possible complementary free DNA testing to determine whether the base pairs are: y were descended from • A with T the Mongol chief and • C with G. warrior Genghis Khan. If found to be related, If one upright you got a free meal! of the ladder (one strand of DNA) has a base sequence of ATTCGTC, the opposite strand would have the complementary sequence, TAAGCAG. It is the sequence of these bases along the length of the DNA strands that is the basis of heredity.

Worksheet 4.4 Model DNA

114

T

A

C

G

phosphate unit

sugar unit

Fig 4.3.1

DNA structure—the lower part is shown untwisted to illustrate the pairing of bases.

Copying DNA When a cell is undergoing mitosis, the DNA is copied exactly in a process called replication. The strands are first unzipped. An exact copy is then made by matching each base with its complementary base. Once a section is copied, one old and one new strand are zipped together to Prac 1 DYO p. 119 produce the duplicate DNA. Replication of DNA

original DNA

2 ‘new’ DNA strands

Fig 4.3.2

Prac 2 p. 119

The genetic code actually consists of sets of three bases, called codons. Each set of three bases codes for a particular amino acid. For example, the base sequence CGG codes for the amino acid alanine, TTT for lysine, CAA for valine, and so on. Most of the 64 different codons code for the 20 different amino acids. A small number code for ‘stop’ and ‘start’ type instructions. The order of the codons on a length of DNA ‘spells out’ the order of the amino acids on a length of protein. The code appears to be universal. The same codon almost always specifies the same amino acid in all organisms.

The genetic code A gene consists of a segment of DNA with a sequence of up to 1000 bases. The difference between one gene and another is the order of bases. The base order forms the genetic code. This code describes the type and sequence of amino acids that cells use to make protein molecules. Proteins are polymers made up of small units called amino acids, joined together like beads on a string. There are 20 different amino acids that join together in different combinations to create thousands of different proteins.

nucleus

Each cell:

• 46 human chromosomes • 2 metres of DNA • 3 billion DNA subunits— (A, T, C, G) • Approximately 32 000 genes code for proteins that perform life functions

cell

chromosomes

DNA

genes T

T

C

T C

C G

A A

A A

A

Genes contain instructions for making proteins

A A

G

T

UNIT

4 .3

T

G

C

T

G C

proteins

Proteins act alone or in complexes to perform many cellular functions

Fig 4.3.3

Proteins determine characteristics by controlling cellular functions.

protein strand

The monkey in me The universal nature of the genetic code strongly supports the idea that all living things are related to each other, and have evolved from common ancestors. Comparisons of DNA are used to provide evidence of the relatedness of different species. The genetic make-up of a chimpanzee is 98.5% identical to that of a human.

Amino acids make up a protein.

alanine

C

DNA strand

G

lysine

G

T

T

valine

T

C

A

A

3 bases form a codon

Using the genetic code—each codon on a DNA strand codes for an amino acid. Amino acids are joined together to form a protein strand.

Fig 4.3.4

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The molecule of life Determining characteristics It is proteins that actually determine characteristics such as eye colour. Most proteins are enzymes that control chemical activities in the cell, and therefore affect the nature of the cell. The normal functioning of organisms is the result of hundreds of chemical reactions catalysed by hundreds of enzymes. In this way, many characteristics are influenced by many genes. Consider the following example involving skin pigments. Tyrosine is a colourless amino acid but in the presence of an enzyme called tyrosinase, it is converted to melanin, a dark-coloured pigment. If the gene for the production of tyrosinase is missing or defective, the enzyme is not made, so tyrosine is not converted to melanin. Without melanin there is no pigment, and albinism results.

section of DNA

A gene codes for production of the enzyme tyrosinase.

Tyrosinase catalyses a reaction.

tyrosine— a colourless amino acid

Fig 4.3.5

melanin— a dark-coloured pigment

From genes to characteristics. If a gene defect occurs, tyrosinase is not produced. Therefore melanin is not produced, resulting in albinism.

Gene expression Each cell contains the same type and quantity of DNA with the same code. Why then does a cell grow into a muscle, nerve or blood cell? Why do some cells produce chemicals such as insulin while others do not? Gene expression refers to the appearance in the organism of the characteristic that the gene codes for. Genes contain information about where and when the gene is to act. As the body develops, certain genes are ‘switched on or off’. For example, in animals the gene for haemoglobin production is switched off in nervous tissue. This switching may be done by chemicals within the cell, but the exact mechanism is not fully understood. Sometimes this mechanism is also affected by environmental factors.

116

Mutations What happens if there is an accident in the copying of the DNA strands during replication? Suppose one base was substituted for another—would it matter? Such accidents do occur, although they are reduced by the action of enzymes that correct copying mistakes. A mutation is any spontaneous change in a gene or chromosome that may produce an alteration in the related characteristic. Mutations that occur in non-sex cells (normal body cells) may affect the organism, but these mutations will not be inherited. Only those mutations occurring in gametes, or the cell that forms when they join, will be inherited.

Mutagens The rate of gene mutation is low, but as each individual has a large number of genes, mutations constantly occur within a species. The rate is increased by exposure to mutagens (mutation-causing agents). These include X-rays, gamma rays, ultraviolet light and a range of chemicals such as benzene.

Single-gene mutations Mutations may involve only one gene, with a section of DNA being incorrectly copied. The disease sickle cell anaemia results from such a single-gene mutation. As a result of the altered gene, the protein making up the haemoglobin in red blood cells of people with this disease has one altered amino acid. This results in distorted haemoglobin, and red blood cells shaped like a sickle. These distorted cells may form clumps and clog small arteries. Victims of the disease usually die young. Normal disc-shaped red blood cells and distorted red blood cells that result from a single-gene mutation, causing sickle-cell anaemia

Fig 4.3.6

Whole-chromosome mutations Parts of chromosomes may break off and rejoin, or whole chromosomes may be lost or added. Sometimes during meiosis, a pair of homologous chromosomes fails to separate. The gamete then has an extra chromosome. The cell resulting from gamete fusion will have three chromosomes instead of a pair. Many such changes result in spontaneous natural abortion long before birth. One that is not always fatal is Tri-21 (Down syndrome), where the individual has an extra chromosome number twenty-one.

Fig 4.3.7

Helpful mutations? Generally mutations cause more damage than improvement. However, A mutation that produces drug sometimes a mutation may prove occur may resistance in bacteria cell 000 000 000 1 every in beneficial. The Granny Smith apple in one divisions. This seems to be of little was the result of mutation in an apple concern until we realise that a colony tree in a Sydney backyard. Breeders 20 every ing of only 10 bacteria divid er numb this out of various species use mutations to carry will tes minu of divisions in around 4–5 hours. develop new and improved varieties If the colony was treated with an of organisms, including dogs, cats, antibiotic such as penicillin, almost those Only horses, sheep and crop plants. die. would ria bacte all the few carrying the mutated, resistant Mutations are responsible for gene would survive. These would in much of the genetic variation we turn produce an entire generation of see today. Maybe all humans had penicillin-resistant bacteria. brown eyes until a blue mutant gene appeared! Mutant bacteria

Chromosomes of a person with Tri-21

The Granny Smith is a mutant apple.

UNIT

4 .3

UNIT

4 .3

Fig 4.3.8

[ Questions ]

Checkpoint The structure of DNA

4 State how one DNA segment differs from another.

Copying DNA

1 List the three chemicals that make up the structure of DNA.

5 Define ‘replication’.

2 Identify what the letters A, T, C and G in a DNA base sequence stand for.

7 Use a diagram to demonstrate the replication of DNA.

3 Outline what is meant by ‘complementary bases’ in the structure of DNA.

6 Explain why DNA must replicate.

The genetic code 8 Outline how one protein differs from another.

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The molecule of life

9 Clarify what is meant by a ‘codon’. 10 Use a diagram to demonstrate how DNA is a code for constructing a protein.

Gene expression 11 Explain what is meant by ‘gene expression’.

Mutations 12 Clarify what is meant by a ‘mutation’. 13 List three mutagens. 14 Disease can be due to mutations involving one gene only. State an example. 15 State the name of a disease that is caused by mutation of a whole chromosome.

Think 16 The following base sequence is part of a gene that codes for a protein: CGGATAAGCTA Identify the complementary DNA base sequence. 17 Calculate the minimum number of bases a section of DNA would need to code for a protein that has 200 amino acids.

>>> 20 Discuss the large-scale use of antibiotic drugs used to treat bacterial infections. Could they lead to untreatable infections in the future?

Analyse 21 Use information from Figure 4.3.5 and your knowledge of mutations to predict an effect on skin appearance from excessive exposure to UV radiation from the Sun. 22 Figure 4.3.7 shows the genes of a person with Down syndrome. a Identify the abnormality on the gene map. b Identify the sex of the individual.

Skills 23 a Draw a diagram to demonstrate a simplified DNA molecule as shown in Figure 4.3.1 but change the base sequence. b Add a genetic mutation to the genetic code in your DNA drawing and predict a possible outcome of this mutation.

18 Mutations are usually harmful. Describe an example of a beneficial mutation. 19 Explain why mutations in a body cell are unimportant to the species as a whole.

[ Extension ] Investigate 1 The 1962 Nobel Prize for medicine was shared by J. Watson, M. Wilkins and F. Crick for their work in creating a model of DNA. Write a short biography of each of these scientists, outlining their contributions to our understanding of genetics. 2 Research the contribution made by Rosalind Franklin to the discovery of the model of DNA. Write a short biography, including the difficulties she encountered as a female in a male-dominated field. 3 Research human genetic abnormalities that involve having the wrong number of chromosomes. Write a report on the types, symptoms, occurrence and treatment of the abnormalities for one disease.

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4 Research gene switching and gene expression. You could start by considering the work of F. Jacob, J. Monod and H. Harris. Summarise your findings using a time line. 5 Research mutagens and use one example to summarise your findings while answering the following questions. • What are they? • Can we avoid them? • Do regulations exist to limit our exposure to mutagens?

Surf 6 Complete the activity on DNA replication by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button. Record your results using a diagram of the model you constructed in the interactive program.

UNIT

4 .3

UNIT

4 .3 [ Practical activities ] Modelling DNA 2 Your model should show all the basic features of DNA, and be able to demonstrate the process of replication.

1 Construct a model of DNA. You might use cardboard for the ‘uprights’ and coloured paperclips for complementary bases. You might use construction blocks or polystyrene pieces. Liquorice, jelly beans and skewers make a very tasty model! Use your imagination!

Prac 1 Unit 4.3

DYO

8 The DNA is still dissolved in solution. Pour 6 mL of ice-cold ethanol down the side of the test tube into your solution to form a layer. The DNA will precipitate into the alcohol. 9 Let the mixture stand until it stops bubbling (2 or 3 minutes).

Extracting DNA Aim To extract a DNA sample from wheatgerm Prac 2 Unit 4.3

Equipment 250 mL beaker, 15 mL test tube, test tube rack, measuring cylinders (10 mL and 100 mL), meat tenderiser, non-roasted fresh wheatgerm, ice-cold 95% ethanol, thermometer, stirring rod, dishwashing detergent, water bath, compound microscope

Method Note: To get good strands of DNA it is essential to be very gentle while stirring! 1 Add 100 mL of water to a beaker and warm to 50–60°C in a water bath. 2 Add one heaped tablespoon (6 grams) of wheatgerm and mix. 3 Add 3 mL of detergent to break down the cell membranes of the wheatgerm. Maintain the temperature at 50–60°C and stir for 5 minutes. Be careful not to form froth or scrape the sides of the beaker.

10 The DNA will float in the alcohol. Swirl a glass stirring rod at the junction between the layers to see strands of DNA. 11 Drag some DNA strands out of the test tube and view under a microscope.

Results You can expect three basic results from your DNA extraction. The actual result will depend on how careful you have been: •

No DNA. Something went wrong—revise your method.

•

Fluffy-looking DNA. This means that it has been broken into many small pieces during extraction. Usually caused by rough stirring.

•

Thin threads of DNA. Perfect.

Extension Try extracting DNA from another plant such as strawberries.

4 Add one level teaspoon (3 grams) of meat tenderiser. 5 Maintain the temperature at 50–60°C and stir for 10 minutes. 6 Remove the beaker from the water bath, and transfer some of your solution from the beaker to fill one-third of a test tube.

Questions 1

Describe your DNA after extraction.

2

Explain why each of the following chemicals was added during the process:

7 Allow the test tube to cool to room temperature. 3

a detergent b alcohol Deduce what factors affected your success in extracting DNA.

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UNIT

context

4. 4 Is it possible to change your inheritance? How would you like to have gills to breathe underwater, or the feathers of a bird? This may sound extreme, but the idea of controlling inherited characteristics is not new. For thousands of years farmers have selectively bred plants and animals with desirable characteristics. Recent scientific research has increased the precision and control with which we can select characteristics. Genes from animals

have already been placed into plants, and genes from humans have been placed in bacteria. Parents can select the sex of their child. Who knows what else may be possible in the future!

Nectarines are a mutant form of peach.

Fig 4.4.2

Selective breeding Selective breeding takes place all the time and is a simple process. Merino sheep produce more and better-quality wool than the breeds from which they were originally bred. Australian wheat was once attacked by a fungal rust disease. Resistance and good yield were gained when wild rust-resistant relatives of wheat were crossed with wheat plants that produce lots of seed.

Keeping the seeds from only the best plants for next year’s crop is a simple example of selective breeding. Other examples include selecting a male and a female with the right mix of desirable characteristics to produce tomatoes that stay ripe longer, dairy cattle with more milk, beef cattle with more meat, or rice that produces more seeds. Sometimes variation is produced by deliberately introducing mutations into a population, then selecting those individuals with desirable characteristics. For instance, nectarines are a mutant form of peach.

Genetic engineering Why use gene technology? Fig 4.4.1

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Reality or fantasy? A square tomato would allow easier stacking and slicing.

Increased research into inheritance and DNA has allowed selective breeding to be carried out in a much more precise and efficient way. Genetic engineering

uses gene technology to manipulate the DNA within an organism. Gene technology allows us to: 1 Isolate a gene 2 Alter the gene 3 Copy the gene and 4 Reinsert the gene into another organism, or into a new position on the DNA of the same organism. The use of gene technology has helped to develop: • larger harvests • plants with greater disease resistance • crops with improved storage and handling properties • fruit and vegetables that last longer and taste better. Organisms that have had their gene sequence altered are called genetically modified (GM) plants or animals. Genetically modified cotton contains an inserted gene. This insertion produces a protein that kills the Heliothis caterpillar when it eats the cotton leaves. The inserted gene comes from a naturally occurring bacterium, Bacillus thuringiensils, or Bt. The modified cotton is called Bt cotton. Australians currently use a number of products from genetically modified crops in their foods. These include canola oil, soy beans in some soy-based products and potatoes in processed snack foods. Genetic modification may have other benefits such as: • producing plants that can reverse the effects of salinity

UNIT

4 .4 • creating bio-fuel bacteria that can produce energy • producing bacteria that can clean up oil spills and process industrial waste • helping to eliminate genetic diseases. Some GM food—potatoes, corn, wheat and soy beans

Fig 4.4.4

Manipulating genes Scientists have known how to manipulate genes since the early 1970s. Gene technology uses naturally occurring enzymes that either cut DNA or join it back together. The enzymes recognise particular base sequences, and cut the DNA near these sequences. Scientists can use different enzymes to cut and join DNA in much the same way as a film editor cuts and splices lengths of film to make a movie. DNA segments may be inserted into bacteria, which then act like factories to copy the segments.

Using bacteria

You may already be eating some genetically modified foods.

Fig 4.4.3

DNA segments are not directly inserted into bacteria. Circular pieces of DNA called plasmids are used. These occur naturally in bacterial cells. A plasmid is cut open using an enzyme, the foreign DNA inserted, and the plasmid rejoined. This creates a mixed molecule called recombinant DNA. Altered plasmids may be put into bacteria, and the bacteria cultured to provide many copies of the introduced DNA. The bacteria will obey the instructions of the inserted DNA and manufacture the protein it codes for. Nearly all the insulin used by diabetics in Australia is now made by this method. Other substances produced using this technology include human growth hormone, some antibiotics, and vaccines against diseases such as hepatitis B.

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Controlling inheritance

Who owns your genes?

4. DNA is cut using an enzyme to isolate a gene. 3. DNA is removed from a human cell.

1. Plasmids are removed from a bacterium.

2. Plasmids are cut using an enzyme.

7. Bacterial cells grow and divide to produce many copies of the introduced gene.

Fig 4.4.5

6. The recombinant DNA is put into a bacterium.

Gene technology using recombinant DNA

Transgenics Inserting modified genes into plant and animal cells is also possible. In animals the gene is inserted into the single-celled embryo from which all the animal’s cells will develop. In plants, the gene may be ‘shot’ into host cells using a miniature gun. The chance of the inserted gene becoming permanently fixed into chromosomes is very low. Many cells are therefore exposed, and the ‘successful’ ones isolated.

The plant or animal with the new gene is called transgenic.

Are there risks? All new technologies have benefits and risks. Gene technology is no exception. There are many issues surrounding the use of gene technology, as people weigh the potential benefits against the potential risks. Listed below are some of these issues. Can you think of others?

Some arguments against gene technology

Some arguments for gene technology

• Genetic modification is not natural. Interfering with

• Gene technology is faster and more efficient than

• • • • • • •

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5. Human gene is inserted into the plasmid to form recombinant DNA.

The use of gene technology has paved the way for the patenting, marketing and sale of genetic materials and techniques. Biotechnology firms patent the data of gene sequences, together with a use for that data. For example, a firm might patent a gene it hopes to use to produce a drug to overcome obesity. There is considerable debate surrounding these patents. Some argue that they are necessary to support the costly research needed to produce new drugs. Others argue that patents inhibit research by giving one firm exclusive rights to a gene, and that monopolies may control genetic remedies.

a highly evolved and delicate system may upset it in unpredictable ways. GM plants with inbuilt pesticides may kill insects that are not pests. Pests will, in time, develop resistance to the inbuilt pesticides in GM plants. GM herbicide-resistant plants may transfer their resistance to other plants, creating ‘superweeds’. GM herbicide-resistant plants may encourage the excessive use of herbicides. GM crops will not necessarily solve the world’s food problems. Food shortages have more to do with economics and politics than with agriculture. Multinational companies own the rights to most GM plants. Farmers will incur costs to use the modified plants. Some religious groups have specific arguments against the use of GM foods.

conventional selective breeding techniques.

• Food production will be increased due to better disease and drought resistance in plants.

• Animals will produce leaner meat, thicker wool and have increased productivity.

• GM foods may be more nutritious, cheaper and keep better than conventional foods.

• GM crops with pest resistance will reduce the use of harmful chemical pesticides.

• GM crops may be produced that tolerate poor soils and salinity, allowing more areas to be farmed.

• Gene technology can be used to locate and study genes causing human disease, and genes that predispose people to other diseases. • Gene technology can be used to create new, improved medical treatments, such as insulin.

Further uses of gene technology Prenatal testing Prenatal testing involves identifying genetic defects or diseases before a baby is born. Prenatal testing is carried out using gene probes. A gene probe is a small piece of DNA with a base sequence identical to part of a gene. This means that a probe can stick to a specific gene. Probes are made that recognise the base sequences of genes associated with diseases. DNA samples from embryos can be tested with probes to determine whether a disease like sickle-cell or cystic fibrosis is present. Prenatal testing is usually carried out in the first 8 to 12 weeks of pregnancy. Cells to be tested are obtained by amniocentesis or chorionic villus sampling. These techniques, shown in Figure 4.4.6, involve inserting a needle into the uterus to obtain cells that ‘fall off’ the foetus during its normal development. Cells are also tested for the type of sex chromosomes and counted to identify chromosome abnormalities (such as Down syndrome). Testing for certain enzymes is also carried out to give further clues to the presence of genetic disorders. If a disease is detected then the pregnant parents undergo genetic counselling to see what action they can take in regards to the disease.

1. Fluid is removed through the mother’s abdomen. placenta

Forensic analysis Gene probes are also used in DNA fingerprinting in criminal cases to identify the parents of children in disputes. DNA fingerprinting relies on the fact that each person has a unique sequence of bases in their DNA (identical twins are an exception). The fingerprinting process is explained in the Science focus section on page 128.

Cloning In 1997, a lamb born in Scotland Woolly flocks captured the world’s attention. The lamb, Why are scientists so called Dolly, was genetically identical to excited by the cloning of Matilda and Suzi? its mother, and was the first successful The technology used clone of an adult mammal. Cloning refers to produce them could to the production of an organism from a help Australia’s wool and dairy industries. single cell. Each body cell contains all It takes many years of the information needed to make a new selective breeding to organism. A clone results when one of develop a flock of sheep with improved qualities these body cells is grown to produce a such as finer wool and new individual. good disease resistance. In May 2000, Australia’s first cloned Given one sheep with the merino sheep (Matilda) and first cloned desired qualities, cloning could produce that flock calf (Suzi) were born. They were in a single generation! produced using techniques similar to those used to produce Dolly. To clone a sheep, a cell from a donor sheep is obtained. An egg cell from another sheep is also obtained, and the DNA is removed from the egg cell. The egg cell and the donor cell are fused to Matilda, the first cloned sheep in Australia, was born in April 2000 but died of unknown causes in February 2003.

amniotic cavity— a fluid-filled region around the foetus. cells which ‘fall off’ the foetus

4. Test for genetic diseases using gene probes.

Fig 4.4.6

wall of uterus

5. Test for enzymes.

UNIT

4 .4

Fig 4.4.7

2. Fluid is centrifuged to separate cells.

3. Cells are isolated and grown in a culture.

6. Test for abnormal number of chromosomes.

7. Test for XY chromosome.

Prenatal testing by amniocentesis. Cells for testing may also be obtained from the placenta in a process called chorionic villus sampling.

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Controlling inheritance create a single cell, the first cell of the new sheep. The fused cell grows as a normal embryo. The embryo is grown for several days in a glass dish, then implanted into a host ewe to develop and be born in the usual way. Fig 4.4.8

Cloning Matilda cell from the donor sheep

egg cell from another sheep

0ATIENT

(EALTHYNORMAL CELLTAKEN $.!OFCELLTRANSFERRED INTOANEGG &ERTILISED EGG

DNA removed two cells fused together

!FTERnDAYS THEEGGGROWS INTOABLASTOCYST

egg cell without DNA

4RANSPORTED BACK WITHOUT REJECTION

)NNERSTEMCELLS ARECOLLECTED FROMBLASTOCYST

Embryo is grown for several days in a glass dish.

3TEMCELLSARE PLACEDIN GROWTHMEDIUMS

Embryo is implanted into a host ewe.

3KINCELLS

.ERVECELLS

-USCLECELLS

Matilda is born.

Fig 4.4.10

Removing DNA from a sheep egg during cloning

Fig 4.4.9

Therapeutic cloning Therapeutic cloning can be used to repair injuries by placing new nerve cells into a damaged spinal cord, growing skin for burns victims, or growing muscle cells to repair damage after a heart attack.

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Therapeutic cloning may also be used to cure many diseases in the future.

Therapeutic cloning involves taking cells from a person, extracting the DNA, and cloning the cells by inserting the DNA into an egg. The egg grows and after a few days the stem cells are removed from the egg. These stem cells are special as they can grow into any type of cell in the body given the right conditions. The cells can then be placed back into the person the DNA came from in order to achieve a desirable outcome. These cells will not be rejected by the body since the cells have the same DNA as the original donor. Maybe we will be able to grow whole organs for transplant this way! Worksheet 4.5 Human cloning

Gene cell therapy Another future prospect is the use of gene cell therapy. This involves removing the genetic material from some body cells, manipulating it and reinserting it into the person. Gene cell therapy could be used to overcome diseases such as cancer, by fixing the cancer-causing mutation. More controversial is the use of gene technology to alter the DNA passed from parent to child, with a view to overcoming diseases such as haemophilia, or even just to select eye colour.

Managing the risks Cloning and gene cell therapy clearly offer benefits, but they are not without risks. Can you think of some of these risks, and of ethical questions raised by the possibility of altering or selecting the genetic material of a child? In Australia, the Genetic Manipulation and Advisory Committee currently reviews all experimental and commercial uses of genetically modified organisms.

The human genome Gene technology relies to some degree on knowing where specific genes are. A genetic map shows the positions of specific genes along the chromosomes. Maps have been worked out for many organisms, including bacteria, fruit flies, some fungi and corn. The Human Genome Project was an international effort to determine the complete genetic code for humans. It identifies every gene that codes for each characteristic, as well as the base pairs that make up the genes. The mapping stage of the project was completed in 2003. Some findings of the project were that much of the genetic code that makes each person unique is in fact 99.9% the same for all people. Only 6% of the DNA actually codes for genes; the rest is termed ‘junk DNA’. Living longer Francis Collins, head The map contains 32 000 genes, far of the Human Genome fewer than the expected 100 000. The Project, said that by 2030 code specifies 26 000 proteins, but the genes involved in the how these proteins all function and ageing process will be fully catalogued. By 2040 gene interact is unknown. There is still therapy and gene-based a great deal to be learned. Armed designer drugs will be ses, with the map, many trials are now available for most disea and the average human under way to attempt to use gene lifespan will then be technology to cure diseases ranging 90 years. from haemophilia to cancer.

Career profile

UNIT

4 .4 Geneticist A geneticist studies how biological traits pass from one generation to the next. They also determine how the environment contributes to the transmission of inherited traits. Geneticists may also alter or produce new traits in a species. Geneticists can be involved in: • studying the genetic, chemical, physical and structural composition of cells, tissues and organisms • determining the influence of the environment on genetic processes in animals (including humans), plants and other organisms • studying organisms in controlled environments to gain an understanding of their survival and growth in real environments • applying the findings of research to maximise the long-term economic, social and environmental return from living resources • writing scientific reports on research • diagnosing or calculating the risk of passing on genetic diseases in humans, and advising parents on these risks. A good geneticist will: • enjoy and have an aptitude for science and research • be able to think logically and analytically and carry out detailed and accurate work • have good communication skills • maintain accurate records • be able to work as part of a team, in both the field and the laboratory.

A geneticist and an agricultural scientist examine transgenic sheep designed to produce more milk and more wool.

Fig 4.4.11

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Controlling inheritance

UNIT

4.4

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[ Questions ]

Checkpoint Selective breeding 1 Describe two examples of selective breeding. 2 List two advantages of selective breeding.

Genetic engineering 3 Define the term ‘genetic engineering’. 4 State two examples of how gene technology has been used to benefit humans. 5 a Clarify what is meant by a ‘genetically modified plant’. b Clarify what is meant by a ‘transgenic animal’. 6 a Use a diagram to demonstrate what is meant by a ‘plasmid’. b State where plasmids are found. c Outline how plasmids are used in gene technology. 7 Describe what is meant by ‘recombinant DNA’.

Further uses of gene technology 8 Explain what is meant by a ‘gene probe’. 9 Outline two uses of gene probes. 10 List three characteristics of an embryo that may be determined by prenatal testing. 11 Outline how the cells used in prenatal testing are obtained. 12 Distinguish between cloning and therapeutic cloning. 13 Clarify what is meant by ‘gene cell therapy’. 14 List two possible uses of gene cell therapy.

[ Extension ]

The human genome 15 Outline what is meant by the ‘human genome’. 16 Describe two features of the genome discovered by the Human Genome Project.

Think 17 Bt cotton produces a protein that kills its major pest, the Heliothis caterpillar. Predict two ways in which other organisms might be affected by the modified cotton. 18 Scientists have suggested that, within five years, pet lovers may be able to clone their dog or cat. a Outline what is meant by ‘cloning’. b Would a cloned cat or dog have all the characteristics of the original animal? Justify your answer. 19 Imagine that a person’s genetic code was mapped and a gene predisposing that person to heart disease was identified. a Explain how the person might use this information. b Predict how an insurance company or a prospective employer might use this information.

Analyse 20 Figure 4.4.5 shows a section of DNA being inserted into a plasmid. Do you consider this procedure beneficial to humans? Justify your answer. 21 Discuss whether the procedure shown in Figure 4.4.6 is ethical. 22 Evaluate the arguments for and against genetic engineering presented in this unit to decide whether it should continue to be investigated.

Investigate 1 It has been suggested that extinct animals could be ‘re-created’ using preserved DNA and cloning. a Research efforts to conduct such a project. b Present a report of your findings, including arguments for and against the ‘re-creation’. 2 Research the use of DNA fingerprinting in criminal cases or in cases involving disputes over who is the father of a particular child. a Present the findings of one example illustrating the DNA fingerprinting. b Discuss whether the findings are foolproof.

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3 Research arguments for and against the use of prenatal testing and early abortion for family planning. Organise a class debate on the issue. 4 Stem cells can theoretically turn into any of the many cell types that make up your body. a Research why stem cells are of great interest to scientists, and why their use is controversial. b Write a newspaper article aimed at informing the public about this issue.

Surf Complete the following activities about genetics by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button. 5 Research the Human Genome Project and summarise your information under the following headings: What is it? Goals Progress History Benefits Ethical issues 6 Imagine that a multinational company owns the patent on a genetically modified variety of wheat that is high yielding and drought tolerant. a Research ways in which this patent could affect an Australian wheat farmer. b Outline the main issues in a letter written to the farmer’s local Member of Parliament. 7 Complete the electrophoresis experiment online to separate your own samples of DNA.

Creative writing

UNIT

4 .4 How do you see it? 1 A genetically modified soybean that can tolerate a commonly used weedkiller has been produced. Using this soybean would allow farmers to spray to kill weeds without killing the soybean crop. It is proposed that this soybean be planted in Australia. Write a letter to the newspaper explaining why you think the planting should be allowed. Write a second letter explaining why you think it should not be allowed. 2 Suppose an experiment is being conducted to genetically modify cow’s milk so that it has a composition more like that of human breast milk. To achieve this, a single human gene is to be inserted into the DNA of a cow’s zygote (the first cell of a new cow). Imagine you are the human gene. Describe what happens to you during the course of the experiment, and explain how you feel about being used in this way.

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Science focus: Biotechnology and DNA fingerprinting Prescribed focus area: Current issues in research and development What is biotechnology? Biotechnology is the use of living organisms and the substances produced by them or biological techniques developed through basic research. Biotechnology products include antibiotics, insulin, interferon, recombinant DNA, and technologies such as waste recycling, bio-batteries and DNA fingerprinting. Humans have already exploited biotechnologies in many ways, such as selectively breeding plants and animals and extracting chemicals from animals and plants to make medicines, glues, health products and fibres. With our ability to manipulate genes and determine the genetic code of any organism, many new biotechnologies are using the manipulation of DNA and particular genes.

Biotechnology and crime Forensic scientists have always sought a ‘universal identifier’ that could be used to accurately identify

the perpetrator of a crime. Fingerprints were originally thought to have provided the answer but criminals soon learned to wear gloves or to make sure they wiped clean any surface they touched while committing the crime. The discovery of the genetic code as a base-pair sequence within the DNA molecule made it obvious that within the cells of each person was a unique genetic code. This code represents a universal identifier that cannot simply be wiped away. A person can leave DNA on anything they touch, by losing a hair or even dead skin cells.

Developing biotechnology There are a few key biotechnologies that are used in the DNA fingerprinting process.

Restriction enzymes Restriction enzymes are protein molecules that can bind to a particular sequence of base pairs in a DNA molecule and then cut the DNA into sections.

Electrophoresis After cutting the DNA molecule into smaller pieces, scientists need to be able to separate these pieces of DNA for analysis. The process for separating DNA is called electrophoresis and is similar to chromatography. The DNA samples are placed in a gel, and an electric current is applied. The current makes the pieces of DNA move, with larger pieces moving more slowly through the gel, and smaller pieces moving faster. Pieces of DNA separate across the gel according to their size.

Fig SF 4.1

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A fingerprint can easily be wiped away from a crime scene, but DNA cannot.

This technician is placing DNA samples into the wells at the end of the electrophoresis gel ready for separation. The result will be a DNA fingerprint.

PCR Fig SF 4.2



Only very small amounts of DNA are now needed to conduct DNA fingerprinting. The DNA required for the process can even be obtained from a corpse or sample where the DNA may have started to break down. Where only a very small amount of DNA is available for analysis, a technique called polymerase chain reaction (PCR) is used. This technique uses enzymes to copy the DNA sample many times, producing much more of the DNA collected. When enough DNA has been produced, the sample can undergo DNA fingerprinting.

DNA fingerprinting Crime scene investigation The process of DNA fingerprinting is outlined in Figure SF4.4. DNA fingerprinting produces a barcode-type result that is unique to each individual. By comparing the DNA found at a crime scene with that of a suspect, the perpetrator of a crime can be identified.

Gene probes There is a huge amount of DNA in a human cell and much of this genetic material is very similar in different people. To use DNA for solving crimes it is necessary to find sections of the DNA that represent genes that produce different but comparable results for different people. For example, the gene for a physical trait such as hair or eye colour can be used for this. Once these genes are identified, a way to mark them while analysing DNA is needed. This is where a gene probe is used. A gene probe is a small piece of DNA with a base sequence identical to part of a gene, which enables it to stick to a specific gene. By attaching a radioactive atom (radioisotope) to the gene probe, the radiation released from the sample can be analysed to determine where the gene probe has become attached. Gene probes that attach to the sections of DNA required for analysis have finally enabled forensic scientists to use the information provided by DNA evidence.

DNA fingerprints on X-ray film

Fig SF 4.3

129

Fig SF 4.4

The process of DNA fingerprinting

1 DNA is extracted from blood or a cell sample.

DNA sample

2 DNA is cut into fragments using enzymes.

3 Pieces of DNA are separated in a gel using electric current. This process is called electrophoresis and is very similar to chromotography. Small DNA pieces move faster and further than larger ones.

power supply DNA samples placed in wells in the gel agarose gel conducting solution

DNA samples move and separate in electric current

4 DNA band pattern in the gel is transferred to a nylon membrane. gel

nylon

5 A radioactive DNA probe is added that binds to specific sequences in the DNA bonds.

radioactive probe

6 The excess probe material is washed away, leaving a unique pattern.

7 The radioactive DNA pattern is transferred to X-ray film, giving the DNA fingerprint.

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DNA fingerprint on X-ray film

S1

S2

V

C

St

who were DNA fingerprinted after a challenge as to who was the father of the child. The results for the child’s mother were also included. The arrows in the diagrams show where the woman has been clearly identified as the mother. For the man to be identified as the father, the child’s DNA must match his result. Which of the two men do you think is the father of the child?

Other uses

Fig SF 4.5

Whodunnit? DNA fingerprints from suspects (S1 and S2), the victim (V), the crime scene (C) and a standard (St). Can we tell who is guilty?

DNA is a very stable molecule and, under the right conditions, and in certain tissues, it can remain intact for a very long time. For example, DNA in bones or hair can remain intact for hundreds of years. Armed with these new techniques for DNA analysis, archaeologists and anthropologists are able to analyse samples of DNA extracted from ancient corpses, such as the Egyptian mummies. The results obtained in these studies are providing information about the relationships between the different races of humans, and about human evolution.

Paternity disputes DNA fingerprinting is also finding roles in other applications and has become a tool in legal cases where the identity of a child’s parents might be in doubt. Figure SF4.6 shows the results for two men

Possible father 1

Possible father 2

[ Student activities ] 1 Some in the community have expressed concern that the increasing use of human DNA and genetic information could lead to an ‘invasion of privacy’ and that the information obtained by screening a person’s DNA might then be used for the wrong reasons. a Discuss this issue with classmates and propose the advantages and disadvantages that screening of each person’s DNA could have for society. b Evaluate this information and make a judgement as to whether the collection of DNA-related information should be allowed in the future, and if so, under what conditions. 2 a Gather information about how one of the following biotechnologies works: electrophoresis, restriction enzymes, gene probes. b Draw a flow chart using a series of diagrams and text to demonstrate how your chosen biotechnology works.

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Fig SF 4.6

Who is the father?

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A AT G C G T C T G ATAT C T C C C AT G C A C G C G C C C G G G AT TA C G TA C C C G G G AT C C G C G TA A C A C T G ATAT C TAT T

3

The diagram above represents a gene located in a section of DNA that a forensic scientist wants to analyse. Only one strand of the DNA is shown. The code for the gene is shown in red. To cut up the DNA, a restriction enzyme that recognises a particular sequence of six bases is to be used. The restriction enzyme uses the base sequence GATATC to allow it to identify the place where the DNA should be cut. a Copy the base sequence shown above and identify each location where the restriction enzyme will attach to the section of DNA for cutting. b Propose reasons why this particular restriction enzyme was chosen to locate the place to cut the DNA. c Construct a sequence of six bases for a gene probe that will attach to the gene shown in the diagram.

4 It has recently been suggested that the use of DNA for crime solving might have serious flaws. The technology is now so freely available that a criminal could potentially take someone else’s DNA, use a PCR (polymerase chain reaction) to make lots of it, and then deliberately spread it around at a crime scene. a Conduct research to find out how DNA is replicated using PCR. b Produce a poster or cartoon to demonstrate how a sample of DNA can be replicated by PCR. c Using an example, assess whether criminals using this technique could influence the use of DNA as evidence of their crime. 5 Imagine you are in a small town where a serious crime has been committed. In order to help catch the criminal, the police have asked everyone to give a DNA sample for analysis. This would either eliminate people as suspects or, hopefully, confirm the criminal’s identity.

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a Discuss whether giving a DNA sample should be voluntary or compulsory. b A person has chosen not to give a DNA sample as they fear their genetic information may be misused. Account for this person’s decision. c Do you think that a person who chooses not to give a DNA sample should be treated any differently than a person who does give one? Justify your answer. d Propose a set of guidelines that could be used when collecting DNA samples for analysis in this town, to convince people that their DNA would not be misused. Police collect DNA using a cottonbud-like swab and seal the sample in a tube for testing. A swab to collect cells is usually taken from the inside of the cheek.

Fig SF 4.7

Chapter review [ Summary questions ] 1 List two influences that make you what you are, giving an example of each. 2 a List two ways in which you resemble your mother. b List two ways in which you resemble your father. c List any of your own characteristics that are like those of your grandparents and not like your parents. 3 In Mendel’s pea plants, long-stem flowers were dominant over short-stem flowers. Stem length is controlled by a single gene with dominant and recessive alleles. Using this example, explain what is meant by the following terms: a b c d e

allele genotype phenotype homozygous heterozygous

4 a Define the term ‘gene’. b State what the letters DNA stand for. 5 Distinguish between genes, chromosomes and DNA. 6 For each term in the table, identify the relevant description. Term Meiosis Mitosis Diploid Haploid Gene DNA

Description Chemical that carries the genetic code A hereditary unit Cell division that produces gametes Cell division that produces daughter cells identical to the parent cell A cell that has two of each type of chromosome A cell that has one of each type of chromosome

7 Use examples to explain the difference between dominant and codominant inheritance. 8 Using examples, explain the difference between continuous and discontinuous variation within a population. 9 Briefly outline the process of replication of DNA.

10 For each term in the table, identify the relevant description. Term Codon Genetic map Plasmid Gene probe Recombinant DNA Transgenic organism Mutagen

Description Causes a spontaneous change in a gene or chromosome A small piece of DNA that recognises a gene An organism with a new gene Shows the positions of genes on chromosomes A circular piece of DNA A molecule containing DNA from two organisms A sequence of three bases that codes for an amino acid

11 Explain what is meant by: a gene technology c gene cell therapy b cloning d therapeutic cloning 12 a State three arguments for the use of genetically modified foods. b State three arguments against the use of genetically modified foods.

[ Thinking questions ] 13 Select the statements from i to v that are correct for: a mitosis b meiosis i It involves replication of DNA strands. ii Two daughter cells are produced. iii Four daughter cells are produced. iv It produces cells with half the chromosome number of the parent cell. v It occurs in most body cells. 14 The ability to taste a bitter chemical known as PTC is dominant over the inability to taste it. Three children in a family can taste PTC; one cannot. Explain whether it is possible for both parents to be: a non-tasters of PTC b tasters of PTC

133

>>> 15 Colour blindness is an X-linked recessive disorder. The symbols used to show the relevant genes are Xn for the recessive gene on the X chromosome and XN for the normal gene on the X chromosome. A colour-blind female partners a non-colour-blind male. a State the two possible genotypes of their offspring. b Their daughters will be carriers of the disorder. Explain what this means. 16 The structure of DNA may be likened to that of a twisted ladder. State: a what forms the uprights of the ladder b what forms the rungs of the ladder c the name given to the structure formed when the ladder is twisted 17 Explain how a mutation may be: a harmful to an individual but have no effect on the species b harmful to the species but not to the individual c beneficial to the species 18 a State the approximate percentage of your total DNA base sequence that is the same as that of your classmates. b State whether it is possible for two people to have exactly the same total DNA base sequence. Justify your answer.

[ Interpreting questions ] 19 In humans the ability to roll the tongue (R) is dominant over the allele for being unable to roll the tongue (r). A tongue-rolling heterozygous person is crossed with a person who cannot roll their tongue. a State the genotype of each person. b State the possible genotypes of their offspring. c Predict the percentage of offspring that would be expected to have each of the genotypes listed in b. d Predict the possible phenotypes of the offspring. e Predict the percentage of offspring that would be expected to have each of the phenotypes listed in c. 20 For snapdragons, a cross between a plant with red flowers (RR) and a plant with white flowers (WW) produces a plant with pink flowers. Predict the expected ratio of red, white and pink flowers in the offspring of a cross between: a a red-flowered plant and a pink-flowered plant b two pink-flowered plants

134

21 The father of a child has blood group AB; the mother has group O. Predict the possible blood groups of the child. 22 Albinism is caused by a single recessive gene (a). Two people heterozygous for albinism produce a child. a Predict whether the parents are albino. b Predict the chances that the child will be albino. 23 A pedigree for a rare X-linked disease is shown in the figure below. The symbols used to show the relevant genes are Xm for the recessive gene on the X chromosome and XM for the normal gene on the X chromosome. a State the genotypes of the following individuals: i II male 3 ii the female partner of II male 3 iii III male 1 b Is the disease carried by a dominant or a recessive gene? Justify your answer. c Predict the probability that a male child of female III 2 and her partner will have the disease.

I

II 1

2

3

III 1

2

IV 1

Worksheet 4.6 Genetics crossword Worksheet 4.7 Sci-words

2

>>>

5

Motion Key focus area

>>> The applications and uses of science

contrast Newton’s Laws of Motion analyse motion using Newton’s Laws explain how gravity and air resistance affect falling objects

Outcomes

explain the terms ‘speed’, ‘acceleration’, ‘force’ and ‘energy’

5.3, 5.6.2

By the end of this chapter you should be able to:

sketch graphs that illustrate various motions calculate speed, force and energies.

hammers fall at the same rate?

2 How long does it take you to react to something?

3 Passengers are thrown forward in a head-on car crash. True or false?

4 Are headrests in cars for comfort or for some other reason?

5 What are the differences between kicking a football and kicking a brick?

6 How does a jet engine propel an aircraft forward?

7 How can the footballer in the photo still be moving if his feet are not touching the ground?

8 Why is motion often blurred in photos?

Pre quiz

1 Where would feathers and

>>>

UNIT

context

5.1 You are in motion all the time. Even when you are asleep, you are travelling at a speed of about 1300 km/h. How can this be? It’s because the Earth is rotating on its axis and revolving around the Sun, carrying you with it.

It’s a journey that you take for granted, but what about other movements like running for the school bus in the morning? Let’s now look at how scientists describe motion.

Distance and displacement

Physics facts

How would you describe your journey to school this morning? Apart from ‘boring’, you might mention the distance travelled and the time it took. Scientists use two terms, distance and displacement, when describing a journey. • Distance can be measured in any length units, but is usually converted into metres (m) for calculations. Likewise, time is usually converted into seconds (s). • Displacement is distance with a difference. Displacement is how far you end up from where you started, and in which direction (up, left, north, towards the window). It is distance with direction. You travel a considerable distance each day, but your overall displacement is likely to be zero. You will end up in the same bed that you crawled out of this morning.

Distance and displacement Symbol in formulas: s (distance has no direction, displacement has direction) Unit: metres Unit abbreviation: m

Speed and velocity Speed In a car, speed is measured continuously by the speedometer in kilometres per hour (km/h or km h–1). This is its instantaneous speed or its speed at any moment in its travels. Speed is the rate at which distance is covered.

Fig 5.1.2

A to B distance = displacement =

8 metres 8 metres to the right B

A A to B back to A distance = displacement =

16 metres 0

8m

The difference between distance and displacement

136

Fig 5.1.1

A cloud of ice crystals forms as an aircraft reaches an instantaneous speed of 1200 km/h.

Police radar guns measure instantaneous speed.

Fig 5.1.3

UNIT

5.1 How to convert speed units ÷ 3.6 km/h

We do not always have a speedo or radar gun with us to measure instantaneous speed. Some simple measurements, however, allow us to calculate average speed: average speed =

distance travelled time taken

s or v = t

Physics facts That’s slow! The speed limit for cars in France was 13 km/h in 1893. Originally all cars in Great Britain had to have a man walking in front of them with a red flag to alert horseriders! In 1896 the speed limit was raised to 20 km/h, and in 1904 to 33 km/h. The first Australian speeding ticket was given to a Tasmanian, George Innes, who was recklessly driving a car through Sydney at 13 km/h—tourists!

Speed and velocity Symbol in formulas: v (speed has no direction,velocity has direction) Unit: metres per second Unit abbreviation: m/s or m s–1

Time Symbol in formulas: t Unit: seconds Unit abbreviation: s

If your school bus took half an hour to travel 10 kilometres to school, its average speed would be: v=

10 = 20 km/h 0.5

This seems slow, but is an average of all the instantaneous speeds the bus did on its journey. The bus went faster than 20 km/h, but also stopped at traffic lights and bus stops. It also had to reduce its speed through school zones and shopping areas.

m/s

That’s fast! × 3.6 Measurements are only Averages are useful but tell as accurate as the device little about what is actually that measures them, and faulty equipment happening. If the distance or will never give accurate time chosen for the average is measurements. This was small, however, average and particularly true when a driver in Belgium was instantaneous speeds become fined after a radar gun closer to each other. A runner measured his speed at might be timed at completing the 3500 km/h! 100 metre sprint in 12 seconds, but it would be better to measure the times taken to run past markers spaced at, say, 10 metres. The average speed of each section would show any changes that Prac 1 DYO p. 142 happened along the way. Spacings of one metre would be even better.

Velocity A weather report of 60 km/h wind gusts is useless to pilots, sailors, surfers and people fishing unless they also know the wind’s direction. Velocity is speed in a given direction. Wind movement is an example of velocity. Average velocity =

displacement time

The ticker-timer A ticker-timer is an instrument that breaks movement into a series of small intervals. It gives us a way of accurately measuring distances travelled and times taken, and provides the data from which speeds can be calculated. A small electric hammer strikes a piece of carbon paper at the same frequency as the AC power supply, 50 times a second or 50 Hz. Motion is then recorded as dots on a strip of paper that passes under the hammer. Fifty dots are produced every second, so a space between dots takes only one-fiftieth of a second or 0.02 seconds to produce.

Don’t even think about stopping! In about 700 BC, King Sanherib of Assyria built a road from his capital, Nineveh, to nearby temples. It was so wide that it would have been equivalent to a modern freeway of eighteen lanes! The king was justifiably proud of his road and didn’t want it spoiled by chariots parked along it. Death was the penalty for doing so, with offenders being impaled on spikes!

137

>>>

Describing motion

The steeper a distance–time graph is, the faster the object is going.

Fig 5.1.6

vibrating arm or hammer paper ticker tape  to AC power pack

 

$ISTANCEM

 dots produced carbon paper disk

4OCALCULATE GRADIENTPICK ANYPOINTS

GRADIENT

 

  

RISE RUN   MS

RISE

 

Fig 5.1.4

Although useful, the ticker-timer can record only motion in a straight line.



RUN

   at constant speed



  4IMES

D

FAST

SLOW

Prac 2 p. 143

T

decelerating

The spacing of dots gives an accurate idea of what is happening in the motion.



D

accelerating

start



Fig 5.1.5

T

D

ATREST

DYO

T

Graphing motion Distance–time graph Graphs are very useful in representing the motion of an object travelling in a straight line. Distance–time graphs show the total distance travelled by an object as time progressed. Time is always placed on the horizontal axis. Steep graphs indicate that the object is covering more distance and travelling faster than flatter graphs. A horizontal graph indicates no movement at all: the object is at rest or stationary. The slope or gradient of a distance–time graph gives us the object’s average speed.

138

Speed–time graph A graph of speed against time gives another picture of what is happening in the motion of an object. As before, time is placed on the horizontal axis. If the object is getting faster, the graph rises. If slowing, the graph falls. Constant speed gives a flat graph. The area under a speed–time graph gives the distance that the object has travelled up to that point. You can count the squares or use area formulas to find the distance travelled.

Calculating distance v

The average speed formula can be rearranged to give another useful formula:

UNIT

5.1 distance = speed × time or s = vt

speed is increasing

A car travelling at an average speed of 20 m/s for 5 seconds will have travelled a distance of:

5

t v Speed (m/s)

4

speed is decreasing

s = 20 × 5 = 100 m

2

area = 8 area = 6

1 0

t

Humans do not respond immediately to emergencies, but take up to 1.5 seconds to react. This is their reaction time. This means that when in a car, a driver will not begin braking until well after they see an emergency. Meanwhile the car is travelling fast towards it. To calculate the distance a car travels while the driver reacts, the speed must be converted into m/s to match the units used for time. Assume a car is being driven at 60 km/h (16.7 m/s) by a driver with a reaction time of 1.5 seconds. The distance the car travels before the driver brakes is then:

3

0

1

2

3

4

5

Time (s)

v constant speed

t

s = 16.7 × 1.5 = 25.05 m (equivalent to five to six car lengths).

Fig 5.1.7

A driver who is distracted (using a mobile phone, changing a CD, or who has drunk alcohol) may take as long as three seconds to react.

The total distance travelled is the area under the graph. The area here is 6 + 8 = 14. The object has moved 14 metres. Prac 3 p. 143

UNIT

5.1

DYO

Worksheet 5.1 Distance–time graphs

[ Questions ]

Prac 4 p. 144

Prac 5 p. 145

Checkpoint Distance and displacement 1 State the symbol, metric units and their abbreviations for: a distance b time

7 Identify the formula used to calculate: a average speed b distance c average velocity

2 Use an example to demonstrate the difference between distance and displacement.

8 To calculate time, t = s/v can be used. Write this formula in words.

Speed and velocity 3 State the meaning of the term ‘speed’. 4 State the symbol, accepted units and unit abbreviation for speed.

The ticker-timer 9 Ticker-timers produce a series of dots on a strip of paper. Outline the information that can be obtained from such data.

5 Define the term ‘instantaneous speed’.

10 State one disadvantage of ticker-timer data.

6 Use an example to demonstrate the difference between speed and velocity.

Graphing motion 11 Outline the type of information found from a distance– time graph.

>>

139

>>>

Describing motion

Skills

12 A motion graph is horizontal. State what this indicates if the graph is a: a distance–time graph b speed–time graph

20 Complete the conversions in the table below (round answers to one decimal place).

13 Outline how a distance–time graph can be used to determine speed.

21 Calculate the average speed of: a a car that travelled 990 km in 9 h b an ant that ran 24 cm in 2 s

14 Outline how a speed–time graph can be used to calculate total distance travelled.

Calculating distance 15 State the formula used to calculate distance. 16 a Clarify what a driver is doing during his/her reaction time in an emergency. b Discuss why differing blood alcohol limits apply to different levels of drivers’ licences.

22 Calculate the distance travelled by: a a jet in 6 h at 800 km/h b a sprinter running at 11.7 m/s in 8 s

Think 17 A distance–time graph always increases and never drops down, while a displacement graph could drop down. Explain why.

UP

START

M KM

M M M

TIMETAKENH START END

END

M

TIMETAKENS

KM

Fig 5.1.8

140

4.0

Race horse Cheetah

19.0 100.0

Greyhound Cockroach

18.3 4.5

Speed of sound Antelope

334 88.0

a Calculate the speed in mm/y at which his hair grew. b State any assumptions made in the calculation. c Explain whether the speed calculated is instantaneous or average.

KM

.

Bushwalker

11.7

25 Thai tribe member, Hoo Sateow, died at the age of 77 in 2001, having made it into the Guinness World Records for having the world’s longest hair. Its length was 5.15 m.

B

KM

Athlete sprinting

24 Scott leaves home for the 1.5 km walk to school at 8.15 and arrives at quarter to 9. Calculate his average speed in km/h.

19 For the motions shown in Figure 5.1.8 calculate: i the distance travelled ii the displacement iii the average speed for the whole trip iv the average velocity for the trip

KM

m/s

a 75 m at 2.5 m/s b 300 km at 60 km/h

Analyse

KM

km/h

23 Use the formula t = s/v to calculate the time taken to travel:

18 List three factors that could be expected to influence reaction time.

A

Speed

26 Light travels at a speed of 300 000 km/s. Calculate how long it takes to travel: a from the Sun to Earth, a distance of 149 600 000 km b the 384 403 km distance between the Moon and Earth c from Earth to Pluto, 5 750 400 000 km away

UNIT

5.1 Fig 5.1.10

27 Copy and complete the following table to calculate the distance a car would travel while the driver is reacting. A

Speed (m/s)

Reaction time (s)

20

0.7

50

0.6

60

0.9

100

0.5

110

0.8

Reaction distance (m) B

C

28 Eight Zuni rockets launched a craft from Woomera, South Australia, in 2001 to gauge its impact in falling back to Earth. It reached a height of 5.9 km in 40 s.

Fig 5.1.9

30 Calculate the gradients of the graph in Figure 5.1.11 to find two different speeds. Fig 5.1.11

a Construct a scale for distance from the photograph. b Calculate the average speed of the craft. c Calculate the distance the craft travelled before landing. d Calculate the approximate displacement of the craft from launch to landing.

6 5

Distance (m)

Speed (km/h)

4 3 2 1 0 0

1

2

e The shape of the trajectory is a familiar one in mathematics. State its name. (Hint: turn the photo upside down.) 29 Measure the distances travelled on the sections of ticker-tape shown in Figure 5.1.10 and calculate the average speed.

3

4

5

6

Time (s)

31 Calculate the area of the shaded parts of the v–t graphs in Figure 5.1.12 to find the distance travelled.

>>

Fig 5.1.12 B

C 









     

3PEEDMS

 3PEEDMS

3PEEDMS

A

   



   4IMES





 

   



   4IMES





 



   4IMES





141

>>>

Describing motion

32 Sharnika graphed a trip she took at the weekend. She drew the displacement–time graph shown in Figure 5.1.13.

6

Distance (km)

5 4 3 2

Calculate the following: a the distance Sharnika travelled in total b her displacement for the journey c the time she was away d her speed for the first leg of the trip e her return speed f the times when she was stationary g her average speed for the whole trip

1 0 0

1

2

3

4

5

6

Time (h)

b Use a diagram to demonstrate your information, including how a sonic boom is created.

Fig 5.1.13

Action

[ Extension ]

3 Research the times taken for the same race (e.g. the men’s 100 m sprint) in each Olympics since 1896. a Construct a graph showing the variation in time for the race through the past century. b Convert these times to speed, and construct a graph of speeds through the century. c Modern athletes can analyse their movement by viewing videos of their races. They can then correct faults in style that may slow them. The way athletes move and the equipment they use has changed over the past century to increase speed. Gather photos to show how the sprint sports of running, cycling and swimming have changed.

Investigate 1 a Investigate how one of the following devices works: i a radar gun or speed camera for measuring speed ii a fish finder for measuring depth and locating schools of fish b Present your information as a booklet to explain your findings to someone who has just purchased the device. 2 a Research the meaning of ‘sonic boom’ and the speed at which it occurs.

UNIT

5.1 Prac 1 Unit 5.1

DYO

[ Practical activities ] They’ve got the runs!

4 Repeat for another student’s run.

Aim To collect data and construct a distance–time

5 Plot the results obtained for each run as a distance–time graph.

graph

Equipment

Questions

Stopwatches (one per person preferably), chalk or other markers, access to a tape measure

1 Identify where the student became faster or slower on the run. Describe what happened to the shape of the graph in these areas.

Method

1 A student is to run a short distance (say, 50 metres). Design an experiment that will enable a group of other students to collect as much data as they can about the run. 2 Make sure you have selected somewhere flat and safe for the run. 3 Gather all the data and display it in an appropriate table.

142

2 Identify where the speed would be reasonably constant. 3 Normally, experiments are repeated a number of times. However, only one set of measurements should be taken in this case. Explain why. 4 Describe what the graph would look like if the student was cycling and not running.

UNIT

5.1 Ticker-timer experiment Aim To analyse motion using a ticker-timer Prac 2 Unit 5.1

Equipment AC ticker-timer, carbon paper circles and tape, power pack, scissors, ruler, graph paper, paper glue

8 Add axes to the cut-and-paste graph and use the values in the table to mark appropriate scales along each axis. 9 On graph paper, plot a distance–time graph for your hand’s motion using the values from your table.

Method 1 Tear off about 1 m of tape and thread it through the timer.

Questions

2 Start the timer, then pull the tape through, changing speed as you go.

1 Explain why it was important to number the sections before cutting.

3 Repeat with new tape, until everyone in the group has their own tape.

2 Describe any trends or patterns in the graphs you have constructed.

4 Draw a line through the first clear dot, then every fifth dot after that. There should be five spaces per section. This represents a time of 0.1 seconds.

3 State how many dots an AC ticker-timer makes in one second.

5 Number each section, then cut along the lines. 6 Paste the pieces in order onto paper to produce a speed–time graph as shown in Figure 5.1.14. 7 Measure the length of each section in millimetres and enter your results in a table like the one below.

4 Once started, describe how long the ticker-timer takes to produce: a a new dot (this is equivalent to a single space between the ‘old’ dot and the new one) b five new dots (equivalent to five spaces) Fig 5.1.14

 S DOTS

  

Section

3PEEDMMS

MEASUREINMM

MEASUREINMM





0 to 5 dots

0.1

6 to 10

0.2

11 to 15

0.3

16 to 20

0.4

21 to 25

0.5



  



         4IMES

S DOTS

Elapsed time (s)

 

Distance of each section (mm)

Total distance (mm)

Average speed (mm/s) Column 3 ÷ 0.1

Measuring speed Prac 3 Unit 5.1

DYO

Design experiments that will measure: • the speed of a moving object • the speed of sound.

You could use simple equipment such as tape measures and stopwatches, or use datalogging equipment with appropriate sensors (light gates, ultrasonic sensors, microphones).

143

>>>

Describing motion

Chain reaction Aim To measure reaction time Prac 4 Unit 5.1

Equipment

8 Send the message back to the right.

Stopwatch, paper and pen to record results

9 The starter can now touch either the left shoulder of their neighbour or they can lean behind them and touch their right shoulder.

Method Part A 1 Gather into groups of 10 to 15 students. 2 Stand in a ring, with everyone facing outwards, about 50 cm apart. 3 One in the group (the starter) has a stopwatch. Another will record the group results.

10 If the left shoulder is touched, pass the message onto your neighbour by leaning behind and touching their right shoulder and vice versa. 11 Have a few practice runs before you record any times.

Questions

4 The starter is to touch the shoulder of the neighbour to their right, starting the stopwatch when they do. When a shoulder is touched, the message is to be passed on.

2 Calculate the average reaction time for each person, for parts A, B and C.

5 Time how long it takes for the message to get back to the starter. Record the time taken and the number in the ring.

3 Discuss whether there was any difference between sending the message to the right and sending it to the left.

6 Repeat at least three times.

4 Part C needed complex thinking. Explain what happened to reaction times when you needed to process information.

Part B 7 Repeat, but send the message to the left, using the left hand.

Fig 5.1.15

144

Part C

Measuring group reaction times

1 Record all results.

UNIT

5.1 Driving reaction times Prac 5 Unit 5.1

Aim To measure your reaction time as a ‘driver’ of a car

3 Place a desk close to a wall, leaving a small gap between them. Place a chair on top.

Equipment

4 One student holds the chair securely. Another (the ‘driver’) sits on it. The ‘driver’ places their right heel on the desk, their toes against the wall, in the position of a car accelerator.

Metre ruler, access to a calculator, access to the Internet

Method 1 Form groups of three. 2 Copy the table below into your workbooks.

Without distractions Ruler drops (cm)

Average drop (cm)

With distractions Average reaction time (s)

Ruler drops (cm)

Average ruler drop (cm)

Average reaction time (s)

5 The third student holds a metre ruler against the wall. This is the ‘brake’ pedal. Align the ruler so that the ‘zero’ is level with the top of the driver’s toes. 6 Without warning, let the ruler go. 7 The driver must pivot their foot onto the ruler and stop it falling. 8 Read off the position of the toes now and enter the reading in the table. 9 Repeat at least three times. Each student must have a turn as ‘driver’. 10 Repeat the test, but now distract the driver (touch their neck, tickle them etc.). 11 Use this formula and your own data to calculate your reaction time: t=

d 490

where t = reaction time (s) and d = average ruler drop (cm) Check that you are doing the calculation correctly. If d = 10 cm the time should come out as 0.14 s. If not, find out what you are doing wrong with your calculator. 12 Copy the new table shown on the next page into your workbook.

Fig 5.1.16

Measuring reaction time

>>

145

>>>

Describing motion

Speed of car (km/h)

Without distractions (m/s)

Reaction time (s)

Reaction distance (m) Column 2 × Column 3

With distractions Reaction time (s)

Reaction distance (m) Column 2 × Column 5

10 30 50 60 80 100

13 Use your reaction times to calculate the distance a car travels before braking. 14 In the yard or corridor pace out each reaction distance. Assume one large pace is about 1 metre. 15 On the Internet, find the site www.happyhub.com/ network/reflex or use the words ‘reflex tester’ to find other similar sites. Compare the reaction time obtained from that test with the time obtained in this experiment.

Questions 1 It was assumed here that the ruler dropped without any resistance. Explain whether this is true. 2 Your first drop was probably the worst. Discuss what this suggests about inexperience in an emergency.

146

3 Explain what distractions do to reaction times. 4 List some distractions a driver might logically encounter. 5 Explain what alcohol in the blood does to reaction time. 6 The Road Traffic Authority estimates that the reaction time of an average driver is between 0.5 s and 1 s. Times from this experiment are probably less. Propose reasons for the difference.

UNIT

context

5. 2 The sudden changes in speed and direction of a rollercoaster give us the sensations and thrill that we are after. The culprit responsible for all this fun is acceleration: the rate at which speed or velocity changes.

Acceleration Imagine two cars taking off at traffic lights. Both reach 60 km/h, but their accelerations are not necessarily the same unless you are told how long each took. If one took 6 seconds, while the other took 16 seconds, it becomes perfectly obvious which one is accelerating the fastest! Acceleration = or

change in speed time taken for the change

a = (v – u) t

where • v is the final speed • u is the initial or starting speed • t is the time taken for the change in speed to occur.

Physics facts Acceleration Symbol in formulas: a Unit: metres per second squared Unit abbreviation: m/s2 or m s–2

Acceleration is measured in speed units per time unit. The most common unit for acceleration is metres per second per second, m/s2 or m s–2.

If an object slows, it is decelerating. Deceleration is negative acceleration.

Calculating acceleration If the speed of a car changes from 0 to 60 km/h in 6 seconds, then its acceleration is: a=

(60 – 0) = 10 6

Acceleration is one factor that makes the rollercoaster a thrill.

Fig 5.2.1

The unit here would be speed units (km/h) per time unit (s) or k/h/s: the car gained an extra 10 km/h every second. For an athlete, speed is better measured in m/s. For example, a runner is jogging along at 2 m/s but then slows her speed over the next 5 seconds until she is running at 1 m/s. Her acceleration would be: a=

(1 – 2) –1 = = –0.2 5 5

147

>>>

Acceleration The units here would be her speed units (m/s) per time unit (s), i.e. m s–2 or m/s2. You can say that her speed decreased by 0.2 m/s every second, or her speed changed by –0.2 m/s every second. The negative sign tells you that it is a deceleration.

If a = 50 m/s2, then 50 m/s is added every second.

Fig 5.2.3

Prac 1 p. 152

t=5s

v = 250 m/s

add 50 m/s

t=4s

v = 200 m/s

add 50 m/s

t=3s

v = 150 m/s

add 50 m/s

t=2s

v = 100 m/s

add 50 m/s

Fig 5.2.2

A multiple-exposure photograph shows different stages in a motion. The spacing between each image gives some idea of speed. Increasing spacing shows acceleration.

t=1s

v = 50 m/s

Calculating speed Let’s say a rocket launches with an acceleration of 50 m/s2. It started at rest, but 50 m/s is added to its speed every second that passes. Its speed will then follow the pattern shown in Figure 5.2.3. If the rocket was already moving at, say, 500 m/s, then the speeds would be those shown in the figure with another 500 m/s added to them. You can write this as: final speed = starting speed + acceleration × time taken or v = u + at

148

add 50 m/s t=0

v=0

Acceleration and graphs High acceleration is a rapid increase in speed. The speed–time graph would be a steeper one than if you accelerated at a lesser rate; that is, the slope or gradient of a speed–time graph gives us the rate of acceleration (see Figure 5.2.4).

v

quick acceleration

v

v deceleration (negative acceleration)

UNIT

5.2 no acceleration constant speed

slow acceleration t

Fig 5.2.4

The gradient or slope of a speed–time graph is the same as acceleration.

5.2 UNIT

t

t

Prac 2 p. 152

Worksheet 5.2 Plotting car performance data

[ Questions ] 11 Calculate the speed of an object every second for the first 4 s if: a it starts at rest and accelerates at 5 m/s2 b it started at a speed of 2.5 m/s instead of from rest

Checkpoint Acceleration 1 Define the term ‘acceleration’. 2 State the formula used to calculate acceleration. 3 Identify the values, and their symbols and units, needed to calculate acceleration. 4 Identify an alternative term for ‘negative acceleration’.

Calculating acceleration 5 A car accelerates at 10 km/h/s. Write a sentence to outline what this means. 6 A runner has an acceleration of –0.2 m/s2. State what she is doing.

Calculating speed

13 An object has zero acceleration. Identify the answer that best describes its behaviour. A The object is at rest. B The object is travelling at a constant speed. C The object is travelling at a constant velocity. D All of the above are possible. 14 Explain why deceleration is always a negative number.

Analyse

7 State the formula required to calculate the speed of an accelerating object. 8 Record the formula v = u + at in words.

Acceleration and graphs

A B C

Speed

12 Which is the most appropriate unit for acceleration for a car? Justify your answer.

9 Identify the graph in Figure 5.2.5 that shows: a slow acceleration b quick acceleration c no acceleration d deceleration

D

15 a Analyse Figure 5.2.2 to decide whether the diver’s head and shoulders were moving faster than his legs. b Analyse whether the diver was increasing or decreasing speed. c Describe what an even spacing of images suggests about speed. d Describe what increased spacing suggests. e List the information that would be needed to calculate speeds from this picture. 16 Describe the motion shown on the ticker-tapes in Figure 5.2.6. Fig 5.2.6 A

Time B

Fig 5.2.5

Think 10 Explain how much speed is gained every second if acceleration is 15 m/s2.

C

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Acceleration

17 The graph in Figure 5.2.7 shows data on distances that the ‘average driver’ needs to stop a car. a Analyse the graph to complete the missing information in the table below. Fig 5.2.7

Total Stopping distance

80

Skills 18 Copy the following table and calculate the acceleration. Starting speed Final speed (m/s) (m/s)

Time taken (s)

0

50

10

10

50

4

50

30

5

At rest

25

10

60

Stationary

12

Acceleration (m/s2)

70

Distance (m)

60

Braking distance

50

19 Use the table below to calculate the final speed that these objects would have.

40 30 Reaction distance

20 10 00

10

20

Speed (km/h)

30

40 50 60 70 Speed of car (km/h)

Reaction distance (m)

80

Braking distance (m)

90

100

Stopping distance (m)

20 50 60 80 100

Starting speed Acceleration (m/s) (m/s2)

Time taken (s)

0

15

3

20

8

5

16

1

4

30

–2

10

15

–5

3

Final speed (m/s)

20 A car accelerates from rest to 50 km/h in 5 s. Calculate the acceleration of the car in: a km/h/s b m/s2 21 Calculate the area and the gradient of each section of the v–t graph in Figure 5.2.8 to find the distance travelled and the acceleration. Fig 5.2.8

10 8

Speed (m/s)

b In November 2003, New South Wales dropped the urban street speed limit from 60 km/h to 50 km/h. Contrast the stopping distances at each speed limit. c It is recommended that the distance between your car and the car in front be equivalent to the reaction distance at that speed. Evaluate how many car lengths a driver travelling at 60 km/h and 100 km/h should leave in front of them.

6 4 2 0 0

1

2

3

4

Time (s)

150

5

6

7

UNIT

5.2 22 Linh, Beth and Brianna had a race. All accelerated smoothly from rest. Linh reached a speed of 24 km/h after 5 s, Beth reached 1.8 m/s after 2 s and Brianna took half a minute to reach 3.0 m/s. a Without changing units, calculate the accelerations of each. b Record the measurements as m/s and s and re-calculate their accelerations. c Assess who broke away the quickest. d Evaluate the accelerations and place the three girls in ascending order. 23 Construct a speed–time graph for the girl opposite accelerating on a skateboard as she drops into the half-pipe.

[ Extension ]

Fig 5.2.9

Investigate 1 The braking distance of a car is affected by the factors listed below. Research one of them and present your information as a print, radio or TV advertisement about the importance of this feature in car safety. a tyre design and tread b disc or drum brakes c ABS braking 2 Investigate why cars sometimes skid when braking and what a driver should do to regain control. Explain how that action works.

ACTIVITY Construct an accelerometer Use Figure 5.2.10 to build an acceleration indicator, or accelerometer. Get it moving along a bench, push it so that it travels at a constant speed or allow it to slide to a stop. Draw what the paperclip ‘needle’ does in each case.

tape (inside lid)

Action 3 a Gather data from car magazines or the Internet on at least two different cars. b Plot speed–time graphs to demonstrate their performance from rest. 4 a Estimate the acceleration and braking decelerations happening in the normal travels of your family car. b Explain how you collected the data and show your calculations. DYO

fill with water glass jar

cotton thread

paper-clip

Fig 5.2.10

An effective acceleration indicator

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Acceleration

UNIT

5.2 Prac 1 Unit 5.2

[ Practical activities ] Braking distances

4 Get your reaction distances from Prac 5 in Unit 5.1.

When cars brake in an emergency, the best deceleration on a dry road is about 90% g or –8.82 m/s2 (you will find out more about g in Unit 5.6).

5 Find the total stopping distance.

Aim To calculate the breaking distances for a car travelling at various speeds

Questions

6 In the yard or the corridor, pace out the stopping distances you found at each speed. Assume one pace roughly equals 1 m.

1 a Predict what would happen if brake performance was less. b Test your prediction by halving it.

Equipment Access to a calculator

Method 1 Copy the table below into your workbook. 2 Convert all the speeds from km/h into m/s. 2

v to calculate the braking distance 3 Use the formula d = 2b for a typical car. v stands for the speed of the car (in m/s) and b stands for the braking deceleration (in m/s2) You will need to follow this order: i Put the speed (in m/s) into your calculator. ii Square it, then divide by 2 and divide again by the braking deceleration (b). iii The answer is the braking distance.

Car speed (km/h) (m/s)

Braking deceleration 90% g (m/s2)

10

8.82

30

8.82

50

8.82

60

8.82

80

8.82

100

8.82

110

8.82

Acceleration and datalogging Prac 2 Unit 5.2

DYO

152

Use datalogging equipment and sensors such as light gates and ultrasonic sensors to measure and plot the speeds and accelerations of a moving object.

2 Once the brakes are applied, the ability and state of the driver have little to do with the braking distance. Assess which of these factors affect reaction distance and which affect braking distance: alcohol and drugs in the blood, bald tyres, tiredness, wet road, noisy kids in the back, icy road, poorly serviced brakes, old car, age of driver, talking on a mobile phone

Braking distance (m)

Reaction distance (m) (from Prac 5, Unit 5.1)

Stopping distance (m) Column 4 + Column 5

UNIT

context

5. 3 Forces act on us every day, causing many different effects. How do these forces act and what is the interaction between them? In 1687, Isaac Newton asked the same question. He then formulated three laws to explain how objects move when a force acts on them. They are often referred to as Newton’s Laws.

Physics facts Types of forces The force you apply is very obvious when you physically push or pull something. This is an obvious contact force. A summary of other forces that you will have met before is given below. Some will be discussed in this chapter.

Contact forces

What is a force? A force is a push, pull or twist that causes an object to either: • increase its speed (accelerate) • decrease its speed (decelerate) • change its direction, or • change its shape. If any of these things happen, then a force caused it.

Newton’s First Law Newton’s First Law examines the forces on an object that is: • at rest • in motion.

No force and not moving Place a pen on the desk. Watch what it is doing. Of course, it’s not moving. This effect is called inertia. Sir Isaac Newton described it in his First Law. Newton’s First Law states: Anything at rest will stay that way unless pushed or pulled. That is, a force is required to get something moving.

No force but still moving Why do you wear seatbelts in a moving car? If you answered, ‘Because you are thrown forward in a car accident’, then you’re wrong! This suggests that something pushed you … the seat must have shoved you so hard in the back that you were flung towards the windscreen! This is of course ridiculous: it implies that seats are capable of throwing you

• Friction: acts between any two surfaces that try and slide over one another. Acts in the opposite direction to the movement or attempted movement. • Air resistance and drag: friction of air (or liquid or other gases) as it travels across a moving object. Like friction, it acts in a direction opposite to the movement. • Buoyancy: ‘floating’ force. Acts upwards, opposing the weight force. • Surface tension: tiny forces between particles on the surface of a liquid that form a ‘skin’ on the liquid. • Lift: caused by air moving over a wing or airfoil. Acts at 90° to the surface of the airfoil. • Thrust: caused by gases or liquid being pushed out the rear of an engine, jet or rocket.

Non-contact forces • Weight: caused by gravity. Acts ‘downwards’, towards the centre of the planet. • Electrostatic: repulsion of like charges (+/+ or –/–) or attraction of unlike charges (+/–). • Magnetic: repulsion of like poles (N/N or S/S) or attraction of unlike poles (N/S).

around whenever they like! In an accident, you don’t get thrown forward: the car stops moving but you keep moving like you were before—until you hit something, like the windscreen, dash or steering wheel, which will provide a stopping (and injuring) force. This continued movement is called inertia, too.

Deadly dogs In accidents, an unrestrained family dog becomes a projectile and can potentially kill or injure anyone in the seating area. Most dogs range from 10 to 50 kg and will not be prepared for the accident when it happens, losing their balance and flying forward, with disastrous results.

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Newton‘s First Law

If a car is travelling at 60 km/h, then so are you. If the car is involved in an accident, it will stop very quickly (typically in about 0.1 to 0.2 of a second). Unbelted passengers will keep travelling, however, at 60 km/h, until stopped by the windscreen or dash. Our head tends to be the first part of the body struck. Seatbelts provide a restraining force and allow you to decelerate with the car. They also spread the stopping force across the chest and waist. Airbags also allow us to stop with the car.

Fig 5.3.1

Fig 5.3.3

The crash test dummy on the motorbike continued at the same speed until it hit the car.

Project BBQ Crash test dummies have been used for over 30 years to develop safer cars. Before that, live but anaesthetised pigs were used in crash tests. A large pork BBQ often followed. Human corpses (cadavers) were also used in tests. Accelerometers and force meters were implanted in the cadavers to measure what was occurring. The results from these experiments led to the development of the modern crash test dummy, the Hybrid 3.

The crash test dummy on the motorbike with an experimental airbag fitted

Newton’s First Law further states: Anything that is moving will keep moving at the same speed and in the same direction unless a force changes it.

Prac 1 p.157

Crash test humans

by the US Air Force to Crash test dummies were first developed in if they ejected from susta determine the injuries that pilots would e the invention of befor tested were ns huma Live . aircraft in flight 26 tests. In one, rwent unde the dummies, and Colonel John Stapp to a speed erated accel that sled open ered t-pow he sat in a rocke less than a in ed stopp was then of 1000 km/h in five seconds, but ng and movi blood and parts body al intern his kept second. Inertia skull. his of out fly would eyes he stated later that he felt as if his sely for 10 profu bled they and burst eyes his in ls Blood vesse sed, but he recovered minutes after the test. His lungs also collap such extreme forces. ve survi to ble possi was it that quickly, proving

Fig 5.3.2

154

Inertia ‘pushes’ John Stapp back as he accelerates, and his body continues moving forward when the sled stops.

Inertia explains why you sometimes ‘feel’ lighter or heavier when in a lift as it first moves off or slows to a stop. It also tells why you ‘move sideways’ when a car corners: you keep trying to travel in a straight line. Fig 5.3.4

UNIT

5.3 Prac 2 p. 158

We keep travelling in a straight line unless a force changes our direction.

passengers keep moving in a straight line

Inflatable seatbelts

ft generally don’t. Apart Most modern cars have airbags, but aircra ents are survivable and accid ft aircra most , sions from mid-air explo elt for aircraft to make seatb able one company is producing an inflat aint Belt inflates in Restr able Inflat ion Aviat The so. them even more nger collapses as passe the 0.070 s to form a large pillow into which es have already airlin Some ent. accid an in halt a to s the aircraft come 600 aircraft. 340– s Airbu and installed them in their Boeing 777

car turns left passengers appear to move to right

Worksheet 5.3 All over in 200 milliseconds!

UNIT

5.3

Fig 5.3.5

The inflatable seatbelt promises to slow passengers in an aircraft accident.

[ Questions ]

Checkpoint What is a force? 1 Define ‘force’. 2 List four possible outcomes when a force is applied to an object. 3 Classify the following forces as either contact or non-contact forces: electrostatic, lift, thrust, weight, friction, buoyancy, air resistance, magnetic, drag

Newton’s First Law 4 Recall the two parts of Newton’s First Law. 5 Define ‘inertia’.

Think 6 Assess whether the following statements are true or false. a An object needs a force to start moving. b Passengers are thrown forward in a head-on collision.

c A typical accident takes 1 to 2 seconds. d You have enough time in a collision to brace yourself to avoid injury. e To keep something moving on Earth, you need to keep pushing. 7 Explain what happens to the occupants of a car when it: a turns left b suddenly accelerates c goes fast over a speed hump d goes over a deep dip in the road e collides head-on with a wall f is parked, but is hit from behind by another car g is parked, but is hit from the left by another car 8 Outline the features of a car that are designed to comfortably stop our forward inertia. 9 Propose why it is preferable to have the stopping force in a car applied to the chest and waist instead of the head.

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Newton‘s First Law

Fig 5.3.7

10 Explain why rockets will keep moving in deep space, needing no engines to do so. then

11 A car on ice is almost impossible to stop or control. a Use the concept of inertia to explain why. b Identify the force required to gain control. 12 People sometimes hold their baby while travelling in a car, thinking that they will react and hold the child in any accident. Assess whether these people are seriously risking the life of the baby.

then

19 Figure 5.3.7 shows three frames of a collision.

13 Evaluate whether passengers in the rear of a car are safe when not wearing seatbelts. 14 Assess whether buses should be required to have seatbelts for all passengers and whether passengers should be allowed to stand. 15 Even when a person is not wearing a seatbelt, their lower body is less likely to be influenced by inertia than their head. Identify which force(s) slow the lower body.

a Predict the type of collision that probably happened here. b Account for what is happening in each diagram. c Use this diagram to explain why modern cars are fitted with headrests. 20 Johanna lets a bucket go at point X when swinging it. Trace the diagram and add an arrow at X to show in which direction the bucket will fly.

16 Seatbelts leave bad bruising and can crack ribs in a car accident. a Explain why they do this. b A friend is arguing that this is a good reason not to wear seatbelts. Propose three reasons that would convince them to buckle up. 17 Truck cabins need to be rigid and able to withstand a heavy blow from the rear. Explain why.

Analyse 18 a Use the diagram in Figure 5.3.6 to explain how a magician can pull a tablecloth out from under a table set with china. b In reality, the china will probably shift slightly in the direction of the tablecloth. Explain why. Fig 5.3.6

X

Fig 5.3.8

156

UNIT

5.3 [ Extension ]

b Imagine you had to sell the Hybrid 3 to car companies. Present your findings as a brochure on its benefits.

Investigate 1 Research the use of airbags in cars. Present your information as a poster of a car that illustrates their use and features, including: a how an airbag is triggered and inflated b where airbags can be installed in a car c how much safer a car is with airbags than without d why most cars in Australia only have driver airbags 2 a Research the development of crash test dummies and the current model, the Hybrid 3.

Surf 3 Investigate Newton’s First Law by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button. You will need to complete a tutorial including animations and questions. Record a log of your progress, outlining any misconceptions you may have discovered and corrected.

CHALLENGE The yoke’s on you! Your task

The material

Use your knowledge of inertia to design a safe container that will protect a fresh hen’s egg from injury in a highspeed collision (vegans can use a light bulb).

1 piece of cardboard of roughly A3 dimensions, sufficient string/sticky tape/staples/glue/other fixings to hold it together

The collision

• tape etc. as reinforcing or padding • extra paper or cardboard for padding or parachutes. All fittings must be made from the original A3 sheet of cardboard.

Drop from a first floor window or balcony onto concrete or bitumen.

UNIT

5.3

[ Practical activities ] Crash test dummies Aim To perform your own crash tests

Prac 1 Unit 5.3

You cannot use:

Equipment Dynamics trolley, ramp, ruler, chalk, a solid barrier such as a brick or wall, plasticine or playdough, talcum powder, sticky tape

Method 1 Mould a small plasticine person. Lightly powder it so that it loses its stickiness. 2 Sit it on the dynamics trolley.

Part A 3 Set the ramp up on a shallow slope and let the trolley run down it and onto the floor. Carefully note what happens to the plasticine person.

4 Place a chalk mark every 20 cm up the ramp, and place a brick on the flat near the ramp’s end. 5 Model a head-on collision by releasing the trolley from a 20 cm mark on the ramp (see Figure 5.3.9). Repeat from the rest of the marks. Note what happened to the plasticine person, particularly to any parts of the body that moved a lot and any parts that moved little. Test which 20 cm mark you consider to be ‘life threatening’ to the plasticine driver.

Part B 6 Build a sticky-tape seatbelt for the driver and repeat. Are there any differences in the results? Which 20 cm mark is now the ‘life-threatening’ one? 7 Take the belt off, but this time add a ‘crumple zone’ to the front of the trolley. Once again, which 20 cm mark do you consider to be ‘life-threatening’?

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Newton‘s First Law

Part C 8 Place the trolley and its driver on a flat desk. 9 Model a rear-end collision by hitting or flicking the back of the trolley with your hand or a ruler. Once again, note which parts moved. Build a safety feature that would minimise injuries in this type of collision.

trolley and ‘person’

bricks/books

20 cm marks

Questions 1 Your backside is probably the least affected part of your body in a car crash. Explain why inertia keeps heads, arms and legs moving but seems to be less effective on your backside.

brick

Fig 5.3.9

Modelling a head-on collision

2 Predict what would stop the forward movement in a car when no seatbelts are worn.

4 Modern cars are designed to crumple in an accident. Propose reasons why.

3 Predict the injuries that are likely to occur in a head-on collision while not wearing a seatbelt.

5 Propose reasons for the use of headrests in a car.

Inertial eggs Prac 2 Unit 5.3

Aim To determine whether an egg is raw or hard-boiled Equipment 1 hard-boiled but unpeeled egg, 1 fresh raw egg, smooth desk, pen or pencil

5 Spin each egg separately again. Place a finger on the egg to stop it briefly, but let go immediately. Note which egg remained stationary and which began to spin again. 6 Repeat step 5 to confirm your results.

Method 1 Copy the following table into your workbook.

Egg 1

Egg 2

7 Crack each egg over a sink. Which was hard-boiled and which was fresh?

Questions

Fast or slow spin?

1 If the shell of the fresh egg was spun, predict what its liquid insides would do.

Began to spin again?

2 Predict whether this would slow the spin of the shell.

Fresh or hard-boiled?

3 In the experiment, once the whole egg was moving the shell was then stopped. Explain what inertia suggests happened to the liquid inside the egg.

2 Mark one egg ‘1’ and the other ‘2’ with a pen or pencil. 3 Place both eggs on a smooth desk and spin each equally hard.

158

4 Note which egg spun the fastest.

4 Explain why this would get the shell moving again when you let go. 5 Discuss why the hard-boiled egg spun faster and why it remained stopped when you let go.

UNIT

context

5. 4 When you ride a bike, you have to apply a force to the pedals to get the wheels turning. The larger the force applied, the faster you accelerate. When you want to stop you have to apply a force, using the brakes, to

Acceleration Acceleration applies to any change in velocity. This may be a change in speed (e.g. from 10 to 20 m/s) or a change in direction (e.g. from north to east). Fig 5.4.1

Force

slow you down. The harder you squeeze the brakes, the faster you slow, or decelerate. This is Newton’s Second Law! Too easy ...

All acceleration requires a force. The bigger the force, the greater the acceleration. Two people pushing a car will be more effective than just one person pushing it. But if the car is a big one, the acceleration will be less: mass affects acceleration. Mass is the amount of matter in an object. It never changes unless you remove a bit from it or add more to it. A 2 kg mass stays as 2 kg regardless of where it is in the universe.

Acceleration depends on mass and the force applied.

Acceleration

Physics facts

Crumpling crashes

Mass Symbol in formulas: m Unit: kilograms Unit abbreviation: kg Twice the force

Twice the acceleration

Newton’s Second Law Newton’s Second Law states: Something will happen if a force is applied: the object will accelerate and the acceleration will depend on the mass of the object. Bigger mass, smaller acceleration Force

The force that you experience in an accident depends not on your speed, but the rate at which you come to a stop. If you decelerate more slowly, then the impact force is less. Modern cars are designed to extend the time you take to stop in a collision. Crumple zones slow the crash, and seatbelts and airbags allow you to decelerate with the car. Without this protection you will strike something hard. Deceleration and impact force will then be high.

force = mass × acceleration or F = ma

This formula can also be arranged to give: m = F/a

and

a = F/m

Prac 1 p. 162

159

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Newton‘s Second Law Spongy heads needed

Physics facts Force Symbol in formulas: F (force needs direction) Unit: newtons Unit abbreviation: N

Prac 2 p. 163

DYO

Our head has very little padding and comes to a stop very quickly if you fall from a bike and it hits the road or kerb. Bike helmets extend the time during which your skull comes to a stop, thereby protecting your brain. The wearing of motorbike helmets has been compulsory since 1963 throughout Australia. In New South Wales, cyclists have been required by law to wear helmets since 1991. If only our heads were more spongy!

A matter of balance

acceleration. You don’t speed up, nor do you slow down (Newton’s First Law). You just remain stationary, or keep travelling, like you were before.

15 000 N (force of ground on car)

There is usually more than one force acting on any object. Some of these forces may balance by cancelling each other out. If cancellation is complete then the overall force is zero and can cause no

UNIT

5.4

weight (force of car on ground) 15 000 N

Forces often balance or cancel.

Fig 5.4.2

Worksheet 5.4 Calculating F = ma

Acceleration 1 Define the term ‘mass’. 2 Describe what happens to acceleration when the same force pushes larger and larger masses. 3 Describe what happens to the acceleration of an object if the force pushing it is increased.

Newton’s Second Law 4 State Newton’s Second Law of Motion in words. 5 Use a mathematical formula to demonstrate Newton’s Second Law of Motion.

A matter of balance 6 Use Newton’s First Law to predict what will happen to acceleration when forces are balanced.

Think 7 A car turns a corner without any change in speed. Identify the incorrect statement: A B C D

160

total force 6000 N

[ Questions ]

Checkpoint

2000 N resistance (air resistance, drag, friction)

8000 N driving force (force from driving wheels)

It has no acceleration. Velocity has changed. Force was required to do the turn. Speed was constant.

8 Running is more comfortable and less likely to jar if you wear sport shoes with spongy soles. Identify the most likely reason. A B C D

They have better grip. They reduce acceleration and impact force. They shorten impact time, making the force less. They stop the foot from rolling.

9 Rugby players often slide to a stop. a Compare the deceleration obtained this way with the deceleration if they dropped to the ground. b Predict the resultant impact force on stopping when sliding. 10 Airbags are designed to inflate rapidly. Explain why they need to deflate as a person collapses into them. 11 Because they need to apply huge forces, hammers are made hard. a Predict whether the deceleration on hitting a nail will be high or low. b Explain why a rubber hammer would provide less force and be less effective.

UNIT

5. 4 Analyse 13 Sarah measured the acceleration of a trolley using the set-up shown in Figure 5.4.4. She found it to be 0.5 m/s2. She then replaced the 100 g with 200 g and then with 300 g. Calculate what she would expect the new accelerations to be.

Use this key to answer questions 12 and 13: A: Tripled B: Doubled C: The same D: Halved E: One-third of what it was 12 Compare the maximum accelerations away from traffic lights of the three identical cars shown. Fig 5.4.3

same mass as car

equivalent to mass of 2 cars

Skill 14 Calculate acceleration or force to complete the table.

Force (N)

Mass (kg)

Acceleration (m/s2)

5.0

4.0

6.1

2.0

12.0

4.0

16.4

2.0

9.3

3.1

15 Calculate the force being applied if: a a 5 kg box accelerates at 4.1 m/s2 b a 1.3 tonne car accelerates at 2 m/s2 c a 400 g ball accelerates at 4 m/s2 16 Calculate the acceleration caused by: a a 40 N force applied to a 0.5 kg mass b a 0.5 N force applied to a 50 kg mass 17 A 35 N force causes a mass to accelerate at 7 m/s2. Calculate the mass. 18 A 3.5 kg body accelerates from rest to 20 m/s in 5 s. Calculate: a its acceleration b the force required Fig 5.4.4

MS

G G G

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Newton‘s Second Law

[ Extension ]

A KG

.

Investigate .

1 Research the different types of seatbelts installed in cars and the advantages of each. Present your information in the form of an advertisement designed to sell a model you think is effective.

. B

.

KG

2 Research bike helmets or sports shoe design and how they reduce deceleration and impact forces. Write an article for a consumer magazine explaining the special features of these products.

.

Surf

.

Fig 5.4.5 19 Calculate the overall force and acceleration on the masses shown in Figure 5.4.5.

3 Investigate Newton’s Second Law by connecting to the Science Focus 4 Companion Website at www.pearsoned.com. au/schools, selecting chapter 5 and clicking on the destinations button. You will need to complete a tutorial including animations and questions. Record a log of your progress, outlining any misconceptions you may have discovered and corrected.

20 The brakes of a car can exert a stopping force of 3000 N. The car is 1.5 t. Calculate the following: a the mass of the car in kg (note: 1 t = 1000 kg) b the deceleration of the car c how long it would take to stop if it was travelling initially at 10 m/s

UNIT

5.4

[ Practical activities ] F = ma Aim To investigate Newton’s Second

Prac 1 Unit 5.4

Law

1 Copy the following table into your workbook:

Equipment Dynamics trolley, 50 g masses, pulley and clamp, block and clamp, string or fishing line, ruler, access to electronic balance or beam balance Either Ticker-timer, tape and carbon paper circles Or Stopwatch Or Appropriate light gates and datalogging equipment to measure acceleration

162

Method

Hanging mass (g) = pulling ‘force’

Mass on trolley (g)

Acceleration of trolley

2 Set up the apparatus as shown in Figure 5.4.6.

block and clamp 50 g masses

single pulley

•

Change the mass and repeat.

•

Each member of the group should analyse one tape.

Method 2: Mathematical •

Accurately measure out a 2 m track on the desk.

•

With the stopwatch, time the run. Repeat three times and find the average time taken.

•

Use the formula below to find the acceleration of the trolley in m/s2. d is the distance of the run.

trolley

a= bench

2d t2

Method 3: Datalogging •

Each equipment manufacturer will have instructions to determine the acceleration of a trolley.

•

Use appropriate sensors to find the acceleration.

50 g masses

Fig 5.4.6

UNIT

5. 4

The basic experiment—measure the trolley’s motion using one of the three methods described.

Part A: Changing trolley mass 3 Find the mass of the trolley and record it.

Questions 1 Copy and complete: a When the mass of the trolley increased, acceleration ______________ b When the mass and the force pulling the trolley along increased, acceleration ______________

4 Measure the acceleration using one of the three methods described below.

2 Explain Newton’s Second Law in your own words.

5 Add a mass to the trolley and measure the new acceleration.

3 Deduce what effect mass had on the acceleration of the trolley.

6 Repeat with at least three different masses.

Part B: Changing force

Forces in sport

Hang 50 g on the line. Method 1: Ticker-timer •

Attach 1 m of ticker-tape to the back of the trolley.

•

Turn on and let the trolley pull the tape through.

•

Draw a line through every fifth dot and measure the distance between the lines in millimetres.

•

Calculate the speed (in mm/s) of each section by dividing the distance by 0.1.

•

Plot a speed–time graph and then calculate the slope of the graph. This will be the acceleration in mm/s2.

Prac 2 Unit 5.4

DYO

Many datalogging companies have specific pracs that test the force and acceleration involved in sport. TAIN has two experiments: • shock-absorbing footwear • starting blocks. Run one of these experiments, or another sport-related one, and report on it.

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UNIT

context

5. 5 A hose flicks about if it is turned on, its nozzle moving in a direction opposite to the water. The hose is pushing the water out, but the water is also pushing the hose back in the opposite direction. This is known as an action/reaction force pair. A similar situation occurs whenever a weapon is fired. The weapon recoils (moves backwards) as the ammunition is shot. The explosion

of gunpowder in a cannon will push a cannonball out (the action) and the cannon recoils because of the force the ball applies back on it (the reaction).

Summary: Newton’s three laws Newton’s First Law Any object at rest will stay that way unless a force acts on it. Any object that is moving will keep moving at the same speed and in the same direction unless a force changes it.

Newton’s Third Law

Newton’s Second Law

Newton explains the action/reaction phenomenon in his Third Law: For every action force there is an equal and opposite reaction force. The forces on both the cannon and the ball are the same (but in opposite directions) but their accelerations are very different. The ball has a relatively low mass and so has a high acceleration and therefore velocity. Having more mass, the cannon is much less affected. In sport an action force is applied on a ball by a bat, racquet or foot. When you hit a golf ball, the club pushes the ball and is pushed back by it. The ball is light, so its acceleration is high. The club is much heavier and the force is usually only enough to slow, not stop, the swing. It might also cause a ‘shudder’ through the handle. You would feel reaction force even more if you played footy with a brick!

If the forces on an object are unbalanced then its motion will change. The larger the force the bigger the change in motion. A change in motion is called acceleration and will depend on the mass of the object. force = mass × acceleration F = m×a

Newton’s Third Law For every action there is an equal and opposite reaction. That is, there is an action and reaction pair of equal and opposite forces, acting on a different object. The action and reaction forces never act on the same object. NOTE: When speaking of an action/reaction pair of forces, there can be more than two forces involved but one group will be action forces, and the other group will be reaction forces.

Worksheet 5.5 The history of forces

Fig 5.5.1

164

Weapons recoil due to Newton’s Third Law.

… 3, 2, 1, lift-off! Rocket engines are sometimes called reaction engines, as they use the action/reaction pair of forces to provide the thrust needed for launch. Rockets expel massive quantities of gases in one direction, which push the rocket in the opposite direction, usually upwards.

Fig 5.5.3

Exhaust gases push a rocket in the opposite direction.

flow-valve control

liquid hydrogen

Fig 5.5.2

The space shuttle and all rockets lift off because of action/reaction.

The exhaust gases are tiny particles but their effect is dramatic due to their high acceleration. The exhaust is produced when fuel, called propellant, undergoes chemical combustion. A liquid propellant engine uses two liquefied gases (for example, hydrogen and oxygen), which are combined in a combustion chamber. The resulting exhaust stream produces thrust—the force which propels the rocket. The thrust produced by the space shuttle at lift-off is 35 meganewtons (35 000 000 newtons), and accelerates ets Animal rock flying the vehicle at three times the The purpleback squid (Sthenoteuthis acceleration of gravity, or 3 g oualaniesis) squirts out (i.e. 30 m/s2). jets of water in order to Initially the thrust is not enough leap out of the sea to feed. It can then easily glide a to overcome the weight of the distance of over 10 metres rocket, so the rocket sits on the in the air. launchpad, making a lot of flames,

UNIT

5.5 combustion chamber

liquid oxygen

coolant

exhaust gases

but not going anywhere. When thrust equals weight the rocket begins to hover, and when thrust is larger Flying frozen chickens! than weight, it lifts off. Birdstrikes have been around as Rockets may also contain long as aviation. It is estimated that 30 000 occur worldwide engines that use solid each year, leading to damaged propellant. These engines are aircraft windscreens and even generally simpler, cheaper engine failure. The US Federal Aviation Administration (FAA) and safer than liquid fuel designed a unique device for engines. The solid fuel testing the strength of windscreens is composed of several on aeroplanes. It is a gun that launches a dead chicken at a chemicals in proportions plane’s windscreen at about the that allow it to burn quickly speed the plane flies. The theory is without exploding. Once that if the windscreen doesn’t crack started, a solid fuel engine from the impact of the carcass, it will survive a real collision with cannot be stopped until a bird during flight. The British all the fuel is used. The needed to test a windscreen on a space shuttle uses two solid new ultra-fast train. They borrowed the FAA’s chicken launcher, rocket boosters (SRBs), loaded a chicken and fired. The which burn for a little over ballistic chicken shattered the two minutes before falling windscreen, smashed the driver’s seat and embedded itself in the into the ocean by parachute alum inium back wall. The British to be retrieved and re-used were stunned and contacted the in future missions. These FAA to see if everything had are the two thin engines on been done correctly. The FAA reviewed the test and had only the side of the main tank one recommendation: ‘Don’t use a attached to the shuttle. frozen chicken’. Jet engines work in a similar way to rocket engines: air is compressed by a series of large fans, and is then pushed out the rear of the Prac 1 Prac 2 engine with high acceleration. p. 168 p. 168

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Newton‘s Third Law

Summary: Newton’s three laws

external tank separation

orbit

manoeuvring before re-entry

solid rocket booster separation

orbiter engines fired to slow descent

main engine and solid rocket booster ignition at lift-off

re-entry into atmosphere

3 For each of the following statements, identify the correct Newton’s Law: a The larger the force the bigger the change in motion. b Any object at rest will stay that way unless pushed or pulled. c For every action there is an equal and opposite reaction. d Any object that is moving will keep moving at the same speed and in the same direction unless a force changes it.

… 3, 2, 1, lift-off! 4 Use Newton’s Third Law to outline how a rocket achieves ‘lift-off’.

approach

5 Use a diagram to demonstrate how a jet engine works using Newton’s Third Law.

landing

Think Fig 5.5.4

The main stages of a space shuttle mission

fuel (kerosene)

combustion chamber fast moving air

air

compressor

fan

A jet engine works by action/reaction.

UNIT

Fig 5.5.5

[ Questions ]

9 Pat throws a netball. a Identify the action force. b Explain what the action force did in this situation. c Identify the reaction force. d Explain what the reaction force did in this situation. 10 Deduce which part of the launch these rockets are in: a thrust = weight of rocket b thrust > weight of rocket c thrust < weight of rocket d thrust = 0 11 Explain why the acceleration of a rocket increases as its fuel is consumed. 12 Rockets normally discard used fuel tanks soon after launch. Discuss the advantage of this.

Checkpoint Newton’s Third Law 1 State Newton’s Third Law of Motion. 2 Describe three examples that show Newton’s Third Law of Motion in action.

166

7 a Firefighters often need to brace themselves or have extra help to hold a firehose while it is on. Explain why. b Predict what would happen if they did not have this help. 8 Michael is stranded on ice that is so slippery that he cannot walk. Recommend a way that he could get himself to nearby hard ground.

turbine

5.5

6 Explain why a balloon shoots around the room when it is allowed to deflate.

Analyse 13 Ben kicks a football. Use a diagram to demonstrate the action/reaction pair of forces acting on the football: a as it lies on the ground before being kicked

b as it is kicked, Ben’s boot touching the ball c as it flies through the air, having no more contact with the foot 14 Copy the diagrams in Figure 5.5.6 into your workbook and draw action/reaction force pairs in each. Fig 5.5.6 a

b walking

UNIT

5.5 [ Extension ] Investigate 1 a Research how squids move and record your findings using a diagram. b List any other animals that propel themselves forward like a rocket. 2 Research the development of either the jet engine or the rocket. Use a time line to summarise the major developments. 3 The V1 and V2 rockets were developed in Nazi Germany and were the first missile-based weapons used in warfare. Use a diagram to demonstrate how these rockets use Newton’s Third Law of motion. 4 Write a brief journal article on the contribution of Werner Von Braun to the understanding of motion.

Action 15 The arrows in Figure 5.5.7 show gases being expelled out the back of the rockets. The longer the arrow, the more gases are being expelled. Copy or trace these ‘rockets’. Identify any thrust forces produced and the direction the rocket would go or turn.

5 Using Figure 5.5.8 as a guide, take a whirly rocket for a spin. Record your observations and deduce whether Newton’s Third Law is obeyed.

Fig 5.5.7

pivot pin

flexible straw

tape centre of mass gases

balloon

gases stick

gases

Fig 5.5.8 gases

Surf 6

gases gases

Investigate Newton’s Third Law by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button. You will need to complete a tutorial including animations and questions. Record a log of your progress, outlining any misconceptions you may have discovered and corrected.

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Newton‘s Third Law

UNIT

5.5

[ Practical activities ]

retort stand 1.25 L plastic bottle

Water rockets Prac 1 Unit 5.5

bosshead and ring

SAFETY WARNING: The launch of this rocket must be done outside. Everyone must stand clear of the launch area.

1 3

fill with water

sanded and cut cork

Aim To observe action/reaction forces in action 1.25 L plastic softdrink bottle, champagne cork (other corks or rubber stoppers may do, but the fit must be tight), sandpaper, Vaseline, safety glasses, access to bike pump or electric pump, access to power drill with fine drill bit, access to hacksaw, retort stand, clamp and ring

Method 1 Cut the champagne cork with the hacksaw, shortening it so that it is a little shorter than the valve of the bike pump.

bike pump

bike valve

Equipment

Fig 5.5.9

Questions 1 Identify the action/reaction force pair in this situation. 2 Identify the ‘fuel’ for this rocket.

2 Sand the sides of the cork so that it fits neatly into the neck of the plastic bottle.

3 List the forces that slowed its ascent.

3 Drill a hole through the centre of the cork. Lightly smear the sides of the cork with Vaseline.

5 More water did not necessarily produce increased height. Discuss why.

4 Fill the bottle to about one-third with water.

7 Evaluate the effect of different-sized plastic bottles on height.

5 Push the valve of the pump through the cork and then secure the cork in the neck of the bottle. 6 Quickly place the bottle upside down in the ring.

4 Recommend how these forces could be reduced.

6 Trigonometry can be used to find the height reached by the rocket. Describe how this can be done.

7 Start pumping, standing well clear of the rocket. 8 Repeat, trying different amounts of water. 9 Repeat, trying different-sized plastic softdrink bottles.

A two-stage rocket Prac 2 Unit 5.5

Fig 5.5.10

Fig 5.5.11 round balloon

long balloon cup

Aim To construct a two-stage rocket using balloons Equipment cup

Plastic cup, scissors, 2 balloons (1 long, 1 round), tape tape

Method 1 Cut the bottom out of one of the paper cups. 2 Partly inflate the long balloon and pull it through the bottomless cup, taping the opening to the side of the cup as shown in Figure 5.5.10. 3 Place the round balloon inside the cup and blow it up so it wedges inside the cup. Hold the opening shut. 4 Remove the tape holding the long balloon on the side of the cup and release the end of the round balloon to launch your ‘rocket’.

168

long balloon

Questions 1 Account for the propulsion of the rocket. 2 a Explain how the rocket could be enlarged to include a third stage. b Assess whether there would be a limit to how many stages you could attach.

UNIT

context

5. 6 Rock climbers appear to defy gravity. Climbers push down on handholds and footholds to advance up the rock. By maintaining a balanced position, climbers can remain stable regardless of their weight. An upward frictional force on the hands and shoes opposes gravity and allows the climbers to move upwards. Gravity is that unseen quantity that is always trying to pull you down.

Gravity Gravity is the rate of acceleration at which objects fall. It seems logical that heavier objects should fall faster than lighter ones but Galileo found that the acceleration due to gravity is the same for all similarly shaped objects. Newton later discovered that the acceleration due to gravity depends on the mass of the planet you are on and the distance you are from the centre of the planet, but not on the mass of the falling object.

g-forces

On the Earth’s surface the acceleration of all objects is 9.8 m/s2. This means that the speed of a falling object increases about 10 m/s every second of its fall. This value is for objects falling in a vacuum. In air, acceleration will be slightly less. An object pushes air out of its way as it falls. The air pushes back with an equal, upward force called air resistance. The more the air resistance, the lower the acceleration of the fall.

Weight The force on a mass that is caused by gravity is called weight. It is the force that pulls objects down to the surface of a planet. Weight depends on the mass of the object and the acceleration due to the gravity of the planet itself. You can write this as:

Our weight often seems to increase because of inertia and g-force is used to describe this. Normally you only feel 1 g (i.e. normal gravity, g). If you experience 2 g, then you are being pushed into your seat twice as much as normal. The body responds, squashing muscles and bones. Formula 1 drivers experience forces of up to 5 g when cornering: neck muscles strain to hold in place a head five times ‘heavier’ than normal and blood is ‘pushed’ sideways. Blood flow to the edges of the eye is disrupted, causing peripheral (side) vision to deteriorate, distorting perspective and making it difficult to judge distances. If an aircraft suddenly increases altitude, blood moves down to the feet and away from the brain. At 8 g to 9 g this reduced blood supply to the brain will cause blackouts.

Prac 1 p. 172

Prac 2 p. 173

DYO

weight = mass × acceleration due to gravity or w = mg

Terminal velocity

The rock climber’s weight force is balanced only by her hand grip on the rocks and the friction of her boots.

Fig 5.6.1

Air resistance increases as speed increases—the faster you are falling, the more the resistance. Eventually it balances weight, and so the total force acting is zero. There can be no more acceleration and the object falls at a constant speed, called its terminal velocity. All objects have a terminal velocity, but its value will depend on the shape and size of the object. A sheet of paper has high air resistance and a low terminal velocity, while the same paper crumpled has lower air resistance and will reach higher speeds.

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Gravity

Air resistance – increases with speed

Leonardo Da Vinci’s 1485 sketch of a parachute

Weight = mg

Fig 5.6.2

A falling object travels at a constant terminal velocity if the weight is equal to the air resistance.

Physics facts Gravity

Worksheet 5.6 Losing and gaining weight

Weightlessness

Symbol in formulas: g Unit: metres per second squared (gravity is acceleration) Unit abbreviation: m/s2 or ms–2

Weight

Falling from the sky

nal velocity of about 50 m/s. Without a parachute humans have a termi nt by changing the shape of desce their ol contr However, skydivers can back’ or catch up to others their body as they fall, enabling them to ‘hang reduces the terminal hute parac open An . tions to create group forma velocity of a raindrop nal termi velocity to 5 m/s, which is just about the , which changes shape its es chang s string ’s chute (7 m/s). Pulling on the tion. its speed and direc sketched his ideas for a Leonardo Da Vinci (painter of the Mona Lisa) leted the first successful comp rin Game Andre , 1797 In . parachute in 1485 a hot air balloon. from m 680 ed parachute jump, having dropp

Symbol in formulas: w Unit: newtons (weight is a force) Unit abbreviation: N

Prac 3 p. 174

Prac 4 p. 174

Fig 5.6.5

polystyrene cup

small hole punched through

Skydivers can change their terminal velocities.

170

Fig 5.6.3

Fig 5.6.4

Water is ‘weightless’ in a falling cup.

water

does water exit?

You have weight whenever gravity is around. True weightlessness (where g = 0) only happens far from the influence of stars and planets. You sometimes ‘feel’ weightless, however, in rides such as the Tower of Terror and the Giant Drop at Dreamworld, when the seat (with you in it) falls. During the fall, the seat cannot push back to give your normal ‘feelings’ of weight. When in orbit, the space shuttle and space stations fall towards Earth. They don’t hit, however, since they are travelling at such high speed ‘horizontally’ that they always miss the planet. Astronauts aboard them have the ‘feeling’ of weightlessness because both they and the floor fall at the same rate. Try the experiment in Figure 5.6.5 as evidence.

UNIT

5.6

UNIT

5.6 [ Questions ]

Checkpoint Gravity 1 Define ‘gravity’. 2 State the symbol, abbreviation and units for gravity. 3 On the Earth’s surface all objects accelerate at the same rate. State this rate.

Analyse 19 Identify the diagram in which the ball will be: a accelerating b getting blown upwards c travelling at terminal velocity Fig 5.6.6

4 Define ‘air resistance’. 5 Define ‘weight’.

A

B

C

6 Record the relationship between weight and mass in words and a formula.

Terminal velocity 7 Define ‘terminal velocity’. 8 List factors that affect terminal velocity.

Think 9 Copy the following, modifying any incorrect statements to make them true. a Heavier objects fall faster than light ones. b Air resistance is high in a vacuum. c Mass changes as you move between different planets. d Weight is measured in kilograms. e You would feel weightless in a falling lift.

20 Complete the ‘photographs’ in Figure 5.6.7 by predicting where the missing object is at each indicated time.

10 Contrast weight with mass. 11 Identify a place that has no air resistance. 12 Spacecraft often have fragile solar panels and antennae projecting from them, but move at very high speeds. Explain why these things don’t get ripped off the craft.

hammer

shotput

feather bullet

13 Compare the rate at which a hammer and a feather would fall on the Moon. 14 Account for the fact that skydivers could throw a pumpkin back and forth between them before they release their chutes, but not once the chutes are open. (Hint: The terminal velocity of a pumpkin is 50 m/s.) 15 a Explain what is meant when it is said that a person experiences a force of 8 g. b Predict what will happen to a human experiencing 8 g. 16 a Propose ways in which the g-forces on a human can be increased. b Propose ways in which these forces can be decreased. 17 Assess whether it is possible to be truly weightless, even in space. 18 When the space shuttle is in orbit, the gravity on its occupants is still approximately 7 m/s2. Account for the fact that they seem weightless.

Earth

Fig 5.6.7

Moon

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Gravity

Skills 21 Amal has a mass of 50 kg. Calculate her mass and her weight on: a Earth (g = 9.8 m/s2) b the Moon (g = 1.63 m/s2) c Mars (g = 3.7 m/s2)

22 Angelo lands on the Planet X. His mass is 70 kg on Earth. a State his mass on Planet X. b If his weight on Planet X is 350 N, calculate the acceleration due to gravity on Planet X. c Contrast the size of Planet X with that of Earth.

[ Extension ] Creative writing Investigate 1 Research Galileo’s gravity experiments on top of the Leaning Tower of Pisa. Summarise your findings by drawing a cartoon. 2 Write a biography of Sir Isaac Newton, highlighting his major scientific achievements. 3 a Research the history of the parachute, and present your information in a style of your choice. b Construct a series of diagrams to show the forces acting during the different stages of descent of a parachute. 4 a Record the value of gravity on different planets of the solar system. b Calculate your weight on each planet.

Surf

UNIT

Aim To experimentally determine acceleration due to gravity

Equipment

Ticker-timer and about 2 m tape, G-clamp, 50 g mass, sticky tape, ruler, access to a calculator

172

PROJECT Videotape a cartoon on TV. Watch carefully the movements that it shows, particularly anything that is falling. (Roadrunner cartoons are ideal!) Prepare a presentation on a short snippet of motion shown in the cartoon. Were the laws of physics displayed correctly? If not, what should have happened? Show the snippet of video to the class and explain the correct/incorrect use of physics.

[ Practical activities ] Finding g graphically

Prac 1 Unit 5.6

This ancient Greek philosopher’s views on gravity shaped thought for over 1500 years. Unfortunately, Aristotle thought heavier objects always fell faster than light ones. You have travelled back in time to explain to Aristotle what gravity is and what it does to falling objects. Because your ancient Greek is not good, you will need to prepare some simple demonstrations to convince him.

Cartoons for homework!

5 Investigate terminal velocity further by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button. a You will need to complete the interactive animation investigating the physics involved when you drop a ball. Make changes to mass, radius and height of drop, and graph the results. b Record your results in a table and state a conclusion about your findings.

5.6

Convincing Aristotle

Method 1 Tape a 50 g mass to the bottom of a 2 m long strip of ticker-timer tape. 2 Clamp, or hold securely, the ticker-timer against a wall or doorframe. 3 Thread the tape into the timer and hold it.

7 Calculate the average speed of each five-dot section. ticker tape

8 Plot a speed–time graph for the drop, drawing a line of best fit through your points.

clamp or hold flat on doorframe/wall

UNIT

5.6 9 Find the gradient of the graph. This is acceleration due to gravity in mm/s2. To convert to m/s2, divide by 1000. 10 How does your result compare to the actual value of the acceleration of gravity of 9.8 m/s2?

tickertimer to AC power pack

sticky tape 50 g mass

Fig 5.6.8

1 Calculate how long it would take for one new dot (equivalent to a space between two dots) and for five new dots (five spaces between 6 dots) to be produced if the AC supply was: a 10 Hz b 100 Hz 2 Explain what the slope of a speed–time graph indicates.

Using a ticker-timer to measure g

3 Discuss whether your graph indicates constant acceleration as the mass fell.

4 Turn on the timer and let the tape fall. 5 Rule a line through every fifth dot. Measure the distance between each line. 6 Copy the table below and enter your results.

Section

Questions

Elapsed time (s)

Time taken for each section (s)

0 to 5 dots

0.1

0.1

6 to 10

0.2

0.1

11 to 15

0.3

0.1

16 to 20

0.4

0.1

21 to 25

0.5

0.1

4 Why would the acceleration measured here be less than 9.8 m/s2? Justify your answer. 5 From the tape, describe how you can tell when the mass hit the ground.

Distance of each section (mm)

Average speed in each section (mm/s) Column 4 ÷ Column 3

Time at which this happened (s)

Datalogging and g Prac 2 Unit 5.6

Use datalogging equipment, appropriate sensors (e.g. light gates) and equipment (e.g. TAIN has ‘combs’) to measure and plot acceleration due to gravity.

DYO

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Gravity

Measuring height with a stopwatch! The formula h = 4.9t2 gives the height that an object drops (measured in metres) when the drop time t is measured (in seconds). It assumes that the object falls with an acceleration of 9.8 m/s2 due to gravity.

Prac 3 Unit 5.6

4 Use the tape measure to find the actual drop. 5 Place all your results in a table like the one below. 6 If time allows, test whether the formula works for the mass being thrown down (instead of being dropped) and for masses that have high air resistance.

Aim To find height using a stopwatch

Questions

Equipment Any small mass that won’t break, stopwatch, metre ruler/ tape measure, string with mass attached

1 You both measured and calculated the height of the drop. Compare your results.

Method

2 Evaluate whether the formula would give inaccurate results for the drop of things like a feather.

1 Find appropriate safe spots around school where you can drop a small mass. 2 Measure the time taken for the drop at each place. Repeat to obtain consistent results.

3 Identify the starting speed required for the formula to work. 4 Present any assumptions made by the formula.

3 Use a calculator and the formula h = 4.9t 2 to calculate the expected height of the drop.

Place of drop

Time of drop (s)

Average time (s)

Height from formula (m)

Measured height (m)

Finding the centre of gravity Prac 4 Unit 5.6

Mass is spread all through an object. Weight, however, acts as if it is concentrated at one particular point, called the centre of gravity or centre of mass.

Aim To locate the centre of gravity of different objects Equipment A photocopy of a map of Australia, scissors, 2 sheets of cardboard, cotton line, small mass (e.g. some paperclips), sticky tape, access to a hole punch, access to photos of athletes (e.g. running, jumping, kicking, throwing)

Method Part A 1 Trace a map of Australia onto a piece of cardboard and cut it out.

174

2 Punch a hole anywhere near its edge. 3 Tie the line to the hole and attach the small mass to the other end. 4 Attach another line at the hole and suspend Australia from it. 5 Use a pencil to trace onto the cardboard the vertical line the mass line makes. 6 Repeat, but place the hole somewhere else on the map. 7 The centre of gravity is where the two lines intersect. Mark its position.

Part B 8 Make a larger version of the ‘person’ shown in Figure 5.6.9 on the other piece of cardboard.

5.6 Fig 5.6.9

Finding the centre of a mass

9 Arrange in a pose and use tape to connect the body parts. Find the centre of gravity using the above method. 10 Arrange the body into the poses of various athletes of different sports and find the centres of gravity.

Questions 1 Propose another method of finding the centre of gravity. 2 Refer the position to an atlas and identify which town is the closest to the ‘heart’ of Australia. 3 Is the centre of mass the same for all human poses? Justify your answer. 4 There are two styles of high jumping: the scissors and the flop. a Identify which one has the lowest centre of mass. b Propose why the flop is the favoured style. 5 Skiers try to keep their centre of gravity as low as possible. Explain why they do this. 6 Predict how the centre of gravity affects the stability of cars and trucks.

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UNIT

context

5. 7 That was hard work! You have probably said that recently, but what does ‘work’ actually mean in science? Basically if you apply a force and move an object, you have done work. That is why the phrase ‘hard work’ really makes sense when you start lifting rocks and stacking boxes. But you probably use a little less energy doing your homework, which, scientifically speaking, is not really hard work after all.

The work done in a car crash is very obvious. The car and its occupants can undergo radical rearrangement: bonnets crumple, windscreens shatter, bones break. Forces are applied and things moved. Work is done. Where did the energy to do this work come from?

Physics facts

Work Movement involves energy. Energy is the ability to do work. Work happens whenever things are shifted or rearranged by a force. The bigger the force, the more work done. Likewise if something is shifted a long way, then more work is done than if it only moves slightly. If it doesn’t move, then no work has been done on it. work = force applied × distance shifted or W = Fs

Force is always measured in newtons (N) and distance in metres (m). Work is a form of energy and, like all energy, is measured in joules, abbreviated as J. If a heavy box takes a force of 500 N to shift it 3 m, then the work done on it is: W = 500 × 3 = 1500 J

Energy Unit: joules Unit abbreviation: J

The Trabi West Germany produced Mercedes Benz, BMW, Porsche, Audi and VW, but East Germany made the 3 Trabant. Its 660 cm twocylinder engine accelerated it to a maximum speed of 80 km/h, a terrifying speed, given that much of the car’s body was made of compressed recycled cardboard! Collisions at speeds as low as 16 km/h were often deadly. Although the Trabant is no longer being produced, there are still lots of old ones on the roads of the old East Germany.

Kinetic energy Movement is needed for cars to crash: no accident will happen if everything is stationary. When something moves it has kinetic energy. The heavier the car, the more kinetic energy it has and the more work and damage it can do. Likewise, the faster you travel, the more work will be done. In fact, if you double your speed, the work done in a collision and the damage caused will be four times what it was at the slower speed. Kinetic energy = 1/2 × mass × speed × speed or KE = 1/2 mv 2

500 N force

Kinetic energy is measured in joules (J), mass in kilograms (kg) and speed in metres per second (m/s). Compare the kinetic energies of a typical 1.5 tonne car (1500 kg). At 50 km/h (13.9 m/s), the car has a kinetic energy of KE = 1/2 × 1500 × 13.92 = 144 908 J

At 100 km/h (27.8 m/s), the kinetic energy is quadrupled: KE = 1/2 × 1500 × 27.82

Fig 5.7.1

176

If the crate shifts 3 m, then 1500 J of work has been done.

= 579 630 J

On braking, all this kinetic energy is converted into heat energy that is dissipated by the brake pads or discs. In a collision, it converts into heat and sound, but mainly into work as the car crumples or crumples other cars or objects—a lot of rearranging is done in an accident.

Gravitational potential energy Similar damage would be sustained if a car ran off a cliff. The higher the cliff, the worse the situation becomes. Obviously height gives you energy too. Potential energy is stored energy—it gives the object the potential to do work. If you lift an object to a height you give it gravitational potential energy. The heavier the object and the higher you lift it, the more energy it will have, and the more damage it will cause when let go. Mathematically it can be written as: gravitational potential energy

= mass ×

acceleration × height due to gravity

GPE = mgh

GPE is measured in joules (J), m in kilograms (kg) and h in metres (m). Like all accelerations, g is measured in metres per second squared (m/s2). On Earth g is 9.8 m/s2. As something falls it picks up speed—gravitational potential energy is converted into kinetic energy. When it hits the bottom, most will be converted into work done on the ground and the object itself. Both the ground and the object will dent and change shape or break.

Elastic potential energy Elastic bands and springs store energy when they are stretched or extended. They store it as elastic potential energy. They have the potential to release energy and do work when they are let go, bouncing back to their original shape. This is very obvious when a slingshot is stretched and let go. You put your own energy into stretching the elastic band. The more a slingshot is stretched, the more energy it stores, the more kinetic energy the projectile will have, the faster it will go and the more damage (work done) it will do. This is also the energy that puts the fun into bungee jumping. A bungee rope stores elastic potential energy ready to release at the bottom of the fall.

Fig 5.7.2

UNIT

5.7

Fig 5.7.3

Gravitational potential energy converts first into kinetic energy (and high speed), then work done (crumpling of the panels).

177

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Work and energy Springs also store energy when squashed or compressed. Tennis balls act as a store of elastic potential energy when compressed on a bounce or when hit. The more the ball stores, the more it releases and the higher it will bounce. Some materials are stiff—they need high forces to change their shape. Others are highly elastic. One measure of stiffness is the spring constant of the material. The higher the constant, the stiffer (and less elastic) it will be. Elastic potential energy = 1/2 × spring constant × extension2 EPE = 1/2 kx 2

Here, x is the extension or compression of the elastic band or spring (measured in metres) and k is its spring constant (in newtons per metre, N/m).

Prac 1 p. 180

Efficiency Friction between moving surfaces wastes useful energy, converting some of it into heat and sound. Efficiency is a measure of how much useful energy is retained in a conversion: efficiency =

Prac 2 p. 181

useful energy after the conversion × 100% energy before the conversion

A rolling ball will eventually stop due to friction. All the kinetic energy it once had has been converted into heat and sound: the efficiency is 0%. A 100% efficient machine would be perfectly quiet and would run forever, because all the energy conversions would be perfect. A ball loses a little of its useful energy each time it bounces. Squash balls have very little bounce and are incredibly inefficient, Prac 3 p. 182 losing most of the energy to heat. The ball gets hot quickly, which then gives it more elasticity and better bounce. Worksheet 5.7 Work and energy

DYO

extension x

5 Use words and symbols to describe the formula used to calculate kinetic energy.

F

k = spring constant = slope

m F = weight = mg

x

UNIT

Fig 5.7.4

[ Questions ]

Checkpoint Work 1 Define the term ‘energy’. 2 Use words to explain the following equation: W = Fs 3 State the name, abbreviations and units for all terms in the equation: W = Fs

Kinetic energy 4 State the type of energy a moving object possesses.

178

Gravitational potential energy 7 Define the term ‘potential energy’. 8 Use words and symbols to describe the formula used to calculate gravitational potential energy.

Calculating the spring constant

5.7

6 State the units for the terms in the kinetic energy equation.

9 State the units for all terms in the formula: GPE = mgh

Elastic potential energy 10 Define the term ‘elastic potential energy’. 11 List two objects capable of storing elastic potential energy. 12 Use words and symbols to describe the formula used to calculate elastic potential energy. 13 State the units for the terms in the equation: EPE = 1/2 kx 2

Efficiency 14 Describe how friction wastes energy. 15 Define the term ‘efficiency’. 16 Write an equation to demonstrate how efficiency can be calculated.

Think 17 Identify the situations in the list below that do not involve any work being done. A A 10 kg crate is lifted up 2 m. B A car is pushed along a road. C A spacecraft travels through the solar system without being affected by air resistance or gravity. D A skateboard rolls to a stop. E A book sits on a desk.

UNIT

5.7 25 Figure 5.7.6 shows the graphs for the extensions of the elastic band combinations shown. Identify the graph that matches each elastic band combination.

19 ‘If speed is doubled, the car accident will be twice as bad.’ Use your knowledge of kinetic energy to evaluate this statement. 20 Crumple zones are incorporated into the front and rear of modern cars to convert the energy of the collision into work on the panels. It does this by allowing them to buckle instead of remaining rigid. If these zones were not there, predict what would absorb the collision energy.

Force

18 State the names given to: a ‘moving’ energy b ‘height’ energy c ‘spring’ energy d ‘rearranging’ energy

A B C D

21 A tennis ball that was 100% efficient would bounce forever. Assess this statement.

Extension

22 In reality, a tennis ball will bounce a little less each time. Explain why this occurs. 23 A slingshot that is stretched twice as far does roughly four times the damage. Explain why.

Analyse 24 List the springs in Figure 5.7.5 in order from stiffest to least stiff. Fig 5.7.5

Force D C B A

Extension

Fig 5.7.6

Skills 26 Calculate the work done: a by a 7 N force that shifts a box 2 m b in shifting a trolley 50 cm by a 20 N force 27 Calculate the kinetic energy in the following: a A 400 kg motorbike travels at 25 m/s. b A 50 kg skateboarder is freewheeling at 9 m/s. c A 20 g stone is thrown at 2 m/s. (Note: 1000 g = 1 kg) d A 30 mg spider runs about at 5 cm/s. (Note: 1000 mg = 1 g) 28 Calculate the gravitational potential energy that the following objects have: a Travis stands on a diving board, 11 m above the surface. His mass is 60 kg. b A 2.5 kg textbook is on a desk that is 70 cm high. (Note: 100 cm = 1 m) c Matthew (65 kg) is on the Centrepoint observation deck, 250 m above the street. d Yee is piloting Flight 007 at a height of 9500 m. Her mass is 55 kg.

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Work and energy

29 Tanya is about to dive off the 10 m board. Her mass is 50 kg. a Calculate her gravitational potential energy before the dive. b This energy had to come from somewhere. Predict where. (Hint: How did she get there?) c When she dives, predict the potential energy conversion. d Specify evidence for the energy conversion in part c. e Calculate her kinetic energy just before she enters the water. f Describe where all this kinetic energy goes when she enters the water. 30 a Calculate the gravitational potential energy before and after a bounce, if a 30 g ball is dropped from 2 m and bounces to a height of 1.5 m. b Calculate its efficiency.

31 Compare the elastic potential energy stored in an elastic band (spring constant 6 N/m) that is stretched 0.1 m with an identical band that is stretched exactly double the distance. 32 Calculate the elastic potential energy stored in each spring (make sure all lengths are in metres): a A slinky spring with a spring constant 5 N/m is extended 3 m. b A spring (k = 25 N/m) is squashed 0.5 m. c A slinky has a natural length of 15 cm, but is stretched to a new length of 90 cm. Its spring constant is 30 N/m. d The slinky in part c is stretched from 15 cm to 4 m in length.

[ Extension ] Investigate 1 Research the methods used to stop a lift falling if the cables break. Record your findings in the form of a safety report that might appear on an advertising brochure. 2 Some cars and trucks have leaf springs in their suspension. Use a diagram to explain how a leaf spring works. 3 Active safety features are those that allow a driver to avoid an accident in the first place (e.g. brakes,

UNIT

5.7

[ Practical activities ] Extension of an elastic band

Prac 1 Unit 5.7

Aim To measure the elasticity of elastic bands Equipment Three similar elastic bands, retort stand, bossheads and clamps, 50 g masses, ruler

Method 1 Copy the table opposite into your workbook.

180

tyre tread, headlights). Passive safety features protect the occupants when an accident occurs (e.g. seatbelts, energy-absorbing bumpers). Search the websites of the major car manufacturers to: a identify the safety features included in modern cars, and list them as active or passive features b design a new safety feature for cars, one that does not currently exist, but you think may be worth including in cars in the future.

Mass attached (g) 0 50 100 150 200 250

Length (mm)

Extension (mm)

UNIT

5.7 6 Plot a graph of mass (g) (vertical axis) against extension (mm). Draw a line of best fit through the points.

2 Measure the natural, unstretched, length of an elastic band. 3 Hang a single band from the retort stand and attach a single 50 g mass.

7 Repeat the process for the other elastic band arrangements shown in Figure 5.7.7.

4 Measure its new length and calculate the extension the 50 g mass has caused.

8 On the same graph as before, plot the graphs of these arrangements.

5 Repeat for 100 g, 150 g, 200 g and 250 g.

9 Repeat the experiment using elastic bands of different thicknesses. Fig 5.7.7

Measuring elasticity

Questions 1 Identify the energy being stored in this experiment. 2 Discuss which arrangement of the elastic band was the stiffest.

retort stand elastic band

50 g mass 100 g mass measure extensions

Efficiency of a roller coaster Prac 2 Unit 5.7

Aim To design a roller coaster and determine the efficiency of different-shaped curves Equipment

Material to make a track out of (clear plastic tubing is ideal), ballbearing or marble, retort stands, bossheads and clamps, metre ruler, access to electronic scales

Method 1 Set up the roller coaster as shown. 2 Let the marble run from one end of the track to the other.

>>

3 Measure the starting and finishing height. Measuring efficiency

Fig 5.7.8

start

measure height

finish measure height

181

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Work and energy

4 Determine the mass of the marble.

Questions

5 Calculate the gravitational potential energy of the marble at the beginning and end of the track.

1 Gravitational potential energy is converted into other forms as a marble drops. Deduce what forms it is converted into.

6 Calculate the efficiency of the track. 7 Change the shape of the track and repeat. 8 Find the most efficient and inefficient shapes for the track. Draw them.

2 Identify the type of energy the marble had at the bottom. 3 The track will never be 100% efficient. Explain why.

Ball bounce Prac 3 Unit 5.7

The coefficient of restitution of a ball is a measure of the rate at which a ball regains its shape on a bounce. It can be calculated by the formula: coefficient of restitution =

height of bounce height of drop

DYO

Aim To calculate the coefficient of restitution of various balls Equipment A variety of balls (tennis, squash, superball, basketball), metre ruler

Method 1 Design an experiment to measure the coefficient of restitution of different balls from a particular height. 2 Run a further test to see if the coefficients change when the starting height is changed.

182

Questions 1 List the balls in order from highest to lowest coefficients of restitution. 2 Deduce whether the coefficient of restitution was the same for each ball for each drop height. 3 A coefficient of 1 is impossible. Explain why. 4 Use your observations to discuss where the energy goes in a bounce. 5 Apart from ball type and height, identify other variables that could affect the coefficient of restitution.

Chapter review [ Summary questions ] 1 From the following list identify the most appropriate unit for the quantities below:

9 Calculate any missing values in the following table and select the appropriate units for each.

J N m/s2 m/s m s °C a b c d e f g

Distance travelled

Time taken

20 m

5s

energy displacement time velocity acceleration force work done

2 Record the symbols normally used for the following quantities: a distance b speed c acceleration d force e mass 3 Contrast the following: a average and instantaneous speeds b mass and weight c work and force

Speed

6h

80 km/h

1000 km

100 km/h

2.5 cm

0.5 s

7.0 m

35 m/s

10 Identify the graphs below that represent an object that is: a b c d

at rest or stationary moving at constant speed accelerating decelerating

v

v B

4 State what a driver is doing during reaction time and braking time.

A

5 Use examples to explain what is meant by ‘inertia’. 6 List two things that need to happen for work to be done. 7 Outline Newton’s three laws.

[ Thinking questions ] 8 Identify the Newton’s law that best explains these situations: a You feel a gun recoil. b You are ‘pushed’ back into the seat when a car accelerates away at traffic lights. c A hose flicks about when the water is turned on. d A hand passes through a piece of wood in a karate chop. e A soccer ball is kicked. f Sand moves under your feet when you run.

t v

t v

D C t

t

11 ‘All things fall at the same rate.’ Is this statement true, false or a bit of both? Justify your answer. 12 Station wagons are more dangerous than sedans. Use your knowledge of inertia to explain why. 13 Use F = ma to explain why high-jumpers and polevaulters land on a spongy mat and not the hard ground.

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Writing chemical equations

14 Dashboards are generally padded but once were made of metal. Explain how a padded dash reduces impact force. 15 Predict what doubling the speed would do to the kinetic energy. 16 Predict the forms into which a car’s kinetic energy will get converted in an accident. 17 Squash balls don’t bounce well and get very hot after a little play. Explain how these two facts are connected.

[ Interpreting questions ] 18 Calculate the distance and displacement of a ball that is thrown vertically, rises to a height 3 m above your hand, and then returns to it. 19 The same ball is thrown up to the same height, but is dropped on its return, falling 1 m to the ground. Calculate its distance and displacement. 20 A cricket pitch is 20.1 m long. The ball is released 0.5 m behind the wicket and reaches the batter’s wicket 0.83 s later. Calculate the average speed of the ball in m/s and km/h. 21 Calculate the final speeds of these objects:

184

Starting speed

Accelerated for this time

Rate of acceleration

0

5s

15 m/s2

0

12 s

4 m/s2

18 m/s

6s

2 m/s2

40 km/h

5s

5 km/h/s

20 m/s

Half a minute

3 m/s2

Final speed

22 Construct separate speed–time graphs for these motions: a A car accelerates away from traffic lights. b A car travels at 100 km/h along a freeway. c A car brakes hard. 23 On the one graph, construct speed–time graphs for these drops: a A shotput is dropped from 2 m. b A tennis ball falls 2 m to the ground. c A piece of crumpled paper falls. d A parachutist jumps out of the plane, waits a short time, opens the chute and then floats to the ground. Worksheet 5.8 Motion and energy crossword Worksheet 5.9 Sci-words

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6

Health

and disease

Key focus area

>>>

The implications of science for society and the environment

use the food pyramid to create a balanced diet contrast infectious with non-infectious diseases describe the agents that cause different infectious diseases explain various methods that the human body uses to defend itself from disease

Outcomes

explain the factors that influence our health

5.4, 5.8.4

By the end of this chapter you should be able to:

explain how vaccinations give immunity describe how lifestyle and environmental factors can produce disease describe how the diet and health of Aboriginal people has changed since the arrival of Europeans.

(excellent). Why have you given yourself this number?

2 How much exercise should you do each week to stay healthy?

3 What diseases have you had so far? 4 What vaccinations/needles have you had in the past?

Pre quiz

1 Rank your health from 1 (very poor) to 10

5 It is usually a waste of time and money taking antibiotics to ‘cure’ you of a cold or the flu. Why?

6 What do kJ, GI, HIV+, AIDS and DVT stand for? 7 What problems are associated with smoking? 8 Is the brain shown in the scan on this page healthy?

185

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UNIT

context

6. 1 Are you healthy? What about you indicates that you are healthy or not? How can you tell? The term ‘good health’ means different things to different people. A person in the Indian slum of Dharavi may think that they are in good health because they are able to walk and work while many others around them can’t. You probably look at that same person and think they are in very poor health because they may be malnourished or have skin diseases from

contaminated water. This example shows that health is a relative term. In general, a person with good health has an overall sense of wellbeing and is able to function well within their environment.

These people might be said to have good health because they are able to function effectively in their environment.

Fig 6.1.2

Good nutrition

Fig 6.1.1

Philippinos living in this Manila slum are prone to malnutrition and infectious diseases.

What is needed for good health? There are many factors that contribute to the overall sense of well-being that makes good health. Three vital components are good nutrition, a healthy mind and adequate exercise. It is important to pay attention to all these factors or you can quickly become unhealthy. It is not enough to eat well but never exercise, or to have a healthy mind but eat only cheeseburgers.

186

To survive, organisms must take in nutrients. A nutrient is any substance that is used by an organism either as a source of energy or to build living tissue. Fats, proteins and carbohydrates can all be used by the human body to make energy and so these are our main nutrients.

Health facts Energy is measured in joules (J) or kilojoules (kJ). 1000 J = 1 kJ An older unit of energy is the calorie: 1 calorie = 4.2 kJ. Fat supplies about 38 kJ of energy per gram, while carbohydrates and protein each supply about 17 kJ per gram.

A balancing act A balanced diet should consist of a variety of foods including fresh fruit and vegetables, breads and cereals, dairy products, fish, lean meats and water. The food pyramid shows the proportions of the various food groups needed for a balanced diet.

no more than 2

meat and alternatives

1 serve (2)

milk and milk products

GI Joe

2 serves (3)

fruits

vegetables breads and cereals

Fig 6.1.3

UNIT

indulgences or extras

6 .1

3 serves (3)

4 serves (4)

5+ serves (9–12)

The food pyramid, showing the relative proportions of each food group for a balanced diet

Chips, fried foods and lollies are fine occasionally, but should make up the smallest part of your food intake. As well as needing energy for movement and normal body functions, your body needs to be kept at 37°C, the temperature at which your organs work best. The amount of energy that different people need depends on their age, health and activity levels. Children need more energy than adults because they are still growing. Highly active The low-down on fat Be careful about following people require more energy than the current trend of eating inactive people. If more energy low-fat food. While a lowis taken in than the body can fat diet can be healthy, use, the excess is stored as fat. If many products advertised as low in fat are in fact very you use more energy than you high in sugar. They have take in, fat and carbohydrates in to add something to make your body are broken down to it taste good! A high-sugar diet can lead to many use for energy. If carbohydrates health problems. and fats run out, your body starts to break down muscle protein.

How much energy? An average teenager requires about 10 000 to12 000 kJ of energy per day. This is roughly the same as the amount of energy it would take to raise the temperature of 38 litres of cold water to boiling point (100°C). In addition to energy-giving nutrients, your bodies need other types of nutrients to stay healthy. Dietary fibre, which cannot be digested, is important for the health of your digestive system. Vitamins and minerals are essential in small amounts. They are naturally

supplied in a balanced diet, and so vitamin and mineral supplements are usually unnecessary. In fact, too much of some vitamins can be just as dangerous as too Prac 1 little. p. 191

Fig 6.1.4

The glycemic index (GI) is enow used to rate carbohydrat a are ars Sug s. food ing tain con GI the and e drat form of carbohy ars in measures how quickly the sug d. bloo the into ed food are absorb out of re sco GI a n give are ds Foo g taken 100, with pure glucose bein Foods ). 100 = (GI dard stan the as ed are orb abs be to that take longer ed sorb -ab fast and GI’ ‘low ed call GI’. h ‘hig ed call carbohydrates Some experts recommend that foods everyone should eat low-GI s give food -GI Low . time the of t mos ed tain sus e mor and a long-lasting that ns mea This rgy. ene of ply sup you will be able to concentrate longer better and be more active for foods -GI low ng Eati . periods of time events ce uran end re befo rs hou two (and such as long-distance running even homework!) may improve are performance. Low-GI foods etics. diab for nt orta imp arly icul part

The uses of some vitamins and minerals in the body and the effects of deficiency

Vitamin A is important for healthy sight Cracks at the corner of the mouth show a lack of B1

Chromium helps maintain the glucose concentration of the blood A lack of iron results in anaemia

Fluoride strengthens tooth enamel and bones Calcium is important in bone and teeth formation Skin problems could mean a lack of zinc

A lack of folate leads to anaemia and intestinal damage

Vitamin K is involved in blood clotting Vitamin C helps form connective tissue Potassium helps carry nerve impulses

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Health A healthy mind

Adequate exercise

An old saying states that ‘the mind is the greatest healer’, implying that the mind strongly influences our well-being. Many alternative healing methods are based on this idea. Thoughts and feelings have the power to affect every system in the body. Aboriginal healing Depression and the eating disorders anorexia nervosa and bulimia nervosa are examples of Traditional Aboriginal mental illnesses. There are many medicine is a complex triggers for depression, including system linked to the belief stress, drug use and family conflict. and culture of the people, Some individuals may be more their knowledge of the land and of its flora and fauna. at risk because of their genetic Traditional medicine and make-up, which may cause health care are holistic, variation in the chemical message taking a whole-being approach. It recognises systems of the brain. Anorexia the social, physical and nervosa is characterised by spiritual dimensions starvation, while bulimia nervosa of both health and life. t poten a ins rema ry Sorce is distinguished by a binge–purge belief and the casting cycle. Other disorders, including and removing of spells is acne and constipation, can be made still practised. Aboriginal rm perfo alians much worse by negative thoughts Austr ceremonies consisting and feelings. of singing songs and painting designs on the sick person. They may also be massaged with fat and red ochre, as well as being given herbal medicines to treat the body.

Aboriginal healing: applying white clay in a healing ceremony

You need to exercise to become healthy and stay healthy. Exercise can range from playing vigorous sports like tennis to a brisk walk. It is important to choose something you enjoy or else you will stop doing it. The exercise you do will need to change as

Fig 6.1.6

Sydney’s yearly City to Surf fun run attracts more than 50 000 entrants.

Fig 6.1.5

Some forms of exercise are not for everyone.

188

Fig 6.1.7

you get older. Whatever your age and fitness, most people should aim to do some type of weight-bearing exercise that increases their heart rate for at least 20 minutes, three times per week. Worksheet 6.1 The glycemic index and load

Aboriginal diet Traditional diet Before White settlement the Aboriginal people were hunter-gatherers. This involved collecting plants, seeds, nuts, fruits and hunting animals. This food was low in fat and sugars (low in kilojoules), but high in carbohydrates, fibre, protein and nutrients. Overall it was a healthy diet. The daily diet of Aboriginal people varied depending on the season and plants or animals available. Some foods like kangaroo meat, honey, witchetty grubs and insects were energy-rich. The hunter-gatherer lifestyle also gave the Aboriginal people plenty of exercise.

UNIT

6.1

[ Questions ]

Checkpoint What is needed for good health? 1 Clarify what is meant by the term ‘good health’. 2 Copy the following passage and select words to fill the missing spaces. Three things needed for good health are ______ ______, a healthy ______ and adequate _______. A ______ diet is essential to good health. Animals must take in _______ to survive. Energy-giving _______ can be either ______, _______ or ______.

Diet-related diseases such as cardiovascular disease and diabetes were uncommon. Modern Aboriginal diets are very different to the diets of their ancestors and have led to an exceptionally high rate of cardiovascular disease and diabetes.

UNIT

6 .1 New foods After Europeans arrived, the traditional Aboriginal diet began to include foods such as flour, sugar and processed meat. Aboriginal people had less chance to gather traditional foods. Settlement had often destroyed the hunting areas of those who remained on the land. New animals, plants and more frequent bushfires further restricted their food-gathering activities. Others had been shifted to government settlements or worked on cattle stations. Here, movement was either restricted or they did not have the time needed to go out foraging in the old way. As a result the typical Aboriginal diet began to lack nutrients such as protein, vitamins and minerals.

Modern diet The typical Aboriginal diet today is much more Westernised—high in fats and sugar, high in kilojoules, but low in nutritional value. Exercise has also decreased because now there is no longer a need to gather food. The range of foods available to outback communities is limited, particularly fresh fruit and vegetables. Surveys indicate that urban Aboriginal people eat more fast food and salt than non-Aboriginal people. Aboriginal people of the Northern Territory consume more sugar, white flour and carbonated soft drinks than the Australian average. The typical modern Aboriginal diet, whether city or country, is especially low in vitamin C, calcium and magnesium. You will find out about some of the diseases that this diet causes in Unit 6.2.

3 Define the term ‘nutrient’. 4 Select the word that best matches each definition. Psychosomatic Nutrient Organism Calcium

Substance taken in and used for energy or to build tissue Caused by the mind A mineral used by the body Any plant or animal

7 State the name of a vitamin and how it is used in the body.

Aboriginal diet 8 Aboriginal Australians were traditionally hunter-gathers. List foods that fit this description. 9 Outline the nutritional benefits of the traditional Aboriginal diet.

5 State the ideal body temperature.

10 List three food types introduced by colonisation.

6 State the name of a mineral and how it is used in the body.

11 List three nutrients that were reduced after colonisation.

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Health

Think 12 State whether the following statements are true or false. a Protein provides more energy per gram than fat does. b Energy is measured in joules or kilojoules. c Your body doesn’t need energy when you are asleep. d Children need more energy than adults. 13 Every day, a teenager needs enough energy to heat 38 litres of water to 100°C just to keep them warm. Identify what this volume is equivalent to. Is it a bucket, a rubbish bin, a bathtub or a swimming pool? 14 Discuss how ‘health’ is a relative term. 15 Do teenage girls need to eat more than teenage boys? Justify your answer. 16 List these people in order from the person who would need to take in the most energy per day to the person who would need the least: • a baby • the NRL players in Figure 6.1.7 • an active teenager • a postie 17 Psychosomatic illnesses are those caused by thoughts and feelings. a List examples of two negative thoughts or emotions. b Predict how these thoughts would affect the body. 18 Astronauts tend to lose muscle mass in space. Propose a reason for this.

19 List age-appropriate activities to keep these people healthy: a a Year 10 student b a 40-year-old man c a 70-year-old woman 20 a List three things you currently do that will keep you healthy. b List three unhealthy things you do that you could change. 21 Explain why the traditional Aboriginal diet was considered a balanced one. 22 Compare the traditional Aboriginal diet with: a a modern Aboriginal diet b your own diet 23 Compare a modern Aboriginal diet with your own diet. 24 a Propose reasons why the Aboriginal diet changed so much after European settlement. b Recommend ways in which society could support Aborigines to improve their diet.

Skills 25 a Construct a daily menu for a balanced diet. Think carefully about what you might include. b Have another person evaluate the balanced diet you have designed. Is it really balanced? Could it be improved?

[ Extension ] Investigate 1 a Choose a vitamin (if you need ideas, look at the side of a jar of multivitamins) and research what happens if you have too much of it (toxicity) or too little (deficiency). b Design a label for a bottle of your chosen vitamin. You should include enough information so that people reading the label will understand exactly how it should be used and what the effects will be. 2 a Investigate the diseases prevalent in slum areas in order to find out: i why these diseases are so common in slums ii how these problems could be eradicated b Write a letter to the World Health Organisation in which you recommend action that should be taken to reduce the amount of disease in slums.

190

3 a Research some alternative healing methods like acupuncture, cupping, candle waxing, homoeopathy, massage, Reiki or reflexology. b Explain how the healing technique works. c Evaluate whether the healing techniques studied are effective. d Write an article for a medical journal to explain your findings. Remember that your information should be backed by scientific evidence.

Action 4 a Construct a journal to record what you eat for one week. DYO b Analyse your findings to determine whether you are eating a balanced diet according to the food pyramid in Figure 6.1.3. c Recommend changes to your diet to make it healthier.

5 Design an exercise routine, and put it in place to ensure that you do a healthy amount of exercise every week.

Surf 6 Find out more about nutrition by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button. Visit the nutrition café and complete the following activities:

UNIT

6. 1

UNIT

6 .1 a Solve the mystery of the missing nutrients for the case studies in the ‘Nutrition sleuth’. Record how many cases you solved. b Find out whether your diet is healthy or not by visiting the ‘Have-a-Bite Café’. Use your findings to deduce which aspects of your diet are already healthy and which aspects could be improved. 7 Visit the ‘Better Health Channel’ and select a healthy menu for one day that provides some of the nutrients you have discovered are missing from your diet.

[ Practical activity ] Vitamin C

Prac 1 Unit 6.1

Aim To investigate which brand of orange juice has the most vitamin C Equipment

Starch suspension, iodine solution, 4 test tubes, test-tube rack, vitamin C solution (dissolve vitamin C tablet or powder in 50 mL of water), 200 mL beaker, 3 different brands of fresh orange juice, stirring rod, dropper, lab coat, safety glasses, gloves Fig 6.1.8

test solution

Method 1 Half-fill the beaker with starch suspension. Add 3 drops of iodine solution. Stir well. The colour of the mixture should now be purple. 2 Pour 3 cm of this into each test tube (make sure your test tubes are the same size). 3 Using the dropper, drop vitamin C solution into the first tube until the blue colour disappears. Record how many drops it took. 4 Do exactly the same for the other three test tubes, but use the different juices instead of the vitamin C solution. Record how many drops of each it took until the solution was colourless. The more drops it took, the less vitamin C that juice contained.

Questions 1. Starch solution + 3 drops iodine

4. Repeat for juices.

2. Put 3 cm in each tube.

3. Continue until colour disappears.

1 Deduce which brand had the most vitamin C and which had the least. 2 List five foods that you know are good sources of vitamin C. 3 Construct a bar graph to show your results.

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UNIT

6.2 context

Forensic pathology

Not feeling well? Then you could have a disease. A disease is anything that makes you feel unwell, or makes you unable to function properly in a given environment. Diseases cause symptoms like nausea, rashes, stiffness in your joints, fever or blurred vision. These symptoms indicate that your body is no longer working properly and that you may need to see a doctor.

Disease The study of disease is called pathology (pathos = suffering, logos = study) and people working in this field are called pathologists. Before examining diseases in more detail, it is important to become familiar with some of the common terms used in pathology. Fig 6.2.1

Some common diseases and their symptoms botulism (a type of food poisoning) causes blurred or double vision and difficulty swallowing

the common cold produces headache and a runny nose

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• An organism is any plant or animal. • A micro-organism (often called a microbe) is a very small organism that can be seen only by using a microscope. Sometimes micro-organisms consist of only one cell. • An agent or pathogen is something that causes disease. • A host is the organism being affected by the agent. • A parasite is an agent that uses the host for food or shelter.

Whenever a person dies, a cause of death must be established before the death certificate can be signed. For unexpected deaths, this is the job of the forensic pathologist. Even when the cause seems obvious (e.g. a gunshot wound or drowning), they must still try to find out as many facts as possible. Sometimes they find out unexpected things. When American President John F. Kennedy was gunned down in Dallas in 1963 the cause of death was clear. However, the autopsy revealed a well-kept secret. His adrenal glands were shrivelled up, a clear sign that he had been suffering from Addison’s disease. Addison’s disease can cause chronic fatigue, nausea, weak muscles, irritability and depression—not a good image for a world leader, especially one who took the USA and USSR to the brink of nuclear war!

mumps causes fever, swelling and tenderness of the salivary glands

chickenpox causes an itchy, blister-like rash. Measles also causes a red, blotchy rash.

influenza causes headaches, fever, chills, cough and body aches

tuberculosis causes night sweats and a persistent cough

Fig 6.2.3

Child with chickenpox

A newspaper article warning of the 1919 flu epidemic in Australia

UNIT

6 .2

Fig 6.2.2

• An infection is an invasion of the body by foreign organisms. If the agent can multiply easily in the host and be passed on to other host organisms it is said to be infectious. • Virulence is a measure of how much damage a Legionnaire’s disease disease does to the host. In July 1976, the BellevueStratford hotel in Philadelphia Highly virulent diseases hosted the fifty-eighth state cause very serious convention of the American symptoms, perhaps death. Legion Department of • There will always be Pennsylvania. Not long after, 34 of the participants were disease in the world. dead of a pneumonia-like Endemic means that a illness and a further 221 were disease regularly affects a seriously ill. small number of people in The following year, the bacterium that had caused the the population. outbreak was identified. It was • An epidemic is when named Legionella in honour there are higher than of those it had infected. Legionella organisms normal numbers of reproduce best in warm, people being affected by stagnant water of the type a particular disease in a found commonly in hot-water tanks, cooling towers, or large certain place. air-conditioning systems. • An outbreak has Outbreaks occasionally occur happened when a in city offices where the airdisease has suddenly conditioning systems have not been correctly maintained. gotten out of control.

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Disease Causes of disease Disease can be caused by many factors, some infectious, some avoidable and others you are born with: • The body could be invaded by micro-organisms such as bacteria, viruses, protozoa and fungi. These diseases are usually infectious. • Parasites such as worms could be ‘caught’ from other infected people. These would then invade the body. • Some part of the body could malfunction due to some imperfection or fault. For example, diabetes can develop if the pancreas isn’t working properly. • Environmental factors might cause your body not to function properly (e.g. air and water pollution, normal but still damaging exposure to UV radiation). • Lifestyle factors can also cause disease. These factors are ‘self-inflicted’ and include drug abuse, overuse of alcohol, smoking, sunbaking and highfat, high-sugar diets. • Genetic disorders or diseases that your parents either had or ‘carried’. You do not ‘catch’ these diseases, but are born with them.

UNIT

6.2

[ Questions ]

Spreading like the plague! Early European settlers brought in many new diseases for which Aborigines had no resistance and no traditional remedies. Smallpox plagues swept through Aboriginal Australia, killing as much as half the population. Influenza, tuberculosis, syphilis and other diseases all reduced the Aboriginal population even further.

Diet-related diseases The change of diet in Aboriginal communities has led to many ‘lifestyle’ diseases, including obesity, cardiovascular disease, diabetes, high blood pressure, certain cancers and stroke. Because these diseases are more common in Aboriginal communities that in non-Aboriginal ones, health organisations are trying to improve the diets of Aboriginal people.

Causes of disease 6 List possible causes of disease, classifying them as: a infectious b lifestyle-related c built into the body 7 Define the following terms: a micro-organism b infectious disease c parasite

Checkpoint Disease 1 Clarify the meaning of the term ‘disease’.

Civilisation arrives in Australia?

2 Use an example to outline the features of a disease and its symptoms.

8 Aborigines caught many diseases from the first colonising Europeans. List four of these diseases.

3 Identify the definition that best matches the term.

9 List two reasons why Aborigines were vulnerable to these diseases.

Symptom

Study of disease

Pathology Microbe Agent Host Parasite Infectious

Causes disease Can be passed on to another host Outward sign of disease Agent using host for food or shelter Very small organism Organism being affected by agent

4 State the role of forensic pathologists. 5 Contrast the terms ‘endemic’ and ‘epidemic’.

194

Civilisation arrives in Australia?

10 Diet-related diseases have also affected the health of Aborigines. List three examples of such diseases.

Think 11 Distinguish between an epidemic and an outbreak. 12 Very small infectious agents spread disease easily. Propose reasons why the size of the agent influences the spread of a disease. 13 Describe three behaviours or actions that could spread disease.

14 a List three diseases that you have had. b Describe the symptoms and treatment for each disease. 15 Copy and modify the following statements so that they are all correct. a Diseased people can still function well in their environments. b A host uses a parasite for food or shelter. c Not all diseases are infectious. d Symptoms like blurred vision are not signs of disease. 16 Propose a definition for a non-infectious disease.

2 a Investigate an outbreak that has occurred in Australia in the past five years. You could look at outbreaks of flu, Legionnaire’s or meningococcal disease. b Present your data using a table. Write a conclusion on the cause of the outbreak and whether it is under control. 3 a Choose a disease, such as meningococcal disease, that has occasional outbreaks in Australia. Research how many deaths have occurred each year in the past 10 years. b Present your findings as a table and graph using an electronic spreadsheet such as MS Excel.

UNIT

6 .2

[ Extension ] Surf Complete one of the following activities related to diseases by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button. 1 a Carry out research to find an example of a virulent disease and a non-virulent disease. b The outcome of each type of disease is very different. Write a report to demonstrate the difference.

Creative writing There have been many films made about outbreaks. Some of these are based on true stories, and others are pure fiction. Imagine that you are writing a scene for a movie about an outbreak of a very serious illness. You are a doctor, in a meeting with local authorities, trying to convince them that the area must be quarantined (isolated) immediately. How do you do it?

Worksheet 6.2 Outbreak!

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UNIT

context

6. 3 One sneeze or cough can send thousands of individual bacteria or viruses into the air. These pathogens have direct access to another host if they are breathed in directly, or if they land on someone’s food or on a bench where a hand is placed. Only a few need to gain entry to infect the new host, making infectious diseases very easy to spread. There are many ways that pathogens can be shared. An infectious communicable disease is a disease that is transmitted easily from person to person.

The disease is said to be endemic if small numbers of cases are present in the population and an epidemic if large numbers of people are affected. An outbreak happens when the disease is suddenly out of control.

Relative sizes of some viruses, bacteria, protozoa and fungi

Fig 6.3.1

Plague The Yersinia pestis bacterium, formerly called Pasteurella pestis, is the pathogen responsible for bubonic plague—the Black Death. Between 1347 and 1352, an outbreak of this disease killed a third of Europe’s population—an estimated 25 million people. It was spread by the fleas on rats!

25

Diseases caused by micro-organisms

yeast

15

malaria syphilis TB

cholera

5

HIV smallpox

10

Ebola

Not all micro-organisms are harmful to humans. In fact, some are very helpful. Some micro-organisms serve as food sources, others help decompose wastes, some help protect us from disease and others aid digestion. Only a few micro-organisms cause disease. The micro-organisms that cause disease are known as pathogens and include varieties of bacteria, viruses, protozoa and fungi. The table below show examples of disease-causing micro-organisms and what Prac 1 they cause.

Length (µm)

20

0

Viruses

Bacteria

Protozoa

p. 201

196

Agent

Type

Disease caused

Symptoms

Rabies

Virus

Rabies

Varicella

Virus

Chickenpox

Vibrio cholerae

Bacteria

Cholera

Clostridium botulinum

Bacteria

Food poisoning

Giardia lamblia

Protozoa

Giardia

Toxoplasma gondii

Protozoa

Toxoplasmosis

Candida albicans

Fungi

Thrush

Creamy mucus, can be oral or vaginal

Tinea corporis

Fungi

Ringworm

Rounded areas of scaling on the body

Paralysis, spasms, fever, overproduction of saliva Fever, itchy blister-like rash Diarrhoea, vomiting and dehydration Blurred vision, weakness, difficulty swallowing and possibly death Nausea, flatulence, diarrhoea Acute form causes fever, chills, rash, exhaustion

Fungi

Bacteria One characteristic that is used to identify bacteria is their shape. They may be rod-shaped (bacilli), spiral (spirilla) or spherical (cocci). All bacteria consist of only one cell, but they Prac 2 can join together in pairs, chains or clusters.

UNIT

6 .3

p. 202

Fig 6.3.4

Common bacteria shapes

Type

All these things were produced with the help of bacteria. The holes in Swiss cheese are bubbles left after gas was produced by bacteria.

Appearance

cocci (singular: coccus)

coccidiosis

diplococci

gonorrhoea

streptococci (chains)

tonsillitis

tetrads (groups of 4)

sarcina

clusters

staphylococcus

bacilli (rods)

diphtheria, typhoid

spirilla (spiral forms)

syphilis

Fig 6.3.2

Does your doctor wear a tie?

neckties worn by In 2004, Israeli researchers found that the t to another! A patien one from se disea mit trans doctors might ital showed hosp York New comparison of the ties worn in a covered in be to likely more times eight were that doctors’ ties security the by worn ties disease-causing microbes than the coughed and on ed sneez get ties rs’ Docto . there guards working e all the unlik but , home go on many times each day. They then then They ed. clean get ever, if , rarely they es, other doctors’ cloth the ted collec bes micro the go to work the next day, loaded with non-living tes, fomi as n know are ties rs’ docto day before. The bacteria. materials that can transmit disease-causing

Bacteria can multiply very quickly under the right conditions. If conditions are not favourable for growth, some types of bacteria can form thick-walled spores that allow them to withstand cold, heat and prolonged drying. They can remain inactive for days or even years. Antibiotics can kill many types of bacteria. Electron micrograph of rod-shaped Salmonella bacteria (bacilli).

Fig 6.3.3

Examples

Fig 6.3.5

Doctors who wear a tie may infect their patients.

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Infectious diseases Viruses Viruses are so small that they can be seen only with an electron microscope. Viruses Bird flu are not considered to be living Bird flu, or more correctly avian things because they do not selfinfluenza A virus, usually only reproduce, feed, grow, produce infects birds. But sometimes these flu strains mutate into more waste or move. They do move dangerous forms. This happened from place to place, but only if in Hong Kong in 1997 when avian they hitch a ride on something influenza A (H5N1) infected both poultry and humans. This was else, like other organisms, wind the first time a bird flu had ever or water. transmitted directly to humans. Viruses are parasitic invaders During this outbreak, 18 people them of six and ed hospitalis were made of DNA (or a similar died. To control the outbreak, material called RNA) in a authorities killed about 1.5 million protein coat. If viruses come chickens to remove the source into contact with a suitable cell of the disease. Further outbreaks occurred in 2003 and 2004. (called a host cell) they can Pathologists are concerned about attach to the cell and enter it. the possibility that genes might They hijack the cell and force swap between bird flu and human flu. This could happen if a person it to make more virus particles. got infected with both diseases The cells make so many virus at the same time. The new bug particles that they burst open, would then have the potential to be as deadly as bird flu, and releasing the virus particles, as easy to catch as human flu. which then invade other cells. It could then bring us the next Some viruses invade cells pandemic. Similar pandemics and remain dormant or inactive have occurred in the past: • 1957–58, Asian flu [A (H2N2)] for long periods of time. An caused about 70 000 deaths. example is the herpes simplex • 1968–69, Hong Kong flu virus, which is responsible [A (H3N2)] caused for cold sores. Cold sores approximately 34 000 deaths. This virus still circulates today. come and go, but the virus is always there, awaiting the right

Fig 6.3.6

198

Cold sores on the lower lip due to the herpes simplex virus (type I)

conditions for rapid reproduction and ‘re-appearance’. Others do not kill the cell they infect, but re-program it in a way that causes it to become cancerous. Viruses are hard to treat as they are not stopped by antibiotics. With most viral infections you have to wait until your body itself stops the invading virus.

The fat virus A virus known as SMAM-1 is a relative of the common cold but has very different symptoms. Instead of coughs and sneezes, SMAM-1 is thought to cause obesity!

Protozoa Diseases caused by protozoa (sometimes called protists) are most often seen in tropical and subtropical areas. Like bacteria, protozoa are singlecelled. Most protozoa are harmless to humans, but some parasitic types can cause serious illness. Protozoa sometimes form protective cysts around themselves if conditions are unfavourable, allowing them to survive between outbreaks. Giardia and Cryptosporidium are both examples of protozoa that contaminate water supplies. Another example is the common tropical disease, malaria. Malaria is caused by Plasmodium, which live in the red blood cells and cells of the liver. Falciparum malaria, the most dangerous type, is fatal in about 20% of untreated cases. Initial infection occurs through a female Anopheles mosquito bite. An Anopheles mosquito, capable of carrying malaria, biting into human skin

Fig 6.3.7

UNIT

6 .3 Fungi Very few fungi cause disease in humans and those that do commonly invade the hair, skin and nails. Fungi are opportunistic pathogens. They are not usually associated with infection, but they can cause infection if the conditions are ideal or if the person’s immune system is not working properly. People can have lowered immunity due to a number of causes and all are more susceptible to these fungal infections. HIV/AIDS lowers immunity, and so do the cancer treatments of chemotherapy and radiotherapy. After transplants, patients are given anti-rejection drugs that also lower immunity. Tinea (athlete’s foot), ringworm and thrush are all opportunistic fungal infections. Fig 6.3.8

A fungal skin infection causing tinea

Fig 6.3.9

Electron micrograph of a cercaria or blood fluke

The adult worms live in blood vessels.

Cercaria mature into adults.

Diseases caused by macroscopic parasites Parasites that can be seen without a microscope are called macroscopic parasites.

Fully grown eggs pass out of the human (in the faeces) into water.

Cercaria penetrate skin and find their way into blood vessels.

Upon contact with water, the eggs hatch into tiny, immature flukes.

miracidium cercaria

Flukes The most common type of disease-causing macroscopic parasite is the flatworm. Parasitic flukes are flatworms, best known for causing disease in many animals, including humans. Intestinal flukes, blood flukes, lung flukes and liver flukes all affect humans, causing damage to the organs they inhabit, resulting in serious illness for the host. For example, blood flukes can damage blood vessels near major organs like the bladder and kidneys.

When they are ready to lay eggs, they push their way into capillaries of the heart, lungs and intestine wall. The eggs cause capillaries to rupture; in the intestinal capillaries, eggs reach the faeces.

Individuals of the free-swimming (infective) stage leave the snail and swim about until they contact human skin.

In the snail host, the young flukes reproduce to form new flukes.

The young flukes swim about and penetrate the soft parts of the snail host, feeding on it.

Life cycle of a blood fluke

Fig 6.3.10

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Infectious diseases Tapeworm Another type of flatworm is the tapeworm, which can sometimes live in human intestines. One type of tapeworm causes hydatid disease. If the tapeworms’ eggs are swallowed by humans, the tiny embryos will hatch from the eggs and move from the intestines into the bloodstream. Cysts develop wherever the embryos end up, most often in the liver. Here they are capable of killing the host human. Worksheet 6.3 Infections

UNIT

6.3

[ Questions ]

Checkpoint Diseases caused by micro-organisms 1 List one way in which micro-organisms can be helpful to humans.

Fig 6.3.11

Electron micrograph of a parasitic tapeworm showing suckers and hooks used to attach to the intestine

2 Define the term ‘pathogen’. 3 List the four types of pathogens responsible for infectious disease. 4 There are three common shapes found in bacteria. State the name of each and draw an example. 5 Identify the bacterium that causes bubonic plague. 6 List the symptoms of a rabies b giardia 7 Explain what viruses do to cells. 8 Viruses are not considered to be living things. Outline two reasons for this. 9 Clarify what is meant by the term ‘protozoa’. 10 Explain what an opportunistic pathogen is.

Diseases caused by macroscopic parasites 11 Explain the term ‘macroscopic parasite’. 12 List three examples of macroscopic parasites. 13 Outline why tapeworms would cause malnutrition. 14 Hydatid disease can cause death in humans. Explain how this may occur.

Think 15 Distinguish between macroscopic and microscopic. 16 Explain why it is important to describe all your symptoms to your doctor when you are sick. 17 Contrast an endemic disease with an epidemic.

200

18 Propose a definition for the term ‘pandemic’. 19 Copy the following statements and modify them to make them correct. a Spherical bacteria are called ‘spirilla’. b Viruses are larger than bacteria. c Many fungi cause disease in humans. d Parasites always kill their hosts. 20 Use a diagram to explain the structure of Staphylococcus bacteria. 21 Explain why many more diseases are caused by bacteria than by fungi. 22 Explain why you should wash your hands after going to the toilet and before eating. 23 Compare the means by which bacteria and protozoa protect themselves in unfavourable conditions. 24 Ebola is an extremely virulent virus that kills incredibly quickly. Propose why this virus rarely spreads beyond the African villages it appears in. 25 a State the name of a tropical region on Earth. b Discuss why malaria is more common in tropical regions. 26 Explain how you could protect yourself from malaria when travelling in tropical regions. 27 Propose some precautions you could take to avoid becoming infected with blood flukes.

Analyse

humans become infected. Once inside the infected person, the eggs become mature worms and live in the intestines. They cause severe digestive problems and malnutrition. Draw a diagram to outline the life cycle of Cowium.

28 Look at the life cycle of a blood fluke in Figure 6.3.10. Explain in words what this diagram is showing. 29 Imagine a recently discovered parasite, Cowium, that lives mainly in cows. Cowium eggs are present in the cow’s milk. If the milk is not treated before drinking,

UNIT

6 .3

[ Extension ] Investigate b Construct two scenarios, with symptoms as clues to the type of malaria. c Present the case studies you researched as information so that another student can identify the type of malaria.

1 Three ways of preserving food are dehydration, canning and radiation. a Research what is done in each process. b Describe how each method kills or slows down the growth of microbes. c Evaluate each method in terms of effectiveness and safety. d Recommend the best method for preserving the following foods: tomatoes, grapes, meat, peanuts. Justify your answer in each case. 2 The most serious outbreak of the bubonic plague occurred in Europe between 1347 and 1352. a Conduct research to find out if this disease exists today. b Present a time line of dates for major outbreaks since 1352. 3 a Investigate different types of malaria and list the symptoms of each type.

UNIT

6.3

Surf 4 Visit the ‘Infection Detection Protection’ website by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button. a Play the game ‘Bacteria in the Cafeteria’. Use your findings to construct a poster that can be placed in your school cafeteria to keep it safe from disease. b Play the ‘Infection’ game and construct a leaflet that could be used in a doctor’s waiting room to protect people from disease.

[ Practical activities ] Making yoghurt Aim To produce yoghurt using bacteria

Prac 1 Unit 6.3

Note: This prac involves observations over several days.

Equipment 250 mL beaker, spoon, plastic cling wrap, 1 cup new UHT milk, 1 large spoon of natural yoghurt with live bacteria, incubator

Method

3 Cover the beaker with cling wrap and place in the incubator at 40°C. 4 Record any changes in its smell and consistency over the next few days.

Questions 1 Explain why you needed to add yoghurt to start the process.

1 Half-fill the beaker with milk.

2 Explain why the mixture was left at this particular temperature.

2 Stir in the yoghurt. This will start the process.

3 Describe the changes in the mixture over three days.

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Infectious diseases

Micro-organisms around us Aim To grow a variety of microbes on nutrient Prac 2 Unit 6.3

agar

5 Seal and label your plate. 6 Put all your plates, including the control, in a warm place for 48 hours.

Equipment 5 Petri dishes containing nutrient agar (agar plates), wire loops, heat-proof mat, Bunsen burner, masking tape, gloves

Method

7 Without un-taping the lids, examine and note the numbers and types of colonies that have grown on your agar plate. Fungal colonies appear fuzzy, while bacterial colonies are smooth.

1 Tape one agar plate closed, label it and put it aside. This will be the control.

Questions

2 Take another agar plate and expose it to the air. Each prac group should sample the air in different locations, for example the toilets, corridor or classroom. Seal your agar plate and label it.

1 Explain the use of a control in this experiment. 2 Compare your results with those of your classmates. 3 Construct a table of the class results. Include the different colours and shapes of the colonies formed.

3 Light the Bunsen burner and heat the wire loop to sterilise it.

4 Evaluate which locations had the greatest numbers of micro-organisms present.

4 Carefully touch the wire loop to a ‘dirty’ surface, then brush it lightly over the surface of the agar of a new plate. Each prac group should sample a different surface.

5 Contrast a fungal and a bacterial colony.

Fig 6.3.12

1 Sterilise the wire loop. Bunsen burner

202

2 Touch the wire loop to a surface. Try not to expose the surface to the air for too long.

3 Very lightly brush over the agar surface and quickly replace the lid.

UNIT

context

6.4 You almost certainly have had the flu before. Did you know that you cannot get the same flu again? If you get sick with the flu next year it will be a different one. This is because your body builds its own defence to any disease that you have had, so that you will not get it again. This idea is also used to make vaccinations that build up your defences by artificially introducing you to a safe form of the disease. Vaccinations stop

Pass it on You can get infectious diseases by direct or indirect transmission. Direct transmission comes about by direct contact with the infected person or by contact with droplets of body fluid. Diseases transmitted by direct contact are called contagious diseases. Indirect transmission occurs through an intermediary agent like an insect, air or contaminated water. Carriers of disease are called vectors. An example of a vector is the Prac 1 p. 210 mosquito that carries malaria from person to person.

Fig 6.4.1

you getting a disease in the first place! Although many infectious diseases are easily spread, modern medicine has some very effective ways of controlling them.

Natural control The first line of defence The human body has several mechanisms for coping with disease. The first defence is the outer layer of the skin, consisting of dead cells. Harmful pathogens on the skin can be shed with the dead cells. There are also a lot of good bacteria on your skin, which help fight the invaders.

The second line of defence The second line of defence is in your blood, as white blood cells or leucocytes. They travel in the blood to the site of infection, converge on the pathogens, digest them and engulf their remains. Dead micro-organisms and dead white cells are left behind and form the discharge call pus. Normal leucocytes, or white blood cells that fight disease

Fig 6.4.2

Direct transmission can occur by pathogens expelled from the mouth during a sneeze.

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Transmission and control of infectious diseases The third line of defence When invaded by a pathogen your body responds by making antibodies. These antibodies are produced in a process called acquired immunity. The antibodies float around in the blood and attach to a specific part of the pathogen, which is called an antigen. The antibody disables the pathogen, which is then easily consumed by white blood cells, thus destroying the threat. A particular antibody will act against the antigens on only one type of pathogen. The body can continue to produce antibodies long after the pathogen has been destroyed. The body will be immune to that particular pathogen as long as the antibodies are present. For example, if you had measles in the past then you may still be carrying antibodies for measles. These antibodies allowed you to recover and may protect you from measles in the future. Unfortunately they cannot protect you from chickenpox or any other disease.

Blood vessel

antibody lymphocyte

2 Millions of different lymphocytes are made in the bone marrow. Thus an almost unlimited number of antigens can be recognised.

3 The lymphocytes move out into the body and the blood. The antibodies are carried on the surface of young lymphocytes. 8 The lymphocytes which make this particular antibody may remain in the blood for many years, giving protection against further attack by this particular virus.

6 The lymphocytes release their antibodies, which bind to the antigens on the virus’s surface and make the virus inactive.

Fig 6.4.3

204

7 Other types of white blood cells then engulf the inactivated viruses and destroy them.

The process of acquired immunity

Artificial control Good nutrition, clean water and

Even though there is a new adequate sleep and exercise will give flu virus every year, there us a degree of natural protection from is one drug that works disease. However, we need additional against them all. This can happen because the different and artificial protection against some versions of the flu always particularly dangerous diseases. have one little part of the virus that stays the same. Vaccinations The drug called RelenzaTM The threat of many of the killer acts against exactly this part and so can tackle every flu diseases of the past has been greatly that has been caught for the reduced, and sometimes eliminated, past 100 years! Although TM by the development of vaccines. Relenza was developed in Australia and is extremely A person can be immunised effective, the government against a certain disease by being is yet to put this drug on injected (inoculated or vaccinated) the Pharmaceutical Benefits Scheme (PBS). Hence it is with a vaccine. Most children in quite expensive to purchase. Australia are routinely vaccinated Most people do not even against diseases like polio, tetanus know it exists!

Bone marrow

1 White blood cells called B lymphocytes are made in the bone marrow in large numbers. Each lymphocyte 4 Foreign particles (e.g. bacteria, makes an antibody which viruses) arrive in the blood. The recognises one particular antigens are on the surface of antigen. Many copies of the virus particles. this antibody can be made by a lymphocyte.

5 A lymphocyte comes in contact with an antigen to which its antibody can bind. This stimulates the lymphocyte to reproduce rapidly.

Relenza TM, relief from influenza

and measles, chicken pox and tuberculosis. In Australia there have been no cases of polio since 1986. Girls are commonly vaccinated against rubella. Why? Although rubella is a nasty disease for anyone, it is particularly dangerous to unborn children, often causing birth abnormalities, if the baby’s mother contracts rubella during pregnancy. Some parents choose not to immunise their children through fear of rare side effects. It is estimated, however, that for every dollar spent on immunisation programs, four dollars are saved in public health costs. Two types of immunity can be produced by vaccines: • Active immunity: the body is stimulated to make its own antibodies. This usually involves injecting a live but disabled version of the virus or bacteria. An example is the Sabin polio vaccine, which uses a live but non-contagious strain of the disease. • Passive immunity: the body is injected with antibodies previously produced by another organism. This is good in emergency situations, where immunity is needed quickly. Unfortunately it does not last as long as active immunity.

UNIT

6 .4 500 million people worldwide during the twentieth century, ending in 1977 when the last case of naturally transmitted smallpox was reported in Africa. In 1980, the WHO officially announced the end of smallpox. Two stocks of the virus remain in highsecurity laboratories in the United Ancient vaccination States and Russia. A doctor injecting a vaccine into the arm of a patient

Aboriginal medicines

Aboriginal Australians use a range of remedies for illness—wild herbs, animal products, steam baths, clay pits, charcoal, mud, massages, string amulets and secret chants. Many of the remedies directly assist healing. The medicinal properties of goanna oil, aromatic herbs and the tannin-rich inner bark of certain trees have long been known to Aboriginal people. Compounds coming from the Moreton Bay chestnut or black bean are currently showing promise as a treatment for AIDS.

Fig 6.4.4

Even active immunity does not last forever. Production of antibodies can reduce with time and a booster shot (re-injection with the vaccine) may be needed. It is recommended, for example, that tetanus booster shots be given every 10 years.

Tamarind seeds, which are traditionally used to treat headache

Antibiotics Antibiotics are drugs that are able to selectively kill off certain pathogens while leaving the patient’s own body cells intact. Although antibiotics can fight many bacterial infections, they are ineffective against viruses.

Fig 6.4.6

Many different antibiotics are available to fight bacterial infections.

The earliest evidence of vaccinations goes back to around 500 BC. Chinese physicians noted that exposing healthy people to particles from smallpox scars gave them a milder form of the disease. This protected them from the more serious form. Only 4% died from this procedure—a phenomenal success rate for that era.

Fig 6.4.5

The first successful vaccination In 1796, the English physician Edward Jenner noticed that milkmaids rarely contracted smallpox. He hypothesised that this was because most had been infected with a similar, milder disease of cows, known as cowpox. James Phipps was then an eight-year-old boy whose family was dying of smallpox. Jenner exposed him first to cowpox, then to smallpox. The boy survived and, within a few years, widespread vaccinations began, with Jenner predicting that eventually smallpox would be completely eradicated. Nearly 300 years later, the World Health Organisation (WHO) started a program of worldwide smallpox vaccination. It is estimated that smallpox killed

Overuse and misuse of antibiotics have led to the development of antibiotic-resistant strains of bacteria. The more antibiotics are used, the more quickly resistant strains emerge. It takes up to 20 years to develop new drugs and soon doctors might be left without any drugs to fight the new strains. Particularly worrying is the recent rise of drugresistant tuberculosis (TB). This form of TB seems to have originated in the overcrowded jails of Russia. Prisoners often did not complete the prescribed course of antibiotics, leading to the development of ‘superTB’. This TB has recently appeared in New York, and there is no effective way of treating it. If you are prescribed antibiotics, make sure you complete the course set by your doctor. Unless the infection is severe, it is best to let your body recover naturally.

The problem with viruses Because they are so small, viruses are difficult to isolate in the laboratory. They also multiply so rapidly that new strains are appearing all the time. Control of

205

Transmission and control of infectious diseases viral infections has relied mainly on vaccines. With so many different strains, however, it is difficult to find effective vaccines. There are so many strains of the common cold virus, for example, that no one can ever become immune to them all. Some chemicals, like AZT which is used for HIV/AIDS patients, are effective in reducing virus effects, but as yet no chemicals can eradicate a viral infection. Prac 2 p. 210

Worksheet 6.4 AIDS

People in Science

>>> CASE STUDY HIV/AIDS Consider these worldwide statistics for HIV/AIDS: • 10 people are infected with it every minute • 6 people die from it every minute • 42 million people live with it • 28 million people have died from it since the epidemic was first identified in the early 1980s. AIDS stands for Acquired Immune Deficiency Syndrome. It is a condition caused by infection with the virus known as HIV—Human Immunodeficiency Virus.

Where did it come from? Joseph Lister Lister is always remembered whenever we rinse our mouths with ‘Listerine’. Joseph Lister was born on 5 April 1827. Lister was an outstanding student and graduated from University College, London, in 1852 with an honours degree in medicine. In 1861 he became surgeon at the Glasgow Royal Infirmary. At that time, almost half of the patients undergoing surgery died of post-operative wound sepsis infection, known then as ‘hospital disease’. In 1865 Louis Pasteur found that decay was caused by fermentation when living matter in the air entered the body. Lister made the connection between Pasteur’s ideas and wound infection. Having heard previously that carbolic acid was being used for the treatment of sewage, he began cleaning wounds and dressing them with a solution of carbolic acid. Soon his wards were completely free of wound sepsis. It was not long before Lister’s antiseptic methods were used worldwide, saving countless lives.

Joseph Lister

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Fig 6.4.7

The earliest known case of HIV-1 in a human was from a blood sample collected in 1959 from a man in Kinshasa, in the Democratic Republic of Congo. In 1999, an international team of researchers discovered the origins of HIV-1, the main strain of HIV. A subspecies of chimpanzees native to west equatorial Africa has been identified as the original source of the virus. Primates carry their own version of HIV, called SIV (simian immunodeficiency virus) and are usually immune from it, suffering little, if any, illness. HIV seems to have emerged through a combination of two monkey viruses.

Fig 6.4.8

The surface of a T cell (green) infected with HIV (red), the agent that causes AIDS

UNIT

6 .4 It is believed that HIV-1 was introduced into the human population when hunters became exposed to infected chimp blood. In 2003, the same team found that the chimpanzees could acquire the disease from eating one of their favourite prey: monkeys. Did a human eat infected chimp meat? We will probably never know for sure.

What does it do? HIV is a type of retrovirus. These viruses incorporate their DNA into the host cell’s DNA. This means that when the host cell reproduces, the virus is also replicated. The HIV retrovirus is unusual because it invades CD4 white blood cells. These are the cells that are supposed to protect the body from disease! This means that the body has trouble fighting off other infections.

Transmission Although the virus is present in all the bodily fluids of an infected person, fluids such as saliva, tears, breast milk and sweat are considered ‘safe’ since the concentration of the virus in them is very low. In contrast, blood, semen and vaginal fluid have high concentrations of the virus and so pose the greatest risk of transmission. Sexual contact, or sharing of drug-injecting equipment, are the most common means of HIV transmission. It can also be transmitted through blood transfusions or blood products. This is now extremely rare, however, due to rigorous screening procedures in blood banks. The virus can also be passed from mother to child in the womb.

AIDS develops, and a small percentage of people who test positive to HIV never develop AIDS. Early signs of HIV infection are night sweats, fever, swelling of lymph nodes, fatigue, unexpected weight loss and concentration problems. AIDS is not really a defined disease. Rather, it is a collection of symptoms caused by opportunistic infections that have thrived due to the sufferer’s struggling immune system. Although symptoms vary from patient to patient, commonly they include: purple markings on the face (Kaposi’s sarcoma, a type of skin cancer), continued diarrhoea, fungal infections such as thrush of the mouth and skin, bleeding, bruises, dementia and an extreme form of pneumonia.

HIV but no AIDS! Not all HIV-infected people develop AIDS. A few remain symptom-free long after the time when AIDS would normally have developed. Everyone has human leucocyte antigen (HLA) proteins in their bodies that attach to virus fragments in infected cells and destroy the cell. Some types of HLA proteins are better at attaching themselves to certain viruses than other HLA proteins. It is currently thought that those HIV-infected people who do not develop AIDS have in their bodies a special type of HLA protein which is good at killing HIV-infected cells.

Prevention Prevention is better than cure: understanding and applying the following information can help stop transmission of HIV: • Practise safe sex: this means using condoms during sexual intercourse. • Do not share drug-injecting equipment: this includes syringes, spoons, water, water containers and tourniquets. • Infection needs to be managed when dealing with physical injuries, especially when someone is bleeding: standard procedures for first aid, such as wearing gloves, are effective in preventing HIV transmission. • Tattooing and body piercing release fresh blood and give ideal conditions for HIV entry unless equipment is correctly sterilised. Hairdressing procedures too are required to comply with infection control and sterilisation guidelines.

Symptoms Many people infected with HIV develop symptoms of a viral illness within a few weeks, much like the flu, although these symptoms soon disappear. It can take many years before

Many children in Third World countries contract HIV/AIDS from their parents before they are born. This child is suffering from pneumonia as HIV/AIDS has weakened his immune system. In these countries familles cannot afford expensive HIV/AIDS drugs.

Fig 6.4.9

Diagnosis HIV is diagnosed by a blood test, which detects whether HIV antibodies are present. If they are, then you are HIV+. It also tests for other indicators of HIV infection such as a very low white blood cell count or a T4 to T8 lymphocyte cell ratio lower than 1 to 1. This ratio is normally 2 to 1 in healthy people.

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Transmission and control of infectious diseases

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Treatment There is currently no cure or vaccination for HIV/AIDS. The huge amount of research being conducted in this area means that treatments for HIV/AIDS sufferers are improving. One major advance was the development of azidothymidine, known as AZT. It prevents new HIV particles being correctly made in cells. It cannot cure the disease, but improves health and adds one to two years of quality life to about 60% of AIDS patients. The main problem with AZT is that it is extremely expensive, has unpleasant side effects and is not effective in all patients.

Fig 6.4.10

UNIT

6.4

1 State what HIV and AIDS stand for. 2 Identify when the first known case of HIV occurred. 3 Explain how HIV can be passed from person to person. 4 Describe the three early signs of HIV infection. 5 Explain what HIV+ means and how HIV is diagnosed. 6 Propose ways to minimise your risk of becoming infected with HIV. 7 Propose reasons why AIDS is spreading so quickly in Third World countries. 8 HIV/AIDS is currently devastating the African continent, with up to 40% of the population in some countries being HIV+. Discuss some of the likely effects that HIV/AIDS may have in these countries. 9 It could be said that no one has ever died of AIDS. Explain what kills people infected by HIV. 10 What hope is there for a vaccine for HIV/AIDS in the future? Evaluate the information listed in this case study to decide whether it is possible. 11 Evaluate AIDS as a disease. Why is it so effective? How does it avoid our control measures so well?

A week’s supply of HIV/AIDS drugs

[ Questions ]

Checkpoint Pass it on 1 Clarify what is meant by ‘direct transmission of disease’. 2 State another name for diseases transmitted by direct contact. 3 Indirect transmission needs an agent or vector to carry the disease. State one example of a vector and the disease it carries.

Natural control 4 Explain how skin acts as the first line of defence against disease.

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[ Questions ]

5 Outline the role of leucocytes in protecting the body from disease. 6 Identify the components of pus. 7 Distinguish between an antigen and an antibody. 8 Explain how your body knows when to produce antibodies. 9 The following passage contains some incorrect facts, spelling and punctuation. Copy it into your workbook, modifying it to correct any errors. antibodies are part of a group of chemicals called imunnoglobens once your body has produced an antibody it can never produce the same one again. Your body is immune as long as antigens are present.

10 Use a diagram to demonstrate what is meant by the third line of defence.

Artificial control 11 Outline how a vaccine is used to protect against disease. 12 State why antibiotics are ineffective against viruses.

19 Jenner found that infection with cowpox gave immunity against smallpox. Describe how an infection with one pathogen could give immunity against a different pathogen.

UNIT

6 .4 Analyse 20 Explain in words what Figure 6.4.11 is showing.

Think 13 ‘The overuse of antibiotics is dangerous.’ Discuss this statement. 14 Identify the correct words in the following list to complete the sentences below: infection, immunity, vaccine, inoculated, antibodies, leucocytes a White blood cells are also called ________. b An invasion of foreign organisms is called an ________. c Being _______ with a ________ can give a person ________ against certain diseases. d A vaccine makes a person’s body produce ________.

Fig 6.4.11

Infection DROPLETS FROM SNEEZING

BLOODCLOT OVERWOUND BACTERIA MOSQUITO BITE

15 Contrast active with passive immunity.

WHITE BLOODCELLS

16 Evaluate the effectiveness of active immunity. 17 Propose a reason why you are unlikely to get measles twice. 18 Propose a reason why immunity does not occur after one cold virus infection.

OPEN WOUND

CONTACT WITHFAECES

[ Extension ]

ANTIBODIES

Investigate 1 Research the arguments for and against vaccination and answer the following questions. a Discuss the use of vaccination in stopping the spread of disease. b Evaluate the importance of vaccination to society. c If you had children, would you get them vaccinated? Justify your answer. 2 How do you think the world’s usage of antibiotics is related to the emergence of new diseases? Gather information about the following issues and present your information as a brochure for doctors and patients on why they should limit the use of antibiotics. a the rate of antibiotic consumption in the world today b the rate at which new diseases or new strains of known diseases are being discovered c how a high rate of use of antibiotics leads to new, more dangerous strains of disease d other factors that could contribute to the emergence of the new pathogens

Surf 3 Research a communicable disease by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button. Some diseases you may like to investigate are anthrax, chickenpox, diphtheria, gonorrhoea, hepatitis A, malaria, rubella, shingles, yellow fever, Giardia, influenza, the common cold, or another of your choice. a For the disease you have chosen, research: i what causes the disease ii how it is contracted iii parts of the world in which it mainly occurs iv how it is spread v signs and symptoms vi how rare/common it is vii the treatment used b Present your information in an electronic format for display (e.g. PowerPoint, Microworlds or a website).

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Transmission and control of infectious diseases

UNIT

6.4

[ Practical activities ] Modelling the transmission of disease

Prac 1 Unit 6.4

Aim To demonstrate the transmission route of a disease

Equipment 1 test tube per person, phenolphthalein indicator, 0.1 M sodium hydroxide, 1 Pasteur pipette per person

Method 1 Each student is given a test tube containing 3 cm3 of liquid. • One of you will have 3 cm3 of 0.1 M sodium hydroxide solution. If it happens to be you, then you are ‘infected’ with NaOH disease, but you won’t know it! Only the teacher will know who the infected person is. • All other students have 3 cm3 of water. 2 You will have 30 seconds to walk around the room, putting five drops of your solution into the tubes of everyone you come into contact with. Note the names of your contacts. 3 After the 30 seconds, add 3 drops of phenolphthalein indicator to your test tube. All ‘infected’ people will see a purple colour in their tubes. Note the number of infected people.

4 Repeat the activity but this time allowing 1 minute for everyone to move around the room. • Half of the students will have 3 cm3 of 0.1 M hydrochloric acid in their test tube. This represents an ‘immunisation’ since the acid will neutralise any ‘infection’ with NaOH disease. • One person will still be ‘infected’ with 3 cm3 of 0.1 M sodium hydroxide solution. • The rest of the students will have 3 cm3 of water in their tubes. • The ‘infected’ and the ‘immunised’ people will not know who they are until later.

Questions 1 Is it possible to work out who was the original infected person? Justify your answer. 2 Describe any difference you observed in the spread of your disease when the time for infection became longer. 3 The spread of disease was different when half of the people were immunised. Describe how.

Effectiveness of antiseptics Prac 2 Unit 6.4

Aim To investigate the ability of various antiseptics to kill disease

Equipment 5 Petri dishes containing the nutrient agar, cotton buds, masking tape, 4 different antiseptics e.g. tea-tree oil, eucalyptus oil, commercial antiseptics, gloves

Method

Rub the cotton bud over the agar in this pattern.

1 Expose all agar plates to the air. 2 Tape one dish shut. This is your control. 3 Dip a cotton bud in one of the antiseptics and carefully brush it in an ‘s’ pattern over the surface of one of the agar plates as shown in Figure 6.4.12. 4 Repeat step 2 for the other three antiseptics.

1 Sketch the appearance of the control and one other plate.

5 Tape all dishes shut and put them in a warm place for 48 hours.

2 Describe the effect that each antiseptic had on the growth of bacteria.

6 After 48 hours, take them out and record your results.

3 Compare the effectiveness of the four antiseptics.

Remember: Do not open the dishes. Look at them through the plates.

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Fig 6.4.12

Questions

3 Which was the most effective antiseptic? Justify your answer.

UNIT

context

6. 5 There are many diseases that are noninfectious. They are not ‘caught’, meaning they are not transmitted or caused by pathogens. The causes of non-infectious diseases are varied and frequently unknown.

Genetic disorders Genetic disorders are caused by abnormalities in one or more genes—this means that the code contained on the chromosomes for building new cells is faulty. These genetic abnormalities may be caused by mutations (see Unit 4.3, page 116 to revise mutations). Sometimes a disorder like diabetes may show up suddenly in a family that has no previous history of the disease. This is caused by a new gene mutation in the sex cells. The cause of gene mutation is often unknown, but mutagens such as radiation, drugs, chemicals and some viruses may be responsible. Once a new gene mutation has happened, the disorder it causes will be passed on to future generations. Fig 6.5.1

Young girl with Down syndrome

Some are genetic disorders, such as Down syndrome, while others, like cancers, seem to be linked to environmental factors such as exposure to certain chemicals and radiation. The cause of others is still unknown.

Haemophilia is an example of an inherited genetic disorder where people lack an important clotting factor in their blood. Down syndrome is not usually inherited, but some women have anomalies in their genes that could increase their risk of having a child affected with the disorder. The chance of a woman having a child with Down syndrome increases with her age. At 25 the risk is 1 in 1250, but by the time a woman is 45 the chance has risen to 1 in 30. It is possible to test for some genetic disorders while the child is still in the womb. The methods used were explained in Unit 4.4.

Diseases caused by diet Malnutrition People in developing countries generally do not have the quantity or range of foods that you have, making them susceptible to malnutrition. Vitamin and mineral deficiencies can easily cause death.

This refugee child is getting adequate carbohydrates, but is at risk of kwashiorkor, caused by protein deficiency.

Fig 6.5.2

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Non-infectious diseases In Australia most people have access to sufficient food. Despite this, many have poor diets, eating too much of one type of food. They therefore have deficiencies in certain essential nutrients, fibre, vitamins and minerals.

Obesity Obesity is a widespread problem in Australia and much of the Western world. Excessive weight places a strain on all body systems, causing high blood pressure, joint and blood vessel problems and an increased chance of developing diabetes.

Eating disorders Anorexia nervosa results in severe weight loss, often enough to cause massive organ failure and death. Bulimia nervosa is a related disorder characterised by a bingeing and purging cycle. The imbalance of electrolytes (mineral salts) that results from this cycle may cause heart failure. Electrolytes are substances that conduct small electric currents through our nerves to our muscles and are responsible for maintaining a regular heartbeat.

Diabetes Diabetes mellitus is a disorder in which glucose, the energy source for your bodies, is not used correctly due to lack of a substance called insulin. Diabetes seems to have some sort of genetic component but there is no defined pattern of inheritance. There are two types of diabetes: • juvenile onset (Type I) • mature onset (Type II). Being overweight is a common factor in Type II cases. Monkey magic If the insulin deficiency Recent research may soon end the daily is serious, regular monitoring insulin injections and injections are needed needed by millions throughout the patient’s life. of diabetics. After

Diseases of the circulatory system In Australia, heart disease is the leading cause of death in males over 35 and females over 60.

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receiving a transplant of insulin-secreting cells, diabetic monkeys did not require injections of insulin. They did, however, need to keep taking a drug that stopped the body’s natural rejection of the transplanted cells.

Fig 6.5.3

Regular exercise is a key to avoiding diseases of the circulatory system.

Many of these diseases are caused by poor diet, smoking and a lack of regular exercise.

Thrombosis and embolism Thrombosis is a disease that causes a large, solid mass (a thrombus) to form on the inside wall of a blood vessel. Sometimes these large masses can detach and end up blocking major arteries, causing death. The blockage of a blood vessel is called an embolism. The embolism can result from a thrombus, gas, fat, tumour cells or some type of foreign body.

Economy Class Syndrome Passengers on long flights do not get much chance to move about, and this inactivity sometimes causes a thrombus to form in blood vessels in the legs or feet. This deepvein-thrombosis (DVT) is in itself not a major problem, but quickly becomes so when the passenger gets moving again. The thrombus will often start moving, only to block more vital blood vessels in other parts of the body, maybe in the lungs, heart or brain. Death often results, perhaps in the terminal after departing the plane. All age groups can suffer from DVT and airlines now recommend that on long flights you exercise your legs and feet to keep blood flow moving in them. You will find these exercises in the in-flight magazines and sometimes on one of the video channels.

UNIT

6 .5 Varicose veins are caused by a fault in the valves.

Fig 6.5.5

deep vein

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connecting vein

superficial vein

varicose vein

spider vein

High blood pressure

Fig 6.5.4

A thrombus (blood clot) in red, blocking about 30% of a coronary artery

Hypertension is the name given to persistent high blood pressure. It can cause arteriosclerosis, or hardening of the arteries, and coronary heart disease. The worst type of arteriosclerosis is called atherosclerosis. It is characterised by fatty deposits within arteries. These deposits can eventually cause arteries to become blocked. Atherosclerosis can occur in any part of the body, not just the heart. It can be inherited, but is also strongly linked to environmental factors like smoking and diet.

Cholesterol is a vital component of all your cells, but too much of it in a diet can lead to arteriosclerosis. There are now margarines available that contain plant sterols, substances which can actually lower the amount of blood cholesterol. This is good news for all those heart patients condemned to low-fat diets—for the first time, margarine may actually make them healthier!

Heart disease

Varicose veins Irregularities in vein walls and weaknesses in the valves can stop blood flowing back to the heart normally. Varicose veins are the result and are usually seen in the legs, where blood must fight gravity to get back to the heart. Unsightly, bulging veins develop wherever blood is trapped. They are more likely to occur in women than in men, and are usually inherited. If you are female and one of your parents has varicose veins, then there is a very good chance that you will develop this condition.

Magic margarine

Flossy hearts Want to know one easy way to help keep your heart healthy? Floss your teeth! Gum disease can result in your mouth having an extremely high concentration of bacteria. These bacteria can end up in your bloodstream and cause damage to your heart.

Coronary heart disease refers to anything that reduces blood flow to the heart and is usually caused by arteriosclerosis. It can cause milder attacks of chest pain, called angina, or a serious heart failure, called a heart attack. About 25% of people with coronary heart disease die suddenly from a

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Non-infectious diseases Fig 6.5.6

What happens during a heart attack. Not everyone experiences all of these symptoms.

A heart attack is initiated by a blockage in a major blood vessel. This stops blood and oxygen getting to the heart. Within 20 minutes the heart starts to die, leading to a heart attack. 1 Stabbing sensation in chest 2 Great pain which can last for hours 1 2 3 3 Dizziness, cold sweat, dry mouth 4 Tingling in wrists, hands, fingers 5 Pain radiates down left arm 6 Chest feels like it is being crushed – often described as ‘like being in a vice’ or like a great weight is on the chest 7 Vomiting, indigestion 4

5

6

7 One in three people die within a few hours of the chest pain starting. Anyone experiencing any of the above symptoms combined with chest pain should call an ambulance immediately.

heart attack. Other diseases, including diabetes, can cause weakening of the heart.

Cancer Cancer is one disease that is on the increase in Australia. Cancer occurs when the cell division that produces new cells occurs uncontrollably. Cell division is a carefully controlled process and even tiny changes within cells can be enough to disturb the process and produce cancer. A tumour is any abnormal growth in the body. There are two types: • A benign growth is one in which the cells are not rapidly dividing. A wart is an example of a benign tumour. • A malignant growth is one in which uncontrollable growth is occurring—this is cancer. A biopsy is carried out to determine whether a tumour is malignant or benign. A small sample of tissue is taken, and is then analysed under a microscope. Cancer can occur anywhere in the body. The most common sites for cancers are the skin and prostate in men, and the breasts in women. Factors that can lead to cancer are: • environmental—cigarette smoking (lung cancer), exposure to the sun (skin cancer), poor diet (bowel cancer), and exposure to certain chemicals, called carcinogens

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A coloured MRI scan showing a malignant breast cancer (blue) at right. Note the increased blood supply to the tumour.

Fig 6.5.7

• genetic predisposition—a family history of breast or prostate cancer suggests that you have a higher risk of developing those cancers. If a malignant growth is found, it needs to be treated before metastasis occurs. Metastasis is when cancerous cells find their way into the circulatory or lymph systems and travel to other parts of the body. The disease becomes very difficult to treat once secondary cancer sites (called metastases) develop. Leukaemia is a type of cancer of the bone marrow and the tissues that produce blood cells. The first symptoms are usually fatigue, unexplained bruising

and anaemia, caused by the lack of red blood cells. An abnormal number of white blood cells appear. Like most cancers, there is no known cure, but many treatment options are available. Common treatments for cancer are surgery, radiotherapy (using radiation to kill localised growths) and chemotherapy (using chemicals to poison cells). These treatments can have serious side effects. The best chance for surviving cancer is to detect it early while it is still small. Never ignore an unexplained lump anywhere on your body. Get your doctor to check it out immediately!

are those that alter mood. Drug use is the controlled, beneficial use of a substance. Drug abuse is when a drug is used in a way that causes negative effects. People who use so-called recreational drugs like Ecstasy or marijuana are often unaware of the serious side effects that can occur. Often, users develop mental disorders that stay with them for life. The table below shows the long- and short-term effects of some psychoactive drugs.

Alcohol and smoking Two of the most widely used and abused drugs in modern society are the legalised drugs—alcohol and nicotine. Because they are legal, their use is much more widespread, open and accepted than illegal substances like heroin and amphetamines. However, their results can be just as devastating, both to the user and to those around them. Alcohol and smoking lead to an unhealthy lifestyle.

Fig 6.5.8

UNIT

6 .5

Fig 6.5.9

Surgery is one way to remove tumours from the body.

Abuse of psychoactive drugs Many people frequently use substances that cause them harm. It is very wrong to think that nasty side effects only occur with prolonged use. Long-term problems can arise just as easily in first-time users. A drug is any substance that has the ability to alter a person’s body chemistry. Psychoactive drugs Drug

Short-term effects

Long-term effects

Marijuana

Euphoria, poor coordination, affects sense of time, increased or reduced appetite, thirst, dizziness.

Respiratory problems, depression, memory problems and levels of sex hormones.

Ecstasy (MDMA)

Feeling of closeness to others, stimulant effect. Can cause increase in body temperature, leading to death.

Long-lasting, possibly permanent, brain damage, especially affects memory.

Speed

Stimulant, increases heart rate, decreases fatigue, feelings of agitation, excited speech.

Can lead to brain damage, memory loss, psychotic behaviour and heart problems.

Ketamine

Delirium, amnesia, affects movement. Can cause fatal breathing difficulties.

Affects attention span and can cause learning difficulties. Also affects memory.

LSD

Hallucinogen. Increased heart rate, higher body temperature, tremors. Effects often unpredictable.

Can result in persistent psychosis and ‘flashbacks’, where hallucinations recur.

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Non-infectious diseases Alcohol In Australia approximately 7% of all male deaths and 4% of all female deaths can be directly attributed to alcohol. Alcohol is technically a depressant drug. Although it doesn’t necessarily make you depressed, it does depress your central nervous system, slowing down its responses. Alcohol has different effects depending on how much is consumed: • Alcohol initially gives a sense of warmth and wellbeing, and a loss of inhibitions. • With a little more alcohol, muscle coordination becomes difficult and speech slurred. Reactions are slower and the senses become dulled. Alcohol is a cause of around one-third of all road deaths. Hence the legal blood alcohol limit in New South Wales for all learner and provisional licence holders was reduced to zero in May 2004. • If more alcohol is ingested, intoxication occurs. The person will be staggering, nauseated, possibly vomiting, and will have difficulty speaking. People are likely to fall into a coma if their blood alcohol content gets to 0.40%. Death through heart and respiratory failure can occur at around 0.60%. This rarely happens, however, since unconsciousness and vomiting have usually forced the person to stop drinking before then. Alcohol also stimulates urine production, dehydrating body cells. Part of the liver is put out of action while it works on processing alcohol. A byproduct of all this processing are poisonous chemicals that are then released back into Sexist alcohol! Alcohol affects different the blood. It is a combination people very differently. of dehydration and these Its effects will depend chemicals that give the on your body weight, fat content, age, mood, symptoms of a hangover. previous exposure to Binge-drinking is alcohol and many other particularly harmful since it factors. Women’s bodies gives no time for the body to have a higher fat content than men’s and so are not process the alcohol. able to metabolise as much Chronic alcohol abuse alcohol as men. Women causes many ill-effects will therefore be affected by smaller amounts. In both including: sexes, even small amounts • digestive problems— of alcohol can make alcohol destroys the the symptoms of mood disorders like depression lining of the stomach. and anxiety much worse.

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• malnutrition and vitamin deficiencies—diet is often neglected. Although alcohol is rich in kilojoules, it has no nutrients. • destruction of the liver—alcohol can cause cirrhosis, a disease where cells are replaced by fibrous tissue • heart damage—alcohol can harden artery walls • destruction of brain cells • slow deterioration of the central nervous system. The abuse of alcohol can result in the disease called alcoholism, where drinking is compulsive and the person dependent on it. This dependence is most often psychological, but can develop into a physical dependence. Worksheet 6.5 Blood alcohol concentration

Smoking The harmful effects of smoking have long been well documented. Despite this, every year young people take up the habit. More young women than men are currently smokers, one common reason being that it

This lung from a heavy smoker shows tar deposits as black spots that would not be present in a healthy lung.

Fig 6.5.10

Increased chance of cancer and heart disease

Environmental hazards

prone to lung infections, persistent cough

can’t smell or taste as well

aging

expensive unfit

bad breath, smelly hair, hands, etc

Fig 6.5.11

UNIT

6 .5 Exposure to radiation, heavy metals such as lead, and chemicals such as asbestos are all environmental hazards that can cause diseases. Although these hazards are usually avoidable, some people are exposed to them without warning. Many environmental diseases have only been diagnosed relatively recently, since many take a long time to develop. Asbestos was once thought to be safe and many people innocently exposed themselves to it in the past. What diseases will develop in the years to come from the materials society uses today?

Some effects of smoking

Radiation is an appetite suppressant. The nicotine in tobacco is addictive and once the habit is formed, it is not an easy one to give up. Withdrawal symptoms include intense craving, anxiety, sweating, depression, sleep problems and difficulty concentrating. It often takes many attempts before people are able to kick the habit for good. Before you think about lighting up, think about these statistics. Smokers are likely to have: • more accidents than non-smokers, due to the slowing down of their reflex actions following a cigarette • constriction of blood vessels, which means that smokers’ brains don’t work as well as non-smokers’ brains • a middle-age death rate twice that of non-smokers • an increased risk of developing many diseases, not just lung cancer • an increased risk of having low birthweight babies with health problems and reduced intelligence if the mother smokes during pregnancy • bad breath • stained teeth and fingers.

Radiation can come from natural sources, like the Sun, or can be generated from artificial sources like X-rays, mobile phones, overhead power lines and nuclear explosions. Radiation most commonly causes mutations in cells, producing various cancers. This cancer of the lower lip was caused by radiation.

Fig 6.5.12

Prac 1 p. 220

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Non-infectious diseases

Depression is a common mental illness that can be overcome with support and counselling.

Whether radiation from mobile phones causes cancer is still a cause for debate and research.

Heavy metals The heavy metals include mercury, thallium, lead and bismuth. The human body has no method of ridding itself of these metals and they build up with each exposure to them. Hence, they are often called cumulative poisons. Throughout history, mercury and lead were used for many purposes before their ill-effects were known, poisoning people as they were used. Lead poisoning has been linked to the exhaust from cars and from flaking old-fashioned leadbased paint. Lead is rarely used in paint these days, but renovators of old homes need to take care when sanding and ripping down walls. Chronic lead poisoning has many ill-effects, including foetal deformities in pregnant women and mental impairment in children.

Mental illness Diseases of the mind can be the most devastating of all. Not only do sufferers have to deal with the disease itself, they must also deal with the terrible stigma that society places on those with mental disorders. In spite of their widespread nature—it is estimated that one in four Australians suffers from a mental health problem severe enough to affect their ability to maintain a normal lifestyle—mental illnesses are not discussed with the same openness as many other illnesses.

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Society’s attitude towards sufferers of mental illness results in them feeling even more isolated, rejected and shamed. Hopefully this attitude will change as people become better educated about mental disorders. Mental illnesses include schizophrenia, depression and bipolar disorder. Mental illnesses are no different to other types of illness—there are symptoms and treatments. They can be inherited or caused by other factors such as drug abuse. All sufferers of illness need acceptance, understanding and respect. Those suffering from mental illness need it too.

6.5 UNIT

Fig 6.5.13

Fig 6.5.14

[ Questions ]

Checkpoint Genetic diseases 1 Outline the causes of genetic disorders. 2 State how errors in genetic coding can occur. 3 Identify some causes of genetic mutations. 4 State the names of two genetically related disorders.

Diseases caused by diet 5 Identify four diseases associated with diet. 6 Describe two effects of obesity on the body. 7 Diabetes is a disease connected with diet. Describe how diabetes affects the body.

Diseases of the circulatory system 8 Describe three causes of circulatory diseases. 9 Define the following terms: a thrombosis b embolism c hypertension d arteriosclerosis

10 Describe three things you can do to keep your heart healthy. 11 Explain what can happen if an embolism forms in: a the brain b the legs of a plane passenger on a long flight

Cancer 12 Identify four factors that can lead to cancer. 13 Cancer can be treated in a variety of ways. Describe three of these. 14 Explain why metastases make it difficult to treat cancer.

Abuse of psychoactive drugs 15 Define the term ‘drug’.

UNIT

6 .5 Analyse 29 Propose reasons why young people are tempted to use illegal drugs like marijuana. 30 The use of ecstasy has some long-term effects. In the light of these effects, assess its use by young people. 31 Discuss the law that prohibits P-plate drivers from drinking alcohol and driving. 32 Mental illness is a common problem. Propose reasons why it is not discussed openly like most other diseases. 33 Look at the person in Figure 6.5.15. Evaluate which non-infectious diseases he is at risk of getting.

16 Use an example to clarify what is meant by a ‘psychoactive drug’. 17 List the side-effects of a particular psychoactive drug.

Alcohol and smoking 18 List three positive and three negative effects of drinking alcohol. 19 Describe the effects of blood alcohol levels above 0.60%. 20 It is well known that long-term alcohol consumption damages one’s health. Describe some of the effects of long-term alcohol abuse. 21 List six withdrawal symptoms that occur when a person is trying to quit smoking. 22 Use Figure 6.5.11 to list six effects of smoking.

Environmental hazards 23 List three types of environmental hazards and the diseases they may cause.

Mental illness 24 List three examples of mental illness.

Think 25 Compare the genetic origins of haemophilia and Down syndrome. 26 Distinguish between a benign tumour and a malignant tumour. 27 State whether the following statements are true or false. a Gene abnormalities are always inherited. b Older women have less chance than younger women of having a child with Down syndrome. c Vitamin and mineral deficiencies can cause death. d An imbalance of electrolytes is not a serious health problem. e Heart disease is the leading cause of death in Australian men over 35. 28 Contrast drug use with drug abuse.

Fig 6.5.15 34 Figure 6.5.16 shows a normal vein. Construct a diagram showing what you think a varicose vein might look like.

direction of blood flow

Fig 6.5.16

A normal vein

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Non-infectious diseases

[ Extension ] Investigate

Surf

1 Construct a poster warning people about a health risk. Examples include heart disease, skin cancer, smoking, drug abuse or something else you find interesting.

4 Explore smoking, alcohol and drug use/abuse further by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button. a Produce a list of reviewed websites that could be recommended to someone who needs support to quit their habit. b Present your reviewed sites as a web page for people looking for help in this area.

2 Research what exercises are recommended by airlines to minimise the risk of getting DVT. 3 As the head of the local health care service, you have $1 000 000 to spend per annum. a Explain how you will distribute this money. b Justify your choices. Remember: all age groups must be catered for. c Discuss this with your class.

UNIT

6.5

[ Practical activity ] TEACHER DEMONSTRATION Effects of smoking

Prac 1 Unit 6.5

Equipment

Questions

Glass tubes, cigarette, cotton wool, sink vacuum pump, matches

Method

2 Identify what the cotton wool represented.

1 Set up the apparatus as shown in Figure 6.5.17. 2 Turn the pump on and light the cigarette.

tap

rubber hosing glass tube

cotton wool

bosshead and clamp cigarette

retort stand

vacuum pump

Fig 6.5.17

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1 Describe your observations as the cigarette was being ‘smoked’. 3 State one poisonous substance produced as a result of cigarette smoking.

Chapter review [ Summary questions ] 1 Outline how health is different from disease. 2 List three types of nutrients.

21 Explain why fungi are called opportunistic pathogens. 22 Explain how immunity is achieved as a result of vaccinations.

3 State an example of a psychosomatic illness. 5 Clarify what is meant by ‘virulence’.

[ Interpreting questions ]

6 Use an example to clarify what is meant by a ‘pathogen’.

23 Use Figure 6.1.2 to assess whether the people shown have good health.

7 List the types of micro-organisms that cause disease.

24 Contrast the effect on health of the activities shown in Figures 6.1.6 and 6.1.7.

4 Specify an example of a disease and its symptoms.

8 Describe ways in which natural control of disease occurs in our bodies. 9 Describe ways in which artificial control of disease is achieved. 10 a Outline the role of chromosomes. b Describe what a mutation is. c List factors that may cause a mutation to occur. 11 List the diseases that can occur in the circulatory system. 12 Distinguish between benign and malignant tumours. 13 Outline the results of metastasis. 14 Recreational drugs often have long-term effects on health. Identify the effects caused by marijuana. 15 Identify three heavy metals.

25 From Figure 6.2.1 it is possible to say that many diseases have common symptoms. State one symptom that all diseases have in common. 26 Use the table on page 196 to state the name of the pathogen that causes: a cholera b thrush c food poisoning 27 Look at the diagram opposite. Specify what is acting as: a the host b the vector

16 Outline the effects of lead poisoning.

[ Thinking questions ] 17 Identify the correct words needed to complete this statement. The study of disease is called _________. A plant or an animal is an ________. A very small ________ is called a _________. An _________causes disease. Parasites use a ________ for food and _________. _________ is a measure of how much a disease damages the host. Another name for an epidemic is an _________. 18 Explain why pathologists carry out autopsies. 19 Describe how the spread of a disease can be prevented if it is: a water-borne b air-borne 20 Some very old bacteria have been found still alive, trapped in ice in polar regions. Explain how they have survived for so long.

28 Identify the types of things vaccines can be made of. 29 Construct diagrams showing the shape of bacteria that cause: a syphilis b sarcina c gonorrhoea Worksheet 6.6 Health and disease crossword Worksheet 6.7 Sci-words

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Evolution Key focus area

5.1, 5.8.3

Outcomes

>>> The history of science

By the end of this chapter you should be able to: explain natural selection, the theory of evolution and their relationship describe the contributions that Buffon, Lamarck, Wallace and Darwin made to our ideas of evolution explain how organisms change when their environment changes explain why organisms with different ancestry might look similar describe alternative theories on how life came to be describe evidence that supports the theory of evolution

Pre quiz

trace the development of modern humans.

1 What was the first life on Earth like? 2 How did giraffes get their long necks? 3 The bright colours of some animals make them easy-to-see prey. Why aren’t they camouflaged instead?

4 What does ‘survival of the fittest’ mean? 5 Charles Darwin is only famous because Darwin was named after him. True or false?

6 Dolphins and sharks have very similar features despite being very different creatures. Why?

7 What is a fossil and what can it tell us? 8 How many different types of ‘humans’ have there been?

7

UNIT

context

7.1 Nearly two million different kinds of plants, animals and micro-organisms are known to be currently living on Earth. More are being found each year. Many more have come and gone, with the average time that a species lasts on Earth being about four million years. Some, like the dinosaurs, are long extinct, and the extinction of others is far more recent.

How did this tremendous diversity of life come to exist on our planet? Evolution suggests that all forms of life stem from the same remote beginnings and that the different species we now know have developed gradually over millions of years.

Surviving in different environments Adaptations Organisms survive and breed in their environments because they have characteristics suited to that environment. Specific structures, functions and behaviours increase their chances of surviving, at least until the organism is able to reproduce. These characteristics are called adaptations. They are inherited and are passed from parents to offspring. Adaptations take many forms and can be classified as either structural (where the adaptation is physical) or behavioural (where the adaptation controls the way they act). Structural adaptations: • Many animals blend with their background so that they cannot be seen by predators.

Cuddles the furry shark New species are usually found in wild and unexplored places, but in 2004 a radically new species of shark was found in a fish tank! Cuddles the shark is a 70 cm female that looks much like other sharks, except that it is covered in red bristles, has bigger nostrils and an extra gill. Cuddles doesn’t swim, but instead hops along the floor of the tank by ‘clapping’ together its shorter-than-normal and more muscular fins. Cuddles now lives in the Sea Star aquarium in Coburg, Germany, but it is thought that Cuddles probably originally came from southern Africa, where, it is suspected, it lived in dark ocean caves. Its bristles are thought to be an adaptation that gives it increased sensitivity to water movement that might suggest food or prey. Cuddles won’t get a mate, however, until scientists find out exactly where it came from. It is very likely that this newly discovered species of shark will ‘disappear’ when Cuddles eventually dies.

Fig 7.1.1

The shingleback skink or two-headed lizard will wave its tail around to try to distract the predator. If the tail is bitten off, it will slowly grow back.

• A few change colour to blend with changing backgrounds. • Others resemble non-living objects such as leaves, twigs or even bird droppings. • With some animals it is difficult for a predator to tell which end is which. The predator attacks the wrong end, giving the prey a chance to escape. • Some extremely colourful animals look like they would be easy prey. Their bright appearance, however, warns predators to stay away, because these animals usually sting, taste bad or are poisonous. • A tricky variation on this is the ‘mimic’. The mimic is not dangerous to predators, but has copied the colourings and shape of another animal, so predators avoid it. • Some animals have features that make them look larger and more frightening to predators. For example, the neck frills of some lizards can be opened to make the head seem like that of a much larger lizard.

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The evolution of a theory Fig 7.1.2

The wings of the owlet moth have bright yellow and black eyespots that mimic the eyes of an owl.

Behavioural adaptations: • Some animals have learned to sit very still or move slowly to avoid predators. • Others are active only at certain times of the day or year to avoid unfavourable conditions such as extremes of heat or cold. • Some have learnt to use tools to access difficult food. For example, chimpanzees commonly use broken twigs to extract termites.

• Some collect and store food for future use. • Many larger animals form herds to provide protection from predators. Adaptations serve many purposes. Arctic fish contain a kind of antifreeze in their blood, allowing them to survive in waters that would freeze the blood of other fish. The long mane of a male lion makes it appear larger to opponents. This kind of adaptation for intimidation is common. Intimidation also involves behaviours such as puffing out the chest and standing up as tall as possible. Plants also have adaptations. One orchid achieves pollination by imitating the shape, colour and smell of a female bee. When a male bee attempts to mate with the orchid, pollen is transferred from flower to flower. The silvery coloured, narrow-shaped leaves of the wattle tree help reduce water loss by evaporation. All organisms have adaptations that assist their survival in their environment.

Fig 7.1.4

To a male bee this orchid looks and smells like a female bee—what happens when the bee tries to mate with the orchid?

Variation Chimpanzees have learnt to use a stick to get to the tasty termites without destroying the nest.

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Fig 7.1.3

Although individuals within a species are very similar, they are not identical. Variation occurs within all species. Much of this variation comes

from the differences in genes and chromosomes that each individual inherits from their parents. These differences are the result of the random assortment of chromosomes during meiosis, and the combination of gametes (sex cells) during fertilisation. Further genetic variation occurs as a result of mutations. Other variations come from environmental factors such as the amount of exposure to the Sun and differences in diet.

Variation and survival

observable, measurable and testable. Like all theories, it is constantly subject to scrutiny, re-evaluation and change.

UNIT

7.1 Alternatives to evolution

The theory of evolution is not the only explanation for the existence and diversity of life on Earth. Most societies have stories about the origin and diversity of life. Creation is the view that regards the world and everything in it as having been made by supernatural means, by a god or gods. The ancient Greeks suggested that the Dreamtime world grew out of Chaos, a dark mass where everything was hidden. From Chaos emerged a god and/or a goddess. The ancient world was Some Australian peopled by them, producing other gods and Aborigines view the Earth goddesses, and then mortal men and women. at the beginning of time

The survival of a species relies on at least some individuals producing offspring. The organisms best adapted to their environment are the most likely to produce offspring. These are the organisms that have favourable characteristics, enhancing their ability to survive and reproduce. Their as a flat, featureless plain. offspring will inherit these favourable Later, in the Dreamtime, characteristics. Over several generations, creatures partly resembling humans arose out of this individuals with favourable characteristics plain. They suddenly will become the most common. In disappeared, but left their contrast, those with less favourable mark as mountains, rivers, characteristics will find the environment animals, plants and all the other features of Earth. inhospitable. They will be more likely to die before they get a chance to reproduce and so will become less common. We can say that favourable characteristics are ‘selected’. Variation in a species is particularly important if environmental conditions change. Some individuals will have characteristics that are favourable, allowing the species to survive the change.

The theory of evolution The theory of biological evolution states that life on Earth has changed over time. Although the idea of a gradual unfolding of life goes back to the ancient Greeks, the modern theory of biological evolution has only been developed in the past 200 years. This gradual development of different species from a common ancestor is called evolution. The word ‘evolution’ is derived from the Latin evolutus, meaning unrolled. It is important to remember that the theory of evolution is just that—a theory. In scientific terms a theory is not just a guess or a piece of speculation. It is a collection of hypotheses that have been tested and supported consistently by available evidence. Scientific theories are concerned with what is

Fig 7.1.5

A rock painting showing dreamtime figures

The Biblical account includes stories of the creation of the Earth and all life on it in six days. There is also an account of the first man, Adam, being created from clay and the first woman, Eve, being created from his rib.

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The evolution of a theory

>>> A busy week in 3928 BC In 1642–1644, Dr John Lightfoot of Cambridge University in England wrote that the world was created on Sunday, 12 September 3928 BC and that man was created on Friday 17 September 3928 BC at 9 am. In 1650, an Irish Archbishop, James Ussher, counted the generations of the Bible, adding them to modern history, and fixed the date of Biblical creation as Monday 23 October 4004 BC.

Fig 7.1.6

ET and me? There have been various suggestions that life on Earth originated ‘somewhere out there’. In his 1969 book Chariots of the Gods, Erik von Daniken proposed that beings from outer space visited Earth and created human intelligence through deliberate genetic mutation. These visits were supposedly recorded and handed down through religion and myths, and in a few physical signs, such as the Nazca lines in Peru. In more recent times, a wellknown astronomer, Sir Fred Hoyle, also proposed that life originated from outer space.

Most societies have stories about the origin of life. This painting (1508–1512) by Michelangelo is called The Creation of Adam and is part of the ceiling of the Sistine Chapel in the Vatican.

A major problem arises when considering these accounts of creation. Are they to be seen as factual? Some people believe the events happened exactly as stated. Other people interpret these accounts as stories with symbolic meaning, as teachings about the relationships between God or gods, the universe and humans. The whole question of the origin of life then becomes bound to religious belief.

Early theories of evolution

Until the late 1700s most scientists believed that the different types of organisms and their characteristics had been fixed for all time. This idea of the ‘fixity of species’ was questioned in the late 1700s by the French naturalist Georges Buffon (1707–88), who suggested that species could change. Erasmus Darwin (1731–1802), grandfather of Charles Darwin, also suggested that

226

one species could change to another, but he had no evidence to support his ideas. The first detailed account of how species could change and evolve came from French naturalist Jean Baptiste Lamarck (1744–1829). Fig 7.1.7

Jean Lamarck, French naturalist

Lamarck, a tutor of Buffon’s son, spent many years classifying plants and invertebrates. He thought that the similarities and differences between living things made sense only if species were evolving. In the 1800s he published several works arguing the case for evolution. Lamarck believed that organisms were guided through their lives by a creative force that enabled them to overcome adverse environmental conditions. Organisms adapted through their struggle to survive. In 1809 he wrote Zoological Philosophy, where he stated two ‘laws’: • Organs are improved with repeated use and weakened by disuse. • Any improvements in or weakening of organs due to the environment ‘are preserved by reproduction [and pass] to the new individuals which arise’. These changes are acquired characteristics, which Lamarck thought were then passed on to the offspring. Giraffes, for example, stretched their necks to reach food high in the trees. This acquired characteristic (a longer neck) was passed on, so that offspring inherited the characteristic of a longer neck. Lamarck pictured evolution as a ‘ladder of life’ from the simplest to the most complex organisms. Lamarck had no experimental evidence for his ideas. Modern genetics shows his ideas to be wrong. Acquired characteristics cannot be inherited. Inherited characteristics come from the chromosomes passed to the offspring via the gametes. These chromosomes are not altered by changes that occur during the life of the organism.

Fig 7.1.8

UNIT

7.1 Darwin’s theory Charles Darwin (1809–82) abandoned his studies in medicine and theology (religion) to follow a career as a naturalist. In 1831, aged 22, he took a position as naturalist on the HMS Beagle, a ship commissioned to survey and chart the coast of South America. For the next five years Darwin observed the geographical distribution of plants, animals, fossils and rocks in various parts of the world. He puzzled over the enormous variety and adaptations of the organisms he saw, and became convinced that species could develop from a common ancestral type.

Fig 7.1.9

Charles Darwin, 18 years after his famous voyage on the HMS Beagle

Darwin in Australia Darwin visited Australia aboard HMS Beagle in January 1836. His journal states that ‘The climate is splendid, and perfectly healthy; but to my mind its charms are lost by the uninviting aspect of the country’. ‘My opinion is such that nothing but rather sharp necessity should compel me to emigrate.’ Darwin in the Northern Territory was named in honour of Charles Darwin when the Beagle made a further voyage to Australia in 1839.

Lamarckian evolution of the giraffe’s long neck

Cut off their tails with a carving knife … Experiments have been conducted to test whether acquired characteristics can be inherited. In one experiment, the tails of mice were removed. The offspring of these tail-less mice were all born with tails. The experiment was repeated for twenty generations. All mice were born with tails. The acquired characteristic was not inherited.

Ancestral giraffes with short necks stretched to reach the tree tops.

The stretched neck (acquired characteristic) was inherited by the offspring.

Continual stretching and inheritance produced the modern giraffe.

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The evolution of a theory Darwin’s finches Some of the most significant of Darwin’s observations were of the wildlife on the Galapagos Islands, about 1000 km off the coast of Ecuador. These islands were of volcanic origin, and much of the wildlife, including flowers, tortoises and birds, differed in small but significant ways from island to island. The islands were effectively isolated from one another by strong ocean currents and a lack of winds blowing from one island to another. Darwin marvelled at the diversity of forms on these islands. He also noted some similarity between island organisms and mainland organisms. Perhaps the most famous of the island’s organisms are the finches, now known as ‘Darwin’s finches’. Darwin found 14 species of finches, all with similar colourings, calls, nests, eggs and courtship displays. They differed, however, in habitat, diet, body size and beak shape. Darwin believed these 14 species had come from a common ancestor, and proposed the process of natural selection to explain it. He suggested that a few finches had arrived on the islands at some time in the past. These finches showed natural variation in their beak shape. On one island, those with beaks of one shape were better able to feed on the cacti found there. Finches with other beak shapes found it difficult to survive. On other islands, other beak shapes gave some finches a feeding advantage. The birds most suited to their island survived to produce offspring, which inherited that beak shape. This is sometimes called ‘survival of the fittest’. The ‘fittest’ were the birds that were able to feed and reach breeding age. The characteristic that gave some beak types an advantage were ‘selected for’.

2

2

1

10

3 warbler finch (one species)

woodpecker finch (one species)

3, 4, 5

1

4 5

vegetarian tree finch (one species) 6

insectivorous tree finches (several species)

10 7

6, 7, 9

8

cactus ground finches (several species)

8

9

large ground finch (one species)

Fig 7.1.10

Darwin’s finches. This evolutionary tree shows how different beaks might have been ‘selected’ for the food available on each particular island.

Over many generations, the birds on different islands became sufficiently different from each other to be recognised as a different species.

Challenging Darwin Darwin spent 20 years collecting and sorting evidence for his natural selection theory of evolution. He used artificial selection techniques to breed various types Darwinian evolution of the giraffe’s long neck

Fig 7.1.11

Who said that? The phrase ‘survival of the fittest’ is usually attributed to Darwin but was first stated by the philosopher Herbert Spencer in 1867, eight years after Darwin first published his theory. Ancestral giraffes had necks of various lengths.

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By natural selection, those with longer necks survived and produced offspring with long necks.

Eventually all giraffes had long necks.

of fancy pigeons. It was not until 1858 that Darwin presented his ideas to the scientific world. He was prompted to publish his work by the publication of a paper by another naturalist, Alfred Russel Wallace (1823–1913). Wallace, unlike Darwin, was raised in poverty and had no formal higher education. Instead he had gained his knowledge of biology through extensive fieldwork in the Amazon and East Indies. Wallace developed his theory of evolution while suffering from a severe malarial fever in the Malayan jungles. Fig 7.1.12

Alfred Russel Wallace

‘During one of these fits, while again considering the problem of the origin of species, … it suddenly flashed upon me that this … process would necessarily improve the race, because in every generation the inferior would inevitably be killed off and the superior would remain—that is, the fittest would survive.’ In 1855 Wallace published his first paper on the origin of species. This made Darwin realise how close Wallace’s research was to his own. Based on his observations, Wallace had reached a conclusion similar to Darwin’s—that evolution occurs by natural selection. His second paper on evolution was presented jointly with Darwin’s in 1858.

UNIT

7.1 Darwin completes his work Darwin’s major work, titled On the Origin of Species by Natural Selection or Preservation of Favoured Races in the Struggle for Life, was published in 1859. Although all 1250 copies of the first edition sold out within a day, much of the reaction did not support him or his theory. Throughout England, religious leaders denounced his work as heretical or against the word of God. The biblical account held that man was formed in the image of God. How then could he have apes as ancestors? Although the Church opposed his theory, Darwin was given a state funeral in Westminster Abbey in 1882.

Surely these are not my relatives! Although Darwin did not initially state that humans were descended from apes, it was implicit in his theory. There was much shock and alarm at this idea. Newspapers and magazines printed cartoons showing the shock of people (and apes) at the idea of being related. Religious opposition to Darwin’s ideas has not disappeared. Even today, some US states require equal time to be given in science classes to the teaching of the biblical story of creation and to evolution.

Caricature of Charles Darwin’s theory of evolution: a pig transforms into a bull, then into Darwin himself.

Fig 7.1.13

Neo-Darwinism Although Darwin was not the first to suggest evolution, he was the first to give a scientific explanation for it. Darwin’s explanation that evolution occurs through

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The evolution of a theory natural selection is one of the most important theories of science and is still regarded as being essentially correct. Darwin formulated his theory with no knowledge of heredity or genetics as there was no understanding of inheritance at that time. Darwin was therefore unable to explain the source of the variation in species that was central to his theory.

UNIT

7.1

[ Questions ]

Checkpoint Surviving in different environments 1 Use an example to help you outline what is meant by an ‘adaptation’. 2 Identify one example of an adaptation that involves the: a structure of the organism b behaviour of the organism 3 State two reasons why individuals within a species are not identical to one another.

The theory of evolution

Worksheet 7.1 Evolution crossword 1

10 Copy and complete the following statements regarding Charles Darwin by identifying the correct alternative. a Darwin (was/was not) the first to think of the idea of evolution. b Darwin was the first to explain how evolution occurred by (natural selection/use or disuse of certain characteristics). c Darwin believed that the evolutionary process involved (inherited/acquired) characteristics being passed on to offspring. d Darwin published his theory (immediately/many years after) he returned from his five-year voyage on HMS Beagle. 11 Explain how the work of Alfred Wallace affected that of Darwin. 12 State what is meant by ‘neo-Darwinism’.

4 Explain what a theory is. 5 Outline why evolution can only ever be considered a theory.

Alternatives to evolution 6 Clarify what is meant by a ‘creationist’ view of the origin of life. 7 Creation accounts can be interpreted in a variety of ways. Present two examples.

Early theories of evolution 8 Use an example to demonstrate the failure of Lamarck’s theory of evolution.

Darwin’s theory 9 Darwin observed 14 species of finches on the Galapagos Islands. Propose two possible explanations for this large number of species.

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Darwin’s theory can be restated in terms of modern genetics. This is sometimes called neo-Darwinism. Evolution is natural selection based upon the natural genetic variation that appears in all populations.

Think 13 Identify whether the red bristles on Cuddles the shark are an adaptation to its tank environment or its original environment of dark ocean caves. 14 Jack rabbits, bilbies and fennec foxes all live in desert habitats, have very large ears and are nocturnal. Explain how their adaptations allow them to live in their environment. 15 Like the males of many bird species, male peacocks are very colourful and carry out spectacular displays with their tail feathers. Propose how these displays and colours allow them to continue their species. 16 Identify the adaptations that match their survival value and the habitat in which they are likely to occur.

Adaptation

Survival value

Habitat

Body colour that blends with the background

Avoidance of the hottest parts of the day

Saltwater

Production of small volumes of concentrated urine

Avoids dislodgement by moving fluids

Desert

Hooks and suckers on the head end of the organism

Enables waste removal with minimal water loss

Rainforest

Broad, flat, bright green leaves

Avoidance of predators

Intestines of a sheep

Live underground by day, and are active at night

Maximum absorption of sunlight

Any

UNIT

7.1 17 State which of the following are likely to be inherited characteristics. a a good suntan b black hair c the athletic ability of a gymnast d high resistance to a bacterial infection e blue eyes 18 Explain what is meant by ‘biological evolution’.

Analyse Ancestral form

19 Describe what the phrase ‘survival of the fittest’ means when used in connection with Darwin’s theory. 20 Draw and label a series of sketches to demonstrate how the long-legged, tree-grazing animal shown in Figure 7.1.14 evolved, according to a Lamarck’s theory b Darwin’s theory 21 Present the main objection to Darwin’s theory by religious leaders when it was first published.

[ Extension ] Investigate 1 Research the significance of the ‘Wallace Line’. Write a journal article summarising your findings. 2 Research the Latin name for shark and propose a scientific name for Cuddles. 3 The ‘steady state’ theory proposes that species did not have a beginning at all but have always existed. Research this theory and write a report evaluating any evidence available. 4 Investigate extraterrestrial theories for the origin of life on Earth. Write a report summarising any evidence for such theories. 5 Research the unique wildlife of the Galapagos Islands and construct a poster showing the variety of organisms. This could be a class project with groups working on different aspects.

Action 6 Even if Darwin had not proposed his theory of evolution by natural selection, he would have been remembered as a renowned biologist. a Work in small groups, each choosing a different aspect of Darwin’s work and research what he did. b Present your information in a five-minute talk summarising Darwin’s other achievements.

Long-legged tree-grazing form

Fig 7.1.14 22 Darwin was unable to explain the natural variation that existed within a species. a Explain how we account for this variation. b Propose reasons why Darwin was unable to explain it as we do.

7 Read about ‘religious’ views on evolution and hold a debate on whether religion or science is correct about evolution.

Surf 8 Complete the following activities on evolution by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7 and clicking on the destinations button. a Complete the interactive activity on the peppered moth. i Record observations for the changes in the peppered moths. ii State your deductions about the observations made. b Complete some tutorials and quizzes on the history of the theory of evolution, and construct a time line showing the development of these theories.

Creative writing What did Darwin see? Trace the voyage of HMS Beagle from 1831 to 1836. Write a page of Darwin’s journal for one place that he visited. Describe the plants and animals he may have seen, and how his observations might have influenced his ideas on natural selection and evolution.

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>>>

UNIT

context

7. 2 How can rabbits survive a virus designed to kill them? How do bacteria become resistant to antibiotics? Why does a dolphin look like a shark, when one is a fish and the other a mammal? How could a bat, a whale and a

Natural selection at work Natural selection is the process in which the environment ‘selects’ favourable characteristics, reducing the frequency of unfavourable characteristics. This means that after many generations of selection, a species will become better adapted to its environment. Individuals will become highly adapted if their environment doesn’t change. Except for mutations, each individual will be very similar, because the amount of variation Prac 1 will have declined. Environments are rarely p. 238 constant, however! Suppose the environment suddenly got colder for a couple of generations of a particular animal. Some individuals within the species may naturally be better

wolf all come from one ancestor? These questions may be answered by looking more closely at how evolution works.

able to tolerate the cold, having thicker coats or some other favourable characteristic. They are better suited to the new, colder conditions than the rest of their species. Over time, natural selection would increase the proportion of individuals with this tolerance of the cold and decrease the proportion of those who don’t. Natural selection takes several generations to become obvious and so it is extremely difficult to observe in large plants and animals. It is more obvious in organisms that reproduce quickly. Bacteria and insects are two organisms in which natural selection can occur quickly enough to be observed.

Selection of peppered moths Over the past 150 years, dramatic changes have been seen in the populations of peppered moths in England. In the mid-1800s, scientists noticed that populations of the peppered moth, Biston betularia, were changing from mostly light-coloured (typica) to mostly dark-coloured forms (carbonaria). Two colour varieties of the peppered moth Biston betularia. In nature the light-coloured form, called typica, is the most common.

Fig 7.2.1

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Will alpine species such as the mountain pigmy possum evolve quickly enough to survive our predicted warmer climate, or is their extinction imminent?

Fig 7.2.2

UNIT

7.2 Moth populations in many of these areas have shifted back towards the lightcoloured forms. Natural selection seems to have taken the moths from light to dark and back to light again.

Selection and rabbit control In Australia, rabbits overran the land for many years, digging burrows, stripping vegetation and causing erosion. The (Left) Peppered moths on a lichen-covered tree trunk. (Right) Fig 7.2.3 myxoma virus, carried by fleas and peppered moths on a soot-blackened tree trunk. Which form mosquitoes, was released in Australia of the moth would be ‘selected for’ in each situation? in December 1950 to control the rabbit The change occurred during the Industrial population. Within two months, 90% of rabbits in Revolution, when coal-burning factories produced a certain areas had died. Ten years later over 99% of lot of pollution in the form of soot. infected rabbits were dead. This means less than 1% When on the soot-darkened trees, the lightof rabbits infected with the virus survived. Ten years coloured form of the moth was easily seen by birds, later, only 25% of rabbits in those same areas would their main predator. The dark-coloured moth blended die as a result of the virus, and around 40% of those with the blackened background, increasing its infected with the virus would survive. These dramatic chances of survival. The dark colour is an inherited changes were the result of natural selection acting on characteristic. Hence, more dark-coloured moths both the rabbits and the virus. survived to produce dark-coloured offspring. Consider what would occur if only one rabbit in After clean-air regulations were implemented, every thousand had a natural, genetic resistance to lichen began to regrow on tree trunks and the the myxoma virus. These resistant rabbits would have trees returned to their original paler colouring. survived the initial myxoma spread, and produced offspring with an inherited resistance. A healthy rabbit may produce seven or more litters of young per year, and therefore within a few years the number of resistant rabbits would have increased dramatically. nearly all dark The myxoma-resistant rabbits were ‘selected for’ survival. mixed light Superbugs and dark Natural selection also works on When penicillin was first introduced it was the virus. The highly virulent form of nearly all light very effective in treating the virus (the one most able to kill) infections caused by kills the rabbit within 6–10 days of Staphylococcus aureus, known as golden infection. A less virulent form might staph. Now, MRSA take 3–4 weeks to kill the rabbit. (methicillin-resistant Since the virus can multiply only Staphylococcus aureus) Manchester is resistant to penicillin within a live rabbit, it is beneficial to and around twenty other the virus for the rabbit to live longer. substances, including The less virulent form was therefore antibiotics, antiseptics and ‘selected for’ survival. disinfectants. Recently, London

Selection and diseases

Peppered moth populations in England in 1950. The moths were nearly all dark in industrial areas, and nearly all light in rural areas.

Fig 7.2.4

There have also been several welldocumented cases of populations acquiring resistance to introduced chemicals. Mosquitoes, which carry the diseases yellow fever and

several strains of MRSA have become resistant to the drug of last resort—vancomycin. If vancomycin fails, the death rate from MRSA will rise dramatically.

233

Evolution unravelled malaria, were treated with chemical pesticides. By natural selection, populations of mosquitoes with a natural resistance to the pesticides developed over the 20-year period following the introduction of the pesticides into their environment. Similarly, many bacteria are now resistant to certain types of antibiotics.

Speciation A species is defined as a group of organisms that normally interbreed in nature to produce fertile offspring. The formation of a new species is called speciation. Natural selection over long periods of time, combined with other factors such as isolation and mutations, can lead to new species forming. Speciation occurs over long periods of time, too long to watch in a lifetime, or even in the recorded history of humans.

Geographic isolation The first step in speciation is geographic isolation of the populations. Suppose a particular population of rabbits was divided, as shown in Figure 7.2.5. If the environments differed on each side of the river, each population would change through natural selection

>>> and the occasional genetic mutation. Eventually the two rabbit populations would have their own characteristics, sufficiently different from each other to be called a variety, or subspecies. Subspecies appear different but are still capable of interbreeding.

Reproductive isolation If the isolation of the populations was long enough, the change might be sufficient to make them incapable of interbreeding. They would then have reproductive isolation. At this point a new species has emerged. Factors that might cause reproductive isolation are: • a change in colour patterns so that mates are no longer recognised • seasonal differences in mating times • a changed chromosome which prevents the sperm of one group from fertilising eggs of the other. Fig 7.2.6

!NCESTRAL POPULATION

'EOGRAPHIC ISOLATIONOF POPULATIONS

-UTATIONSAND NATURALSELECTION OPERATETOFORM TWOSUBSPECIES

2EPRODUCTIVE ISOLATION PRODUCES TWOSPECIES

Fig 7.2.5

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Stages in speciation—geographic isolation leads to different evolutionary paths and eventually reproductive isolation.

Will the cheetah become extinct from a lack of genetic variation?

Will the cheetah survive? There is very little genetic variation among cheetahs. The differences are about the same as are found in brothers and sisters in other species. It is thought that at one time all but one mating pair of cheetahs died. This means that all cheetahs are closely related. Interbreeding between close relatives usually results in the population becoming homogeneous, with very little genetic variation. Such a population is less likely be able to respond to environmental change, and could easily become extinct.

Types of evolution Divergent evolution The Galapagos Island finches and the geographically isolated rabbits illustrate the idea that many new forms can evolve from a single ancestor. This is known as divergent evolution. The idea is that new environments are inhabited, causing the evolution of new species. Divergent evolution results in a phenomenon known as adaptive radiation. As the ancestral organisms adapt and evolve in their different environments, they take on new forms. The various pentadactyl limbs shown in Figure 7.3.10 in the next unit are an example of adaptive radiation. Australia’s marsupial ancestors have evolved and radiated into many different forms, from tree-dwelling, fruit-eating possums to blind, meat-eating underground moles, and the more familiar kangaroos and koalas.

Fig 7.2.7

UNIT

7.2 Adaptive radiation among mammals. The mammals shown are all thought to have evolved from the shrew-like ancestor in the centre. bear

antelope

wolf deer shrew

bat gopher seal flying squirrel

beaver sea cow monkey

Fig 7.2.8

Australia’s marsupial ancestors have evolved into many different forms including the spotted cuscus and the red kangaroo.

sloth

whale

Convergent evolution Evolution can produce similar structures in organisms of quite different origins. For example, even though they are not closely related, Australia’s different marsupials show resemblances to cats, wolves, moles, mice and squirrels.

Convergent evolution, or convergence, occurs when organisms evolve and end up having similar adaptations. This is due to: • living in similar environments, and • having similar habitats and lifestyles.

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Evolution unravelled In similar habitats the same types of characteristics are ‘selected for’, resulting in organisms that look similar despite having very different genes. These organisms may have analogous structures, structures that look similar but which have come from different ancestors. One example is the gliding membrane found between the front and rear limbs of Australia’s gliding possums. Similar membranes are found in the flying squirrels of North America, Europe and Asia,

Placental mammals

Marsupial mammals

wolf

the extinct Tasmanian ‘wolf’ (tiger)

and in the flying lemurs of South-East Asia. These three animals are similar in their lifestyle—they are nocturnal herbivores.

Parallel evolution A third type of evolution is parallel evolution, which occurs where related species evolve similar features while separated from each other. The result is organisms that look alike and have common ancestry, but are found in different locations. Old and New World monkeys share many features. New World monkeys like the vervet have prehensile tails to hold onto branches, whereas Old World monkeys lack prehensile tails since they have evolved to live on the ground.

Fig 7.2.11

Parallel evolution. (Top) This monkey can use its prehensile tail to hold onto a branch. (Bottom) Old World monkeys like the mandrill lack a prehensile tail.

flying phalanger

flying squirrel

Fig 7.2.9

Convergent evolution—Australian marsupials and placental mammals of other continents have many similarities, but are not closely related.

shark (cartilagenous fish)

ichthyosaur (extinct reptile)

dolphin (mammal)

Convergent evolution—despite having quite different ancestors, the shark, ichthyosaur and dolphin have evolved a similar set of characteristics (streamlined body, bilobed tail, fins and flippers).

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Fig 7.2.10 Worksheet 7.2 Natural selection

UNIT

7.2

UNIT

7.2 [ Questions ]

Checkpoint 1 Define the term ‘natural selection’.

19 Humans have developed new breeds of domestic animals by artificial selection in a relatively short time. Explain why natural selection takes so much longer to develop new breeds or subspecies.

2 State the main advantage of natural selection.

20 Contrast convergent, divergent and parallel evolution.

3 Using the peppered moth example, explain what is meant by: a natural variation b natural selection

21 Predict which species are most likely to become extinct if a dramatic change in environmental conditions happens.

Natural selection at work

4 Following its release to control rabbits, propose a reason why the less virulent strain of the myxoma virus was naturally ‘selected for’. 5 List two examples of where natural selection is a disadvantage.

Speciation 6 Propose two reasons why isolated populations of a species might evolve differently from one another. 7 Present the following events in the order in which they occur during the process of speciation: reproductive isolation, natural selection, formation of a species, further natural selection, geographic isolation, formation of a subspecies 8 Describe three events that might lead to geographic isolation of a population.

22 The African aardvark and the South American anteater have similar feet and tongues, but they are not closely related. a Identify the type of evolution that gives rise to these similarities. b Propose ways in which these similarities are explained.

Analyse 23 In Figure 7.2.3, which form of the moth will be ‘selected for’ in each situation? Justify your answer. 24 Discuss whether alpine species such as the mountain pigmy possum are likely to survive in the warmer climates caused by global warming. 25 Discuss whether the cheetah will become extinct because of a lack of genetic differences.

9 State the criteria needed for two subspecies to be classified into two different species.

Types of evolution 10 Identify three different types of evolution. 11 Define the term ‘divergent evolution’. 12 State the conditions required for divergent evolution to occur. 13 With the aid of examples, explain what is meant by ‘adaptive radiation’. 14 Use an example to define what is meant by ‘analogous structures’. 15 Use an example to define what is meant by ‘parallel evolution’.

Think 16 Propose a definition for the word ‘virulence’. 17 Explain how natural selection can give rise to a population of antibiotic-resistant bacteria. 18 Mosquitoes carrying the disease yellow fever have an acquired resistance to chemical pesticides once sprayed to kill them. Propose ways in which the gene for the chemical resistance might have originated.

[ Extension ] Investigate 1 Examine the special problems posed by living in a rainforest, a desert, the ocean or the tundra. a Research the adaptations of plants and animals living in your chosen habitat. b Construct a poster showing your findings. (A good place to start would be David Attenborough’s The Living Planet.) 2 Extensive studies have been made of populations of brown-lipped snails, Cepaea nemoralis. a Gather evidence from these studies. b Describe how changes in these snail populations illustrate the process of natural selection. 3 a Research the use of DDT and other chemicals in programs to control mosquito populations. b Write a report to assess how the problem of the acquired immunity of mosquitoes is being tackled.

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Evolution unravelled

4 a Investigate the use of artificial selection to develop breeds of cattle or dogs. b Write a report comparing artificial selection with natural selection.

Surf

www.pearsoned.com.au/schools, selecting chapter 7 and clicking on the destinations button. a Record observations for the changes in the peppered moths. b State your deductions about the observations made.

5 Complete the interactive activity on the peppered moth by connecting to the Science Focus 4 Companion Website at

UNIT

7.2

[ Practical activity ] Natural selection Aim To model natural selection

Prac 1 Unit 7.2

4 Record the number of each colour toothpick collected.

Equipment 100 green toothpicks (to represent green worms), 100 reddish-brown toothpicks (to represent brown worms), a grassy area and a brown earth area

5 Gather up all the toothpicks. 6 Repeat the procedure until five ‘feedings’ have occurred. 7 Repeat the procedure on the brown earth area.

Method 1 Draw up a results table.

8 Total the numbers of each type of worm in each area.

Feeding 1

Feeding 2

Feeding 3

Feeding 4

Feeding 5

Total

Green worms on grass Brown worms on grass Green worms on brown earth Brown worms on brown earth

2 Scatter the 200 toothpicks on the grassy area.

Questions

3 Allow your partner (acting as a predator of the worms) 30 seconds to pick up (feed on) as many toothpicks as possible, picking up one at a time between the thumb and forefinger.

1 Account for the differences (if any) between the numbers of ‘worms’ caught in each area. 2 This experiment is testing one factor that might affect the ability of a ‘worm’ to survive. a Describe this factor. b State three other factors that affect the survival of worms in their normal habitats. 3 Discuss the relevance of this experiment to the study of natural selection.

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UNIT

context

7. 3 The theory of biological evolution is the most widely accepted scientific explanation of life on Earth. It is also one of the most controversial scientific theories ever presented. It still causes arguments among

The fossil record Direct evidence for evolution comes from palaeontology, the study of fossils. The fossil record from all over the world provides evidence of continual

PERIODS Quaternary 1.8

Tertiary 65

Cretaceous

ERAS 141

Cenozoic

Jurassic

0 65 Mesozoic 248

195 248

Palaeozoic 570

280 345

Triassic Permian Carboniferous Devonian

395 435

Silurian Ordovician

scientists, and provokes strong disagreement from some religious groups. What is the evidence for the theory, and why is there still disagreement?

changes in life forms from over 3500 million years ago until the present. Fossils are the preserved evidence of past life usually found in sedimentary rocks. Fossils may be the: • actual remains of organisms (e.g. mammoths frozen in ice, insects trapped in a type of sap called amber) • hard parts of organisms (e.g. shells, teeth and bones) • impressions of organisms (e.g. EPOCHS hollowed casts, moulds where Recent substances have replaced the 0 Pleistocene 1.8 Pliocene organism) or 5.5 • evidence of the presence of Miocene organisms (e.g. footprints). The ages of fossils, and 22.5 Oligocene the rocks in which they are 37 found, can be estimated using Eocene radioisotope-dating techniques. These techniques have enabled 54 scientists to devise a geological Palaeocene time scale, dividing the history 65 of the Earth into eras. These eras are subdivided into periods, which are further subdivided into epochs.

500

Cambrian

PreCambrian

4500

Fig 7.3.1

570

Formation of Earth's crust

The geological time scale. Ages are shown in millions of years before the present.

Using the fossil record The fossil record allows us to trace major events in the history of life on Earth. Life seems to have begun around 3500 million years ago. The first organisms were probably simple, single-celled, anaerobic (no oxygen was available) bacteria which fed on organic compounds in the primitive

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Evidence for evolution seas. Later, photosynthetic bacteria and blue-green algae appeared, releasing oxygen into the atmosphere. This oxygen release allowed ozone (O3) to form and accumulate, screening out some of the ultraviolet (UV) radiation. This gave some safety to the newly evolving organisms.

gases used in the experiment are no longer believed to represent the atmosphere of early Earth, later work using a more accurate composition of gases produced similar results. No experiments, however, produced a living cell.

An explanation for the appearance of life?

Around 1500 million years ago, organisms with more complex cellular structure appeared. Sexual reproduction appears to have begun at around this time. Organisms recognisable as animals appeared around 600 million years ago. Thousands of specimens of these invertebrates have been collected from sandstone deposits at Ediacara, in the hills north of Adelaide. They are possibly related to present-day jellyfish and earthworms.

One hypothesis to explain the initial appearance of life was put forward by a Russian scientist, A.J. Oparin, in 1924. The early atmosphere is thought to have consisted of gaseous methane (CH4), ammonia (NH3), hydrogen (H2) and water vapour (H2O). Energy from lightning, ultraviolet rays or gamma rays split some of these gas molecules. New bonds formed to create complex organic molecules, which collected in pools to form an ‘organic soup’. Over millions of years this ‘organic soup’ became concentrated, more complex molecules formed and the first cells appeared. In 1953, S. Miller and H. Urey tested the idea in a laboratory experiment at the University of Chicago. Electric sparks were passed into a gas mixture that was thought to be similar to the early atmosphere of the Earth. Organic molecules were produced! While the

More complex life evolves

Fig 7.3.3

Ediacarans are life forms that appeared 600 million years ago. Were they the first animals? The fossil shown is of Dickinsonia, a primitive flatworm.

electrodes

to vacuum pump

spark mixture of NH3 CH4 H2 H2O

condenser

From bacteria to humans

mixture containing amino acids and other complex organic molecules

The Miller/Urey experiment. Given suitable conditions, molecules can combine to form organic molecules.

240

Fig 7.3.2

An abundance of fossils from the Palaeozoic era (570 to 248 million years ago) show the existence of bacteria, algae, soft-bodied invertebrates and representatives from all the major animal groups we know today. Characteristic organisms from the earliest Palaeozoic era were the trilobites. The earliest known land organisms (vascular plants) appeared around 400 million years ago. The first land vertebrates (amphibians) appeared slightly later. At this time the greatest diversity and number of species lived in the sea.

A fossil of the Composognathus, one of the smallest known dinosaurs

Fig 7.3.5 Years before present (millions)

First land organisms

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First animals

First land organisms

Dinosaurs extinct

First human-like ancestral organisms

Worksheet 7.3 When am I?

The Mesozoic era (248 to 65 million years ago) is often called the age of the reptiles because of the abundance and diversity of reptilian forms (including dinosaurs) that lived in this era. The earliest mammals, flowering plants and birds also appeared in this era. Fossils from the most recent era, the Cenozoic era (from 65 million years ago), show the increasing dominance of mammals and the appearance of humans (around 200 000 years ago).

The history of life on Earth recorded as a one-year period. Each day represents approximately 10 million years. The recorded history of humans is less than one minute.

Fig 7.3.6

A changing record The fossil record provides evidence of continual change. A vast number and variety of species have emerged from the earliest life forms. Whole groups of organisms have appeared, become abundant and then disappeared. Some of these changes include:

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Evidence for evolution • Dramatic climate change and altered sea levels may have caused the disappearance of 50% of all shallow-water marine invertebrates around 225 million years ago. • The impact of a large asteroid, and consequent dust storms, are thought to have caused the extinction of the dinosaurs around 65 million years ago.

• Other organisms, like clubmosses and jawfish, have appeared, been abundant, but now survive in small numbers only. • Others, like the flowering plants, insects, mammals and birds, were present in small numbers for some time, then became abundant. • Mammals increased dramatically after the demise of the dinosaurs.

An incomplete record?

Fig 7.3.7

The fossil record is, however, far from complete. Only a small proportion of the plant and animal species thought to have existed are preserved as fossils. While the fossil history of aquatic organisms is extensive and detailed, the fossil history of land animals is far less so. Fossilisation is a rare occurrence. Organisms must ‘fall’ into conditions where decay does not occur. The soft tissues of organisms usually do not form fossils. Fossilisation is more likely in seas, lakes, swamps and caves, but unlikely on land. Geological processes, and human activity, are constantly moving and destroying the sedimentary rocks that contain fossils. Fossil evidence shows an excellent record for the evolutionary development of some organisms such as the horse.

A living fossil. Coelacanths, the ancestors of which are thought to have given rise to amphibians, have remained unchanged for 400 million years. Why didn’t they evolve further?

An eye problem

Miocene from 30 mya

4

2 1.0 m

Pliohippus 3

5 Merychippus

1.0 m

4

2 3 Oligocene from 40 mya Eocene from 60 mya

0.6 m

grazing horses browsing horses

Mesohippus

0.4 m

Hyracotherium (Eohippus)

crown

2

3

4

enamel

5

The evolutionary history of the horse, showing reconstructions of the fossil species. Many branches have left no modern descendants (mya = million years ago).

242

Structure of molar teeth

1.6 m

Pleistocene from 1 mya Pliocene from 10 mya

Structure of forefeet

Equus

Recent

Major adaptations such as the lens in the eye of vertebrates present a problem. The eye would be of use only when fully developed. The eye lens and retina must coexist to be of any use. It is hard to see any sequence of evolutionary development in which each one is separately of adaptive value. How then did such an intricate organ come into existence?

Worksheet 7.4 Evolution of the horse

cement

Fig 7.3.8

Transitional forms For major groups of organisms, transitional forms have been found in their evolutionary pathway. Modern vertebrates appear to have evolved first as jawless fish, then bony fish, then amphibians, reptiles, birds and finally mammals. Transitional forms provide the links between them all, including the air-breathing crossopterygian fish, and the bird-like reptile, Archaeopteryx.

Fig 7.3.9

Transitional fossil forms in the evolution of vertebrates. (Top) An air-breathing fish (400 million years ago). (Bottom) Archaeopteryx, a small dinosaur with feathers (170 million years ago)

UNIT

7.3 Evidence from other studies Anatomical studies Comparisons of the anatomy of various plants and animals provide indirect evidence of their evolution from common ancestors. The front flipper of a seal, a cat’s paw, a horse’s front leg, a bat’s wing and your own hand all look different and perform different functions. However, they all consist of the same number of bones, muscles, nerves and blood vessels arranged in a similar basic pattern. The basic pentadactyl limb (a limb with five digits) can be traced back to the fins of certain fish from which the first amphibians are thought to have evolved. These fundamentally similar structures are called homologous structures.

1 bat (flying) 2

Useless structures

A number of structures such as your appendix and the muscles near your ears have no apparent function. They are called vestigial organs. Why do we have these useless structures? It is thought that they had some function in our ancestors, but that evolution has reduced these structures so much that they are no longer functional. Since there is no evolutionary disadvantage to these structures, they remain today.

monkey (grasping)

5 3

4

1 2 34 5 pig (walking)

5

whale 4 (swimming)

1

For many groups of organisms there are large gaps in the fossil record, often with no transitional forms being found. This lack of transitional information may possibly be explained by considering the process of speciation. Speciation is most likely to occur in a small, isolated population. Environments where the conditions are changing are the most likely sites for natural selection to operate and ultimately give rise to new species. Speciation may therefore occur in too small a group and in too small an area for fossil records of the transitional stages to be seen.

1

3 2

1 2

Fig 7.3.10

2 45 3

anteater (tearing) 5 4 3

3 4

2

5

horse (running)

3

Homologous structures—all limbs have the same basic structure but have been modified for different uses.

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Evidence for evolution Fig 7.3.11

This 49 million year old fossil of a monkey hand shows a basic pentadactyl limb.

The differences seen in the structures may reflect adaptations to different environmental conditions. Their similarity strongly suggests a common ancestor.

Prac 1 p. 248

Embryonic development The development of embryos provides further evidence of evolution. One of Darwin’s contemporaries, German biologist Ernst Haeckel, proposed that by examining an embryo you could see its entire evolutionary history as it developed from one stage to another. Although there are similarities present, Haechel’s original drawings exaggerated the embryonic similarities between species.

shark

Fig 7.3.12

244

lizard

chicken

chimpanzee

Comparison between the embryos of five chordates. What similarities can be seen?

Humans with gills!

The early stages of all vertebra te embryos are very similar. The early human embryo resembl es a fish embryo with gill slits, a tail and a ‘fish-like’ heart and kidn ey. The later human embryo has a ‘reptile-like’ heart and kidney. Later again, the seven-month embryo is covered with hair and has the body proportions of a baby ape. These developmen tal stages are thought to reflect evolutionary history, and indi cate common ancestry.

human

The relationship between evolution and embryonic development is more complex than was once thought.

The distribution of plants and animals

A bird with teeth? Birds do not have teeth and have not had them for the past 60 million years. In an experiment, tissue from the mouth of a mouse embryo was placed near the mouth tissue of a chicken embryo. After incubation, the chicken began to grow teeth, not like mouse teeth, but like those of the oldest known fossil with feathers. Although modern birds do not have teeth, they still have genes that code for making them. All they appear to lack is the mechanism to ‘switch on’ these genes. Are these ‘teeth-making genes’ evidence of the evolutionary past of the bird?

Biogeography is the study of the distribution of plants and animals, both now and in the past. As Darwin saw in the Galapagos Islands, the organisms found on oceanic islands resemble those living on the nearest mainland, yet include species found nowhere else. As oceanic islands have never been attached to the mainland, their inhabitants are thought to have somehow arrived from the mainland, to then evolve in isolation. There are two main mechanisms involved, as described below. Mechanism 1: Isolation followed by divergent evolution This is shown by Australian flora and fauna. Modernday monotremes (the platypus and the echidna) are found only in New Guinea and Australia. Fossils have been found only in Australia, not in Asia. This suggests that monotremes probably evolved in Australia and diversified here. Many groups of organisms found in Australia are distributed only across the southern hemisphere. An example is the group of flightless birds known as South America the ratites, which occur in: • New Guinea (cassowary) • Australia (emu and cassowary) • New Zealand (kiwi) • South America (rhea) • Africa (ostrich).

UNIT

7.3 Studies of DNA show the emu to be most closely related to the cassowary, with the kiwi a second cousin. The rhea and ostrich are more distantly related. One hundred and thirty-five million years ago, Africa, India, South America, Antarctica, Australia and New Zealand were all part of one southern supercontinent, Gondwana. Around 80 million years ago, this large southern continent started to move. First Africa separated from South America. India drifted northwards, and New Zealand separated from the eastern edge of Australia. The ancestral ratites evolved in isolation in each of the separated southern continents. The order of separation of the continents suggests the same degree of relatedness among the different birds as the genetic information. Mechanism 2: Migration followed by divergent evolution The fossil record of the camel family is relatively complete. Distribution of fossils suggests that the first camels developed in North America. Some of these migrated to Asia across an ancient land bridge, and then into Africa. Others migrated to South America. Once isolated, the ancestral camels evolved, giving rise to the llama in South America, the dromedary camel in Africa, and the bactrian camel in Asia. How can the southern distribution of the flightless birds known as ratites be explained?

ostrich

Fig 7.3.13

cassowary

Africa

Papua New Guinea kiwi

Australia rhea

emu New Zealand

245

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Evidence for evolution

Europe

Asia

Human mice

North America

Africa

South America

llama

Australia

bactrian dromedary

Probable point of origin Past distribution

The genetic make-up of mice is very similar to that of humans. In fact it is so similar that mice are one of the best animals to use for testing medical techniques before applying them to humans. The results shown in tests with mice are very similar to results gained with humans.

Current distribution

Fig 7.3.14

The distribution of members of the camel family can be explained by migration and then independent evolution.

Genetic evidence The structure of DNA and the genetic code provide us with more evidence for evolution. The code is universal. Apart from some viruses, all organisms use the same basic code. This supports the idea that all living things are related and have evolved from common ancestors. Comparisons of DNA are used to provide evidence of how closely different species are related. For example, the genetic make-up of a chimpanzee is 98.5% identical to that of a human. Gorilla DNA matches human DNA except for the last 2.6%. The genetic make-up of other primates is also similar to our own.

Gene duplication Scientists are examining the idea of gene duplication, where an organism may have an extra gene for a particular characteristic. For example, an essential difference between reptiles and mammals is milk production by mammals. One protein in mammalian milk is very similar to a protein (protein X) present in reptile eggs, and in some mammalian fluids such as tears. Mammals produce both the milk protein and protein X. It is possible that an error in meiosis produced an organism with a duplicated gene for

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production of protein X. While one gene continued to code for the usual protein, the extra gene mutated and began to code for milk production.

Biochemistry The biochemistry of different organisms is very similar. Chemicals such as the energy-carrying molecule, ATP, and organelles such as mitochondria, are almost universal. Chemical reactions, such as respiration, are very similar in all animals and plants. Biochemical evidence for evolution comes from studies of amino acid sequences of the same protein in different organisms. Proteins are large molecules made up of small units called amino acids. The longer ago two species had a common ancestor, the more likely it is for gene mutations to have occurred to produce small changes in their protein structure. Studies have been made of protein in haemoglobin. A particular sequence of 340 amino acids is identical for humans and chimpanzees. Gorillas are different by two amino acids, and monkeys are different by twelve. Similar results are obtained for other protein studies. This supports the idea of evolution due to mutation and natural selection.

UNIT

7.3

[ Questions ]

17 Propose a reason why it is unlikely that the first organisms on Earth were able to carry out photosynthesis.

Checkpoint

18 Stromatolite fossils help date evolution. Explain how they do this.

The fossil record

19 Present two reasons why fossils are relatively rare.

1 Define the term ‘palaeontology’. 2 a Define the term ‘fossil’. b Use examples to demonstrate two different types of fossils.

20 Identify the times of occurrence that match the events.

Event

Time (millions of years ago)

Time (millions of years ago)

Life on Earth begins

0.2

Cenozoic

248–65

First land organisms appear

4500

Pre-Cambrian

570–248

Humans first appear

1500

Mesozoic

65–present

Complex cellular structures appear

3500

4500–570

Dinosaurs become extinct

600

Earth forms

65

First animals appear

400

3 Identify the time that matches its era. 4 List three gases thought to be present in the early Earth’s atmosphere.

UNIT

7.3

Era

Palaeozoic

5 Coelacanths are considered to be living fossils. Explain why. 6 Outline why Archaeopteryx is considered to be a transitional form in the evolutionary pathway of vertebrates.

Evidence from other studies 7 List three types of evidence for evolution that come from other studies. 8 Use an example to demonstrate how anatomical studies can provide evidence of evolution. 9 a Outline what is meant by ‘homologous structures’. b State how homologous structures are useful in the study of evolution. 10 Explain how vestigial organs are used as evidence of evolution. 11 Describe how embryological studies support the idea of evolution.

Analyse 21 Figure 7.3.6 shows the history of life on Earth as a calendar year. Explain why the history of humans is less than one minute. 22 Use Figure 7.3.14 to account for the worldwide distribution of members of the camel family 23 The map in Figure 7.3.15 shows the distribution of members of the family Proteaceae, a group of plants that includes banksias and proteas. Species of the genus Banksia are found only in Australia and New Guinea. Species of the genus Protea are native only to South Africa.

Genetic evidence 12 Describe how DNA supports the theory of evolution. 13 a Clarify what is meant by ‘gene duplication’. b State how gene duplication could arise. c Propose a way in which gene duplication contributes to the evolution of organisms. 14 Based on DNA studies, identify the organism that: a humans are thought to be most closely related to b humans would be least closely related to 15 Use one example to present evidence of how biochemical studies other than DNA support the theory of evolution.

Think

Proteaceae distribution

Fig 7.3.15

Distribution of the family Proteaceae

>>

16 Contrast analogous with homologous structures.

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Evidence for evolution

a Explain why the family Proteaceae has the southern distribution shown. b Explain why different types (Banksia and Protea) are found on different continents.

>>> 24 Use diagrams to explain how homologous structures can support the theory of evolution. 25 Draw diagrams to demonstrate how comparative embryology can be used to support the theory of evolution.

[ Extension ] Investigate 1

a Investigate how scientific theories are proved or disproved. You might start with the ideas of Karl Popper and Thomas Kuhn. b Assess whether the evidence for evolution actually proves the theory.

2

a Examine the origins of Australia’s marsupials. b Write a report to account for the fact that marsupials are widespread in Australia but almost non-existent elsewhere.

3 The ear bones of mammals seem to have evolved from the jaw bones of reptiles! Fossils have been found that document the steps. a Research this strange evolutionary story. b Write a report analysing the information, and identifying problems with this story.

UNIT

7.3 Prac 1 Unit 7.3

5 Complete the activities on evolution of the horse by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7 and clicking on the destinations button. View the ‘Amazing Feets’ link to learn about the evolution of the horse. Using illustrations, account for the evolutionary adaptation of horses’ feet.

Investigating fossils

Questions

Design an activity or series of activities to investigate fossils. Bones are a good way to begin. You can prepare bones by following these steps:

1 Can the bones be ‘unearthed’ without breaking them? Justify your answer.

2 Remove the meat from the bones. 3 Soak the bones overnight in detergent to help remove any remaining meat pieces. 4 Bleach the bones by soaking overnight in a bleaching liquid like White King. 5 Dry the bones in the sun. 6 Using your prepared bones, ‘design’ a fossil. For example, you might bury some bones in ‘rock’ using plaster mix and an ice-cream container.

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Surf

[ Practical activity ]

1 Thoroughly cook a chicken or a rabbit (a pressure cooker is handy for this). DYO

4 Research gene frequencies and how they change as a result of natural selection. You might start with the Hardy–Weinberg principle, and the idea of genetic drift. a Gather information on an inherited characteristic. b Analyse your information using the Hardy-Weinberg principle.

2 Can a skeleton be reconstructed from a set of bones? Justify your answer. 3 Evaluate whether a mixture of bones from different animals can be sorted effectively to reconstruct their skeletons. 4 Compare your activities with the work of palaeontologists.

UNIT

context

7. 4 Evidence from the fossil record and other studies supports the theory that modern humans evolved from a common ape-like ancestor. However, not everyone agrees with this theory. The evidence suggests that there

have been many species of humans, some of which have become extinct, while others evolved into modern humans. Among scientists there is ongoing debate regarding the details of human evolutionary pathways, and even the mechanisms of evolution.

Primates

0 2 4 6 8 10

Prosimians e.g. lemurs

New World monkeys

Old World monkeys

Apes

Humans

15 Millions of years ago

Humans belong to the order Primates and have many of the features of the primate group. Primates (including us) have: • forward-facing eyes that allow binocular vision • pentadactyl digits (five fingers/toes on each limb) • four upper and four lower incisor teeth • opposable thumbs (for grasping things) • nails (not claws) on the fingers and toes • large brains for their body size • a flexible skeleton, with arms that rotate in the shoulder socket to allow them to reach behind their body (great for swinging in trees!). Humans are unusual, as we also: • walk upright (are bipedal) • have fewer and smaller teeth than the apes • have a flattened face • have a very large skull capacity, and large brain, about three times larger than that of apes • make and use tools • use various verbal and visual languages to communicate • are self-aware. Fossil evidence suggests Old is new and new is old! that primates arose from treeFigur e 7.4.1 might be a dwelling, shrew-like insectivores little confusing since it has around 50 million years ago. the New World monkeys This group soon split into being older than the Old World monkeys! Here, Old several divergent evolutionary World refers to those areas lines, giving rise to the modernof the world long known to day primates. These are the the Europeans, i.e. Europe, parts of Africa and of Asia. prosimians (pre-monkeys, The New World is those similar to lemurs), New World areas discovered later by monkeys, Old World monkeys Europeans (predominantly North and South America). and hominoids.

20

25

30

35

40

45

50

Ancestral tree-dwelling shrew-like insectivores

Fig 7.4.1

A possible evolutionary tree for primates

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>>>

Human evolution Fig 7.4.2

Typical primates—can you see any similarities?

Dryopithecus (appeared approximately 25 million years ago)

Fig 7.4.3

Ramapithecus (appeared approximately 15 million years ago)

Dryopithecus and Ramapithecus—possible ancestors of modern apes and humans

The Southern ape

Evolution of humans The most recently evolved group of primates is called the Hominoids. The hominoids include the lesser apes (gibbons), great apes (gorillas, chimpanzees and orang-utans) and humans. The earliest humans almost certainly arose from the same common ancestor that produced the other hominoids. Although they have similar ancestors, apes and humans are very distantly related, taking different evolutionary pathways millions of years ago. Relatively few human fossils have been found, and the human evolutionary process is not definitely known. There is no accurate record of the emergence of modern humankind, and the exact relationships linking the few existing fossil remains to today’s humans are controversial.

Our distant relatives A picture of the common ancestor of modern apes and humans is based largely on the fossils of Dryopithecus, an ape-like animal that first appeared 25 million years ago. Ramapithecus, another ape-like animal, appeared 14–16 million years ago and lasted another 6 million years. Some believe Ramapithecus to be the ancestor of the Asian orang-utan, while others see a relationship to other apes and humans. There are significant gaps in the fossil records of 5 to 8 million years ago.

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Although apes and humans had similar ancestors in the past, the Homo line diverged from the apes. The first true ‘human-like’ fossils belong to the genus Australopithecus (meaning ‘southern ape’, after the first fossils found in South Africa).The oldest known fossils, Australopithecus afarensis (A. afarensis), are around 4–5 million years old. A. afarensis is most likely to have evolved into a number of new species, including A. africanus, A. robustus and A. boisei. These species were fully bipedal, walked on two legs, and had a brain size of 400 cm3, less than one-third that of modern humans. All fossil australopithecines have been found in Africa. One of the most famous is a 40% complete skeleton of a female named Lucy. Fossil hominoid skeleton known as Lucy

Fig 7.4.4

Recent finds indicate that some australopithecines lived alongside the early members of the genus Homo (the genus to which modern humans belong). This suggests that A. afarensis is the ancestor of both the Homo and australopithecine lines.

areas, such as Asia and Africa. Others maintain that Homo sapiens evolved in Africa, and spread from there some 200 000 years ago. This would mean that all present-day variation in humans has arisen in the past 200 000 years.

%XTINCTION (OMONEANDERTHALENSIS

-ILLIONS OFYEARS

The seven daughters of Eve

 (OMOSAPIENS %XTINCTION





!USTRALOPITHECUS BOISEIAND !USTRALOPITHECUS ROBUSTUS

(OMOERECTUS

(OMOHABILIS



UNIT

7. 4

 !USTRALOPITHECUS AFRICANUS

Mitochondrial DNA is a peculiar form of DNA . It that is passed directly from mother to child e femal of chain a trace to used be fore can there ,a ancestry. Using this method, Bryan Sykes sed geneticist at Oxford University, has propo nal that 90% of Europeans can trace their mater the e (henc n wome seven only of one to ancestry Eve). title of his book, The Seven Daughters of The most distant of these seven lived 45 000 years ago, and the most recent 10 000 years ago. Sykes supports the idea of a relatively recent expansion of Homo sapiens from its use of African origin. Despite these findings, the . ioned quest being mitochondrial DNA is now



Other fossil humans





!USTRALOPITHECUS AFARENSIS

Fig 7.4.5

A possible family tree for humans

More recent ancestors The first clear representation of the Homo line is Homo habilis (‘handy man’). Fossils found in East Africa dating to 1.5–2 million years ago reveal major anatomical and behavioural changes from Australopithecus afarensis. The brain size was 50% larger, and they used tools. Homo erectus (‘upright man’) came next. Although fossils have been found in Europe, China and Africa, Homo erectus is often called ‘Java man’, after the initial discovery site. The oldest fossils are 1.5 million years old. Homo erectus had an average brain size of 1000 cm3, lived in caves and used fire. The evolution of Homo erectus into Homo sapiens (‘intelligent man’) is the subject of considerable debate. Some maintain that Homo erectus evolved worldwide into Homo sapiens but retained local features. This gave rise to different forms in different

Other species of the Homo line have also been identified. These include Homo neanderthalensis (‘Neanderthal man’), which is thought to be approximately 35 000–100 000 years old. The Neanderthals were cave dwellers who used tools and buried their dead, indicating some religious beliefs. They are thought to have become extinct due to a change in climate or through competition with other human species in Europe. The common ancestor of humans and Neanderthals probably lived in Europe around 600 000 years ago. ‘Cro-Magnon man’ (10 000–40 000 years old) was a nomadic hunter-gatherer who used tools and developed art. Anatomically Cro-Magnons were similar to modern humans, but more robust. Cro-Magnons lived in Europe and the exact reasons for their extinction are not known.

Anatomical changes While the exact details are the subject of debate, there are a number of identifiable changes in the evolution of Homo sapiens from an ape-like ancestor. Anatomically, the various forms have walked more

251

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Human evolution

A convincing hoax The skull of ‘Piltdown man’ was discovered in a grave pit in southern England in 1912. It had an ape-like jaw, with a large, modernlooking cranium. The scientific world was excited by the find, particularly the English, who thought that the first human was one of them! It was not until 1955 that the skull was revealed as a forgery—a human skull joined to an orangutan’s jaw and treated to give an aged look.

Fig 7.4.6

Fossil human skulls. The three skulls from bottom left to top centre are Australopithecus africanus, Homo habilis and Homo erectus. The black skull in the upper right is from a ‘modern’ human, Homo sapiens, around 92 000 years old. The pale skull at the front is from a Cro-Magnon human about 22 000 years old. Note the changes in face shape and brain capacity.

upright than their ancestors. They have also developed smaller teeth, reduced eyebrow ridges, shorter arms, flatter feet, non-opposable big toes, flatter faces and a progressively larger brain size.

Cultural evolution

Humans have changed in many non-physical ways. We have learned how to use tools, and have developed speech, forms of writing, artistic creativity, reasoning powers and a sense of right and wrong. It is these changes that most distinguish modern humans from their ancestors. Humans have highly complex social structures, and an accumulation of learning and knowledge. This stored experience is passed from generation to generation, and affects survival—that is, a type of cultural evolution occurs.

Homo neanderthalensis

Australopithecus afarensis

Homo habilis

proconsul (hypothetical African ape)

Fig 7.4.7

252

Human form during the stages of evolution

Homo erectus

Modern Homo sapiens

Fig 7.4.8

UNIT

7. 4 Cultural evolution—stored experience is passed from generation to generation.

Fire starter

It is estimated that of all the animal species that have ever existed, only 1% are alive now. The ultimate fate of most species appears to be extinction. Homo habilis lasted for around 1 million years, Homo erectus around 1.5 million. Modern humans have existed for about 200 000 years. With cultural evolution, humans continue to acquire knowledge, enabling them to exert more control over their environment than any other species ever has, but we have probably done more damage also. What does this mean for the future of Homo sapiens?

UNIT

7.4

Fig 7.4.9

Cultural evolution—the knowledge of fire is passed from one generation to the next through practice and observation.

Worksheet 7.5 The ‘Hobbit’

Fire is probably the most important tool that humans have learned how to control and use. Aborigines in Australia traditionally used fire to hunt and manage the land. The knowledge of using fire, and the skill of starting a fire, is passed from one generation to the next. This is an example of cultural evolution.

[ Questions ]

Checkpoint Primates 1 List the characteristics of primates. 2 List the following primates in correct order of evolution: Old World monkeys, apes, humans, prosimians, New World monkeys 3 Primates are thought to have a common ancestor. Outline what this ancestor was like. 4 State the name of the genus (group) to which the first true ‘human-like’ fossils belong. 5 List two examples of non-physical features that distinguish humans from other primates.

Evolution of humans 6 State two evolutionary trends that have occurred in primates. 7 Use examples to clarify the meaning of the term ‘hominoid’. 8 List the following in their probable order of evolution from earliest to most recent: Ramapithecus, Neanderthal, Australopithecus afarensis, Homo habilis, Dryopithecus, Cro-Magnon 9 State three physical changes that have occurred in the evolution of humans from an ape-like ancestor.

>> 253

>>>

Human evolution

Analyse

Cultural evolution 10 Clarify what is meant by ‘cultural evolution’.

17 Use Figure 7.4.1 to compare the two typical primates.

11 List three examples of cultural evolution.

18 Propose an order in which you think the skulls shown in Figure 7.4.10 evolved. Justify your choice.

Think 12 Contrast humans with primates. 13 Bipedalism was a major development in the evolution of humans. a Define the term ‘bipedalism’. b Propose two reasons why bipedalism would be an advantage to an organism. 14 Contrast Homo habilis, Homo erectus and Homo sapiens in relation to what they were capable of doing. 15 Larger brain sizes allowed early humanlike forms to develop rapidly. Explain the advantages of a larger brain. 16 Contrast cultural evolution with Lamarckian evolution.

A

C

Fig 7.4.10

[ Extension ] 1 Research the work of the Leakey family in searching for hominoid fossils in Africa. Write a biography to summarise their discoveries.

Action 2 When anthropologists study fossils to determine whether they are ape or human, they look particularly at the teeth and jaw, and at skeletal modifications for bipedalism. a Research the structural differences and similarities between apes and humans. b Work in small groups to construct various models of examples that demonstrate your research.

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B

19 Use Figure 7.4.3 to answer the following questions. a Dryopithecus and Ramapithecus looked very different. Contrast their appearances. b Propose reasons for the differences in appearance.

Science focus: Putting flesh on old bones: archaeology and Australia today Prescribed focus area: The history of science

D

discovery sparked a major archaeological program. Bowler named this previously unknown lake as Lake Mungo. Lake Mungo is one of a series of lake basins formed by a channel of the ancient Lachlan River, known as the Willandra Creek. The bones proved to be the cremated remains of a young woman, now known as Mungo Lady. Four years later and just 400 metres away on the same beach sands where Mungo Lady was found, Bowler noticed the tip of a cranium being uncovered by natural erosion. Excavation by archaeologists revealed this to be the fully articulated skeleton of a human male, now known as Mungo Man.

Mungo Man

W

B og an

illan d ra Billab o

Lake Mungo

Mildura

an chl La

Mungo Lady

R

a r li n g River

The landscape we know in Australia today was very different during the last ice age, from about 100 000 to 10 000 years ago. How does science discover and tell us just how the land has changed during ice age events? We would expect more ice on the mountains of south-eastern Australia and in Tasmania during an ice age. But what happened to the dry inland areas at this time? How did they change? Were people actually living there during such times? In 1967, geologist Jim Bowler was studying ancient inland lake basins in western New South Wales. Though these basins are now completely dry, in the past they acted as giant rain gauges, filling when the climate was wet, and drying and forming dunes during dry phases. In 1969, while mapping evidence of ancient shorelines in the dry basins of western New South Wales, Bowler discovered some burnt human bones buried in the beach sands of an ancient lake. This

River

Bathurst Katoomba Sydney

Griffith M urrumbidgee Riv er Cr Yanco Wagga Wagga

Echuca

Goulburn Canberra

Albury rray Rive r Mu

Fig SF 7.2

Mungo Lady and Mungo Man were discovered 400 metres apart on the same beach sands of ancient Lake Mungo.

How old are Mungo Lady and Mungo Man? Melbourne

Lake Mungo is located in western New South Wales.

Fig SF 7.1

The Mungo discoveries changed our understanding of when the earliest Australians arrived, and of the changing landscape in which they lived. Before the Mungo discoveries, the oldest known evidence of human occupation in Australia was from about

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20 000 years ago. Suddenly at Lake Mungo that evidence was nearly doubled. Mungo Lady was first thought to have been buried about 26 000 years ago, and Mungo Man about 30 000 years ago. Following additional work on the geology of beach and dune sands, Bowler later revised Mungo Man’s burial age to near 44 000 years ago.

How does science actually provide burial ages? Grave sites can be dated by two different methods: • by dating the actual bones or human remains, or • by dating the age of the layers below and above the grave. Dating is a complex business and often provides only approximate answers. Because some doubt remained about the age of Mungo Man, a group of scientists at the Australian National University attempted to date the bones. Their results ranged from 50 000 to 70 000 years, and from this they estimated the most probable age as near 62 000 years. As this disagreed markedly with earlier estimates, a team from four universities used a second dating method—dating the age of the sand layers below and above the grave. The results provided firm evidence that both the Mungo Man and Mungo Lady burials had occurred between 40 000 and 44 000 years ago.

An ancient people in a now dry land

Fig SF 7.3

256

Mungo Man being unearthed approximately 44 000 years after being buried

During the recent drought, landholders even on large properties in this now dry region of western New South Wales had great difficulty making a living from the parched, dry landscape. It was too dry for wheat and there was not enough water for sheep. The occupants experienced extreme financial and psychological stress. By comparison, the occupants of that same land 40 000 to 50 000 years earlier had enjoyed an abundance of water and food, including fish and freshwater mussels. Animals were abundant and stone tools readily available. People lived and died on sandy lakeshore beaches. The environment was almost certainly able to sustain a larger population per square kilometre than it supports today. But the period of abundant water was not permanent. The ice age, which had entered its early phase of cooling 80 000 years ago, involved gradual further cooling of the Earth as the ice caps expanded in the northern hemisphere, particularly in North America and Scandinavia. As temperatures dropped, evaporation from the oceans decreased. Less water was available for atmospheric transport, and so less rainfall was available on the continents. In this way, cold climates became drier. By 40 000 years ago, the once abundant water had begun to diminish. Some basins across Australia dried

We now know that, like Lake Mungo, every part completely and the dune fields expanded. People of Australia was affected by ice age conditions, gathered close to drying water bodies, living on the which were sometimes wetter, sometimes drier than remaining beaches and burying their dead there. At today. We now have a picture of people doing battle about this time, large numbers of animals disappeared with droughts and floods, just like us, only some completely from the land. This included giant 40 000 years ago. kangaroos, the giant lizard (Megalanea), the marsupial lion (Thylacaleo) and many other megafauna. Many people believe this may have A 60–40 000 years ago been due to excessive hunting by N S Aboriginal people. Others think it may have been due to climate change. Golgol It may have been aspects of both, but certainly something of major B Earliest dune sands Lower Mungo quartz sand dune in excavations importance happened to the Australian Mungo man burial Soil formed in Carbonate soil formed large animal populations at about earliest dunes over burial site that time. Gravel beach to Joulni For the next 20 000 years the climate Golgol oscillated between wet and dry. By 20 000 years ago, in the coldest part C About 40 000 years ago of the ice age, the Willandra basins Dust had dried completely. Under these conditions Bass Strait was dry and dunes extended even as far as northeast Tasmania. People adapted, learning D About 32–25 000 years ago to live in these cold, harsh, dry conditions. Much of this story of landscape Lake Mungo change and human occupation has E emerged from Lake Mungo—this is 20–18 000 years ago Dust such an important site that it was Final dune layer declared a national park in 1979. In 1981 it was listed as one of Australia’s Joulni first World Heritage areas, known as Willandra Lakes World Heritage area. A North-south diagram through Lake Mungo shoreline near the Mungo Man

The significance of the Lake Mungo area Lake Mungo has national and international significance, as it provides us with a new understanding of two important aspects of Australia: • how the Australian landscape evolved during dry ice age conditions • the antiquity and cultural patterns of the earliest inhabitants of this land.

burial site. Lake flooding extends north and south of the dune ridge. B Shoreline enlargement shows vegetated beach and dune sands on margin of freshwater lake with fish and shellfish used as human food resources. Mungo Man was buried here as the lake began to dry near 44,000 years ago. C Dry lake generates dust clouds sweeping across dry land adding to the growth of Lake Mungo dune. D Water returned briefly to the lake system approaching the time of maximum glaciation in the upland catchments. E Cold dry period of maximum glacial phase. Clouds of dust and salt were swept from the dry lake floor.

Fig SF 7.4

Australia’s landscape at Lake Mungo has changed dramatically over the past 40 000 years. People had to adapt to the changing conditions in order to survive.

257

Scientists and Aboriginal communities at Mungo devised a way of working together. In 1992, on the sands at Mungo where Mungo Lady had been buried so long ago, her remains were ceremonially handed back to the tribal community. Politicians also introduced laws that recognised Aboriginal ownership of all artefacts of indigenous cultural heritage, and such ownership remains with the traditional owners of the appropriate region. Today it is illegal to remove Lake Mungo today is affected by droughts. Fig SF 7.5 Dunes and erosion can be seen clearly. or interfere with any object of archaeological significance, The discoveries at Lake Mungo took on new including stone tools, shell middens, ancient fire significance in the early 1970s during the early battle places and, of course, human remains. for Aboriginal land rights. The Aboriginal people’s This has resulted in a new relationship between claim that they have been here for more than 40 000 Aboriginal people and the scientific community. At years was enshrined in their banners of protest, and Lake Mungo and other places, members of indigenous was supported by science. Their claim later gained communities must approve any scientific investigation political recognition. of their past. Entire tribal communities now work side by side with scientists in ongoing investigations, Cultural battles exploring and expanding our understanding of The contributions of science to Aboriginal Australia’s past, with its important implications for all people have not always been so positive. For many Australians about the dignity and cultural status of the years through the early twentieth century, human original occupants of this land. biologists collected large numbers of Aboriginal skeletons, trying to prove that the dark-skinned races Handing back the remains of Mungo Lady to the tribal community was a step towards were inferior to whites. They did this by measuring ongoing collaboration between Aboriginal brain size from human skulls. Hundreds of graves Fig SF 7.6 communities and scientists. were robbed, and the bones collected and sent to universities and museums around the world. In this way science had been used as a partner in committing a great injustice against the Aboriginal people— reverence for the dead had been forgotten and the feelings of living descendants had been completely disregarded. Following the discoveries of Mungo Lady and Mungo Man, the Aboriginal people of the region protested that science, by once again disturbing their dead, was committing a great offence against their cultural traditions. At the same time some Aboriginal people acknowledged the value of documenting their own history, as this proved to the world their longestablished rights of occupancy.

258

More information Special thanks go to Jim Bowler for writing this feature. Jim’s dedication to understanding Australia’s past, present and future has also led him to produce an interactive CD that covers geology, archaeology and scientific history, including: • Australia’s natural history and evolution • swings in Australia’s ice age climate and environment • how ice age Australians lived • early human–land relationships essential to understanding the present • more about the tensions between science and indigenous traditions. To obtain a copy of this CD, connect to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, select chapter 7 and click on the Destinations button. Jim Bowler on the Lake Mungo dunes

Fig SF 7.7

[ Student activities ] 1 a Outline some methods that might be used to explore and develop our understanding of ice age Australia. b Propose reasons why such information is important today. c Compare life in arid regions of Australia today with that of the people at Lake Mungo 40 000 years ago. d Describe how the land near where you live may have been affected by conditions in the last ice age. 2 Research your local area to answer the following questions. a Who are the traditional owners of the area in which you live? b What archaeological research has been carried out near where you live? 3 Where did the first Australians come from and how did they get here?

4 a What is the relationship between Aboriginal people and your own family’s ancestry? b Where do you think your ancestors may have been 40 000 years ago? Describe what their life would have been like. 5 Lake Mungo National Park has tourist facilities to allow people to explore the area. a Investigate the features of the Mungo area that make it an interesting tourist destination. b Produce an information brochure, website or display for tourists. Your brochure should outline: • some of the attractions that may interest tourists • the cultural history of the area • the discovery of Aboriginal remains at the site • the importance of the scientific research that has been done at Lake Mungo.

There are many theories about how people came to occupy Australia. Conduct research to answer the above question, and then share your findings with others through an interactive presentation or display.

259

>>> Chapter review [ Summary questions ] 1 A whale has many adaptations that make it suited it to its marine environment. a Define the term ‘adaptation’. b List some of the whale’s adaptations. 2 Natural selection is the process whereby the environment selects favourable characteristics. a Outline the meaning of the term ‘favourable characteristics’. b State the main outcome of natural selection acting on a species. 3 Specify the events that are missing in the following process: Geographic isolation, ……..… …………., formation of a subspecies, r…………. i…………., further natural selection, formation of a species 4 Fossils can support the theory of evolution. Describe how they do this. 5 a Clarify what is meant by ‘homologous structures’. b Identify the type of evolution that gives rise to homologous structures. c Clarify what is meant by ‘analogous structures’. d Identify the type of evolution that gives rise to analogous structures. 6 Natural variation can occur within species. Identify two sources of this. 7 Describe two ways in which knowledge of genetics has improved our understanding of Darwin’s theory. 8 a Define the term ‘biogeography’. b State one example of how biogeography provides evidence of evolution. 9 Identify three anatomical features that distinguish humans from primates. 10 List two ancestors of Homo sapiens. 11 Homo sapiens have undergone much non-physical evolution. State a general term for this.

[ Thinking questions ] 12 Two scientists who have contributed to our understanding of evolution are Lamarck and Darwin. For each idea below, identify the scientist who developed it. a evolution by inheritance of acquired characteristics b adaptive radiation of the Galapagos Island finches c evolution by natural selection d organisms are guided through their struggle for existence by a creative force 13 a Describe how Lamarck would account for the evolution of an elephant’s trunk. b Describe how Darwin would account for it. c Compare the theories of Darwin and Lamarck. 14 List the following statements in sequence to explain the process of natural selection. i Rabbits with a gene for cold resistance survive, while other rabbits die. ii Over several generations the number of rabbits with cold resistance increases. iii Members of a rabbit population show variation in their resistance to cold. iv Offspring of the surviving rabbits inherit the gene for cold resistance. v The rabbits’ habitat becomes colder due to a major climate change. 15 a State two ways in which a population may become geographically isolated. b Propose ways in which a geographically isolated population would be likely to evolve differently from the remainder of the species. c Identify two factors which might cause a population to become reproductively isolated from the remainder of the species. 16 Chemical reactions are thought to have formed the first living things on Earth. It is not possible for these reactions to occur on Earth today. Explain why. 17 Present three possible reasons for the ‘gaps’ in the fossil record of life on Earth. 18 a State two similarities between an early human embryo and a fish embryo. b Explain how these similarities may have come about.

260

19 Identify the description that matches the correct term. Term Parallel evolution Convergent evolution Divergent evolution

Description Results in structurally similar but unrelated organisms Evolution that results in adaptive radiation Produces structurally similar, closely related organisms that live in different places

20 Use the theory of evolution to account for the following observations. a The scales on a bird’s legs are similar to the scales on a reptile’s body. b The ocelot (a placental cat found in South America) and Australia’s marsupial cat are not genetically similar, but have many similar features. c Many plant-eating mammals have a large, useful appendix. Humans have a small, useless appendix. 21 Describe two changes which are thought to have occurred in the evolution of a Australopithecus afarensis to Homo habilis b Homo habilis to Homo erectus c Cro-Magnon to modern humans 22 Copy the following statements and modify each to make them correct. a Adaptations are inherited characteristics. b Speciation usually involves reproductive isolation followed by geographic isolation of a population. c Charles Darwin was the first to think of the idea of evolution. d DNA testing shows that the closest species to humans is the chimpanzee. e The fossil record shows clearly that all organisms have evolved slowly and gradually. f A bat’s wing, a seal’s flipper and a human arm are all homologous structures. g Modern humans evolved from modern apes. h Most of Darwin’s ideas regarding evolution are now thought to be incorrect. 23 Present three alternative explanations for the existence and diversity of life on Earth.

[ Interpreting questions ] 24 Identify the fossil names that match the correct classifications and approximate times of appearance. Name Upright man Cro-Magnon Handy man Neanderthal Lucy

Classification Homo sapiens Homo habilis Homo erectus Australopithecus Homo sapiens

Time of appearance (years ago) 40 000 1.5 million 5 million 100 000 2 million

25 Suppose the approximate 3600 million year history of life on Earth were condensed into a 24-hour day. Select proposed times to match the events listed. Each hour would represent approximately 300 million years. Event Complex cells first appear Australopithicines first appear Dinosaurs become extinct The Palaeozoic era begins Land organisms first appear

Time 10.40 pm 11.47 pm 7.00 am 11.59 pm 10.00 pm

Worksheet 7.6 Evolution crossword 2 Worksheet 7.7 Sci-words

261

Global issues Key focus area

5.4, 5.6.5, 5.10, 5.11.1, 5.11.2, 5.12

Outcomes

>>>

The implications of science for society and the environment

By the end of this chapter you should be able to: explain how greenhouse gases cause global warming explain how certain chemicals can deplete the ozone layer predict the consequences of both global warming and ozone depletion, and describe ways to reduce these identify commonly used fuels describe the effects of different energy sources explain what happens when an atom emits nuclear radiation list some of the properties, uses and problems of nuclear radiation describe how energy is released in a nuclear fission reaction

Pre quiz

describe alternative energy sources.

1 Most people like warm weather, so why is global warming a concern?

2 Is El Niño a type of Mexican food or a change in weather patterns?

3 You probably have some very radioactive material in your home. Where is it?

4 Radiation can both cause cancer and be used to treat it. How?

5 What is an ‘alternative energy’?

>>>

8

UNIT

context

8.1 In the movie The Day After Tomorrow extreme blizzards and colossal storm waves devastate New York, tornadoes rip apart Los Angeles, and huge hail pounds Tokyo. While all this made a good film plot it’s not what we can really expect from global warming.

The greenhouse effect The greenhouse effect is caused by the gas carbon dioxide (CO2) together with other trace gases in the atmosphere. These gases, commonly called greenhouse gases, provide a ‘blanket’ that keeps the Earth warm. Too little carbon dioxide, and the planet would be too cold to sustain life. Too much, and the resulting high temperatures would also be unsuitable for life. The greenhouse effect is natural and is required for the continued survival of all Earth’s species.

The hot car effect A car left in the sun on a fine day can become very unpleasant inside. The temperature can easily reach 50°C even when the temperature outside is only between 20°C and 30°C. Heat enters the car easily but much of the heat cannot escape. For this reason,

a

Fig 8.1.1

b

Scientists have investigated climate change for several decades. It is only recently that they have looked at its likely impact on specific locations. Will it be as devastating as the events portrayed in the movie?

animals and young children should not be left in cars: these high temperatures can kill. The greenhouse effect could well have been called the ‘hot car effect’, but it is named after greenhouses that trap heat from the Sun to help plants grow more quickly.

How does it work? Carbon dioxide and other gases in the atmosphere behave like the glass in a greenhouse or car windows. Energy from the Sun reaches the Earth as electromagnetic waves with a short wavelength. These waves are able to pass through the atmosphere (and glass). The energy is absorbed by the Earth and re-emitted into the atmosphere as long-wavelength radiation. Carbon dioxide (and glass) effectively blocks the transmission of long-wavelength radiation, stopping it from reaching space. Much of this energy is therefore trapped in the atmosphere, warming the Earth to a temperature suitable for life. If not for the greenhouse effect, the Earth would be about 30°C colder on average!

c

a The surface temperature on Mars is –100°C. Its atmosphere is too thin to produce a life-sustaining greenhouse effect. b The Earth’s atmosphere is just the right thickness to keep its average temperature at around 22°C. c A massive greenhouse effect caused by Venus’s thick carbon dioxide-rich atmosphere causes surface temperatures of 500°C.

263

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Global warming The enhanced greenhouse effect Over the past century the levels of greenhouse gases in the atmosphere, particularly carbon dioxide, have increased. The blanket of greenhouse gases in the Earth’s atmosphere has effectively become thicker.

3HORTWAVELENGTHRADIATION PENETRATESATMOSPHERE

)NNERLAYEROF GREENHOUSEGASES INATMOSPHEREACTS LIKEAGREENHOUSE -OSTENERGY ISTRAPPEDIN THEATMOSPHERE WARMINGTHE %ARTH

3OMEENERGY ESCAPESBACK INTOSPACE

%ARTHABSORBSRADIATION ANDEMITSLONGER WAVELENGTHRADIATION

)NNERLAYEROF GREENHOUSEGASES INATMOSPHEREACTS LIKEAGREENHOUSE

,ESSENERGY ESCAPESBACK INTOSPACE

-OREENERGYIS TRAPPEDINTHE ATMOSPHERE

%ARTHABSORBSRADIATION ANDEMITSLONGER WAVELENGTHRADIATION b

a The ‘natural’ greenhouse effect b The enhanced greenhouse effect will lead to global warming.

264

Greenhouse gases: where do they come from? The main greenhouse gas is carbon dioxide. Carbon dioxide is naturally cycled through the environment during photosynthesis and respiration. Over Earth’s history the amount of carbon dioxide in the atmosphere has stayed fairly stable since it is both absorbed into living systems and released back into the atmosphere.

CO2 revolution

a

3HORTWAVELENGTHRADIATION PENETRATESATMOSPHERE

This results in the enhanced greenhouse effect, where the same amount of heat energy is coming in from the Sun, but less is escaping back into space. The enhanced greenhouse effect Prac 1 is leading to global warming, increasing the p. 271 average temperature of Earth.

Fig 8.1.2

Emergency! Have you ever noticed those green and white exit signs in cinemas and shopping malls? There are lots of them and they all need electrical power. It is estimated that in New South Wales alone they generate 126 000 tonnes of greenhouse gases (mainly CO2), equivalent to the output of 25 000 cars! Self-illuminating signs that draw their power from sunlight or from other light sources are available, but make up only 1% of the world’s exit signs.

The factories, steamships and locomotives of the Industrial Revolution needed fuel to fire their boilers. This came mainly in the form of timber or coal. The modern world also needs fuel. In mainland Australia, coal is still used, mainly to fire the boilers of electrical power stations. Coal, and the other main fuels, gas, petrol and oil, are termed fossil fuels, since they are made from the fossilised remains of long-dead plants You’ve got gas! and animals. Carbon dioxide If we spread Australia’s is released whenever fossil of ction yearly produ fuel is burnt. In effect, burning CO2 over the surface of mainland Tasmania (area ‘unlocks’ carbon that has been 64 103 km2) it would form stored in the Earth for millions a three-metre high blanket of years, producing CO2 as it over the island. Each year Australia does so. Car exhausts, coal produces 542 600 000 and gas power stations and tonnes of greenhouse industry are leading producers gases, of which 70% is of carbon dioxide. The clearing CO2. One tonne of CO2 occupies 556 000 litres or of land (deforestation) by 556 m3 (about the volume burning forests has a double of a four-bedroom house). effect. Not only are greenhouse

a Burning fossil fuels is a leading source of excess CO2 in the atmosphere. b Land clearing releases stored CO2 into the air.

a

gases released when forests burn, but the destroyed trees are no longer available to store carbon dioxide. With our modern demand for fuel and electricity, humans are making more carbon dioxide—around 27 billion tonnes per year—than ever before. Some is absorbed, but the rest builds up in the atmosphere. Of this 27 billion tonnes of carbon dioxide output, about: • 7 billion tonnes are absorbed by oceans • 7 billion tonnes are taken up by forests • 13 billion tonnes accumulate in the atmosphere each year.

b

     #/PPM

Fig 8.1.3

UNIT

8.1

   

Other gases



Although carbon dioxide is the main greenhouse gas, others include the following: • Methane (CH4) is produced when vegetation breaks down in the absence of oxygen—e.g. in rice paddies and rubbish tips, and when cattle (or you!) burp or pass wind. Methane is 21 times more effective than carbon dioxide in blocking the escape of radiant heat from Earth. Luckily, less methane than carbon dioxide is produced. • Nitrous oxide (N2O) is produced from burning forests, car exhausts and artificial fertilisers. • CFCs or chlorofluorocarbons were, until recently, used in aerosol spray cans, refrigerators and air conditioners, to clean circuit boards and in the manufacture of polyurethane foam used in packaging. They are now banned in many countries and are becoming less commonly used worldwide. • Surface ozone is generated as part of photochemical smog, produced by the action of sunlight on motor vehicle and industrial pollution.

  

















9EAR   

#(PPM

   )CECORESAMPLES   



 9EAR

Source: CSIRO

Fig 8.1.4

Concentrations of carbon dioxide and methane between the years 1000 and 2004

265

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Global warming

CO2 and temperature over 420 000 years 650

Predicted level CO2 in 2100

600

Methane

60% 26%

Nitrous oxide

6%

Other

8%

Hanging around

Greenhouse gases remain Source: CSIRO 2002 National Greenhouse in the atmosphere for many Gas Inventory, released April 2004. years. Carbon dioxide persists for more than 100 years, and methane remains for 11 years. You can see why we need to take action now to reduce emissions.

Evidence in the ice Scientists collect ice cores from Antarctica by drilling into the ice. The deeper you go into the ice, the older the ice is, as new snow falls on top each year. When the snow falls, air bubbles are trapped in the ice. Analysis of these trapped gases reveals the amount of carbon dioxide present in the atmosphere in the past. So far scientists have drilled down 3.27 kilometres, which means we have data about carbon dioxide levels going back roughly 900 000 years. The graph in Figure 8.1.6 shows carbon dioxide levels in the Earth’s atmosphere for the past 420 000 years. It is normal for the level of carbon dioxide Fig 8.1.5

Part of an Antarctic ice core showing hundreds of tiny trapped air bubbles

550 500 450 400 Current level

350

20

300

10

250

CO2 (ppm)

Carbon dioxide

Australia produces approximately 1.4% of the world’s greenhouse gases—per person this makes it one of the world’s worst greenhouse-polluting countries.

Temperature (°C)

Australian greenhouse gas production (excluding land clearing)

200 0

150

–10 400 000

300 000

200 000

100 000

Years before present CO2

Fig 8.1.6

now

100

Predicted temperature rise by 2100

Temperature

Carbon dioxide levels over the past 420 000 years. The graph shows a prediction for the year 2100 if humans keep increasing carbon dioxide levels at the current rate.

to go up and down, but the amount of carbon dioxide in the atmosphere is now at its highest level ever. Notice that the Earth’s temperature changes when the amount of carbon dioxide in the air changes. The troughs on the temperature graph represent the ice ages, when average temperature was up to six degrees lower than today. The peaks are when warmer periods occurred on Earth.

The future Predicting the temperature rise

Killing Kyoto In 1997, the Kyoto Protocol called for developed nations to reduce emissions of greenhouse gases by 5% by 2012. The Australian Government has decided not to ratify the Kyoto Protocol because it is not in Australia’s economic interest to do so. The government is committed, however, to Australia’s target level agreed under the Kyoto Protocol. Over the period 2008–2012, greenhouse gas emissions will be limited to only 8% more than the levels emitted in 1990. To achieve this, all Australians will need to conserve energy.

Over the past 100 years or so, the Earth’s average surface temperature has increased by about 0.5°C and a further increase of between 1°C and 4°C is expected by the end of this century. Such a rise, though seemingly small, is enough to raise sea levels by an estimated half a metre—possibly up to a metre—and cause flooding of low-lying coastlines due to the increase of water in the oceans and melting of land ice. Many of the island nations in the Pacific and Indian Oceans would virtually disappear.

266

UNIT

8.1  YEARMEAN

4EMPERATUREANOMALIES#





n

n 2EFERENCEPERIOD n 









Source: Bureau of Meteorology

Fig 8.1.7











9EAR

Temperatures in Australia compared to the 1961–1990 average 6

See us while we’re still here!

a little above the waters The island nation of the Maldives is only constructed in the past of the Indian Ocean. Breakwaters have been waters. In 2004, the rising from Mali, l, capita ten years to protect its artificial island gular rectan Maldives completed construction of a is expected to which Mali, of lation popu the te that will accommoda marketing now is board t ‘go under’ in the next 40 years. The touris in the visit to ssible impo be will that ation the Maldives as a destin ), (USA ns Orlea New as future. Some cities around the world, such (UK) and on Lond as such s, Other level. sea are already below are threatened with every Venice (Italy), are just above sea level and them have been built for ct prote to rs Barrie tide. storm surge or kingfor Venice. Will this be ed New Orleans and London, and are plann en Sydney Heads! betwe wall a ine Imag ? future commonplace in the

Predicting local effects We do not fully understand the implications of global warming for society and the environment. Some regions will be drier, some wetter, some cooler and most will be hotter. We can also expect more storms, droughts, floods, hurricanes and temperature extremes.

Temperature change (°C)

5 4

range due to emissions uncertainty and climate response uncertainty

3

range due to emissions uncertainty

2 1 0 2000

2020

2040

2060

2080

2100

Year

Predicted global warming compared to 1990

Fig 8.1.8

Australian scientists predict that some of the following changes may occur: • The melting of much of the polar ice caps will raise sea levels, flooding coasts, cities and some entire island countries. • Liquid water expands slightly when warmed and so the oceans will expand, also raising sea levels, causing further flooding.

267

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Global warming • Increases in the numbers of wild storms and cyclones. Cyclones could move further south. • More droughts and heatwaves • More bushfires • Less rain and snow. Managing and saving water will become more important. • Habitats will change, causing the extinction of some animals and plants. • Increased temperatures may cause bacteria to grow faster, causing more disease in humans and other organisms. • Some plants may grow faster with higher temperatures. This would be good for farmers, but less rain may mean fewer plants grow and fewer varieties can survive. • Increased heat may cause more heat stroke and illness. Prac 2 p. 271

An angry beast

Historical records show that abrupt clima te change is not only possible—it is the normal state of affairs. The present warm, stable climate is a rare anomaly. Scientists need to learn as much as they can about the climate system to enable them to predict when the next abrupt shift in climate will come. In the words of geochemist, Dr Wallace S. Broecker, ‘the climate system is an angry beast, and we are poking it’.

Worksheet 8.1 Temperature change predictions Worksheet 8.2 Global warming revision

Will this become a more common sight in the future?

Fig 8.1.9

Fig 8.1.10

Antarctica covers twice the area of Australia.

El Niño

Antarctic meltdown

Another factor adding to weather extremes, possibly blurring the effect of global warming, is the El Niño effect. The water of the Pacific Ocean is warmer than other oceans. In a normal year, trade winds push this warmer water west towards the east coast of Australia, where high levels of evaporation cause normal amounts of rainfall. Every few years, the El Niño effect occurs, in which trade winds weaken or reverse, allowing warmer water to move towards the west coast of South America around Christmas time (El Niño means ‘Christ child’ in Spanish). The result is that Australia experiences drought and South America experiences increased rainfall.

If all the ice in Antarctica were to melt, sea levels would rise by 61 metres! If the rest of the ice in the world were taken into account, the rise would be 68 metres, with many inland areas becoming beachfronts! Antarctic statistics Area: 14.2 million square kilometres or 10% of Earth’s surface (double that of Australia) Ice thickness: average 2.5 kilometres, maximum 4.7 kilometres Elevation: average 2300 kilometres (Australia’s average elevation is 340 metres) Ice content: 90.6% of the world’s ice Fresh water: 70% of the world’s fresh water

%VAPORATIONOFWARM WATERPRODUCES STORMCLOUDSOVER 3OUTH!MERICA

4RADEWINDSFAILTOKEEP WARMWATERINTHEWEST

0ACIFIC/CEAN WATERCOOLER THANUSUAL

#URRENTHELPSTOPUSHWARM WATERTOWARDS3OUTH!MERICA

WATERWARMER THANUSUAL

COLDWATERTRAPPEDUNDERWARMWATER

The El Niño effect

268

Fig 8.1.11

UNIT

8 .1

UNIT

8.1 [ Questions]

Checkpoint The greenhouse effect 1 State the name of the main gas responsible for the greenhouse effect. 2 Explain why greenhouse gases are useful to the Earth. 3 Explain how greenhouse gases trap heat from the Sun. 4 Without greenhouse gases outline how the temperature of Earth would change.

The enhanced greenhouse effect 5 State the cause of the enhanced greenhouse effect. 6 Describe how the enhanced greenhouse may affect Earth’s climate.

Greenhouse gases: where do they come from? 7 List two causes of carbon dioxide build-up in the atmosphere. 8 Clearing land can enhance the greenhouse effect. Explain how. 9 State the amount of carbon dioxide now being released. 10 List all the greenhouse gases. 11 Use an example to clarify how long greenhouse gases persist in the atmosphere.

Evidence in the ice 12 Scientists use ice cores to determine the levels of greenhouse gases in the past. Explain how air becomes trapped in the ice. 13 Outline how the levels of carbon dioxide in air bubbles in ice cores have changed in the past 420 000 years. 14 Describe the relationship between the level of carbon dioxide in the atmosphere and the Earth’s temperature over the past 420 000 years.

Think 19 Methane blocks the escape of radiant heat much more than carbon dioxide. Explain then why carbon dioxide and not methane is considered the main greenhouse gas. 20 Imagine that all greenhouse gas emissions stopped today. What impact would this have on concentrations of greenhouse gases in the atmosphere? Justify your answer. 21 Discuss how global warming might cause greater rainfall. 22 Many believe that the technology exists to produce cars that travel twice as far on each tank of fuel. Assuming that such technology does exist, propose reasons why such cars are not being manufactured.

Analyse 23 Given adequate rainfall and suitable temperatures, wheat yields may actually increase in response to higher CO2 concentrations. Assess why. 24 Analyse whether population control would reduce global warming. 25 Permafrost is permanently frozen soil and is found in many resorts and villages in European mountain ranges. Predict a dangerous phenomenon that may occur in these regions as a consequence of global warming. 26 Use Figure 8.1.1 to identify which planet near Earth has a very enhanced greenhouse effect.

Skills 27 Copy and complete the following table to summarise the main greenhouse gases, their chemical formulas and sources.

The future 15 Identify the average temperature rise during the past 100 years. A 0.3°C B 1.0°C C 0.5°C D 5°C 16 The effects of global warming on the weather are largely uncertain. List three possible effects.

El Niño 17 Clarify what is meant by the term ‘El Niño’. 18 Outline two effects of El Niño on Australia.

Greenhouse gas

Chemical formula

Sources

28 The following question relates to the graphs of carbon dioxide and methane concentrations in the atmosphere in Figure 8.1.4. a Describe atmospheric levels of each gas between the years 1000 and 1400. b Identify when the amount of carbon dioxide and methane in the atmosphere suddenly increased.

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Global warming

c Estimate the rise in CO2 and CH4 concentrations between the years 1800 and 2000. d Calculate as percentages your answers to part c. 29 Construct a pie chart showing Australian production of greenhouse gases. 30 A single cow emits an amazing 280 litres of methane as burps and farts every day. The number of cattle in Australia (referred to as the ‘national herd’) is about 27 million. Estimate the volume of methane emitted by the national herd: a per day b per year 31 Carbon dioxide emissions per person for several countries are listed below. a Construct a column graph showing this information. b Use these figures to deduce which countries produce the most or least carbon dioxide per person. Country

Carbon dioxide emissions per capita, 2003 (tonnes per 1000 people)

Australia

18.9

United States

19.8

Canada

16.2

New Zealand Germany

8.3 10.2

United Kingdom

9.3

Japan

9.6

[ Extension ] Investigate 1 Research the climate projections of organisations like the CSIRO and the United States Environment Protection Agency and construct a poster that summarises their findings. 2 a Research the Kyoto protocol in order to summarise Australia’s position on this. b Write a letter to the government arguing whether or not Australia should sign the Kyoto protocol. Back your arguments with as much evidence as possible. 3 Research and construct a map showing the countries or islands most at risk of partially or totally disappearing due to rises in sea levels. 4 a Research El Niño, La Niña and the North Atlantic Oscillation (NAO).

270

32 Use the temperature change graph in Figure 8.1.8 to answer the following questions. a There are two pairs of lines on the graph due to two factors affecting temperature rise. Describe what they are. b Assess the range of the global average temperature rise (compared to 1990) in: i 2040 ii 2080 33 There is roughly one car for every two people in the United States (population 293 million people). In China (whose population is over 1300 million or 1.3 billion people) the figure is approximately one car for every 1400 people. There are currently about 500 million cars in the world. a Estimate how many cars are in the United States. b Estimate how many cars are in China. c Estimate how many cars would be in China if the car-to-person ratio was the same as that in the United States. d Analyse the consequences for global warming if China had the same car-to-person ratio as the United States.

b Explain how each of these is thought to be linked to global warming. c Evaluate the impact of these phenomena on the Australian climate.

Surf 5 Use the Australian Greenhouse Calculator to investigate the household gas emissions in your house by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. a Complete the investigation and write a report including bar graphs to show your household emissions compared to ‘green’ and ‘typical’ household usage. b Recommend actions that can reduce your greenhouse gas emissions.

Creative writing Greenhouse politics Several countries (including Australia) are reluctant to agree to definite targets for reduction of greenhouse gases because their governments think this could harm their economies. What does this mean? What is your opinion?

UNIT

8 .1

UNIT

8.1 [ Practical activities ] The greenhouse effect 2 Turn on the lamp and measure the temperature at regular intervals (e.g. every minute) for 10 minutes.

Aim To simulate the conditions Prac 1 Unit 8.1

required for the greenhouse effect

Equipment

Small cardboard box (e.g. a shoebox), 2 thermometers or temperature probes and datalogging equipment, sheet of glass or polythene plastic, lamp

Method 1 Assemble the apparatus as shown in Figure 8.1.12. Fig 8.1.12

3 Turn off the lamp, but continue to measure temperature for another 10 minutes. 4 If time permits, investigate the effect of an additional layer of glass or plastic.

Questions 1 Construct a graph showing temperature versus time for each section of the box. 2 Summarise any differences in the temperature patterns in each section. 3 Describe what takes the place of the glass or plastic sheet in the global greenhouse effect.

light source

4 Identify what adding another layer of glass or plastic represents if modelling the Earth. glass or perspex sheet

temperature probe

mark water levels

to datalogger

ice cubes

shoebox

water

ice

Icebergs

Fig 8.1.13

Aim To investigate the effect of melting ice on Prac 2 Unit 8.1

water levels

Equipment

Ice cubes (4–6), cold water, beaker, another identical beaker containing frozen water as shown in Figure 8.1.13.

Method 1 Place some ice cubes (representing icebergs) in the empty beaker. 2 Add the same amount of water to each of the two beakers and mark the water level on the outside of each beaker.

3 Allow each beaker to warm enough so a significant amount of ice melts in each. 4 Compare the water level to that initially marked on each beaker.

Questions 1 Deduce whether the melting of floating icebergs contributes to a rise in sea levels. 2 Deduce whether the melting of ‘land ice’ contributes to a rise in sea levels.

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UNIT

context

8.2 The ozone layer acts as a shield, absorbing around 90% of the harmful ultraviolet (UV) radiation from the Sun. Though we need some UV rays on our skin for production of vitamin D for healthy bones, high levels

What is ozone? Ozone is a gas that occurs naturally in the stratosphere at about 20 to 30 kilometres above the Earth’s surface. When people refer to oxygen, they usually mean the oxygen we use when we breathe. This type of oxygen, O2, consists of molecules each made of two oxygen atoms. Ozone, O3, is another naturally occurring form of oxygen, the molecules being made of three oxygen atoms. Ozone is a colourless gas that has a very pungent odour. Although ozone performs a vital role in the stratosphere, at ground level it is a pollutant. It is poisonous, causing eye, nose and throat irritation and lung damage, and has even been found to cause asthma.

increase the likelihood of skin cancers and eye damage. High UV levels also slow photosynthesis in plants. The ozone layer is vital to life on Earth. Its depletion poses a major threat to us all.

Ultraviolet light also splits ozone molecules, so ozone is continually being created and destroyed, with UV light being absorbed in the process. The region of the stratosphere in which ozone is thinly distributed is called the ozone layer.

Ozone creation in the atmosphere

Fig 8.2.2

56LIGHT OXYGENMOLECULES INATMOSPHERE

FREEOXYGENATOMS

NEWLYCREATED OZONEMOLECULE

oxygen atom

oxygen molecule (used when we breathe)

ozone molecule

Chlorofluorocarbons Fig 8.2.1

Oxygen atoms, O, may combine with each other to form oxygen, O2, or ozone molecules, O3.

The ozone layer Ozone is created when UV light splits oxygen molecules in the stratosphere into single oxygen atoms. These single oxygen atoms then join other oxygen molecules to form triplets of oxygen atoms, or ozone molecules. O2 + O

272

→ O3

Chlorofluorocarbons (CFCs) were invented in the 1920s and were once called ‘wonder chemicals’ because they were non-poisonous, odourless, stable and cheap to produce. Until recently they were used extensively as propellants for aerosol sprays and as coolant gases in refrigerators and air conditioners. They also made the bubbles within polystyrene and other foam packaging. We now know that CFCs are greenhouse gases and can destroy ozone. They do this by drifting upwards into the stratosphere

where they break down, releasing chlorine. Each chlorine molecule released this way reacts with ozone molecules, breaking them apart into oxygen molecules and oxygen atoms. The chlorine acts as a catalyst and is not part of any new substance formed. It is then free to go on and destroy more ozone molecules!

Common ozone-depleting gases and their average life in the atmosphere Chemical formula

Average life in atmosphere (years)

CFC 11

CCl3F

65

CFC 12

CCl2F2

110

CFC 13

CClF3

160

Freon (Halon 1301)

CF3Br

110

Nitrous oxide

N2O

130

Methane

CH4

11

Chlorine atoms continue a cycle of ozone destruction.

Fig 8.2.3

ozone molecule +

+ chlorine monoxide chlorine atom released by CFC molecule that has drifted into stratosphere

oxygen molecule

The hole story The ‘thickness’ of the ozone layer is measured in Dobson units or DU. Remember that the ozone is spread throughout a region of the stratosphere, so the term ‘thickness’ is somewhat misleading. In considering ozone layer ‘thickness’, we imagine all the ozone brought down to ground level and concentrated into a pure ozone layer. One hundred Dobson units correspond to a layer of pure ozone one millimetre thick at ground level. Remote-sensing satellites collect data on the amount of ozone in the stratosphere. If all the ozone molecules in the ozone layer were brought to ground level, it would form a layer averaging only 500 DU (5 mm) thick. A value of less than 220 DU is considered to be an ozone ‘hole’. The ozone hole situated over Antarctica was discovered by British scientist Dr Joseph Farman in 1985. The Antarctic ozone hole appears at around the end of winter in August each year, and is most pronounced by the end of October, when the day breaks after the Antarctic winter. At this time chlorine is very effective at breaking down ozone molecules. In November, winds carry ozone-rich air from other regions over the Antarctic, repairing the hole, but leaving lower ozone levels over Australia and New Zealand.

 chlorine released to attack another ozone molecule

Other ozone attackers CFCs are not the only ozone destroyers. • Nitrogen oxides also speed up ozone destruction. These gases are produced when jet aircraft engines burn fuel. Supersonic aircraft fly higher and inject these gases directly into the stratosphere. • The space shuttle releases ozone-attacking hydrogen chloride when its boosters fire during launch. Each launch releases 68 tonnes of hydrogen chloride gas (gaseous hydrochloric acid!) into the atmosphere.

 4OTALOZONE$OBSONUNITS

Gas

• Volcanoes also release hydrogen chloride. • Lightning causes reactions that split ozone molecules.

UNIT

8.2

      

Fig 8.2.4

-ONTHLYAVERAGESFOR/CTOBER 



 9EAR





Ozone layer ‘thickness’ over Antarctica in past years

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The ozone layer

 !REAMILLIONSOFSQUAREKM

   

AREAOF!USTRALIA



































9EAR

Fig 8.2.5

A graph of the size of the ozone ‘hole’ between 1979 and 2003, obtained from satellite-based instruments

A NASA satellite image of the recorded ozone ‘hole’, taken on 9 September 2000. Blue denotes regions of low ozone concentration.

Fig 8.2.6

The future One hundred nations agreed in the Montreal Protocol of 1987 to either stop manufacture of, or limit their use of, CFCs by 2000 or earlier. Despite most nations honouring their commitment to the protocol, levels of CFCs in the atmosphere are still rising, as it takes 10 years or more for them to reach the ozone layer. Unfortunately, many developing countries still use CFCs as they are cheap and easy to make. It is expected that ozone levels will return to normal by 2045.

UNIT

8.2

Worksheet 8.3 Analysing ozone

[ Questions]

Checkpoint What is ozone? 1 State where ozone can be found in the atmosphere. 2 Draw a diagram to demonstrate the difference between oxygen and ozone. 3 List two physical properties of ozone. 4 Outline the harmful effects of ozone.

The ozone layer 5 Use a diagram to demonstrate how ozone is formed in the upper atmosphere. 6 Define ‘ozone layer’.

Chlorofluorocarbons 7 List three properties of CFCs. 8 Use a diagram to describe how CFCs destroy ozone.

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Already there is some evidence that the reduction in the use of CFCs is starting to have an effect. Recent monitoring has indicated that the ozone hole is now not as big as the record hole in September 2000. It is hoped that international cooperation to repair the damage is working. Only time will tell the whole story. Meanwhile, apply that sunscreen!

9 List four ways in which CFCs have been used. 10 Identify the element in CFCs that does the actual damage to ozone. 11 Identify two other sources of the element identified in Question 10. 12 Apart from CFCs, describe other ways in which ozone can be destroyed.

The hole story 13 State the name and abbreviation of the units for measuring ozone. 14 Clarify how much ozone is described by 100 DU. 15 Identify the level of ozone measurement that indicates an ozone ‘hole’.

16 The Antarctic ozone hole varies throughout the year. Identify the time of year when the ozone layer is the thinnest.

The future 17 List the major outcome of the Montreal Protocol.

31 Construct a graph to estimate the ozone thickness we could expect if:

UNIT

8.2 a CFC use stopped immediately b CFC use continues at the present rate c CFC use increases

18 CFC levels in the atmosphere are still rising. Explain whether the levels will ever reduce.

Think 19 Contrast the effects of ozone in the stratosphere with ground level ozone. 20 List some harmful and beneficial effects of UV radiation. 21 A thinner ozone layer could affect food supplies. Propose reasons why. 22 The ozone layer occupies a space between 20 and 30 kilometres above the Earth. This is a layer 10 kilometres thick. Account for it also being described as 5 millimetres thick. 23 The term ‘ozone hole’ is not entirely correct. Explain why. 24 The ozone hole is not directly over Australia but we are still concerned about it. Discuss why. 25 High levels of UV can reduce the number of plankton (microscopic plants and animals in the oceans). Predict some possible consequences of this. 26 Identify a way of telling whether a spray can is ozone friendly.

Analyse 27 Use Figure 8.2.5 to identify: a the largest area of the ozone hole recorded. b when this record-sized hole occurred. 28 Explain why there are short lines extending on each side of the points on the graph in Figure 8.2.4. 29 Analyse Figure 8.2.5 to clarify the following: a the area of the ozone hole (in millions of square kilometres): i in 1982 ii in 1995 b when the ozone hole first measured: i 20 million square kilometres ii 150 DU c when the ozone hole became larger than Antarctica (which has an area of about 14 million square kilometres)

Skills 30 If all the ozone in an ozone layer that measures 220 Dobson units were brought to ground level, calculate the thickness of this pure ozone.

[ Extension ] Investigate 1 a Investigate specific types of eye damage caused by UV radiation. b Produce a brochure aimed at increasing the public’s awareness of the risk of UV exposure to the eyes. 2 TOMS is an instrument carried by a satellite to measure the ozone layer. a Conduct Internet research into TOMS measurements. b Examine the data presented and produce a news report commenting on the current status of ozone over Australia. 3 a Research details of the Montreal Protocol. b Summarise Australia’s participation in the agreement.

Action 4 a Construct and report on a survey of chemicals used as propellants in spray cans. b Assess whether the ozone layer is at risk from these products. c Ozone-friendly chemicals are being used in place of CFCs. Investigate two of these chemicals and evaluate their effectiveness.

Creative writing Ozone hole—fact or fiction? Articles have appeared in the press suggesting that the ozone hole is part of a natural cycle, and will disappear without the need for humans to take corrective action. Write an article in response, either supporting or arguing against these articles. Include an attention-grabbing headline and scientific evidence to back your opinions.

275

UNIT

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context

8.3 Sunlight is a form of radiation, as are radio waves. The term ‘radiation’ refers to energy in the form of fast-moving particles or electromagnetic waves. Nuclear radiation, as the name suggests, is radiation that comes from the nucleus of an atom. Controlled nuclear radiation can be very useful. It can treat medical conditions like cancer and can be used to generate electricity. It can also be extremely dangerous if it leaks accidentally from nuclear waste from medical use or from power plants.

Radiation and radioactivity There are 92 protons in the nuclei of uranium atoms. They are all positively charged and each one repels the others. Logic says they should fly apart and the nucleus should disintegrate into 92 parts. But this doesn’t happen. Protons in a nucleus stay together because of another more powerful force, called the nuclear force. Nuclear force acts between all particles in a nucleus and is more than sufficient to hold the nuclei of small atoms together. When a nucleus A radioactive discovery becomes very large, French scientist When however, the nuclear Henri Becquerel placed force might not be strong some uranium in a dark enough to hold the nucleus drawer containing some wrapped photographic together and bits might plates in 1896, he was break off. In doing so, surprised to find later that the nucleus gets smaller the plates had become . He deduced that they foggy and more stable. Nuclear have been affected by must radiation is the energy something coming from the and the particles that are uranium, something able to released from the nucleus penetrate the wrapping. He had observed one effect of in its break-up. An element radioactivity. whose atoms emit nuclear radiation is said to be

276

radioactive. Uranium and most of the elements after it in the periodic table (atoms of higher atomic number) are radioactive.

Atoms and isotopes Atoms with the same number of protons belong to the same element. Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei. For example, all lithium atoms have three protons. Ninety-three per cent of all lithium atoms have three neutrons. The rest have four. Hence lithium has two isotopes, which we can write as: MASS NUMBER = number of protons + neutrons

6 3

Li

and

7 3

Li

ATOMIC NUMBER = number of protons

Uranium atoms always have 92 protons. The most common isotope has 146 neutrons, a less common isotope has 143 neutrons and a few have 142 neutrons. Hence we can write them as: 238 92

U

235 92

U

234 92

U

Not surprisingly, a radioactive isotope is called a radioisotope. When referring to a radioisotope, we often give just its mass number. Because all uranium atoms are radioactive, the radioisotopes of uranium could be written as uranium-234, uranium-235 and uranium-238. Actinium, astatine, carbon, francium, thorium, protactinium, polonium, radon and radium are all radioactive elements and, like uranium, occur naturally. Many synthetic or ‘artificial’ elements are also radioactive. Hydrogen has three isotopes. Approximately 99% is ‘normal’ (stable and not radioactive), 1% is deuterium (stable but toxic in high doses) and a few are tritium. Tritium is unstable—it is a radioisotope.

Three isotopes of hydrogen

HYDROGEN  HYDROGENOR PROTIUM  

HYDROGEN  DEUTERIUM  

( +EY

HYDROGEN  TRITIUM  

(

0ROTON

Fig 8.3.1

.EUTRON

Marie and Pierre Curie

(

%LECTRON

n husband Pierre Polish-born Marie Curie and her French-bor uranium and with work ering Curie are famous for their pione use the term to first was Marie nts. eleme g mittin other radiation-e element the for name the us ‘radioactivity’, her birthplace gave name for the e becam me surna s’ Curie the and polonium, Po, Nobel Prize for physics curium, Cm. The couple shared the 1903 e the first person to becam Marie , 1911 In . uerel with Henri Becq the Nobel Prize for ed award win two Nobel Prizes when she was ium. Pierre was polon and m radiu of very disco her chemistry for 1906 and Marie in le vehic n killed in an accident with a horse-draw ng so closely worki of t resul a as bly proba , 1934 in died of leukemia life. her of most for with radioisotopes

Three types of nuclear radiation When a radioisotope emits radiation, it usually transforms into another element. We say it has undergone radioactive decay. There are three main types of radioactive decay, each emitting a different type of radiation: • alpha radiation • beta radiation • gamma radiation.

UNIT

8.3

Alpha radiation One way in which radioactive nuclei can get smaller and more stable is by throwing out a cluster of two protons and two neutrons. This cluster is known as an alpha particle (denoted by α), but is really just a helium nucleus, 42He. Uranium-238 emits an alpha particle and in doing so decays into thorium-234, as shown in Figure 8.3.3. Fig 8.3.3

Alpha decay

uranium-238

238 92

U

alpha particle

thorium-234

234 90

Th

+

4

α

2

The equation is balanced, with the same number of protons and neutrons on each side. You can check by adding up the mass numbers on the product side of the reaction: they add up to 238, the same as we started with. Likewise, the atomic numbers add up to 92. Alpha particles move at speeds of up to one-tenth the speed of light. Alpha decay can be thought of as nuclear fission, since a parent nucleus splits into two daughter nuclei.

Beta radiation

Fig 8.3.2

Marie Curie

When there is an imbalance of neutrons and protons in a nucleus, a neutron may change into a proton and an electron. The newly created electron is called a beta particle (denoted by β), which is then emitted from the nucleus. Carbon-14 is a radioisotope that decays into a new element, nitrogen, by emitting a beta particle from its nucleus. We can represent this decay as in Figure 8.3.4.

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Nuclear radiation: good or evil? Fig 8.3.4

Beta decay carbon-14

alpha particle

nitrogen-14

14 6C

14 7

N

+

beta particle

+

0 β –1

beta particle gamma ray

An extra proton has been created from a neutron, so the atomic number of the atom increases from 6 to 7, meaning that a new element has been formed. The mass number of the beta particle is zero since it really is just an electron, and they have negligible mass. The –1 at the bottom indicates the negative charge on a beta particle. Once again, the atomic numbers give the same total (6 = 7 + –1). Beta particles move at speeds of up to nine-tenths the speed of light and so pass through materials better than alpha particles.

thick sheet of paper

1 mm sheet of aluminium several centimetres of lead or concrete

Fig 8.3.6

Gamma radiation Both alpha and beta radiation consist of particles. Earlier it was mentioned that radiation may also be in the form of electromagnetic waves or rays. Sometimes when an alpha particle or beta particle is emitted from a nucleus, the new nucleus is still unstable, and emits extra energy in the form of a gamma ray to become more stable. A gamma ray (denoted by γ) is a burst of high-frequency electromagnetic radiation that has no mass or charge. Gamma rays are more powerful than X-rays. The beta decay of iodine-131 is accompanied by gamma emission as shown in Figure 8.3.5. Like all electromagnetic radiation, gamma rays move at the speed of light (300 000 km/s). Their incredible speed means they penetrate materials even more than beta particles. Fig 8.3.5 iodine-131

Gamma decay

131 53

278

I

131 54

Xe

+

0

β –1

Worksheet 8.4 Uranium decay series

Half-life The time required for half of the atoms in any given quantity of a radioactive isotope to decay is the halflife of that isotope. Each particular isotope has its own half-life.

Some common radioisotopes and their half-lives Radioisotope

Half-life

Radon-222

4 days

Iodine-131

8 days

Cobalt-60

5.3 years

beta particle

Americium-241

460 years

gamma ray

Carbon-14

5730 years

Plutonium-239

24 000 years

Uranium-238

4.5 million years

xenon-131 +

The penetration abilities of alpha, beta and gamma radiation. Alpha particles are stopped by a thick sheet of paper or human skin; beta particles are stopped by a thin sheet of aluminium; and most gamma rays are stopped by a thick layer of lead or concrete, though some still get through.

+

0

γ 0

Effects of radiation Alpha, beta and gamma radiation are sometimes called ionising radiation because of their ability to ionise (knock electrons off) atoms or molecules, causing them to become charged. Charged atoms or molecules are called ions. Alpha particles have after 3 after 1 after 2 high ionising ability, while beta and half-lives half-life half-lives gamma radiation have low ionising ability. Because ions attract other The number of atoms of a radioactive element in a sample halves Fig 8.3.7 atoms and molecules, they are more after each half-life. How many radioactive atoms would you expect likely to become involved in chemical to remain after one more half-life? reactions. If these radiations hit body cells, they may cause chemical reactions that can: A 1 kg sample of pure uranium-238 would decay • destroy cells—this may appear as over time to leave the following amounts: a ‘burn’. Cells on that site may not be replaced. Time Mass of U-238 in sample • cause abnormal cell growth—this may appear as a tumour or 0 years 1 kg Radioactive water cancer. In Fujian province in 4.5 million years 500 g

China, millions of people obtain drinking water from wells in granite rock. Radon-222 leaches from the granite into the water, making it 150 times more radioactive than water in more developed counties. Not surprisingly, cancer rates in the region are the highest in China.

9 million years

250 g

Measuring radiation

13.5 million years

125 g

18 million years

62.5 g

Nuclear radiation may be detected using a Geiger counter. Gas molecules within a tube are ionised by any radiation that enters. The resulting ions produce a pulse of electrical current that is fed to a small speaker and counter. The speaker makes a clicking sound with each pulse of current. The activity of a radioactive sample is the number of disintegrations per second, and gives an indication of the number of radioisotopes present. People working in areas of high radiation levels, such as at nuclear facilities or medical staff, wear special detectors called dosimeters.

Prac 1 p. 284

Sources of nuclear radiation Nuclear radiation may be produced artificially by bombarding atoms with neutrons or other subatomic particles. Most radiation we receive comes from natural sources, however. The Earth is continually being struck by solar radiation and cosmic radiation produced, for example, by collapsing stars. Terrestrial radiation originates from substances in the Earth’s crust. The decay of natural underground uranium produces radioactive radon gas, which we inhale in the air we breathe.

Source

Approximate percentage of annual radiation received

Terrestrial (from natural radioactive underground deposits)

75%

Solar and cosmic (from space)

13%

Medical (from medical procedures and X-rays)

10%

Manufactured (from burning coal, electromagnetic devices, fallout from weapons testing)

UNIT

8.3

2%

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Nuclear radiation: good or evil?

>>> Radioactive money!

Uses of nuclear radiation Nuclear medicine Nuclear radiation is not always bad. Radioisotopes can cause cancers but are also used in nuclear medicine to diagnose and treat them. Radiotherapy involves directing high, localised doses of radiation to cancer sites by using an external focused beam or a surgical implant, or by swallowing a radioactive medicine. Rapidly dividing cells such as cancerous cells are more sensitive to nuclear radiation than other cells—

Fig 8.3.9 Fig 8.3.8

Between 1945 and 1989 Germany was divided into two separate countries (East and West Germany). As part of the ‘cold war’, East German secret police used radioactive scandium-46 to invisibly label political opponents so they could be tracked using hidden Geiger counters that vibrated in response to radioactivity. Labelling occurred in a variety of ways. Floors were treated, as were documents and money. This practice exposed victims and anyone near them to dangerous levels of radioactivity, since scandium-46 is both a beta and a gamma emitter. Radioactive cash in your pocket would both give you away to the secret police and very likely reduce your fertility!

This device directs gamma rays from cobalt-60 onto cancerous growths within the body.

A researcher using a Geiger counter to monitor radiation

There are several units for measuring nuclear radiation doses. One of the main units is sieverts (Sv). The table below refers to millionths of a sievert, or microsieverts (µSv). A dose measured in sieverts or microsieverts takes into account the energy per kilogram ‘delivered’ by nuclear radiation and its ability to ionise. You receive a dose of about 300 µSv annually from cosmic radiation, and 1400 µSv from terrestrial radiation.

Biological effects of nuclear radiation

280

Dose (µSv)

Short-term effects

Long-term effects

Less than 10 000

None

Possible effect on unborn babies

10 000 to 100 000

None

Unborn babies likely to contract leukemia

100 000 to 500 000

Cell damage

Increased likelihood of cancer (including leukemia)

500 000 to 1 000 000

Radiation sickness—symptoms include nausea, vomiting, diarrhoea, hair loss, internal bleeding; white blood cell count drops

Greater likelihood of contracting cancer

1 000 000 to 8 000 000

Severe radiation sickness, possible death within a month

Very high probability of developing cancer

they self-destruct if their DNA is damaged. Unfortunately, Golden poo! The source of the balls some nearby healthy cells are of matter washing up also killed, leading to short-term on Sydney beaches was illness and side-effects. uncertain. Did they come Nuclear medicines are also from sewage or another source such as waste used to give images of internal from a passing tanker? organs, blood vessels and bones. Scientists ‘labelled’ Gamma-emitting radioactive outgoing sewage with radioactive gold-198, a tracers are swallowed or injected radioisotope with a half-life and tend to collect in particular of 2.7 days. Soon after, parts of the body. They are then the balls washing up on beaches were found to be detected by a gamma ray camera radioactive, showing that placed outside the body. The they indeed came from gamma rays coming from inside discharged sewage. the body are then converted to an image. For example, iodine-123 concentrates in the thyroid gland and so may be used to help diagnose thyroid conditions.

UNIT

8.3 Carbon dating All living things contain radioactive carbon-14. It is continually decaying but is constantly being replenished. While the organism is alive the percentage of carbon-14 it contains will remain constant.

Industrial applications

Smoke detectors contain a small amount of americium241. Alpha particles emitted by the americium ionise the air and create a small current, which keeps the alarm from sounding. When smoke enters, the ions are attracted to the larger smoke particles, and move more slowly. The reduced current is then unable to stop the alarm sounding, and a high-pitched sound is emitted.

Radiation may be used to check the thickness of materials.

sheet of metal

rollers

Fig 8.3.11

Samples of bone being prepared for radiocarbon dating

When an organism dies, the amount of carbon-14 reduces due to its continuous beta decay into nitrogen14. In contrast, the amount of normal non-radioactive carbon (carbon-12) stays constant. The approximate age of once-living matter can be determined by comparing the amounts of both types of carbon in it and then using the graph shown in Figure 8.3.12.

110 100

Fig 8.3.10

beta or gamma source

radiation detector

Carbon–14 atoms remaining (%)

Smoke detectors

Nuclear radiation can be added to liquids or gases flowing in pipes to trace leaks or check for fractures. The thickness of metal or rubber sheets can be verified by measuring the amount of radiation transmitted through the material.

90 80 70 60 50 40 30 20 10 0

roller control

Time (years) Half-lives

5730

1

11460 17190 22920 28650

2

3

4

34380 40110

5

Decay graph for carbon-14

6

7

45840

8

Fig 8.3.12

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Nuclear radiation: good or evil? Dirty bombs

Other uses

A dirty bomb is not a traditional nuclear bomb. It is basically any bomb that has radioactive material such as nuclear waste in it. This radioactive material is spread as very fine particles across large areas when the bomb explodes, floating in the air and contaminating water and food. It would be impossible to clean up the radioactive material and it could cause contamination problems for hundreds of years. There has been talk of terrorist organisations using dirty bombs and therefore it is important that radioactive waste is tightly controlled to ensure it does not fall into the wrong hands.

Food that has been exposed to gamma radiation lasts much longer than normal, without becoming radioactive itself. Bacteria and fungi are killed by the radiation, but vitamins may also be destroyed and new chemicals might be created within the food. For this reason, many consumers are uncomfortable with the idea of food irradiation. Nuclear radiation is also used to sterilise medical and surgical equipment. Needles used by diabetics are sterilised in this way. Radioisotopes can be injected into or fed to animals in order to trace their movement using radiation detectors, or to trace the movement of nutrients through the food chain. Fertilisers with added radioisotopes are used to study the uptake of nutrients by crops. Radioactive material left over from nuclear power generation is used to make nuclear bombs and ammunition that can pierce the heavy armour of tanks.

UNIT

8 .3

[ Questions ]

Checkpoint Radiation and radioactivity 1 Copy and modify the following statement so it is correct. Radiation can be fast moving ________ or electromagnetic ________.

Half-life

2 State the type of force that acts on particles in the nucleus of an atom to: a hold them together b push them apart

Atoms and isotopes 3 Define ‘radioisotope’.

11 Iodine-131 has a half-life of 8 days. Calculate the amount left from a 2 kg sample after: a 8 days b 16 days c 24 days

Sources of nuclear radiation

4 List four radioactive elements. 5 Explain why large atoms are more likely to be radioactive than small ones. 40 20

6 Identify which atom is an isotope of atom X. Is it atom 42 42 22Y or atom 20Z?

Three types of nuclear radiation 7 List the three main types of radiation. 8 Identify the type of nuclear radiation that: a is the same as in a helium nucleus b can pass through paper but not aluminium c is not made of particles d requires the conversion of a neutron into a proton and an electron. e is the product of nuclear fission. 9 Contrast the speeds and penetrating abilities of the three radiation types.

282

10 Clarify the meaning of ‘half-life’.

12 List two natural ways in which radiation is produced. 13 Radon gas is present in our atmosphere. Outline how it is produced.

Effects of radiation 14 Explain why ions produced by radiation are more likely to affect our cells than other atoms. 15 Nuclear radiation may be detected in several ways. Describe two of these. 16 State the size of the radiation dose you are likely to receive over the next year.

Uses of nuclear radiation 17 List two uses of nuclear radiation in industry. 18 State an advantage and a disadvantage of food irradiation. 19 Describe what is meant by a ‘dirty bomb’.

Think 20 Gold-198 does not exist naturally. Describe how it can be made. 21 Radioactive decay of uranium in the ground produces radon gas, which bubbles up through the ground to reach the air. Radon in turn decays to produce polonium, an alpha particle emitter. Although alpha particles cannot penetrate the skin, uranium-miners are at increased risk of radiation diseases. Account for this increased risk. 22 Explain why radiotherapy harms cancer cells more than healthy cells. 23 Outline how nuclear radiation is used to obtain images of internal organs.

Analyse

UNIT

8.3 29 Evaluate the danger of the following doses of radiation: a 1 microsievert received in a short burst b 500 microsieverts received over the course of a year c 100 000 microsieverts received in a short burst

Skills 30 Copy the following table and summarise the details for each of the main types of nuclear radiation. Alpha particles

Beta particles

Gamma rays

Sketch Charge Mass Speed Penetration ability (High, medium or low)

Stopped by 24 Would an alpha particle emitter be suitable Ionising ability for measuring the thickness of cardboard in a packaging manufacturing plant? Justify your answer.

25 Propose two reasons why alpha particles are never injected for medical diagnosis. 26 Propose a reason why hair cells are often damaged during radiation therapy. 27 In the Gulf War, ammunition made of depleted uranium was used to pierce tanks. Burning uranium from such ammunition forms tiny particles that may be inhaled. Explain why this is of concern even today, more than ten years after the war. 28 Explain why young children are more likely to be affected by radiation doses than adults.

[ Extension ]

31 Modify the following nuclear reactions so that they are complete: 4 a 218 84Po → ___ Pb + 2α 24 b 11Na → ___ Mg + –10β c 133 54Xe → ___ Xe + γ 59 d 26Fe → ___ Co + –10β + γ 32 Calculate the fraction of a sample of pure radon-222 that would remain after 12 days.

33 Assess whether the radioactivity of a sample of plutonium would be very different after 10 years. 34 Construct a pie graph, a stacked bar graph or a column graph showing the percentage of radiation we receive from major sources. 35 A fossil is found to contain one-sixteenth of the amount of carbon-14 of a living specimen. Calculate the age of the fossil.

Investigate 1 Research the lives of the Curies and use a time line to summarise key events in their lives. 2 a Research other methods of nuclear radiation detection such as film badges or cloud chambers. Use a labelled diagram to explain the workings of one method.

b There are a large number of units for measuring nuclear radiation including gray, rem, rad, curie, becquerel and roentgen. Explain what one of these really means, and give the abbreviation for the unit. 3 Choose one example where a PET scan is used. With the aid of a diagram, explain how it works.

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Nuclear radiation: good or evil?

4 a The Shroud of Turin has been claimed to be the burial cloth of Jesus Christ. Explain how carbon dating has been used to date the Shroud. b Use this evidence to make your own deduction about the age and authenticity of the Shroud. 5 a Investigate dirty bombs and how they work. b Discuss whether this type of terrorist attack is likely, supporting your information with evidence.

UNIT

8 .3

Action 5 Simulate decay of a radioisotope using computer software or a model to present your information in visual form. 6 a Arrange an excursion to ANSTO to investigate the products made there. b Working in small groups, give oral presentations on a range of ANSTO products.

[ Practical activity ] Half-life of polonium-218

Prac 1 Unit 8.3

The table below shows the activity of a sample of polonium-218 measured at 1 minute intervals for 20 minutes.

4 Assess how long after this it took for the activity to halve again. 5 Assess how long after this it took for the activity to halve a third time.

Questions 1 Construct a graph showing activity (vertical axis) versus time (horizontal axis). 2 Draw a curve of best fit through the data.

6 Calculate the average of the half-lives determined in questions 3, 4 and 5 above. 7 Predict the count rate at the end of another 30 seconds.

3 Use your graph to calculate the time it took for the initial activity to halve.

Time (mins) Activity (counts per minute)

284

0

1

2

3

200 161 127 115

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

86

67

56

33

31

22

17

15

13

11

7

7

5

4

3

2

2

UNIT

context

8. 4 The world has an impending ‘energy crisis’. We need to quickly find alternative sources of energy, as fossil fuels will run out in the next 50 years if we continue to use them at current rates. Many countries have invested heavily Comparing wastes in nuclear power, and although

Generating nuclear energy Fission

Australian consumption of electrical energy is about 8000 kilowatt-hours per person every year. To generate this much electricity, 3000 kg of black coal is required. This produces wastes including up to 500 kg of ash as well as 8000 kg of carbon dioxide and sulfur dioxide—enough to fill three Olympic-sized swimming pools. In comparison, only 30 to 70 kg of uranium ore is required to generate the same amount of electricity, producing just 0.006 kg or 6 grams of highly radioactive waste.

Australia has no nuclear power stations it is one of the biggest suppliers of uranium for them. Nuclear energy is an alternative energy source to fossil fuels. Although not a renewable resource, it provides vast amounts of energy from a small amount of fuel. For example, 1 kilogram of uranium ore can produce as much energy as 100 kilograms of coal and does so with far less of the greenhouse gas carbon dioxide being released. Is nuclear power the future of energy, or should we be investing in other alternatives?

Fig 8.4.2

Einstein predicted that nuclear energy could be calculated using the equation E = mc2.

When uranium-235 absorbs a stray neutron, it becomes extremely unstable, and something very interesting happens. Instead of emitting an alpha or beta particle or a gamma ray, the uranium-235 isotope splits into two smaller atoms along with two or three neutrons. Heat energy is released in the process. The splitting of an atom is called fission. Lone or ‘stray’ neutrons are produced this way in the atmosphere by cosmic rays.

fission fragments + heat energy

E = mc 2

neutron absorbed

neutron 235

U

Fig 8.4.1

very unstable nucleus

Nuclear fission

Einstein’s famous equation

is often quoted, but what doe s it really mean? In normal chemical reaction s, mass always stays the sam e. Not so in nuclear fission, how ever! During nuclear fission, there is a slight loss of mas s. Einstein found that this lost mass is converted to energy, and that the amount of energy created (E) is equal to the lost mass (m) multiplied by the speed of light (c) squared. Alth ough only around 0.1% of each tiny nuclear mass is con verted to energy, the energy released quickly builds up due to the incredibly large number of atoms in any radioactive sample (1 gram of uranium-23 5 contains 2.5 billion trillion atom s!), and the fact that the speed of light equals 300 000 000 metres per second.

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Energy crisis Chain reaction Normally the extra neutrons released by the fission of uranium-235 escape the sample or are absorbed by the more stable and more numerous uranium-238 atoms (natural uranium contains only about 0.7% uranium235). A chain reaction will occur, however, if these neutrons strike other uranium-235 atoms. This causes more fission and more neutrons, which then hit more uranium-235 atoms, which then release even more neutrons ... and so it goes on and on. Huge amounts of energy are released in a fraction of a second. For a chain reaction to ‘take off’, the uranium sample needs careful preparation by either: • enriching it so that it contains 2.5% or more uranium-235 • forming it into a shape to prevent too many neutrons escaping without first interacting with other atoms (spherical is good), or • making it large enough (the required mass is called the critical mass). A fission chain reaction

A fatal slip On Tuesday 21 May 1946 during a critical mass experiment in a secret laboratory in New Mexico, USA, Louis Slotin was gradually moving two halves of a beryl lium-coated plutonium sphere closer together, using a screwdriver to stop them coming suddenly too close. Tragically the screwdriver slipped, allowing the two masses to come together. The plutonium went supercritical, causing a mass ive increase in fission. There was a blue flash as air in the room was ionised by gamma and neutron radiation and Slotin ’s Geiger counter went ‘off the scale’. He knew he had receiv ed a lethal burst of radiation, and heroically shielded his nearb y colleagues while he quickly separated the two plutonium mass es. He died a few days later. 12.5 R

12 R .3

6 R 9 7. R

Fig 8.4.3 Fig 8.4.4

fission fragments

uranium-235

neutron

heat energy released

Nuclear bombs A nuclear bomb uses uranium enriched so that over 90% of the sample will be uranium-235. A massive and uncontrolled chain reaction results. The bomb dropped on the Japanese city of Hiroshima on 6 August 1945, nicknamed ‘Little Boy’, contained two half-spheres of 90% pure uranium-235.

286

A sketch used by doctors to determine the radiation doses received by those near Slotin’s accident

Each piece by itself was smaller than the critical mass needed for a chain reaction, but when forced together by an explosive charge, they formed a supercritical mass which then exploded.

Nuclear reactors A nuclear reactor is like a controlled nuclear bomb, but uses uranium that has been enriched to about 2.5% uranium-235. To prevent an uncontrolled chain reaction, control rods made of neutron-absorbing boron or cadmium are used to ‘soak up’ neutrons so that on average only one escapes from each fission to go on to cause another fission. Heat generated by nuclear fission in a reactor core is used to generate steam, which spins a turbine and produces electricity in the same way as conventional electricity generators (see Unit 3.1). Nuclear reactors currently provide around 17% of the world’s electricity. Several countries obtain about half their electricity from nuclear power plants. Submarines and space probes often use on-board nuclear reactors.

Unit

8.4 High pressure water transfers heat to a separate water system where it forms steam to spin a turbine.

Control rods absorb neutrons to prevent an uncontrolled chain reaction.

pump

turbine

Fuel rods contain uranium oxide fuel pellets.

Water surrounding the fuel rods slows down reactor core neutrons so they are more likely to be absorbed and cause fission. Neutrons that are not slowed down tend to ricochet off uranium atoms. A substance that slows neutrons is called a moderator. Another water circuit acts as a coolant to remove excess heat and turn steam back into water.

Fig 8.4.5

A nuclear reactor, showing the main components



Country

Electricity generated by nuclear power plants



Australia

0%



Britain

21%



USA

22%



Japan

24%



South Korea

48%



Sweden

52%



France

73%



Australia’s only nuclear reactor—the HIFAR reactor at ANSTO in southern Sydney—is a small reactor used for the production of nuclear medicines such as those discussed in the previous unit.

Nuclear dangers Nuclear power at one time seemed like the answer to the world’s energy needs, but the initial enthusiasm has been tempered by a series of accidents and the problem of how to safely store deadly waste products.

Australia’s nuclear research reactor at ANSTO (the Australian Nuclear Science and Technology Organization)

Fig 8.4.6

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Energy crisis

Radioactive coal

Nuclear accidents There have been several well-documented accidents at nuclear power plants in which radiation has been released into the environment. The most dramatic occurred at Chernobyl in the Ukraine (then part of the USSR, now an independent country) on 25 April 1986. Automatic safety systems were turned off during a test of reactor number 4, to measure the turbine’s power output as it slowed after its steam supply had been shut off. When power levels fell dangerously low, engineers withdrew most of the control rods. Fuel rods then heated up and turned the moderator water into steam. The steam absorbed fewer neutrons, causing a power surge that heated the fuel rods even more. The super-heated fuel rods then exploded, and in turn caused a steam explosion which lifted the 1000 tonne steel-and-concrete lid off the top of the reactor.

A coal-fired generator A five-kilometre-high plume of es more radioactivity releas debris released more radioactivity into the environment than into the atmosphere than 100 a nuclear power station— Hiroshima bombs. The explosion unless there’s an accident! started a fire that burned for five days. There were 31 immediate casualties. Nearby Belarus lay downwind of Chernobyl and much of it remains uninhabitable. Cancer rates there have also risen dramatically and the long-term toll may reach many thousands. A gigantic concrete structure called a sarcophagus was built around the damaged reactor to help contain the radiation, although this structure itself is now decaying and needs replacement.

Nuclear waste disposal Nuclear waste is classified into three levels. • Low-level waste does not require a great deal of protective covering and includes things like air filters and gloves used by people such as nuclear power plant workers and hospital staff who handle radioactive substances. Low-level waste may be incinerated, stored in strong containers or buried at special sites. • Intermediate-level waste is more radioactive and includes things like reactor parts. It is typically packaged inside cement within steel drums and buried in deep trenches. • High-level waste is lethal and consists of wastes from either used fuel rods or generated from reprocessing the rods to obtain uranium and plutonium. Used fuel rods are stored under water for several years while they cool and their radiation levels drop before being reprocessed or disposed of. High-level waste is melted to form glass blocks and may be stored underground in stainless steel drums.

Two sides of the story

Deadly speck If inhaled, a pinhead-sized speck of plutonium-239 is enough to cause lung cancer!

Fig 8.4.7

288

The Chernobyl nuclear power station shortly after disaster struck in 1986—many clean-up workers, photographers and their pilots died in the years after the accident from cancers caused by massive doses of radiation received as they worked around the devastation.

Because nuclear waste products can remain radioactive for many thousands of years (the half-life of plutonium is 24 000 years), there is plenty of time for something to go wrong. Deterioration of storage containers or natural disasters could both cause leakage into the environment. Many people argue that the consequences of potential accidents involving

nuclear waste or nuclear power plants are just not worth the risk. Others argue that damage being done to the environment (e.g. pollution and global warming) from the use of fossil fuels is greater than that resulting from the use of nuclear energy. Coal miners suffer more ill-health as a result of their work than nuclear workers. Oil spills from supertankers regularly kill huge numbers of marine and bird life. There are risks associated with both fossil fuels and nuclear power. Maralinga meltdown Between 1952 and 1957 What do you think?

Fig 8.4.8

A nuclear explosion at Maralinga in South Australia in 1956. Dangerous levels of radioactivity remain.

Australia also needs to consider its involvement in dealing with nuclear waste. As we supply much of the world’s uranium, should we be responsible for helping to deal with the waste produced? How much Australian uranium has already been used for illicit purposes such as nuclear weapons?

UNIT

8.4

Worksheet 8.5 Nuclear devastation

Alternative energy sources There are many alternatives to fossil fuels and nuclear energy that will meet our energy needs in the future.

the British government conducted a series of tests, setting off twelve major nuclear explosions Fusion and hundreds of smaller One of those alternatives is in fact another form of ones at Maralinga in South Australia, forcing nuclear energy! Nuclear fusion is when two small the relocation of the nuclei combine or fuse, releasing an enormous local Aboriginal people. amount of energy as they do so. An example of Britain assured Australia nuclear fusion is the combination of a deuterium that it had cleaned up the Maralinga site by 1967. In nucleus and a tritium nucleus to form helium. 1984 Australian scientists measured radiation more An example of a nuclear fusion reaction Fig 8.4.10 widely spread and at levels 10 times higher than predicted. The clean-up tritium (13H) of the site was finally completed in 2000 with financial contributions from Britain. One process helium (42He) used in the clean-up, in-situ vitrification (ISV), involved generators heat released providing up to 5 megawatts of power to electrodes implanted in nuclear waste pits to melt waste into huge glassy 2 neutron (01n) deuterium (1H) masses. This prevents nuclear waste from leaching into surrounding soil and eliminates the need for excavation or Nuclear fusion has a couple of big attractions—no removal of hazardous radioactive waste products are created, and there is a material.

Four giant electrodes can be seen at the top of the in-situ vitrification equipment. The large pipe connected to the truck channels exhaust gases from the melt for analysis.

Fig 8.4.9

vast supply of deuterium in the ocean. But there’s a catch! Temperatures of millions of degrees are needed to force two positively charged nuclei together and temperatures of hundreds of millions of degrees are needed to keep it going. It is nuclear fusion reactions that power the Sun. Even if we could generate a sustained fusion reaction, how could it be contained? Current research involves the use of a powerful toroidal (doughnut-shaped) magnetic field within a device called a tokamak to hold the superheated deuterium. The word ‘tokamak’ is from the Russian

289

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Energy crisis An experimental tokamak fusion reactor

Fig 8.4.11

Fig 8.4.12

Spherical ball of plasma (pink) inside a tokamak

Other alternatives superheated deuterium contained within a magnetic field

word for toroidal. If the costs and difficulties involved in sustained fusion generators are overcome, fusion may provide the bulk of the world’s energy in the future.

290

Other alternative sources of energy that offer potential for the future include: • solar • wind • hydro-gravitational, wave or tidal • geothermal • fuel cells • bio-batteries. Some alternative energy sources for the future. A: hydro, B: wind, C: geothermal, D: solar

A

B

C

D

Fig 8.4.13

UNIT

8 .4

UNIT

8.4 [ Questions ]

Checkpoint Generating nuclear energy

16 With the aid of diagrams, demonstrate why a sphere is a more effective shape than a flat sheet for a critical mass of enriched uranium.

1 Use a diagram to explain the term ‘nuclear fission’.

17 Identify a word that means ‘less than critical mass’.

2 In a chain reaction, huge quantities of energy are released. Outline how this happens.

18 Identify two countries that would be most affected if uranium ceased to be mined and processed.

3 Describe how a nuclear bomb works.

19 Explain why Australia has a nuclear reactor.

Nuclear reactors

20 Propose a meaning for the term ‘magnetic bottle’.

4 Compare a nuclear bomb with a nuclear reactor. 5 Describe how an uncontrolled chain reaction is prevented in a nuclear reactor. 6 Nuclear fission reactors produce lots of energy. Identify three situations where a nuclear reactor may be used. 7 Identify which part of a nuclear reactor: a slows down neutrons to speeds at which they are more likely to cause fission b absorbs neutrons to prevent them causing other atoms to split c transfers energy to a turbine

Nuclear dangers 8 Describe two dangers of using nuclear energy. 9 Outline how high-level nuclear waste is stored. 10 There are risks involved in storing nuclear waste. Describe some of these risks.

Alternative energy sources 11 Use a diagram to demonstrate how nuclear fusion occurs. 12 State the main advantage of nuclear fusion. 13 Explain why using nuclear fusion is technically difficult. 14 List three other types of alternative energy.

Think

Analyse 21 The following questions relate to the Chernobyl nuclear accident. a Propose ways in which the disaster could have been prevented b Propose how Swedish scientists became aware of a nuclear accident in Russia. c The likely death toll will be far greater than the initial 31 people killed. Explain why. 22 Predict whether waste plutonium would be safe in: a 100 years b 1000 years c 10 000 years 23 Explain how fallout from the Chernobyl accident could result in children drinking radioactive milk. 24 Explain why the air pressure inside nuclear reactors is kept lower than the outside atmospheric pressure. 25 Classify each of the following as low-, intermediate- or high-level nuclear waste: a spent fuel rods b gloves used by nuclear reactor technicians c a non-fuel-rod reactor part 26 Discuss whether we should be investing in nuclear power or other alternative energy sources for the future.

15 Copy and modify the following statements so they are all true. a Uranium provides much more energy per kilogram than coal. b Unstable atoms absorb radiation. c Natural uranium contains 93% uranium-235. d A critical mass of uranium-235 is one that will not start a chain reaction. e Fission is the splitting of an atom. f One type of fusion reactor is a tomahawk.

291

Energy crisis

>>>

[ Extension ] Action 1 There are many alternative energy sources apart from nuclear power. Work in small groups, with each group selecting a different type of alternative energy source. a Describe how energy is produced in this way. b Assess the efficiency of this energy source. c Outline the advantages and disadvantages of your alternative energy source. d Evaluate whether this energy source would be suitable for use in the future. e Present your information as an oral presentation.

Creative writing Wasteland Some people have suggested that outback Australia (even the interior of Uluru!) be used as a long-term storage site for the world’s nuclear waste. This is because of the area’s geological stability. Write two letters/e-mails to a newspaper—one supporting and one opposing the proposal.

2 Have a class debate to discuss whether nuclear energy should be used.

Investigate 3 a Research a significant nuclear accident such as Chernobyl, the Three Mile Island disaster in the United States or the leak at Britain’s Windscale (now called Sellafield) plant. b Propose a set of safety rules that would prevent this type of accident in the future. 4 So-called ‘fast breeder’ nuclear reactors use plutonium and produce more fuel than they consume. Use chemical equations to demonstrate how this is achieved. 5 Research an Australian invention called SYNROC designed to store radioactive waste. Use a diagram to explain how the waste is stored. 6 Construct a poster that shows where uranium is mined in Australia and the steps in the process needed to produce ‘yellowcake’.

292

Creative writing Four futures You may have read a novel in which the reader has a choice of paths for the story to follow. Write an essay describing life in the future when reserves of fossil fuels finally run out. You must write four different ‘endings’ that are based on the following scenarios: 1 The world becomes totally reliant on nuclear energy. 2 Both fossil fuels and uranium reserves run out, and the world concentrates on the development of renewable energy sources such as wind, wave and solar energy. 3 Nuclear fusion technology improves to the point where fusion reactors become the most economical source of energy. 4 A totally new and plentiful energy source is discovered.

Chapter review [ Summary questions ] 1 List three main greenhouse gases. 2 List three ways in which greenhouse gas emissions could be reduced. 3 List some possible future consequences of continued global warming. 4 Use a diagram to identify the location of the ozone layer. 5 Identify an ozone-unfriendly element. 6 Four types of radiation may be emitted from a nucleus. List them. 7 Identify the subatomic particles emitted during fission that cause a chain reaction. 8 State the lethal dose of radiation in sieverts. 9 Outline how each of the following work: a Geiger counter b smoke detector c radioactive tracers d radiotherapy e carbon dating

16 Explain why uranium ore in the ground does not explode. 17 A so-called ‘fast breeder reactor’ uses plutonium fuel and does not require a moderator to slow the neutrons hitting it. Contrast the ability of plutonium to absorb neutrons with that of uranium. 18 One older method of disposing of nuclear waste was to simply dump it in the ocean in sealed drums. Discuss why this is not desirable. 19 Propose reasons why fusion reactors are currently not economical.

[ Interpreting questions] 20 Australia releases about 320 million tonnes of carbon into the atmosphere each year by burning fossil fuels. Given that our population is approximately 18.5 million people, estimate Australia’s carbon emission per person.

10 Construct a simplified sketch showing the main parts of a nuclear reactor.

21 Sulfur has an atomic number of 16. Calculate the following numbers for the atom formed after sulfur-35 undergoes beta decay: a atomic number b mass number

[ Thinking questions ]

22 Radium (atomic number 88, mass number 226) undergoes radioactive decay and changes into radon (atomic number 86, mass number 222). Assess the type of radiation that radium emits.

11 There are many older refrigerators still in use that contain CFCs. Explain how these CFCs could still end up being released into the atmosphere.

23 Construct a balanced equation for the chemical reaction for Question 22 (the symbol for radium is Ra, and for radon is Rn).

12 Propose reasons why it is more difficult for lessdeveloped countries to comply with the Montreal protocol.

24 Xenon-133 has a half-life of 2.3 days. Calculate how much would be left of an 8 gram sample of xenon-133 after almost a week.

13 Identify the type of radiation that would be suitable for measuring the thickness of a sheet of a metal b thin rubber

25 It has been estimated that the world’s oil reserves may run out in 45 years, gas in 60 years and coal in 300 years. Construct a graph to show this information.

14 It has been calculated that a lump of nuclear reactor fuel the size of a bowling ball would provide enough energy for one person for their lifetime. Estimate how many bowling balls of coal would be needed.

Worksheet 8.6 Global issues crossword Worksheet 8.7 Sci-words

15 Contrast nuclear fission with nuclear fusion.

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Individual research project

>>>

Key focus area

5.2, 5.13, 5.14, 5.18, 5.22.1

Outcomes

>>> The nature and practice of science By the end of this chapter you should be able to: identify different types of investigations, then independently plan and carry out one of these describe different types of skills required for working independently gather information from first- and second-hand sources plan and carry out a controlled experiment analyse, present and evaluate information and data collected draw conclusions based on the information gathered in an investigation solve problems creatively as they arise work to planned time lines and goals

Pre quiz

communicate the findings of an investigation through various media, including a written report.

1 Do you prefer to work by yourself or as part of a team? Why?

2 Identify a complex task you completed predominantly by yourself.

3 What task have you done in the past that you are particularly proud of?

4 Apart from a written report, how else can you pass on information to others?

5 What skills would you need in order to construct a model in science?

6 What should be included in a report on an experiment? 7 Research can take you to interesting places. What do you think the diver in the photo is trying to find out?

9

3.1 UNIT

UNIT

context

9.1 Everyone is good at something: each one of us has certain skills that we excel at. When we work as a group, the different skills of each group member can be used. When you work as an individual, however, you need to have all those skills yourself. Individual research can be very demanding. You need to be able to take an idea, put it into practice and see it

through to completion. Working by yourself does not mean you are alone, though. Finding people to support you and offer advice is one skill that may get you through when your ideas run low. Let’s look at some of the skills that are needed for success in individual research.

Independent work skills Performing and assessing a science investigation is like any other task you undertake in life. Decisions need to be made, plans need to be set out and good organisation is required. This project will allow you to apply and develop important skills, some being: • setting suitable time lines • designing, conducting and evaluating an investigation • working safely with a variety of equipment in different environments • developing and applying scientific thinking and problem-solving techniques • identifying problems and applying creative solutions to them • finding a mentor to support you in difficult times • presenting data and information in appropriate forms • communicating information, and your understanding of it, to your peers.

Surviving on your own On the following page are some of the characteristics required for success when working alone. As an individual you will be good at some of these, and probably not so good at others. Each person is different, with their own strengths and weaknesses. When working by yourself you have to build on your strengths and find ways of dealing with your weaknesses. As you complete your project, try to identify the characteristics that you already have and which ones need improving.

Sometimes it is necessary to complete a task by yourself. This requires organisation and self-discipline.

Fig 9.1.1

295

>>>

What to do?

Being an individual

Creativity: a creative person will be able to come up

Organisation: an organised person will plan time lines and

with new ideas, see relationships between results and information, and invent new ways of doing things. They will often solve problems in unusual ways.

resources carefully. They might make lists, find out what they need, and collect resources before they start working. They will often proceed in a series of planned steps.

Resourcefulness: being resourceful involves thinking ‘outside the square’. It involves making the most of the resources you have available. It may also include changing or modifying the plan as new ideas emerge, and taking advantage of any opportunities that arise.

Dedication: dedicated people want to achieve. They are able to meet goals and see a project through to completion. Fig 9.1.2

296

Individual work skills

Self-motivation: self-motivated people know why they want to do something. Make sure you choose a topic for investigation that you will find interesting and challenging, since this is likely to keep you motivated.

UNIT

9.1

Sheep drag

Fig 9.1.3

Scientists in Australia have carried out resea rch on the forces required to drag sheep over various surfa ces. Their aim was to find a simple and inexpensive way to make it easier for shearers to drag sheep in for shearing. The results showed that the dragging forces for different floor textures and slopes range d from about 360 N to 420 N. Their analysis indicated that a timbe r floor with a slope of 1:10 (about 6°) and boards parallel to the sheep’s drag path reduced the force by 64 N. This research could make life a lot easier for shearers, who each drag around 150 sheep per day, each with a mass of up to 45 kg. That’s a total of 6750 kg of sheep!

A shearer drags 6750 kg of sheep a day. Research into how to make this easier is helping Australians get the job done.

Career profile Science teacher Science teachers in secondary schools teach science to Year 7 to 10 students. In Years 11 and 12 they specialise in teaching physics, chemistry, biology, earth and environmental science or senior science. They will have studied the subjects they teach at university as well as undertaken special studies in education.

Fig 9.1.4

A science teacher presenting a genetics lesson

Science teachers are involved in: • preparing daily lessons and long-term teaching programs • teaching, using different techniques such as classroom activities, discussions, experiments, projects, assignments and excursions • taking into account the different needs of students • using information technology to assist in lesson preparation, delivery and reporting • setting assessments, projects, assignments and homework, marking these and collating the results • evaluating and reporting on the progress of students, and discussing individual performance with students and parents • participating in the wider school community through activities such as sports, camps, student support groups and extra-curricular activities. A good science teacher will be able to: • plan and organise various activities on a daily basis • show enthusiasm for learning and a love of science • communicate concepts and instructions clearly • enjoy working with young people and other teachers • relate well to and communicate with people of all ages and backgrounds • be patient in dealing with people • work as a member of a team • keep accurate records and prepare reports.

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Being anchemical Writing individualequations Fluffy belly buttons Dr Karl Kruszelnicki carried out the world’s first bellybutton lint (BBL) survey. Some variables included in the survey were the degree of overall body hair, ‘innie’ or ‘outie’ belly buttons, skin type and whether you have a navel ring. The study collected information about whether the colour of your belly-button lint is related to clothing colour and whether clothes were washed in a top-loader or front-loader. The results showed that you are ‘more likely to have BBL if you’re male, older, hairy, and have an ‘innie’’. This important research won Dr Karl an Ig Nobel Prize for Popular Science.

Think 6 The five characteristics of independent learning listed below are not the only ones that you may possess. Describe another characteristic that you may need to be successful when working alone. 7 Evaluate the importance of having a mentor when working alone. 8 Describe an example of when a person you know was resourceful. 9 Propose ways to keep self-motivation high. 10 Compare the characteristics of creativity and resourcefulness. 11 a Although part of a team, teachers do a lot of independent work. State the key characteristics of a good science teacher. b Justify your choice in each case.

Analyse Fig 9.1.5

UNIT

9.1

The winner: older, hairy males with an innie have the most belly button lint.

[ Questions ]

Checkpoint Independent work skills 1 From those listed in this unit, identify four skills that you are good at. 2 List the eight skills in order from what you consider to be most important, down to least important. 3 Explain what is meant by a ‘mentor’.

Surviving on your own 4 Match the characteristic below with the correct description. 5 Which characteristics are your individual strengths? Identify two of them from the list below. Explain why you chose each. Characteristic Resourcefulness Self-motivation Creativity Organisation Dedication

298

12 Imagine you are a lone astronaut orbiting Earth in a space station. Suddenly there is an explosion and cabin oxygen slowly begins to leak into space. What will you do? a Identify the two main skills you will need to solve this problem. b Identify the two main characteristics that you think will be required to get out of this situation alive. c Is one skill or characteristic more important than others in this situation? Justify your answer. 13 You have been chosen to spend six months in an undersea research centre off the coast of New South Wales. During this time you will perform a series of experiments. You will be able to communicate with other scientists onshore but will be working alone. a Identify the three key characteristics you will require to complete this task. b Identify three key skills you will require. c Which skill or characteristic do you think will be most important in this situation? Justify your answer.

Description Make lists and collect resources before starting work and then proceed in a series of steps. Meet goals and see a project through to completion. Make the most of the available resources and take advantage of opportunities. Comes from being interested, and knowing the reason why you want to do something. Invent new ways of doing things and solve problems in unusual ways.

Science focus: Science can be funny! Prescribed focus area: The nature and practice of science Can frogs really levitate? One scientist Can you believe that science can be funny? To be a good scientist requires not just reasoning and objectivity, but creativity and curiosity, which usually come from people with interesting and even funny personalities!

Fig SF 9.1

proved that they can, with the help of an electromagnet.

Classic investigations Believe it or not, scientists engage in some very amusing research. There are subjects you would never have thought of unless you were a scientist with too much time on your hands. Some classic investigations have included: • Why toast often falls on the buttered side • The five-second rule • The best way to dunk a biscuit • How to levitate frogs and a sumo wrestler with an electromagnet • The effects of ale, garlic and sour cream on the appetites of leeches (sour cream was the biggest appetite stimulant) • Chicken plucking as a measure of tornado wind speed • The role of elevator music in preventing the common cold • How herrings communicate by farting • Chickens’ preference for beautiful people • The belly-button lint survey conducted by Australian scientist Dr Karl Kruszelnicki • How to make a teapot spout that doesn't drip • The invention of software that detects when a cat is walking over your computer keyboard • Why shower curtains billow inwards. All of the above investigations have been awarded Ig Nobel Prizes. The Ig Nobel prizes are awarded for science that ‘first makes people laugh, and then makes them think’. The idea of these awards is to celebrate unusual science, to honour the imagination and promote popular science in the wider community. It is said that the Ig Nobel prizes honour those

achievements that ‘cannot and should not be reproduced’. Prizes are awarded at Harvard University in the USA, and the prizes are handed to the Ig Nobel winners by genuine Nobel Prize winners, who are amused at their colleagues’ investigations. Many Ig Nobel winners are actually serious scientists. One Ig Nobel prize winner is physicist Dr Len Fisher. Dr Fisher is an Australian (based at Bristol University in England) who has devoted much of his time to understanding the science behind everyday life. He combines scientific reasoning and method with an enthusiasm for the bizarre. Dr Fisher’s Ig Nobel prize was awarded for his research into dunking biscuits. The following outlines some of Dr Fisher’s more unusual research projects.

The physics of dunking biscuits Dr Fisher and his research team showed that a dunked biscuit releases up to 10 times more flavour than a dry biscuit. A biscuit is basically lumps of starch glued together with sugar. When dunked, the hot tea or coffee enters the pores in the surface of the biscuit and is absorbed by the starch grains that swell. The sugar

299

also begins to melt, giving a biscuit that is purely starch but much softer than the original biscuit, which in turn makes it unstable. Eventually the team used an old formula devised in 1921 that describes the dunking process. This is how it works: the perfect dunking time is equal to the height (L) the liquid rises up the biscuit squared, multiplied by four times the viscosity (η, density of liquid) divided by the surface tension (γ) of the tea, multiplied by the average pore diameter (D). t=

L24η γD

This equation is specific to cheddar cheese, and the value 2.8 changes with different types of cheese. This formula was derived using a series of experiments that involved inserting a tube up the nose to measure the concentration of aromas produced while chewing and swallowing a cheese sandwich. This formula shows that the perfect cheese sandwich requires a slice of cheddar cheese 2.8 mm thick, to gain maximum percentage cheesiness. Thinner slices will have lower percentage cheesiness and not be as tasty. Try working it out yourself with the formula!

The research is yet to be completed as Dr Fisher believes that the temperature of the tea also has an impact on dunking times. This research was sponsored by a biscuit company that will print advice for consumers on its biscuit packets. The best dunking time for a gingernut biscuit was three seconds, and eight seconds for a digestive biscuit. Soon a more user-friendly version will be available that gives the best time for dunking for different types of biscuits. If you want to get the most out of your biscuits, keep an eye out for it!

Fig SF 9.3

The optimum dunking time for gingernut biscuits is three seconds.

Fig SF 9.2

The perfect cheese sandwich The perfect cheese sandwich is another of Dr Fisher’s great discoveries. This work was sponsored by the British cheese board. Being a physicist, Dr Fisher could not help but develop an equation to describe this phenomenon: % cheesiness = (100/2.8) × thickness of cheese (mm)

300

Testing the cheesiness of a sandwich using an aroma-detection device

After a certain thickness no amount of extra cheese will add to the cheesy aroma impact of the sandwich. Dr Fisher also discovered that adding butter or margarine enhances cheesiness, probably because the fat in butter and margarine dissolves the flavours, and the fat then coats the mouth and tongue and holds the flavours in the mouth longer. What is the impact of this research? It is thought that more research should be undertaken that will allow us to better understand the design of healthy and tasty foods, in order to produce maximum flavour release.

Wasted gravy Want more? Another bizarre example of Dr Fisher’s work comes from British people wasting 681 912 litres of gravy a week. This is gravy poured onto plates and then not consumed.

To solve this problem the gravy absorbency index was developed: % gravy uptake = (W – (D/S)) D × 100 where:

W = weight of uncooked food D = weight of cooked food S = shrinkage factor

Scientific method was used to measure the weight of gravy absorbed according to time at different gravy temperatures. Research findings: • Absorption times can be accelerated by 20% if gravy is very hot. • A food’s ability to mop up gravy is also dependent on the time it is in contact with the gravy, and the density of the food. • For efficient gravy absorption, food should be eaten in the correct order. – Start with meat as it absorbs no gravy. – Green vegetables should be eaten next as they absorb up to 15% of their dry weight within 30 seconds.

Fig SF 9.4

Bread should be swirled in a circular motion around the plate using both sides of the bread for maximum gravy absorption.

– Roast potatoes should be eaten last as they absorb up to 30% of their dry weight, and take as long as five to ten minutes to absorb this amount. • Ciabatta, an airy Italian bread, is better than ordinary bread at soaking up leftover gravy, absorbing 120% of its dry weight. • Dr Fisher even has a suggestion for using popcorn. Popcorn has an ‘off the scale’ gravy absorption rate of 600% plus. Fisher added, ‘You just have to move fast before it goes all soggy’. The study showed that there is a scientific reason for gravy wastage. People eat their food in the wrong order!

Nuts for physics A bowl of mixed nuts may be good Christmas food, but for physicist Paul Quinn it’s a nutty physics project. Quinn was puzzled by an odd nut-bowl phenomenon. Brazil nuts always seem to sit on the top of smaller nuts. But shouldn’t gravity pull the heavy nuts to the bottom of the bowl, while lighter nuts rest on top? Quinn calls the phenomenon the Brazil-nut problem, or BNP. Quinn found that a nut ‘sinks or swims’ depending on the ratio of two properties: mass and diameter. If a fat nut is twice the mass and diameter of the other nuts in the bowl, it surfaces. But if the nut is six times the mass and only twice the diameter of smaller nuts, it sinks.

2 a Use the formula for the perfect cheese sandwich to complete the following table:

Thickness of cheddar cheese (mm)

Calculation

% cheesiness

2.8

% = (100/2.8) x 2.8

100%

2.5 2.0 1.5 1.0 0.5 0.0

[ Questions ] 1 Find out more about the Ig Nobel Prizes by connecting to the Science Focus 4 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button. Watch past presentation ceremonies online, see a list of past winners and their research ideas, and be amused.

b Gouda cheese was discovered to have a percentage cheesiness of 100% at a thickness of 3.1 mm. Calculate the percentage cheesiness of a sandwich containing a slice of gouda that is 2.3 mm thick. 3 Gather information from the Internet about an unusual science research project that involves creativity and curiosity, and is funny. Present your information to the class, outlining how the research was done, what was discovered, and how this information is thought to be useful. Remember not to take yourself too seriously.

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context

9. 2 Performing an investigation can be fun! As well as completing belly-button lint research Dr Karl also completed the Great Fart Survey. This unusual scientific research showed that Aussie kids fart 24 times a day. It also revealed that although boys like to talk a lot more about their farts than girls, there was no difference between the amount and types of farts that boys and girls do. A baked bean experiment was included which showed that beans make girls

fart more than boys, although the types of farts were different, with girls doing more ‘silent but friendly’ (the opposite to a ‘silent but deadly’, a ‘silent but friendly’ fart is quiet with no smell—the only type you can get away with in public) or ‘squirter’ farts, and boys doing more ‘common’ and ‘thunder’ farts. Selecting an interesting investigation will make your research more successful. It may be something that interests you during science classes or at home, or it may even be to do with your favourite hobby, sport or pastime. Otherwise, be creative and investigate something unusual!

Types of investigation Selecting an investigation is a very important part of your project. The investigation should allow you to apply the skills that you have learnt in science. When choosing your investigation make sure: • you are interested in learning about your chosen topic • it is challenging enough for your level of ability The five-second rule • it is safe and does not pose High-school student Jillian a danger to people or the Clarke investigated the tific validity of the scien environment ‘five-second rule’ You know • you can get the required the rule: If food falls to the equipment and materials floor and it’s in contact with the floor for fewer than five • it can be finished in the seconds, it’s safe to pick it agreed time up and eat. She found that • it is open-ended, meaning 70% of women and 56% there are many possible of men are familiar with the rule, and most use it to solutions and it cannot make decisions about tasty be answered with simple treats that slip through answers such as true/false their fingers. The rule dates back to the or yes/no. time of Genghis Khan, who There are three main types first determined how long it of investigation that you may was safe for food to remain undertake for your individual on a floor when dropped. Khan had slightly lower project. Each type is explained standards, however—he here, with examples to help you specified 12 hours! in selecting a topic.

302

First-hand investigation A first-hand investigation can be an experiment or series of experiments to investigate a topic of your choice. By completing this type of investigation you will show your skill at planning, conducting and reporting on an area of interest in science. You will need to design a fair test that will give accurate and clear results. Examples: • Do people listen to their headphones at potentially dangerous levels? • Does heart rate increase with music type or increasing volume? • Who is generally fitter—males or females? Who has the lowest average heart rate, and how long does heart rate take to return to normal after exercise? • Which type of sausage contains the most fat? • Which home insulation works best? • What factors affect the growth of bread mould? • Which type of sunglass lens blocks the most light? • How does coffee affect blood pressure? • What percentage of lawn seed in a package will germinate? • How much water is in different fruits? • Does the human tongue have definite areas for certain tastes?

• • • • •

Ohm’s law Chemical and physical change Photosynthesis and respiration Diffusion Refraction, reflection and dispersion

Fig 9.2.2

Fig 9.2.1

UNIT

9.2

A student demonstrating the scientific principle of photosynthesis by measuring oxygen produced by a plant

A student performing a first-hand investigation in chemistry to find out how acidic different lemonades are

• What are the effects of different fertilisers on plant growth? • How does light direction affect plant growth? • What is the best insulation for making an insulated coffee mug? • How does the colour of a material affect its absorption of heat? • How does our hearing change as we age? • Which soft drink has the most bubbles or dissolved gas?

Demonstration of a scientific principle By completing this type of investigation you will show your skill in understanding a basic principle of science. You will have to interpret this principle and then design and conduct an experiment or series of experiments to prove that it is correct. Examples: • Conservation of matter in chemical reactions • Conservation of energy • Simple inheritance of a characteristic—dominant and recessive • Natural selection • Bioaccumulation • Sound travels by waves • Gravity acts at 9.8 m/s2 • Newton’s Laws of Motion • Brownian motion

Construction of a model, either static or working By completing this investigation you will show your skill at building a model and manipulating materials in order to demonstrate a scientific principle or investigate an aspect of science of your choice. You will have to plan, design and construct your model. This will involve understanding the scientific principles behind your model in order to make it informative and accurate. Examples Build a model to demonstrate or investigate: • The greenhouse effect • Collisions: airbags or crumple zones • Generation of electricity—wind power • A solar car or device • An electrical device • A speaker • The carbon cycle • Part of the body such as the ear or heart • Atoms: solids, liquids and gases

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My investigation • • • • • • • •

Atoms: molecules and chemical reactions Reproduction of a virus or other microbe Ohm’s law The structure of DNA Newton’s Laws of Motion The operation of a remote-sensing satellite Different types of earthquake waves An optical device such as a microscope, telescope, projector or binoculars, showing how it works • A nuclear reactor, showing how it works • The best direction for a house to face—how do we keep sunlight out in summer, and let sunlight in during winter? • How a lung works—how does the movement of the diaphragm relate to the volume of air inhaled? • How the current and voltage in a circuit affect the power of an electromagnet • The perfect beach—how the depth of water affects the height of waves • How infectious disease can be spread • The amount of tar in cigarettes—you may need teacher and parent permission to complete this investigation • How the mass of an object affects stopping distance • How lifting an object is made easier by ramps or pulleys • Reproduction rates in bacteria using computer modelling • The aerodynamic shape of different car designs using a wind tunnel. Note: There are many other investigations that you could do, but you will need to negotiate with your teacher if you select a different problem. Further ideas can be found by searching the Internet.

Murphy’s Law and others

• • • • • • •

You will have heard of Murphy’s Law: ‘Anything that can go wrong will go wron g’. There are other similar ‘rules’ that you may encounter throughout your project, so be prepared. Nothing is as easy as it looks. Everything takes longer than you think. Always keep a record of data. It indicates that you’ve been working. In case of doubt, make it sound convincing . Experiments should be reproducible—they should all fail in the same way. When you don’t know what you are doing , do it neatly. If it is green or it wiggles, it’s Biology. If it stinks, it’s Chemistry. If it doesn’t work, it’s Physics.

Scientific method You will be required to produce a report based on your work and findings, whichever type of investigation and topic you choose. The following is a review of the scientific method to help you in designing, conducting and reporting on your investigation.

Aim The aim outlines the idea or scientific question you are trying to test.

Hypothesis A hypothesis is a prediction or ‘educated guess’ about what you might find in an experiment. A hypothesis is something that can be tested in measurable terms.

Variables Identify all the variables that may affect your results. Remember that variables can be classified into three groups: • independent variable—the variable that is changed • dependent variable—the variable that is being measured • controlled variables—the variables that are kept the same throughout the experiment.

Equipment List all the equipment and materials that you need.

Method The method is a step-by-step set of instructions that other scientists at your level of experience could follow to accurately repeat your experiment. Fig 9.2.3

304

A student using a model to investigate the structure of DNA

When writing the instructions, include the following information: • the one variable that you are going to change • how you are going to change it and by how much • how you are going to control all the other variables • diagrams, drawings or photographs • how you are going to measure the changes • how you are going to record the changes, such as in a results table. Your experimental method should be replicated a number of times so that a more accurate conclusion can be drawn.

Results Results can be of two types: • Results or data that are numerical are called quantitative as they usually measure amounts or quantities. • If you are using your senses to observe, you are making observations. Qualitative observations are written down as a description or recorded as a picture or diagram. You should also record any other things you notice, particularly any problems you had with your investigation. If appropriate, include a photographic essay of your project steps or results. These will assist in your final analysis. You may be asked to keep a detailed process diary of observations, data, and results while completing your experiment.

Discussion In the discussion you should analyse and evaluate your results in detail: • Analyse and present your data or observations in different ways to show any patterns or trends. This is where a graph may be useful. Line graphs should be used when both the independent and dependent variables are numerical. • Explain any trends or patterns in your observations, data and results. • Explain why the results occurred and what they demonstrated. • Evaluate the success of your investigation. • Outline any errors that may have affected your results. Errors are unavoidable, but mistakes are because of clumsiness. Report your errors, not your mistakes.

UNIT

9.2 • Describe any difficulties or problems you had in doing the investigation. • Explain how your experiment could be improved to gain better or more dependable results.

Conclusion A conclusion is simply a summary of the results of your experiment. A good conclusion will: • answer your aim • identify whether your experiment proved or disproved your hypothesis. Use any trends you saw in the results as proof. Nuclear beer froth • identify any changes that you A scientist in Germany would make if you had to repeat demonstrated that the this investigation. volume of beer froth decays

Resource list This is sometimes called a bibliography and is a list of all the resources and references you used. You may also wish to make any acknowledgements here.

exponentially with time, just like radioactive decay. The experiments showed that the decay constant depended on the brand and type of beer.

Communicating When working independently it is vital to be able to communicate your results and knowledge to others. As well as your written report you may be required to present your findings in another way. When selecting your topic, consider the type of presentation that would best suit your investigation. As you perform your investigation, collect any information that will allow you to present your findings in a creative and interesting way. Presentations could take the form of: • an oral presentation (use props to assist you) • a demonstration of a model to the class • a website • a PowerPoint presentation • a poster or visual display • photographic, video or audio material • a journal article • a newspaper article. Use worksheets 9.1 and 9.2 to help you plan your investigation. Worksheet 9.1 Proposing my big idea Worksheet 9.2 Planning my investigation

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My investigation

Career profile Science laboratory assistant A good laboratory assistant will be able to: Laboratory assistants prepare experimental equipment and • enjoy scientific activities chemical solutions and maintain a chemical storage area in • work as part of a team accordance with safety requirements. They support science • communicate and negotiate effectively with people teachers and scientists in their work, ordering stock, disposing • solve problems in creative ways of waste and helping them improve experiments. They often • keep accurate and detailed reports help with research, carrying out preliminary experiments. • follow detailed experimental instructions. Laboratory assistants can be involved in: • working with teachers or scientists in planning experiments • cleaning, maintaining and setting up equipment for use in experiments • performing calculations to prepare correct chemical Flatus odour judge solutions Odour judges are common in the research laboratories of mouthwash • completing routine experiments to help in an companies. Volunteers with bad breath blow gusts of air in the judges’ faces investigation to test product efficiency. Gastroenterologist Michael Levitt recently took • checking chemical and equipment supplies and ordering the job to another level. Sixteen healthy subjects volunteered to eat baked stock beans and insert small plastic collection tubes into their anuses. After each ‘episode of flatulence’, Levitt syringed the gas into a sterile container. The • keeping records of stock odour judges then sat down with at least 100 samples, opened the caps one • checking that all equipment and chemicals are stored at a time, and inhaled. For comparison with the judges’ comments Levitt also safely chemically analysed the samples. He found that the ‘smelliest’ component • disposing of waste in a safe manner. of the human flatus was hydrogen sulfide (H2S). Make sure you read the job description very carefully before taking on any laboratory job!

Fig 9.2.4

306

Laboratory assistant preparing for an experiment

UNIT

9.2

UNIT

9.2 [ Questions ]

Checkpoint Types of investigation 1 Describe three things to consider when selecting a topic for investigation. 2 List the three types of investigation that may be undertaken. 3 Distinguish between building a model to demonstrate a scientific principle, and building a model to investigate an aspect of science.

Scientific method 4 List the sections of a scientific report. 5 Distinguish between a dependent variable and an independent variable. 6 Define ‘controlled variable’. 7 Distinguish between qualitative and quantitative observations. 8 Clarify the purpose of a conclusion.

Communicating 9 Identify two ways in which you could communicate the findings of your investigation.

Think 10 Compare an aim and a hypothesis. 11 List three ways in which you could present the results of an investigation. 12 Explain why you should only change one variable at a time in any experiment. 13 The following types of information could be collected in an experiment. Classify each as quantitative or qualitative data. a colour f force b mass g texture c smell h length d time i current e weight j temperature 14 Everyone has different learning styles. Explain why it is important to use different techniques when communicating information. 15 Describe two props that could be used in an oral presentation to help you pass information in visual form to learners. 16 Distinguish between a newspaper article and a journal article.

17 Discuss the purpose and contents of a discussion in an experimental report. 18 Evaluate the need for a conclusion when writing an experimental report. 19 Explain why an experiment should be replicated.

Skills 20 Classify the following as either open or closed questions. a Is it possible to reduce friction using oil? b Is the average weight of boys in your class greater than the average weight of girls? c Which type of material is best for making a shopping bag? d What is the best colour for a flashing light so that it can be seen easily at night? e Is it further to Mars than to Venus? f How does the amount of sugar in water change the boiling temperature? 21 You have been asked to design an experiment to test the amount of light that can pass through different types of glass. You have the following equipment available: different glass samples including transparent, opaque, translucent and coloured; a light sensor and data logger; torch; ruler. a Construct an aim for this experiment. b Construct a hypothesis. c Identify the independent and dependent variables. d List the variable(s) that would need to be controlled. e Outline any observations you would make. f Outline any measurements you would make. g Propose a method for this experiment. h Design a table in which you could record your results. 22 Marika completed an experiment to test the effect of fertiliser on the growth of plants, using the equipment shown in Figure 9.2.5. a b c d

Identify the independent variable. Identify the dependent variable. List the controlled variables. Propose a hypothesis for this experiment.

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My investigation

Chapter review [ Summary questions ] 1 Copy and complete the following paragraph about the skills required for completing an independent investigation.

10 grams

5 grams

0 grams

communicate, time lines, conduct, data, identifying, evaluate, safely, creative, scientific, mentor, solving, alone When completing an independent investigation you will need to set suitable _____________. You will need to work ___________ while you design, ___________ and ___________ your investigation.

Amount of fertiliser added 250

Plant fertiliser

Measuring cylinder

As problems arise you may need to apply ___________ thinking and problem-_____________ techniques. This will involve _____________ problems and coming up with _____________ solutions to them. Having a ___________ ___ to support you through difficult times can help when working __________. After completing an investigation it is necessary to______________ information and results to others. This will involve presenting _________ and information in suitable forms.

200

150

100

50

20

electronic balance 0

1

2

3

4

5

6

2 Outline three personal characteristics needed for working independently.

Water 7

8

9

10

11

12

13

14

15 cm

3 Construct three open-ended questions that may be suitable for investigation.

Ruler

4 Identify whether the following statements are true or false. a The topic you select for investigation should not pose a danger to people or the environment. b A closed question cannot be answered with a true/false or yes/no. c A conclusion sums up the results of an investigation. d An aim and a hypothesis are the same thing and only one of them should be included in a report of an investigation. e A graph of results would appear in the conclusion of an investigation.

Fig 9.2.5 Marika recorded the results shown in the table below. e Construct a line graph to show these results. You will need three lines on the one graph. f Describe any patterns and trends that you see in the results. g Use these results to deduce what effect the fertiliser had on the height of the plants. h Could you rely on these results, or believe any conclusion based on them? Justify your answer. i Evaluate the experiment to decide if it is a fair test. j Propose any improvements to the experiment.

308

Amount of fertiliser (grams)

Start

Day 2

Height of plant (cm) Day 4 Day 6

0

5.0

6.0

6.5

5

5.0

6.5

10

5.0

6.4

Day 8

Day 10

6.5

6.5

6.5

8.6

10.5

12.8

14.7

8.2

9.2

11.0

12.1

[ Thinking questions ] Report section

Purpose

Description of what should be included

Title

To identify the project and what it is about

A title

Aim Hypothesis

A statement about what you will be finding out about A prediction or ‘educated guess’ about what you may find in an experiment.

Equipment

List of equipment and resources

Variables To provide clear, unambiguous instructions that other scientists could follow to accurately repeat your experiment Results Discussion

To analyse and evaluate your results in detail Whether you answered the aim. Whether the hypothesis was proved or disproved and why

Bibliography

5 Copy and complete the table above to summarise the structure of a scientific report. 6 Explain the difference between an investigation to demonstrate a scientific principle and an investigation into an aspect of science of your choice.

[ Interpreting questions ] 7 Peter decided to investigate the solubility of gases in water and apply the results to explain the El Niño effect. From texts and the Internet he found that marine animals depend on oxygen in the same way as animals on land. He also found that the gases oxygen and carbon dioxide are soluble in water. Peter then used datalogging equipment to test the solubility of oxygen in water. His experiment produced the results shown opposite: a Construct a line graph to display these results. You will need four lines on the one graph. b Identify any experimental results that may be wrong. Predict the correct values for these points. c Describe any patterns and trends that you see in the results. d Use these results to deduce how oxygen solubility is affected by temperature. e Evaluate the experiment to decide whether it was a fair test. Peter searched the Internet to find information about the El Niño effect. His search allowed him to summarise the effect as follows:

Lists of resources including books, websites, journal articles etc.

‘On the west coast of the South American continent, a cool ocean current (called the Humboldt or Peru current) brings nutrient-rich water to the coast. This provides valuable food for the fish. But every two to seven years, at about Christmas time, a warm current comes and leaves the coastal fishermen with empty nets. The fishermen called this phenomenon ‘El Niño’, meaning ‘Christ Child’.’ f Use the findings from Peter’s experiment to propose an explanation for the empty fishing nets.

Temperature °C

Tap water

Boiled tap water

Sea water

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5

13.1

7.1

10.9

6.8

10

11.8

6.8

9.5

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10.5

6.6

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9.7

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8.4

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3.9

35

7.1

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Australian Aboriginal diet, 189 dreamtime, 225 healing, 188 medicines, 205 use of resins, 45 use of natural fibre, 47 AC/DC, 64 acceleration, 147 acquired characteristics, 227 acquired immunity, 204 action/reaction forces, 164 adaptations, 223–4 adaptive radiation, 235 ADSL, 88 agitation, CD9 air resistance, 169 albinism, 106 alcohol, 18–19, 215–16 alkanes, 16 alkenes, 17 alkynes, 18 alleles, 100 alloys, 25–6 alpha radiation, 277 alternating current, 64 aluminium, 39 AM-FM, 80 amino acids, 115 amplitude, 77 analogue network, 85 anatomical studies, 243 anodising, 39 antibiotics, 205 antibodies, 204 antigen, 204 attenuation, 86 atomic mass, CD2 Australopithecus, 250 Avogadro’s number, CD2 bacteria, 197 balanced forces, 160 balancing equations, 4–5 bandwidth, 86 base pairs, in DNA, 114 behavioural adaptations, 224 beta radiation, 277–8

biotechnology, 128 blast furnace, 33 blood groups, 107 blood pressure, 213 blow moulding, 46 Bowler, Jim, 259 broadband, 89 Buffon, Georges, 226 cancer, 214 capacitors, CD15 carat, 26 carbon dating, 281 carbon dioxide, 264–5 carbon fibres, 49 careers geneticist, 125 medical laboratory technician, 110 science laboratory assistant, 306 science teacher, 297 cell division, 98–9 chain reaction, 286 chemical formulas, 3 chemistry, organic, 15 Chernobyl, 288 chlorofluorocarbons (CFC), 265, 272–3 chromosomes, 97 circuit types, 63 cloning, 123–4 therapeutic, 124 coaxial cable, 86 codominance, 101 combustion, 19 communicating, 305 communication waves in, 76–80 history of, 84–5 communication network 85–9 contagious disease, 203 convergent evolution, 235–6 copying DNA, 114 corrosion of metals, 38–9 protection against, 38–9 covalent bonding, 3 cracking, 17 creation, 225

cultural evolution, 252–3 Curie, Marie, 277 current, 61, 62 AC/DC, 64 Darwin, Charles, 227 theory of evolution, 227–9 Darwin’s finches, 228 deceleration, 147 diabetes, 212 diatomic, 4 diet, Aboriginal, 189 digital network, 85 diodes, CD16 diploid cells, 97 direct current, 64 disease, 192 contagious, 203 control of, 203–4 heart, 213 infectious, 196 non-infectious, 211 transmission of, 203 X-linked, 110 displacement, 136 distance, 136 distance–time graph, 138 divergent evolution, 235 DNA, 97 copying, 114 fingerprinting, 129–30 recombinant, 121 structure of, 114 dominant trait, 97 door latch, 69 drug abuse, 215 dynamo, 71 eating disorders, 212 Einstein, Albert, 285 El Niño, 268 elastic potential energy, 177 electric bell, 69 electric circuit, 60–2 types of, 63–4 water analogy, 61–2 electricity, 60 electrolysis, 32

311

Index electronics, CD14–17 electromagnet, 68 electromagnetic spectrum, 77–8 electromagnetism, 68 embryonic development, 244 emulsion, CD9 energy, 176 elastic potential, 177 gravitational potential, 177 kinetic, 176 potential, 177 enhanced greenhouse effect, 264 epidemic, 193, 196 evolution, 223 convergent, 235–6 cultural, 252 Darwin’s theory of, 227–9 divergent, 235 evidence for, 239–46 human, 249–53 parallel, 236 theory of, 225 experiments cheese sandwich, 300 dunking biscuits, 299–300 gravy, 300–1 extrusion moulding, 46 eye colour, 107

gamma rays, 78 gangue, 32 gene cell therapy, 125 gene expression, 116 gene probes, 129 gene technology, 120–1, 122 generator, 71 genes, 97 genetic code, 115 genetic disorders, 211 genetic engineering, 120–1 genetic evidence, 246 genetic map, 125 genetically modified organisms, 121 genotype, 100 geographic isolation, 234 geological time scale, 239 glass fibres, 49 global warming, 266–8 glycemic index (GI), 187 graphs distance–time, 138 speed–time, 138–9, 148 gravitational potential energy, 177 gravity, 169 greenhouse effect, 263 enhanced, 264 greenhouse gases, 264

fermentation, 19 fibreglass, 49 fibres natural, 47 synthetic, 47–8 fission, 285 flatworm, 199 flukes, 199 food pyramid, 187 forces, 153 action/reaction, 164 balanced, 160 types of, 153 forensic analysis, 123 formula mass, CD3 fossil record, 239–43 fossils, 239–40 fractional distillation, 17 frequency, 76 fungi, 199 fusion, 288–9

half-life, 278–9 hard and soft water, CD9 health, 186 heart disease, 213 hereditary factors, 97 HIV/AIDS, 207, 208 Homo sapiens, 251 homologous pair, 97 human evolution, 249–53 human genome, 125 human inheritance, 106–10 hydrocarbons, 16

galvanised iron, 39 gametes, 97 gamma radiation, 278

312

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incomplete dominance, 102 independent work skills, 295–6 individual research project, 294 industrial reactions, 10 inertia, 153, 155 infection, 193 infectious diseases, 196–200 infra-red rays, 79 injection moulding, 46 integrated circuits, CD17 investigations, 302–4 ionic bonding, 4

iron, smelting of, 33 isotopes, 276–7 Jenner, Edward, 205 kinetic energy, 176 Kyoto Protocol, 266 Lamarck, Jean, 226 theory of evolution, 227 lasers, 87 lather, CD9 Law of conservation of mass, 5 Law of conservation of matter, 4 Law of Constant Proportions, CD5 life on Earth, 241 light-dependent resistors, CD15 light waves, 77 Lister, Joseph, 206 maglev trains, 70 magnetic field, 71 malnutrition, 211 manipulating genes, 121 Maralinga, 289 measuring radiation, 279–80 meiosis, 99 Mendel, Gregor, 96 mental illness, 218 metals, 3, 24 extraction, 32 mining, 31 properties of, 24 pure, 24 methane, 265 micromechanics, 55 microphone, 71 microwave ovens, 92 microwaves, 80, 87, 91 minerals, 30 mining process, 31 mitosis, 98 mobile phones, 88 mole, CD2 monofilaments, 48 monomers, 44 Morse code, 84 motion graphs, 138 distance–time, 138 speed–time, 138–9, 148 multiple bonds, 15 multiplexing, 86 Mungo man, 255–9

nanobots, 56 nanometre, 54 nanotechnology, 54 native elements, 29 natural fibres, 47 natural selection, 232–4 Newton’s laws, 164 First law, 153 Second law, 159 Third law, 164 nitrous oxide, 265 non-infectious diseases, 211 nuclear accidents, 288 nuclear dangers, 287– 9 nuclear energy, 285–6 nuclear radiation, 276–80 sources of, 279 uses of, 280–2 nuclear reactors, 286–7 nuclear waste disposal, 288 nutrients, 186 obesity, 212 Ohm’s law, 63–4 optical fibres, 86 ores, 30 organic chemistry, 15 alkanes, 16 alkenes, 17 alkynes, 18 ozone, 272 destruction of, 273 hole, 273–4 layer, 272 pandemic, 198 parallel circuits, 63 parallel evolution, 236 pathogen, 192, 196 pedigrees, 108–9 pentadactyl limb, 243–4 peppered moth, 232–3 phenotype, 100 plant and animal distribution, 245 plasmids, 121 plastics, 43 properties of, 43 thermoplastic, 43 thermosetting, 44 polar molecules, CD8 polarisation, 79 polymers, 17, 43

potential energy, 177 power transmission, 72 prenatal testing, 123 Priestley, Joseph, CD4 primates, 249 products, 3 properties of metals, 24 protozoa, 198 Punnett square, 101 quantum computing, 57 rabbit control, 233 radiation, 217, 276 effects of, 279 types of, 277–8 uses of, 280–2 radio waves, 80 radioactivity, 276 radiotherapy, 280 rates of reactions, 11–12 reactants, 3 reaction engines, 165, recessive trait, 97 recombinant DNA, 121 recycling, 34 relay, 69 reproductive isolation, 234 resistance, 62 resistor code, CD14–15 resistors, CD14 rockets, 165 rusting, 38 saponification, CD9 science fun, 299–301 scientific method, 304–5 selection, 225 selective breeding, 120 series circuits, 63 sex linked inheritance, 109 smelting, 33 smoking, 215–16 soap, CD8–11 solenoid, 68 speakers, 69 speciation, 234 speed, 136–7 speed–time graph, 138–9, 148 spring constant, 178 states of matter, 6 steel, 25 stem cells, 124 stroke, 212 structural adaptations, 223 sulfuric acid, 11–12

synthetic fibres, 47–8 synthetics, 48 tapeworm, 200 telegraph, 84 telephone, 85 television, 70 terminal velocity, 169 theory of evolution, 225 therapeutic cloning, 124 thermistors, CD15 thermoplastic, 43 thermosetting plastics, 44 thrust, 165 ticker-timer, 137 tokamak, 288–90 traits, 96 transformers, 72 transgenics, 122 transistors, CD17 true breeding, 96 tuberculosis (TB), 205 tumour, 214

INDEX INDEX

mutagens, 116 mutations, 116, 117

ultraviolet radiation, 79 vaccinations, 204 vaccines, 204 variation within a species, 108, 224 varicose veins, 213 vector, 203 velocity, 136–7 terminal, 169 vending machine, 72 viruses, 198 visible light, 79 voltage, 61 Wallace, Alfred, 229 water, CD8 wavelength, 77 waves, 76 weight, 169 work, 176 X and Y chromosomes, 109 X-linked diseases, 110 X-rays, 78 yield, 10

313