Science Focus 3
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Sydney, Melbourne, Brisbane, Perth and associated companies around the world
>>>
Kerry Whalley Isabella Brown Peter Roberson Greg Rickard Geoff Phillips Faye Jeffery Janette Ellis Karin Johnstone 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 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 Ltd Pty) 2004 First published 2004 Reprinted 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 Prepress work by The Type Factory Set in Melior 10 pt Printed in Hong Kong National Library of Australia Cataloguing–in–Publication data: Whalley, Kerry. Science focus 3. For secondary school students. ISBN 0 12 360446 X. 1. Science - Textbooks. I. Roberson, Peter. II. Rickard, Greg. III. Title. IV. Title : Science focus three. 500
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2.1 What are chemical reactions and why do they happen?
Chapter review
38 45 51 57 67
3
Origin of the universe
68
3.1 3.2 3.3 3.4 3.5
The expanding universe The big bang The life of a star Are we alone? Future space travel Science focus: International space station Chapter review
69 73 77 80 83 87 90
4
Light
91
4.1 Bending light 4.2 Lenses and curved mirrors 4.3 Colour
2.2 Naming compounds 2.3 Reaction types 2.4 Acids and bases
Chapter review
92 99 110 117
UNIT
37
5.1 5.2 5.3 5.4 5.5 5.6
Plate tectonics At the edges Earthquakes Volcanoes Landscaping the crust Geological time Chapter review
120 127 134 143 148 156 162
Reproduction
164
UNIT
Chemical reactions
UNIT
2
UNIT
Science focus: Discovery of the elements 1.3 The role of electrons 1.4 Metals, non-metals and semimetals 1.5 Families of elements Chapter review
3 9 14 17 23 29 36
119
6.1 6.2 6.3 6.4
Types of reproduction Human reproductive systems From gamete to birth Reproductive problems Chapter review
165 172 177 183 186
7
Energy in ecosystems
188
UNIT
2
Earth’s fragile crust
7.1 Energy for life Science focus: Bioaccumulation 7.2 Recycling in nature 7.3 Human intervention—energy crisis Chapter review
189 194 197 204 215
8
Sense and control
216
UNIT
1.1 Atoms and elements 1.2 Arranging the elements
5
8.1 8.2 8.3 8.4 8.5 8.6
Sight Hearing Smell, taste and touch Responding Nervous control Chemical control Science focus: Remote sensing Chapter review
217 226 231 237 241 248 256 260
9
Simple machine technology
263
6
UNIT
The Periodic table
vi vii x 1
UNIT
1
UNIT
Acknowledgements Introduction Curriculum grids Verbs
9.1 The ramp 9.2 Levers 9.3 Going for a spin: wheels, axles and gears
9.4 Pulleys 9.5 The technology of complex machines Science focus: Indigenous technology Chapter review Index
264 269 277 284 289 293 297 299
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We thank the following for their contributions to our text book: akg-images: fig. 6.4.1. Australian Museum: fig. 5.6.9. Australian Picture Library: figures 1.1.2, 1.3.4, 1.4.1, 1.4.2, 2.0.1, 2.3.2, 2.3.5, 3.1.2, 3.2.2, 4.0.1, 4.1.11, 4.2.16, 5.2.3, 5.4.1, 5.5.8, 5.6.1, 5.6.4, 5.6.5, 6.3.6, 6.4.4, 7.1.2, 7.3.8, SF7.5, SF7.6, 8.6.8, 9.0.1, 9.5.1, SF9.8. Cancer Council Victoria: fig. 8.3.4. David Malin/ Anglo Australian Observatory: fig. 2.1.1. Dorling Kindersley: figures 2.1.7, 4.2.10, 5.5.12, 5.6.3, 6.3.2, SF9.1, SF9.7; Colin Keates©Dorling Kindersley, Courtesy of the Natural History Museum, London, fig. 5.6.6. Getty Images: figures 4.3.7, 5.4.3, 6.1.8, 6.1.9, 8.2.5. Greg Rickard©2004: fig. 1.5.1. Gordon Aird©2004: figures 2.1.9, 4.1.1. John Wiley & Sons Australia: Lofts & Evergreen Science Quest 2 2nd edn©2004 reprinted with permission, fig. 1.1.10. Kerry Whalley©2004: fig. 5.3.1. Lennart Nilsson/ Albert Bonniers Forlag: fig. 6.2.3. Lochman Transparencies: fig. 7.2.5. Mary Evans Picture Library: fig. 3.4.1. NASA©2004: figures 3.2.3, 3.2.6, 3.3.4, 3.4.2, 3.4.3, 3.5.2, 3.5.4, 5.2.2, 5.5.4, SF8.5; Great Images in NASA (GRIN), figures 2.4.5, 3.0.1, 3.2.4, 3.2.5, 3.3.1; NASA Image Exchange (NIX), figures SF3.1, SF3.2, SF3.3, SF3.4, SF3.5; NASDA: fig. SF8.6.
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National Oceanic & Atmospheric Administration (NOAA): fig. 5.3.11. Paramount/The Kobal Collection: fig. 3.5.3. Pearson Education Australia©2004: Karly Abery, figures SF7.2, 9.2.4t, 9.2.7tr, 9.3.2tr, 9.3.8r; Tricia Confoy, figures 9.2.2, 9.2.4b; Lisa Piemonte, figures 2.2.7, 2.4.1. Photolibrary.com: figures 1.0.1, 1.1.3, 1.2.1, 1.5.4, 1.5.6, 1.5.7, 1.5.9, SF1.1, SF1.2, SF1.3, 2.1.3, 2.1.6, 2.3.3, 2.3.7, 2.4.3, 2.4.6, 2.4.9, 3.3.2, 3.3.3, 3.4.4, 3.5.1, 3.5.2, 4.1.3, 4.3.1, 4.3.3, 5.1.1, 5.5.5, 5.6.7, 6.0.1, 6.1.2, 6.1.3, 6.1.4, 6.1.5, 6.3.1, 7.2.1, SF7.1, 8.0.1, 8.1.6, 8.1.11, 8.3.2, 8.5.3, 8.5.6, 8.6.5, 8.6.7, 8.6.10, SF8.1, SF8.4, SF8.7. Picture Source: figures 8.6.13, 9.3.6. Pier Vido©2004: fig. 9.3.2.tl. Retrospect Photography: Dale Mann, figures 9.3.3, 9.3.5. Royal Victorian Eye & Ear Hospital: figures 8.1.5, 8.1.7, 8.1.15, 8.2.3. Sandia National Laboratories: James Pacheco, fig. 7.3.4. Sanitarium Australia: fig. 1.1.9. Science Image Online (CSIRO): fig. SF8.3. Snowy Mountains Hydro Electricity Scheme: fig. 7.3.10. Telstra: fig. 7.3.5. US Geological Society: figures 5.1.7, 5.2.7, 5.4.8. Every effort has been made to trace and acknowledge copyright. However, should any infringement have 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 Prac 1 incorporate the Unit 1.2 practical work. Cross references to practical activities within the units signal DYO 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 • labelling • matching • fill in the blanks.
Destinations A list of reviewed websites is available— these relate directly to chapter content for students to access. Technology activities These are activities that apply and review concepts covered in the chapters. They are designed for students to work independently, and include: • animations to develop key skills and knowledge in a stimulating, visual way • drag-and-drop activities to improve basic understandings in a fun way • interactives to enhance the learning of content in an interactive 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 1.7 Sci-words
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 7.3 Energy in the community
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Science Focus 3
Stage 5 Syllabus Correlation
A fully mapped and detailed correlation of the stage 5 curriculum outcomes is available in the Science Focus 3 Teacher Resource Pack.
chapter
1 23456789
outcomes
The Periodic table 5.1 5.2
Chemical reactions
Origin of the universe
▲
•
•
•
▲
Light
• ▲
5.3
Earth’s fragile crust
Energy in Sense and Reproduction ecosystems control
• •
▲ ▲
▲
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:
x
Simple machine technology
▲ indicates the Key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Areas.
• • • • • • • • • • • • • • •
• • • • • • • • • • • • • • •
Verbs Science Focus 3 uses the following verbs in the student activities. Account
state reasons for, report on
Gather
collect items from different sources
Analyse
identify components and the relationships among them; draw out and relate implications
Identify
recognise and name
Investigate
plan, inquire into and draw conclusions
Apply
use, utilise, employ in a particular situation
Justify
support an argument or conclusion
Assess
make a judgement of value, quality, outcomes, results or size
List
write down phrases only without further explanation
Calculate
determine from given facts, figures or information
Modify
change in form or amount in some way
Clarify
make clear or plain
Outline
Classify
arrange or include in classes/categories
sketch in general terms; indicate the main features of
Compare
show how things are similar or different
Predict
Construct
make; build; put together items or arguments
suggest what may happen based on available information
Contrast
show how things are different or opposite
Present
provide information for consideration
Define
State meaning and identify essential qualities
Produce
provide
Demonstrate
show by example
Propose
Describe
provide characteristics and features
Design
provide steps for an experiment or procedure
put forward (e.g. a point of view, idea, argument, suggestion) for consideration or action
Discuss
identify issues and provide points for and/or against
Recall
present remembered ideas, facts or experiences
Distinguish
recognise as being distinct or different from; note differences between
Recommend
provide reasons in favour of
Record
store information and observations for later
Draw
draw conclusions, deduce
Research
Evaluate
make a judgement based on criteria; determine the value of
investigate through literature or practical investigation
Select
choose one or more items, features, objects
Examine
inquire into
Specify
state in detail
Explain
relate cause and effect; make the relationships between things evident; provide the ‘why’ and/or ‘how’
State
provide information without further explanation
Summarise
express concisely the relevant details
Use
employ for some purpose
1
The periodic
table
Key focus area
5.1, 5.7.1, 5.7.2
Outcomes
>>> The history of science By the end of this chapter you should be able to: draw a simple diagram of an atom showing where you would find the protons, neutrons and electrons use the number of protons to identify similar and different elements describe how the electrons are arranged in the atom use the periodic table to identify elements that would act in a similar way
Pre quiz
identify different and important ‘families’ of elements and explain why they are similar.
1 Identify some of the metals around you right now.
2 Draw what you think an atom looks like.
3 Roughly how many different types of atoms do you think there are? Would it be ten, a hundred, thousands or millions?
4 Why do scientists often use symbols instead of names for elements?
5 Why do some elements have apparently illogical symbols, such as Fe for iron and Na for sodium?
6 Do fish swim in H2O or H2O2 and what’s the difference anyway?
7 The picture on this page is of an alchemist. What were these scientists trying to do?
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1
UNIT
context
1.1 All around us is matter: we breathe it, we drink it and we sit on it. But what is matter made from? This question has been asked many times throughout history. As early as 400 BC the Greek philosopher Democritus thought all matter was composed of atoms of the four elements: earth, air, fire and water. It was believed that atoms could not be broken down or made smaller. The word atomos is Greek for ‘indivisible’.
Atoms Last year you discovered that atoms were smaller-thanmicroscopic particles that make Spacious! up all matter. Atoms are made up were the size atom an If from even smaller particles called of the 2000 Olympic protons (often shown as p+), stadium in Sydney, the nucleus would be about neutrons (n) and electrons (e–). the size of a pea sitting Protons and neutrons are roughly at the centre. The 1800 times more massive than electrons would be specks of dust floating electrons and are located at the around the stands. centre of the atom, in the nucleus. Electrons spin fast around the nucleus in a region of empty space. Neutrons are neutral, having no electrical charge. Protons have a positive charge and electrons a negative charge. Opposite charges attract each other and this keeps the electrons from spinning out from the atom. A simple model of a helium atom
e–
Fig 1.1.1
Fig 1.1.2
Sydney’s 2000 Olympic stadium
Atomic and mass numbers The number of protons in an atom is called its atomic number. Atoms are electrically neutral and must have the same number of electrons as protons. In a neutral atom: atomic number of number of = electrons number = protons The total number of particles in the nucleus (protons + neutrons together) is called the mass number. Neutrons do not add any charge to an atom, so there is no rule connecting them with protons or electrons. mass number of number of + neutrons number = protons These numbers can be shown as:
p+ n nucleus n p+
e–
Mass number: 19 Symbol of the element Atomic number: 9
19 9
F
This indicates that the atom is fluorine and has: • 9 protons and 9 electrons • 10 neutrons (19 – 9 = 10)
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Atoms and elements
>>> Get it right!
Elements Elements are the basic building blocks of all matter and each element is made up of only one type of atom: gold contains only gold atoms, and oxygen contains only oxygen atoms. If atoms belong to the same element then they have the same number of protons and the same atomic number. There are about 112 different types of basic atoms, so there can only be 112 different elements. Each element is given its own symbol. Those known in ancient times often have Latin or Greek names but the rest are more logical.
• Atoms of the same element are alike. • Atoms join together in different ratios. Dalton also produced a table showing symbols and atomic masses of the elements. A section of the table is shown in Figure 1.1.3. We now know that Dalton was not 100% correct. Later chemists discovered that it is possible to break down atoms into protons, neutrons and electrons.
There is a correct way of writing symbols for elements. The first letter is always a capital and the second is always in lower case. For example, calcium is Ca, not CA or ca.
Worksheet 1.1 Finding the symbols for elements
A short history of the elements Aristotle’s theory that all matter was made from the four ‘elements’—earth, air, fire and water—lasted for nearly 2200 years and pushed Democritus’s idea of atoms into the background. In the twelfth century, alchemists began to learn a lot about the chemicals and elements that they worked with in their attempt to change base metals such as copper into gold. This new knowledge made the ancient Greek ideas of the four elements seem less than satisfactory. Over the next six hundred years, scientists continued to improve their understanding of the properties of matter. Using some of Democritus’s original ideas, in 1808 the English scientist John Dalton proposed a new ‘atomic theory’. This stated: • All matter was composed of tiny particles called atoms. • Atoms could not be broken into smaller particles.
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John Dalton’s table of elements
Fig 1.1.3
Molecules and lattices Atoms do not normally exist by themselves but exist in molecules or lattices. A molecule is a group of atoms bonded or joined together. In a crystal lattice, atoms keep bonding together until something stops them. Molecules and lattices have a chemical formula that tells us what type of atoms they contain and the proportion of atoms in them.
Fig 1.1.6
A compound is made up of many identical molecules or units.
H H
H
O
H
H H
O H H H O O H H H O H O H
H
H H
H
O
O
O
H O
H H
O
H
H
H
O H2O
H
O
O
H
UNIT
1.1
H H H2O2
O
Mixtures Fig 1.1.4
Molecules of water and the bleach hydrogen peroxide are both made from hydrogen and oxygen atoms. What a difference a single O atom makes!
carbon atoms
A mixture can be separated by simple physical techniques such as filtration or evaporation since it is made of different elements or compounds simply thrown together. No formula can be written for a mixture. Examples of mixtures include salt water, a can Prac 2 p. 8 of cola, soil, air and blood.
water sugars
An example of a lattice—this one is diamond
Fig 1.1.5
Compounds Compounds are formed when different elements chemically combine. Compounds can either be many identical molecules or a lattice: a drop of water contains millions of H2O molecules and a grain of salt has millions Prac 1 p. 8 of NaCl units.
colourings and flavourings
carbon dioxide
Soft drinks are mixtures of many compounds.
Fig 1.1.7
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>>>
Atoms and elements
UNIT
1. 1
[ Questions ]
Mixtures 13 Use an example to outline how a mixture can be identified.
Checkpoint Atoms 1 Identify which of the three subatomic particles (p+, n, e–): a is the smallest e is neutral b is the heaviest f spins around the nucleus c is positive g are in the nucleus d is negative 2 Use Figure 1.1.1 to help you describe the structure of an atom using the terms ‘protons’, ‘neutrons’ and ‘electrons’.
Atomic and mass numbers 3 Explain the relationship between the number of protons and electrons in an atom. 4 Clarify the following expressions. a atomic number b mass number c nucleus 5 Identify the number of protons, neutrons and electrons that would be found in each of these atoms 26 56 Fe,
28 59 Ni,
29 197 64 Cu, 79Au
6 What information would you use to distinguish between atoms of different elements?
14 A chemical formula could never be written for a glass of cordial. Analyse this statement.
Think 15 Copy the following and modify any incorrect statements so they become true. a The mass number is usually bigger than the atomic number of an atom. b The chemical symbol for iron is FE. c Salt is the compound NaCl. d Most of the atom is empty space. e A molecule is the same as a lattice. 16 Identify each of the following as an element, compound or mixture. Explain your choice for each. a lead, Pb d ammonia, NH3 b nitric acid, HNO3 e peanut butter c sea water 17 Copy the diagrams in Figure 1.1.8 into your workbook. Identify and label each diagram as: atom, molecule, compound, lattice or mixture. Fig 1.1.8 a
b
Elements 7 Use an example to identify the smallest unit of an element. 8 a Dalton proposed his atomic theory in 1808. Outline the theory. b Explain which part of Dalton’s atomic theory was later found to be incorrect.
Molecules and lattices
e c
d
9 Use examples to distinguish between atoms and molecules. 10 Construct a diagram to represent: a an atom of carbon, C b a molecule of water, H2O c a molecule of oxygen, O2 d the lattice of sodium chloride, NaCl
Compounds 11 Describe how compounds are formed. 12 a Identify three examples of compounds b Describe where these compounds may commonly be found.
6
Analyse 18 Distinguish between: a an element and a compound b the element iron and an atom of iron c the compound water and a molecule of water d a compound and a mixture e an atom and a molecule
19 State the elements, and how many there are of each, in a single molecule of: a SO2 b H2S c C12H22O11 d H2SO4 e CH3COOH (take care!)
Atom
Atomic number
Carbon
32
6
12 6C
16
8 9
Number of Symbol for electrons the atom
12
Oxygen Fluorine
Number of neutrons 6
11
Iodine
Skills
Number of protons
6
Sulfur Sodium
Mass number
UNIT
1.1
8
19 127
74
20 Atoms can be compared by examining their atomic structure. Copy and complete the table opposite. 21 Construct edible models of various chemical compounds using toothpicks to represent the bonds between atoms, and different types of confectionary to represent different types of atoms.
Fig 1.1.9
Build models of: • the molecules H2O, H2O2 and other molecules found in this unit • the lattices of diamond and sodium chloride. • a mixture that could represent a soft drink.
Creative writing Journey to the centre of the atom You board your spacecraft-like machine and ready yourself for subatomic miniaturisation. Your mission: to explore the 40 K. Write an account of your journey atomic world of atom 19 to the centre of the atom, describing what you see, particle size, distances travelled and the problems you encounter.
[ Extension ] Investigate 1 Check the nutrition information on the labels of: • a canned food • a breakfast cereal • a milk drink • a soft drink List the ingredients under the headings: element, compound, mixture. 2 Find what foodstuffs are rich in these elements: Na, Ca, Fe, Mg, Zn, I. 3 Find out what an isotope is. Illustrate this concept using examples and diagrams.
Surf 4 Elements in comics? Explore some comic strips by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 1, and clicking on the destinations button.
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>>>
Atoms and elements
UNIT
1. 1
[ Practical activities ] Making a compound
Prac 1 Unit 1.1
2 test tubes, test-tube rack, drinking straw, 1-hole rubber stopper with glass tubing, limewater, marble chips, 2 M hydrochloric acid, safety glasses
PART A 1 Place 5 mL of the limewater in a test tube. Place a fresh straw in the test tube and gently blow bubbles through the limewater. Record your observations. PART B 1 Add a couple of marble chips to another test tube. Cover with 2 cm of hydrochloric acid. 2 Stopper immediately and pass the rubber tubing into a test tube filled with limewater. 3 Record what you see happening in both test tubes.
rubber stopper
2M hydrochloric acid
limewater
marble chips
test tube rack
Preparing CO2
Fig. 1.1.10
Questions 1 Identify the gas that humans breathe out. 2 Evaluate evidence to determine whether the gases made in Parts A and B are the same. 3 Is carbon dioxide an element, compound or mixture? Explain.
Compounds in soft drinks Prac 2 Unit 1.1
glass tubing
Equipment
Method
Aim To compare the amount of carbon
5 Empty the drink into the beaker and stir until it is ‘flat’.
dioxide in soft drinks
6 Find the mass of the beaker and flat drink.
Equipment
7 Repeat for other drinks or share your results with other groups.
Access to an electronic balance (accuracy 0.01 g), 500 mL measuring cylinder, large beaker (over 400 mL), stirring rod, a selection of 375 mL cans of soft drinks, including ‘lite’ drinks
Questions
Method
2 Calculate the mass of CO2 in each drink.
1 Did all the cans contain their advertised volume? 3 Predict which drink you would expect to go ‘flat’ first. Which drink would you expect to stay ‘fizzy’ for longest?
1 Copy the table below into your workbook. 2 Record the mass of a full, unopened can. 3 Find the mass of the empty beaker.
4 ‘“Lite” soft drinks are lighter than normal drinks.’ Assess the validity of this statement.
4 Pour the entire can into a measuring cylinder. Record the actual volume.
5 What does ‘lite’ refer to?
Drink
8
rubber hose
Aim To prepare the compound carbon dioxide
Ingredients
Mass of full can (g)
Mass of empty can (g)
Mass of empty beaker (g)
Volume of drink (mL)
Mass of beaker and flat drink (g)
Mass of CO2 (g)
UNIT
context
1. 2 The story of the periodic table begins in 1829, with the German chemist Johann Dobereiner. He was the first to see a relationship between the properties of the 55 elements known at that time and their atomic masses.
A short history of the periodic table In 1864, the English chemist John Newlands arranged the sixty or so known elements in order of increasing atomic mass. When placed in columns of seven, similar elements tended to be in the same horizontal rows. Unfortunately, the rows of his table also contained some dissimilar elements, but at least it was a start. Later, in 1869, Russian chemist Dmitri Ivanovich Mendeleev arranged the known elements in order of atomic mass, putting the known ‘families’ into vertical columns. To do this he needed to leave gaps in the table, predicting that these were elements not yet discovered. Using ‘family likeness’, Not a bad guess! Mendeleev predicted what Mendeleev left spaces in his table for chemical properties these undiscovered elements unknown elements could have. and predicted their When eventually these elements properties. The table for shows his predictions were discovered, their properties ment that is below ele the closely matched his predictions. ic silicon on the period ed In 1868–69, German chemist table, and that he nam nt me ele e Th n. Lother Meyer constructed a Eka-silico ered in 1886 cov dis s wa similar table to that of Mendeleev w called and is no germanium.
Mendeleev’s prediction
Germanium
72
72.6
Dirty grey
Grey/white
Density (g/cm )
5.5
5.35
Boiling point (ºC)
Below 100
84
Property Atomic mass Colour 3
Dobereiner showed that groups of elements acted remarkably similar to each other, as if they belonged to the same ‘family’: their physical properties (colour, melting and boiling points, density, hardness) and chemical properties (the way they reacted with other chemicals) were alike. He noted that the properties of the element bromine seemed halfway between those of chlorine and iodine. Being able to group similar elements together was the beginning of the periodic table.
A portrait of Mendeleev
Fig 1.2.1
by comparing the physical properties of elements with atomic mass. He did not leave gaps for undiscovered elements and went into print in 1870, one year after Mendeleev. Despite losing the race to be first, Meyer is acknowledged as a joint ‘father’ of the periodic table. The present periodic table (see Figure 1.2.2) is very much like the later table designed by Meyer.
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Period 1 Period 2 Period 3 Period 4 Period 5 Period 6 Period 7
Group I
H Hydrogen
Group II
Ce
Special blocks
Tc transition elements lanthanides
Fig 1.2.3
Lu Lr
Group VI Group VII Group VIII
O
9
Fluorine
F
10
Neon
Ne
Group V
N
8
Oxygen
Group IV
C
7
Nitrogen
Group III
He
B
6
Carbon
2
Helium
5
Boron
Ar
actinides
Cl
18
Argon
Be
1
U Np
S
Chlorine
Li
Th
P
Sulfur
4
Si
Phosphorus
Beryllium
Al
Silicon
3 Mg
Aluminium
Lithium
Na Magnesium
transition synthetic
Sodium
Kr
17 Zn
Br
Cu
16 Ni
Se
Co
As
Fe
15
Mn
36
Krypton
14
Cr
35
Bromine
Ge
V
34
Selenium
Xe
33
32
I
Arsenic
31
Te
Gallium Germanium
Sb
30
Sn
Zinc
In
29
Cd
Copper
Ag
28 Pd
Nickel
Rh
54
Xenon
27
13 Ti 25
Ru
53
Iodine
Cobalt
Ga
Sc 24 Tc
52
Rn
Tellurium
At
51
Po
Antimony
Bi
50 Pb
Tin
Tl
49 Hg
Indium
Au
86
Radon
48
45
Pt
85
Astatine
Cadmium
44
Ir
84
Polonium
47 Os
83
Bismuth
Silver
Re
82
Lead
46
41 W
81
Thallium
Ruthenium Rhodium
40 Ta
80
Mercury
Palladium
26
12
23 Mo
43
Technetium
Vanadium Chromium Manganese
Nb 42
Molybdenum
Hf
79
Gold
Zirconium Niobium
Iron
Ca 22
Titanium
K 21
Scandium
11
20
39
Yttrium
La*
Zr
Calcium
38
Y
19 Sr
Potassium
Rb 37 Ba
Rubidium Strontium
Cs
78
Platinum
Lu
Lr
Yb
No
Tm
77
67
Md
Er
Iridium
Uub 112
66
Fm
71
76
Uuu 111
65
Es
Lutetium
Osmium
Uun 110
64
Cf
70
75
Mt 109
Ho 63
Bk
Ytterbium
Rhenium
Hs 108
Dy 62
Cm
97
symbol name atomic number
96
98
99
100
101
102
103
Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium
Am 95
Curium
Pu 94
69
74
Ns 107
Tb
93
Thulium
Tungsten
Sg 106
Gd 61
92
H 1
Hydrogen
68
73 Ha 105
Eu
Hahnium Seaborgium Nielsbohrium Haffium Meitnerium Ununnilium Unununium Ununbium
Sm 60
Np 91
metals metalloids non-metals
Ersium
Tantalum
72
Lanthanum Hafnium
57
56 Rf
Barium
Ac** 104
Rutherfordium
55 Ra 89
Actinium
Cesium
Fr 88
Radium
Pm 59
U
Samarium Europium Gadolinium Terbium Dysprosium Holmium
Nd
Pa
Praseodymium Neodymium Promethium
Pr
87
90
Thorium Protactinium Uranium Neptunium Plutonium Americium
Th
58
Cerium
Ce
Francium
*Lanthanides 58–71 **Actinides 90–103
The periodic table
gas at room temperature
liquid at room temperature
Legend
Fig 1.2.2
10
>>> Arranging the elements
The final ‘modern’ periodic table was the result of work by a young English physicist, Henry Moseley, in 1913. He suggested that the physical and chemical properties were related to the atomic number, rather than mass. He refined the previous periodic tables to come up with a more accurate one with fewer errors Prac 1 and fewer missing p. 12 elements.
Henry Moseley World War I deprived the world of one of its most promising young experimental physicists. Moseley died on 10 August 1915 in the Battle of Suvla Bay, just north of Anzac Cove, Gallipoli. He was only 27 years old.
Features of the periodic table About 80% of the elements in the periodic table are metals. Another smaller set of elements are classified as non-metals. Separating the metals and non-metals is a set of elements that act a little like both—the semi-metals (sometimes called the metalloids).
UNIT
1. 2
UNIT
1.2 The most reactive metals (for example Fr) are in the bottom left of the table and the most reactive non-metals are in the upper right (F). Horizontal rows in this table are called periods and are numbered 1 to 7. Vertical columns are called groups and are given the Roman numerals I to VIII. There are blocks of elements Warning, warning! without normal group numbers: Pure fluorine is an extremely dangerous gas the transition elements, the that will react violently lanthanides and the actinides. with just about anything. There are at least fifteen It was not successfully synthetic (artificial) elements, made prepared until 1886 and only after several solely in the laboratory by nuclear scientists died. reactions. All of these quickly break down into other stable elements. Some change so quickly that few experiments have been able to be Prac 2 performed on or with them. p. 13
Worksheet 1.2 Who am I?
[ Questions ]
Checkpoint A short history of the periodic table 1 a Identify three scientist who worked on the periodic table. b Outline the contribution that each scientist made. 2 Explain why Mendeleev left some gaps in his original table.
Features of the periodic table 3 Copy the following and modify any incorrect statements so they become true. a Horizontal rows in the periodic table are transition metals. b Vertical columns are called ‘periods’. c The most reactive metallic atom would be lithium, Li. d The most reactive non-metallic atom would be fluorine, F. e The transition elements are all metals. 4 Identify the following elements and classify them as either metal, non-metal or semi-metal: Cl, Na, Ar, Si, Cu, Ge 5 List the names of the semi-metals. 6 List the symbols of the non-metals. 7 List five common transition elements.
8 Identify the groups that most metals and non-metals are found in. 9 Identify five physical properties that can be used to describe elements. 10 Identify three elements that: a are in Group VI b are in Period 3 c would be in the same ‘family’ but not in Group VI d would show similar chemical properties but are not in a, b or c above e are noble gases
Think 11 The symbols of some elements come from their Greek or Latin names. Use the periodic table to interpret which elements these names describe: a cuprum d wolfram b aurum e bromos c plumbum 12 The word ferrous means ‘containing iron’. Use the element symbols to recommend a reason why. 13 Plumbing pipes were once made of lead. Deduce where the words ‘plumber’ and ‘plumbing’ came from.
>>
11
>>>
Arranging the elements
Analyse 14 Identify the Roman numeral for each of the following numbers. a 5 b 4 c 7 d 2 15 Use the periodic table to predict the mass number of: a a hydrogen atom with 3 neutrons b a chlorine atom with 20 neutrons c a nickel atom that has 30 neutrons
[ Extension ] Investigate 1 The scientists below had elements named after them. Investigate their lives and the important work done by each of them. Write a short biography to summarise your information. Curie, Mendeleev, Einstein, Nobel, Lawrence, Fermi
Create 2 a Research an element of your choice and gather the following details. i name of element, symbol, atomic number and whether it is a metal, non-metal or semi-metal
UNIT
1. 2
Aim To compare the density of some elements and compounds
Equipment DYO
Cubes or cylinders of aluminium, brass, lead, wood, ice; a collection of small items such as pebbles, candles, chunks of concrete or cement, copper wire; access to an electronic balance, rulers, beakers and measuring cylinders
Method 1 For each sample of material you need to measure its mass in grams. 2 You must also find the volume. Use a mathematical formula for samples with a regular shape such as a cube. You need to develop a way of measuring volume
12
ii iii iv
appearance: include a colour photograph and state (solid, liquid or gas) at room temperature at least two uses of the element a brief history of its discovery
b Present your information as a poster.
Surf Find out more about the following science applications by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 1, and clicking on the destinations button. 3 Do some further research on the properties and uses of the elements. 4 Compare Mendeleev’s original periodic table with the one we use today. What differences and similarities are there? 5 Compare alternative versions of the periodic table. List the advantages and disadvantages of the different versions.
[ Practical activities ] Investigating a physical property
Prac 1 Unit 1.2
16 Construct a timeline to represent the historical development of the periodic table. Include dates, scientists’ names and their main contribution.
accurately for strange shapes. Volume must be measured in ‘centimetres cubed’ or cm3. You can measure in mL, but will need to convert your measurement into cm3 (1 mL = 1 cm3). 3 Draw a series of sketches showing how you intend to measure the volume of the irregular shapes. 4 Collect all the necessary measurements for each sample you have. 5 Test whether each sample floats on water. 6 Density measures the mass of material that fits into a certain volume. Use the following equation to calculate the density of each sample. Density =
mass (g) volume (cm3)
7 Place your results in a table like the one on the next page.
Sample
Mass (g)
Dimensions (cm)
Volume (mL)
Volume (cm3)
Density (g/cm3)
UNIT
1.2 Float/sink
Elements of death Depleted uranium (DU) and tungsten are twice as dense as lead, so ammunition shells made from them can penetrate even the heaviest of armour on tanks. The tips of tungsten shells become ‘rounded’ on impact but DU burns at the edges on impact, making it thinner, sharper and even more penetrating. DU shells have been used widely in various military conflicts since the late 1990s. A large number of troops and civilians have since developed leukaemia—a possible side effect of exposure to the burnt shells?
8 Take measurements to find the density of a sample of water.
Questions 1 Propose a rule about densities and floating. 2 Identify how to convert between mL and cm3. 3 The density of water is 1.0 g/cm3. How does your answer compare to this? Identify the errors that may have caused your answer to be different. 4 What is heavier, a tonne of lead or a tonne of feathers? Account for your answer.
Comparing elements Prac 2 Unit 1.2
Aim To examine the physical and chemical properties of common elements
Equipment Samples of sulfur, aluminium, carbon, silicon, tin, zinc, lead, magnesium, calcium, iron; steel wool; 3 to 4 test tubes and rack; power pack about 2 V or battery; wires with alligator clips; light globe; safety glasses
AC
ammeter
DC
VOLTS 0.2
0.4
0
1 Construct a table in your workbook like the one below.
–
2 Describe the appearance of each sample.
power pack
5A V
0.6
1.0
AMPS
0.8
Method
1A
3 ‘Shine’ the sample with the steel wool. Record its appearance now. 4 Try and bend the sample. Does it bend or crumble? 5 Place some of the sample in water: does it float? Watch for any reaction.
material to be tested
6 Test whether the sample conducts electricity.
Questions
switch alligator clip
1 Identify the properties that are similar in each of the metals. 2 Identify the properties that are similar in each of the non-metals. Element
Metal or non-metal
Appearance
Shiny or dull when polished
Fig 1.2.4
Floats/sinks
Does it conduct?
Action with water
Electrical conductivity
13
Science focus: Discovery of the elements Prescribed focus area: The history of science Paving the way for Dalton’s atoms By 1808, John Dalton had provided a solid scientific basis for an atomic theory of matter. In producing his theory, Dalton had benefited from the ideas and studies of many who had gone before him. An idea proposed by Frenchman Pierre Gassendi in 1649 was important in paving the way for the idea of atoms to become accepted. The Church had originally adopted Aristotle’s idea that matter was composed of the four elements: earth, air, fire and water. However, it had opposed ‘atomism’ and equated atoms with ‘godlessness’ due to the original suggestion by Democritus that there was no end to the universe since it had not been created by any outside power. But unlike the early Greeks, Gassendi suggested that atoms existed and moved dei gratia (as a gift of God). This new view was important in allowing the atomic view to gain eventual acceptance by the Church.
The path to the elements The alchemists based their ideas on Aristotle’s four elements. Although they didn’t succeed in their aim to transmute (change) base metals into gold, they did provide a lot of useful information about the composition and properties of many materials. The materials that were considered elements by early chemists like Dalton were those that could not be separated into simpler parts. The English scientist Robert Boyle (1627–1691) supported an atomic view, having suggested in his 1661 book, The Sceptical Chymist, that ‘the chemical elements must be actual, physical substances rather than the “principles” used by the alchemists’.
Fig SF1.2
Lavoisier used sound scientific method to investigate elements. In this experiment done in 1776 he separated air and discovered the element oxygen.
The French chemist Antoine Lavoisier (1743–1794), who clearly established chemistry as a modern science, also suggested that matter was composed of elemental atoms. The following text is an excerpt from his book, Elements of Chemistry, published in 1789. The text reveals his insight into atoms, and clearly demonstrates how he applied the scientific method to his work. Fig SF1.1
14
The four elements of matter as proposed by Aristotle: water, fire, earth and air
… if, by the term elements we mean to express those simple and indivisible atoms of which matter is composed, it is extremely probable that we know nothing at all about them; but if we apply the term elements, or principles of bodies, to express our idea of the last point which analysis is capable of reaching, we must admit as elements all the substances into which we are capable, by any means, to reduce bodies by decomposition. Not that we are entitled to affirm that these substances that we consider as simple may not be compounded of two, or even of a greater number of principles; but since these principles cannot be separated, or rather since we have not hitherto discovered the means of separating them, they may act with regard to us as simple substances, and we ought never to suppose them compounded until experiment and observation have proved them to be so.
A discovery provides a valuable tool Towards the end of the eighteenth century, the list of known elements had begun to grow rapidly. The development of the electrochemical cell (battery) by Alessandro Volta in 1800 provided those exploring matter with the first continual source of electricity to use in experiments. It wasn’t long before electricity had been used to break up water into the elements hydrogen and oxygen using electrolysis. In 1807, the English chemist Sir Humphry Davy used a large battery with conducting electrodes to explore soda and potash, which were believed to be elements. He found that as the solid blocks melted, drops of shiny metal began to form which burnt spontaneously. When he removed air to prevent combustion, Davy was able to produce two undiscovered, highly reactive metal elements, sodium and potassium. This proved that soda and potash were in fact compounds.
Quantitative studies bring increased understanding The use of electricity significantly improved the understanding of matter and elements over the next few years. New quantitative ways of measuring elements were developed, and as scientists discovered new elements the properties of these were studied carefully. Many scientists carrying out quantitative physical and chemical investigations identified patterns from this research. Ultimately this
Lavoisier gives a definition of an element and suggests different atoms for each element but little understanding of them. Lavoisier refines definition of an element to suggest that they cannot be further decomposed by the methods available. Here Lavoisier suggests that the then-current methods might not reveal the whole picture, and that perhaps atoms are made up of parts. Lavoisier clearly suggests that the scientific method is the best way to develop our understanding of atoms.
Sodium metal is highly reactive and burns in contact with air.
Fig SF1.3
new information led to Mendeleev developing the periodic table. The search for the missing elements predicted by Mendeleev as gaps in his periodic table eventually led to all but a few of the elements with an atomic number less than 92 being found.
The final steps: artificial elements As a greater understanding of the structure of atoms developed, particularly knowledge about the nucleus and nuclear forces, it became obvious that the missing elements would not exist naturally.
15
In order to complete the picture, humans have used nuclear reactions to artificially create (synthesise) the missing elements, including promethium (61) and technetium (43). The use of nuclear reactors, and the explosion of nuclear weapons, have added to the known elements. A number of new artificial (synthetic) elements have been created that have an atomic number greater than atomic number 92, uranium.
Different-sized atoms The element uranium, number 92 on the periodic table, is the largest and heaviest naturally occurring element. Hydrogen, number 1 on the periodic table, is the smallest, lightest atom. The nucleus of a hydrogen atom is just a single proton; all other elements have neutrons in the nucleus as well.
[ Student activities ] 1 Explain some of the reasons why the list of elements was so small in 1750 (less than 20 known elements). 2 Research and outline some of the sources of electricity that were available before the invention of the electrochemical cell by Alessandro Volta.
16
The order of discovery of the elements Discovery period
Elements in order of discovery
Total number known
ancients
C, S, Au, Cu, Ag, Fe, Pb, Sn, Hg
alchemists
Sb, As, Zn, Bi, P
14
1735–1745
Co, Pt
16
9
1745–1755
Ni
17
1755–1765
None discovered
17
1765–1775
H, N, O, Cl, Mn, F
23
1775–1785
Mo, Te, W
26
1785–1795
U, Zr, Sr, Ti, Y
31
1795–1805
Cr, Be, V, Nb, Ta, Ce, Pb, Rh, Os, Ir
41
1805–1815
K, Na, Ba, Ca, Mg, B, I
48
1815–1825
Li, Cd, Se, Si
52
1825–1835
Al, Br, Th
55
1835–1845
La, Tb, Er, Ru
59
1845–1855
None discovered
59 63
1855–1865
Cs, Rb, Ti, In
3 The real breakthrough with organising the elements into the periodic table came with the development of quantitative methods for measuring properties. a Explain the term ‘quantitative’. b John Dalton developed a way to measure the relative atomic mass of the different elements. Research and describe the meaning of the term ‘relative atomic mass’, using examples.
1865–1875
None discovered
63
1875–1885
Ga, Yb, Sm, Sc, Ho, Tm
69
1885–1895
Pr, Nd, Gd, Dy, Ge, Ar
75
1895–1905
He, Eu, Kr, Ne, Xe, Po, Ra, Ac, Rn
84
1905–1915
Lu
85
1915–1925
Hf, Pa
87
4 Examine the table showing the discovery of elements over time.
1925–1935
Re
88
1935–1945
Tc, Fr, At, Np, Pu, Cm
94
a In small groups discuss reasons why some elements were easy to find and obtain, while others proved to be very difficult. b Construct two lists: • things that make elements easier to find and purify • things that make elements difficult to find and purify c The element potassium is difficult to identify and collect, while the element carbon is easy. Propose possible reasons for this difference. 5 Choose one of the scientists mentioned in this chapter and research their background. Find out: a when they lived and died (or are they still alive?)
1945–1955
Am, Pm, Bk, Cf, Ex, Fm
100
1955–1965
Md, No, Lr
103
1965–1999
Db, Rf, Sg, Bh, Hs, Mt, Uun, Uuu, Uub
112
b what contribution they made to the knowledge of the periodic table, elements and science d whether they worked with other scientists, and if so, with whom. Present your research to the class as a short presentation (2 to 3 minutes long).
UNIT
context
1. 3 Atoms in the periodic table are arranged according to their atomic numbers. Some physical properties (such as density) depend on an atom’s atomic number and mass number. In chemical reactions, however, the electrons are far more important. The British physicist J.J. Thomson discovered electrons in 1897, and this led to our current understanding of chemical reactions and properties. In fact, electrons determine all the chemical reactions that an atom takes part in and the numbers of each atom in any new compound formed.
Chemical reactions happen when atoms bump into each other. The protons and neutrons are relatively unaffected by the bump, being at the centre of the atom in the nucleus. The outermost electrons, however, are greatly affected and are easily ‘grabbed’ or shared by other atoms.
Fig 1.3.1
Heavy fleas! Imagine that all the empty space from eve ry atom in our body is removed. The electron s are now stuck to the nucleus and we are the size of a flea! We stil l have the same weigh t as before though!
The structure of an atom showing energy levels, and a convenient way of imagining it!
Electron shells Electrons do not orbit just anywhere around the atom, but in shells or energy levels, which are numbered 1, 2, 3 and 4. It is easy to picture these shells if we imagine a pea as the nucleus of our atom. The pea sits in the middle of a table tennis ball (our first shell). All this sits inside a tennis ball (second shell), which sits inside a basketball (third shell), which sits inside a beach ball (fourth shell). Imagine electrons as ants on the outside of each ball. Each ant stays as far away as possible from the other ants (electrons repel each other because of their negative charges). Only two ants fit on the first ball (otherwise they would be too close) but more ant-electrons can fit onto the next three balls because those balls are bigger. The number of electrons that can actually fit in each shell is:
First shell
Second shell
Third shell
Fourth shell
Maximum of 2 e–
Maximum of 8 e–
Maximum of 18 e– but happy if it holds only 8
Maximum of 32 e– but happy if it holds only 8
Well I hate you both!
e– N I hate you too!
M
e–
e– e–
e– e–
L K
+ve
e– e– I hate you!
e–
Electronic configuration The arrangement of electrons in the shells is called the atom’s electronic configuration. Silicon (Si) has 14 electrons. Two electrons go into the first shell, eight into the second and the remaining four go into the outer shell: its electronic configuration is written as 2,8,4.
17
>>>
The role of electrons The electronic configurations of the first 20 elements are shown in the table at right.
Periods, groups and electrons
Group I Period 1
H 1
Period 2
Li 2,1
Notice that: Period 3 Na 2,8,1 • the number of shells used by an atom is the same as the Period 4 K 2,8,8,1 period number • the group number is the same as the number of outer shell electrons (helium, He, is an exception). For example, F has the configuration 2,7. It has two shells, so it is placed in Period 2. It has seven electrons in its outer shell and so is placed in Group VII. If two atoms are in the same group, they have the same number of outer shell electrons and will have similar properties. As we move down a group, more shells are used. The atoms get bigger and slight differences in properties Prac 1 can be expected. p. 21
Atoms that react and atoms that don’t Group VIII (sometimes called Group 0) contains elements that are stable and rarely react. Group VIII elements are called the noble gases. Helium (He) was the first to be discovered—in 1894 by the British scientists Lord Rayleigh and Sir William Ramsay. Ramsay later discovered all the other noble gases and added them to Group VIII. The noble gases are stable
VIII He Ne
Group II
Group III
Group IV
Group V
Group VI
Group VII
Group VIII He 2
Be 2,2
B 2,3
C 2,4
N 2,5
O 2,6
F 2,7
Ne 2,8
Mg 2,8,2
Al 2,8,3
Si 2,8,4
P 2,8,5
S 2,8,6
Cl 2,8,7
Ar 2,8,8
Ca 2,8,8,2
because He and Ne atoms have their outer shells filled and Ar, Kr, Xe and Rn have eight electrons in their outer shell. All other atoms react so that they can become as stable as the noble gases: they also want a filled outer shell, or eight electrons in it. To do this, atoms gain electrons, lose electrons or sometimes even share electrons. Knowing this allows us to start to predict what atoms will do in a chemical reaction!
Ions If the number of electrons changes in an atom, it becomes electrically charged and we call it an ion (a Greek word for ‘the ones that move’). • If an atom loses electrons, it becomes a positive ion. • If an atom gains electrons, it becomes a negative ion. To see an example of how ions form, let’s look at how common table salt, sodium chloride, is formed. If a sodium atom meets a chlorine atom, the sodium loses its outer shell electron to form the sodium ion, Na+. Chlorine takes the electron from sodium to become the ion Cl–. It now has a new name: chloride. Both ions are stable and happily exist as Na+Cl–… sodium chloride (common salt).
Ar
Sodium
Kr
Before
Xe Rn
The noble gases don’t want to react.
18
Fig 1.3.2
+
p
11
Chlorine After 11
Before
After
+
17
17
–
p
–
e
11
10
e
17
18
Charge
Neutral
+1
Charge
Neutral
–1
Element
Atomic number
Number of electrons
Electronic configuration
The atom could lose
Or it could gain
Most likely scenario
Most likely ion formed
H
1
1
1
1e–
1e–
Uncertain
H+ or H-
He
2
2
2
Unreactive –
UNIT
7e
Lose 1 e–
Li+
3
3
2,1
1e
Be
4
4
2,2
2e–
6e–
Lose 2 e–
Be2+
B
5
5
2,3
3e–
5e–
Lose 3 e–
B3+
C
6
6
2,4
4e–
4e–
–
–
Uncertain –
3–
N
7
7
2,5
5e
3e
Gain 3 e
O
8
8
2,6
6e–
2e–
Gain 2 e–
O2–
F
9
9
2,7
7e–
1e–
Gain 1 e–
F–
Ne
10
10
2,8
Unreactive
_
_
_ _
+
_
+ _
+
+ _
+
_
+
+
+
[ Questions ]
N
No ion formed
+
Prac 2 p. 22
1. 3
No ion formed –
Li
The attraction between the positive and negative ions holds the salt crystal together as shown in Figure 1.3.3. Ionic charges for several common elements are shown in the table above.
UNIT
1.3
+ _
+
_ _
+
Checkpoint +
Electron shells
_
+
1 Define the term ‘energy levels’. 2 Identify the number of electrons each shell normally holds.
The sodium chloride lattice: positive and negative attract
Fig 1.3.3
Electronic configuration 3 Clarify what the electronic configuration of an atom shows. 4 Describe the electronic configuration of magnesium.
Periods, groups and electrons 5 Describe what the following have in common: a atoms in the same group b atoms in the same period
Atoms that react and atoms that don’t 6 Identify which group contains elements that rarely react. 7 Distinguish between atoms that react and atoms that don’t react.
Ions 8 Compare a chlorine atom with a chloride ion. 9 Describe what happens when a sodium ion forms. 10 Explain the difference between the formation of a positive ion and a negative ion. Use a diagram to clarify your answer. 11 Identify three positive and three negative ions by name and symbol.
Think 12 Explain why noble gases do not form ions. 13 Sodium chloride has charges but no overall charge. Explain.
>> 19
>>>
The role of electrons
Skills
14 Identify the period and group these atoms belong to: a an atom with configuration 2,4 b an atom with configuration 2,8,6 c an atom with seven electrons d an atom with 15 electrons e Ca f Ne 15 Write the electronic configuration of these atoms. a an atom in Period 2, Group VI b an atom in Period 3, Group VIII c an atom in Period 1, Group VIII (be careful) d an atom of Mg e an atom of S 16 ‘We don’t worry about the number of neutrons when calculating the charge of an ion.’ Justify this statement.
18 Copy out the table on ionic charges (on page 19). Extend and complete it to include all the elements up to calcium, Ca. 19 Copy the following table into your workbook and complete it.
Number of protons
Number of neutrons
Number of electrons
8
6
8
10
10
10
11
10
10
17
16
18
15
15
18
19
18
+1
20
19
+2
8
7
10
Overall charge
Is it an atom or an ion?
Symbol
+
K
–2
Analyse 17 a Copy the following table into your workbook with space for eight more rows: Atomic number
Element (name and symbol)
7
Nitrogen (N)
Number of: Protons Electrons 7
7
b Below is information about eight different atoms. Find their atomic number, name and symbol, number of protons and number of electrons. Place all this information in the table. i an atom with 8 protons ii an atom with 18 protons iii an atom with an atomic number of 3 iv an atom with an atomic number of 19 v an atom in Period 2, Group VII vi an atom in Period 3, Group II vii an atom of phosphorus viii an atom of aluminium c Write the electronic configuration for each of the above atoms and then predict their likely ionic charges. d Construct diagrams to show the structure of four of the above atoms.
20
[ Extension ] Create 1 Construct a mobile of an atom. You could use different-coloured plasticine to represent protons, neutrons and electrons. Wire could represent each electron shell. Shells increase in diameter as you move from the first shell outwards. Use string to assemble the atom so that each shell is free to move independently of the other shells. Have the nucleus hanging in the centre.
Investigate 2 Fireworks display various bursts of colour and brilliance. Research the following about fireworks: a When were fireworks first used and by whom? b What determines the different colours that we see?
UNIT
1. 3
[ Practical activities ] Firework colours
Prac 1 Unit 1.3
UNIT
1.3 2 Briefly place the stick soaked in water in a blue Bunsen flame, then remove it. Record any colour that it gave the flame.
Aim To identify elements by the coloured flames they produce Equipment Bunsen burner, bench mat and matches; tongs; safety glasses; wooden icy-pole sticks soaked overnight in distilled water and solutions of barium chloride, copper chloride, potassium chloride, sodium chloride and strontium chloride; spectroscope (optional) The original Chinese fireworks burned yellow/white only. Today fireworks include metal salts to colour them. The colours come from electrons jumping back and forth from shell to shell.
spectroscope
look for colour tongs blue flame icy-pole stick Bunsen burner
Fig 1.3.4
bench mat
What colour is produced?
Fig. 1.3.5
3 Briefly place each of the other sticks in the flame and record the colour you see. 4 Optional: Point a spectroscope towards a bright portion of the sky (not the Sun). Draw the spectrum you see. Observe each of the coloured flames through the spectroscope, recording what you see.
Questions 1 Clarify the purpose of the stick soaked in water only.
Method
2 Explain why the water needs to be distilled and not from the tap.
1 Copy the following table into your workbook. List all the solutions used.
Solution
Compound formula
Distilled water
H2O
Barium chloride
BaCl2
Colour of flame
Metallic element in solution
Non-metallic element in solution
Ba
Cl
3 The non-metallic element did not add colour to the flame. Describe any proof you have. 4 Identify which of the solutions you tested would be best to colour a firework: a red b green c blue/green
>>
21
>>>
The role of electrons
5 The grains that spray out and give colour are made of starch soaked in the appropriate salt. Construct a diagram of a grain that would burn and give the colours: a blue/green, then purple b red, then green
grains of starch covered with explosive black powder propellant charge
6 Propose where the electrons got the energy to jump shells.
Fig 1.3.7
You need these jigsaw pieces. grain of 2 salts fuse and 3 x
3x
Fig 1.3.6
A firework ‘grain’
Na+
Mg2+
2x
O2– Al3+
F
Ions get together!
N3–
–
Aim To construct models of ionic compounds Prac 2 Unit 1.3
using an ion jigsaw
Equipment
To make a compound: magnesium fluoride
Photocopy of worksheet 1.3
F–
Worksheet 1.3 Ions get together
2+
Mg
F–
Method
MgF2
1 Carefully cut around the jigsaw pieces on the sheet provided by your teacher. 2 Copy the following table into your workbook with space for nine rows. Compound name
Positive ion used
Negative ion used
Compound formula
3 Use the jigsaw pieces to ‘create’ the following compounds: sodium fluoride, sodium oxide, sodium nitride, magnesium fluoride, magnesium oxide, magnesium nitride, aluminium fluoride, aluminium oxide, aluminium nitride 4 Put all the relevant information about each compound in the table.
22
Total positive charge
Total negative Overall charge charge of compound
5 Re-label some of the pieces to create: lithium chloride, calcium bromide, barium sulfide, strontium phosphate
Questions 1 Identify whether the overall charge of each compound was positive, negative or neutral. 2 Propose a rule that allows you to predict the formula of a compound.
UNIT
context
1. 4 When the Egyptians used native metals such as gold in 2000 BC, they recognised that these metals had different physical properties to other materials. Whether they distinguished between metals and non-metals is not known.
What is a metal? In the periodic table, metallic elements outnumber non-metallic elements four to one. Metals: • allow heat and electricity to pass easily through them. They are excellent conductors of heat and electricity. • shine when polished or freshly cut. We describe metals as lustrous. • can be hammered into new shapes. Scientists call this malleable. • are ductile. This means that they can be stretched and drawn into long thin wires.
In 1789 Lavoisier grouped the 31 known elements into four groups based on their chemical properties. The groups were: • simple substances belonging to all kingdoms of nature—gases • simple substances not metallic—non-metals • simple metallic bodies—metals • simple earthy substances—earths. You probably noticed that Aristotle’s idea of four elements—earth, air, fire and water— still played a part in the above groups. In this unit we will investigate the differences between some of these Prac 1 p. 26 groups.
• are solid at normal room temperature. (Mercury, however, is a liquid.) • have high densities. Most metals sink in water. • have atoms that form lattices.
Prac 2 p. 27
Prac 3 p. 27
About non-metals
Metals (from left to right): copper, mercury (liquid only) and magnesium
Fig 1.4.1
Non-metals share the following properties: • All (except carbon) are either poor conductors of electricity or do not conduct at all (insulators). • They have relatively low melting and boiling points and are usually liquids or gases at normal room temperature. • They are brittle and tend to crumble into powders. • They are dull, having little or no shine. • Group VIII atoms can exist as single atoms. • Most other non-metallic atoms form molecules containing two atoms. Some have more atoms than this, and a few form lattices. Prac 4 p. 28
23
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The role of electrons
Non-metallic atom
Name of atom
Ion formed
Name of ion
F
Fluorine
F–
Fluoride
Chlorine
–
Chloride
–
Bromide
2–
Oxide
3–
Nitride
Cl Br O N
Bromine Oxygen Nitrogen
Cl
Br O N
The odd couple: H and He Fig 1.4.2
Non-metals (clockwise from top left): sulphur, bromine (liquid only), phosphorus, iodine and carbon
Those electrons again! The strength with which an atom holds its electrons is called its electronegativity. Metal atoms have low electronegativity and non-metals have high electronegativity. Metals have little control over their outer electrons, while non-metals have tight control over theirs and are greedy for more. In a ‘fight’ (or chemical reaction), non-metals try to ‘rob’ metals of their outer-shell electrons: they each end up with eight electrons in their outer shells. The metal forms a positive ion and the non-metal forms a negative ion. The name of the nonmetal often changes too, as shown in the table above right.
UNIT
1. 4
[ Questions ]
Checkpoint What is a metal?
Coa 1.3 parts per million of uranium. It is estimated that in 1991 alone, 6630 tonnes of uranium was belched into the sky. Of this, 47 tonnes was weapons-grade U-235, sufficient to make 1700 atom bombs!
Semi-metals The semi-metals or metalloids act like non-metals in most ways. They do, however, have some properties that are metallic: most importantly, they can conduct electricity.
1 State whether metal atoms form molecules or lattices. 2 Choose one metal from Figure 1.4.1 and describe some of its properties.
About non-metals 3 Explain the various atomic structures in which non-metals can exist. 4 Choose one non-metal from Figure 1.4.2 and describe some of its properties.
24
Hydrogen has only one electron so it can either lose it to become the hydrogen ion, H+, or it can gain Helios, the Sun another one to become the hydride Helium (He) was discovered on the Sun ion, H–. It can therefore act like a before it was discovered Group I or Group VII element, on Earth. How? The Sun depending on what it comes into emits electromagnetic radiation (light) and one contact with. particular frequency Helium’s two could not be explained. electrons fill its It was coming from a outer shell and new element that was given the name helium, therefore it acts after the Greek word for Don’t breathe: very similar to the Sun, helios. it’s dangerous! the noble gases of ning bur Each year the of Group VIII. It coal around the world es tonn could be placed in Group II but is releases 26 000 of the semi-metal usually placed in Group VIII arsenic (As) into the air! because of family resemblances. l also contains about
Those electrons again! 5 Identify which has a higher electronegativity: a metal or a non-metal. 6 Identify the ions that these atoms would probably form. a Na b S c I
d P e Al
The odd couple: H and He 7 Explain why H could be placed: a in Group I b in Group VII c by itself 8 Helium could be placed in Group II. Explain. 9 Explain why helium is normally placed in Group VIII.
Semi-metals 10 a Identify another name for the semi-metals. b Outline the properties of semi-metals. c Identify two examples of semi-metals.
Think 11 Define the following words. a lustrous b malleable c ductile d brittle e electronegativity f semi-metal
UNIT
1. 4 13 At normal room temperature, identify how many non-metals exist as: a solids b liquids c gases 14 Identify three non-metallic elements that: a are gases at room temperatures b are liquids at room temperatures c are in Group V d are in Period 2 e would be related to chlorine f would have larger atoms than those of oxygen 15 Outline the likely charges of the ions that belong in Groups I, II, III, V, VI, VII and VIII.
Skills 16 Construct a table to classify the following properties into those that belong to metals and those that belong to non-metals: ductile, normally gas or liquid, dense, malleable, brittle, lustrous, excellent conductors, dull, poor conductors, normally solid
12 Identify the metal(s) that: a is the only metal that is a liquid at 25°C b are in Period 3 c are in Group IV d would form +2 ions
Creative writing War of the electrons
[ Extension ] Investigate 1 Investigate the metals lead and mercury. a Find out why they are cumulative poisons and what this means. b Find out the main sources of these metals. c How do they affect us? d Create a warning leaflet that could be placed in particular areas to alert people of the potential dangers of exposure to lead and mercury. 2 The Iron Age represented a massive advance in the technology of food collection and warfare. Find when this was and explain how iron (and its alloy, steel) changed the lives of people at that time.
Atom meets atom. They both want electrons. They fight for control. They form an alliance of atoms, where they join in relative peace. You are a sub-microscopic war correspondent reporting on the battle taking place in a chemical reaction. Write a short history of the war. Your report must identify: • the atoms taking part • their relative strengths • what electrons are affected • the fate of the electrons • what the atoms look like after the war. Suitable choices could be: • the Monarchy Alkali (say, Na, K) and the Republic of Halo Genes (F, Cl, etc.) • the Empires of the Alkaline Earths (Mg, Ca, etc.) and the Halo Genes. • •
For researching correspondents: bromos and his evil-smelling twin brother Br magnos and her brightly burning twin sister Mg.
25
>>>
Metals, non-metals and semi-metals
UNIT
1. 4 Prac 1 Unit 1.4
[ Practical activities ] Metal crystals
3 Pour the agar solution into a Petri dish and gently place the zinc strip in the centre.
WARNING: Silver nitrate stains skin badly. Lead nitrate is very poisonous and reactive. Wear safety glasses and gloves at all times when dealing with it.
4 Allow the agar to cool and set into a jelly.
Aim To examine the crystal shapes of compounds containing metal ions. Equipment Sterilised Petri dish; 250 mL beaker; Bunsen burner; tripod; gauze mat; bench mat; 1 cm x 4 cm strip clean zinc sheet; one 0.3 g sample of silver nitrate, lead nitrate, copper sulfate or tin chloride; 0.5 g agar powder; 40 mL distilled water; stirring rod; stereo microscope (optional); safety glasses; gloves
Method 1 Place 40 mL of deionised water in the beaker and sprinkle 0.5 g of agar into it. Warm gently over the Bunsen burner, stirring until dissolved. 2 Remove the beaker and add one of the 0.3 g samples to it. Stir until dissolved.
5 Place the lid on top. 6 Inspect the metal crystals that form over the next few days. If available, use a stereo microscope for a better view. 7 Draw the shape of the crystals you see in each group’s Petri dish. Describe any colour changes.
Questions 1 Explain why the crystals were grown in agar and not in a liquid. 2 Would these crystals be molecules or a lattice? Explain. 3 Describe what happened to the colour of the agar with dissolved silver nitrate. This is also what happens if silver nitrate comes into contact with your skin. 4 Petri dishes and agar are often used in pathology. Investigate how and why they are used.
Part A 0.3 g sample
folded paper
stirring rod Part B 0.5 g agar in 40 mL water agar solution with dissolved sample
zinc sheet
Petri dish
Making an agar plate
26
Fig. 1.4.3
Changing the properties of metals
More crystals Aim To make silver metal crystals Prac 2 Unit 1.4
Prac 3 Unit 1.4
Equipment 100 mL conical flask, cork or rubber stopper, silver nitrate solution, 10 to 15 cm length of copper wire and/or strip of copper foil
DYO
Method 1 Use Figure 1.4.4 to write your own method for another way to prepare silver crystals.
UNIT
1. 4 Aim To observe the effect of heating and cooling on crystal size
Equipment Four steel hairpins (steel is about 98% iron), steel wool, Bunsen burner, bench mat, matches, 250 mL beaker filled with water, wooden peg, safety glasses, pliers (optional)
Method 1 Copy the table below into your workbook.
Treatment
Number of bends needed to break pin
Effect of treatment
None Normalising
cork stopper
Quenching Tempering
copper wire copper foil
2 Repeatedly bend a hairpin until it breaks. Count how many bends it took. silver nitrate solution
3 Normalising: Take another hairpin and heat the middle in a blue Bunsen burner flame until it is red hot. Allow it to cool on the bench mat. 4 Quenching: Heat another hairpin in the same way, then drop it into a beaker of water.
hairpin peg blue flame top of blue cone
Fig 1.4.4
Making silver crystals
2 Have your teacher check your method and, if it is approved, set up your experiment. 3 Place the flask in a safe, dark place for a few days.
Question 1 ‘Copper ions give solutions a blue colouring.’ Describe two observations to support this inference.
cold water quenching
Rapid cooling produces small crystals.
Fig. 1.4.5
>> 27
Metals, non-metals and semi-metals
5 Tempering: Heat and quench the remaining hairpin, then polish it with steel wool. Re-heat the shiny part of the pin. Remove the pin occasionally to check whether it has gone blue. Once it has, remove the pin from the flame and allow it to cool on the mat. 6 Bend each of the pins until they break. Record your counts.
Questions 1 Describe what the terms ‘normalising’, ‘quenching’ and ‘tempering’ mean. 2 Identify the treatment that caused the steel to become: a more brittle b more malleable 3 Fast cooling produces small crystals; slow cooling makes bigger ones. Identify which of the samples produced the biggest crystals.
>>> Using metals to make non-metals Prac 4 Unit 1.4
Aim To make a non-metal compound from a metal
Equipment Samples of magnesium, iron and copper, 2 M hydrochloric acid in a dropping bottle, test tubes and rack, matches, safety glasses
Method 1 Place the samples of metal in separate test tubes. 2 Use the dropping bottle to add sufficient hydrochloric acid to cover the metal in each. 3 If bubbles form, test the type of gas produced by placing a lit match near the mouth of the tube. You may need to place a stopper in the mouth to gather sufficient gas to test.
4 Propose a reason why bigger crystals make steel tougher.
Making and testing a gas
Fig 1.4.6
5 Distinguish between iron and steel. burning match
4 Record your observations.
Questions 1 Identify the gas present if a lit match: a causes a ‘popping’ sound b flares up brightly c is extinguished 2 Classify the gases in Question 1 as elements or compounds. 3 Draw a conclusion about the reaction of metals with acids.
28
UNIT
context
1. 5 Aristotle’s idea of 2400 years ago that some elements had similar properties eventually led to the grouping of elements we use today. Although all members of an element’s ‘family’ are different, they do share some common characteristics.
Noble gases get bigger and heavier as we go down the group.
Fig 1.5.2
helium
neon
argon
krypton
xenon
rises quickly
rises slowly
falls slowly
falls quickly
falls very quickly
density of gas increases 4
20
40
2
10
18
He
Ne
Ar
84
131
36
54
Kr
Xe
mass of atom increases
Group VII: the halogens
Group VIII: the noble gases The nobles gases are colourless gases that occur naturally in the atmosphere. All can be separated by distillation of liquid air. They are very stable and react only in rare and extreme circumstances. Helium is safe and light enough to be used for balloons and airships. Balloons of the other noble gases get progressively heavier: although the atoms get bigger, they also get heavier and more dense.
Squeaky voices Our voices go high and squeaky when we breathe in helium from a party balloon. Because helium is lighter than air, our vocal cords vibrate more quickly, making the pitch go higher. Don’t try this, though! Some people have actually died from performing this trick.
VII F Cl Br I At
The halogens
melting/boiling points increase
Elements belong in families: they are different but have many similarities.
more reactive
Fig 1.5.1
The halogens: • form ions with a charge of –1. • are never found in their pure form in nature but are in various types of salts, including sea salt • have coloured and poisonous vapours • all form molecules, each being made up of two atoms.
Fig 1.5.3
29
>>>
Families of elements
Group VII
State at room temperature
Melting point (°C)
Boiling point (°C)
Fluorine
Uses of halogen compounds
Greenish yellow gas
–220
–188
Chlorine
Green gas
–101
–35
Bromine
Red liquid with red vapour
–7
59
Photographic film, sedatives
Iodine
Black solid with purple vapour
114
184
Disinfectant, control of goitre
Prevention of tooth decay, etching of glass, insecticides, Teflon and the anaesthetic Fluothane Disinfectant, sterilising agent, bleach, food seasoning, PVC, neoprene rubber, insecticides
gas out chlorine gas in
iron wool
heat Hot steel wool glows brightly when chlorine passes over it. Brown smoke and brown solid form.
Fig 1.5.4
Prac 1 p. 34
Group I: the alkali metals The alkali metals: • form +1 ions • are far too reactive to be found free in nature, but are found in mineral salts • have typical metallic properties • display similar chemically extreme behaviours. Lithium, sodium and potassium are light enough to float on water and are so soft that they can be cut with a knife. They all burn in chlorine gas (and in the other halogens) and produce similar white salts. 2Li + Cl2 → 2LiCl 2Na + Cl2 → 2NaCl 2K + Cl2 → 2KCl
30
bromine liquid heat The iron glows less brightly when bromine is used. Brown smoke and brown solid form.
Alkali metals and alkaline earths
Halogens (from left): chlorine, bromine and iodine
As we move down the group the atoms get bigger and become less reactive.
iron wool
The Swedish chemist Carl Scheele separated chlorine gas in 1774 and wrote that he was glad that he ‘did not take more than a tiny whiff’ as ‘a large bumblebee died instantly when put into the vapour’. Scheele often tasted his discoveries and this is probably what killed him at the age of 43.
heat
The iron glows even less brightly with iodine. Brown smoke and brown solid form.
Fig 1.5.5
They all react violently with water, producing an alkaline (basic) solution and hydrogen gas, which often ignites due to the heat produced. 2Na + 2H2O → 2NaOH + H2 Sodium burning in water. Reactions become more violent as we move down Group I.
Dead bumblebees!
iron wool crystals of iodine
Fig 1.5.6
UNIT
1. 5 Group I
Melting point (°C)
Boiling point (°C)
Uses of Group I compounds
Li
181
1342
Alloys, carbon dioxide filters, water absorbent
Na
98
883
Vapour lamps, fertilisers, sedatives in manufacture of paper, soap, textiles and other chemicals
K
63
760
Alloys, coolant in nuclear reactors
Rb
39
686
Radioactive tracer used to detect brain tumours
Group II
Melting point (°C)
Boiling point (°C)
Uses of Group II compounds
Be
1278
2970
Watch springs, spark-free tools
Mg
649
1107
Alloys, rust protection, anatacid, laxatives
Ca
839
1484
Alloys, quicklime in mortar, plaster, cement
Sr
769
1384
Fallout from nuclear explosions
Ba
725
1640
Used in medical diagnosis, rat bait
Group II: the alkaline earths These metals all act in a similar but slightly less reactive way to Group I.
Group IV Group IV begins with atoms that are non-metals (carbon and silicon), moves through the semi-metal germanium, then the metallic atoms of tin and lead, to finish with the synthetic element ununquadium. Carbon exists in molecules in every living thing on Earth (e.g. trees) and anything that was living (wood and paper come from trees). Pure carbon exists in three different forms or allotropes: amorphous carbon, diamond and graphite. Amorphous carbon is the black powder on the top of burnt toast, charcoal and coal. Diamond is the hardest known natural substance and does not conduct electricity. Over 80% of diamonds are not gem-grade but are used as
Prac 2 p. 35
tips for dentist drills, glass, metal and masonrycutting tools or are crushed to make abrasives. Graphite is a soft solid. It conducts electricity well and is used as the central electrode of non-rechargeable batteries and as ‘brushes’ in
Have you seen my ring? Sir Humphry Davy (1778–1829) demonstrated that diamond was a form of carbon by burning a diamond that belonged to his wealthy wife! All that was left was carbon dioxide. Diamond needs to be heated to about 800°C to be converted to graphite. To turn graphite into diamond a pressure of between 50 000 and 120 000 times that of normal air pressure is needed.
Diamond, an allotrope or form of carbon
Fig 1.5.7
31
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Families of elements Fig 1.5.8
The transition metals
The layered structure of graphite makes it slippery.
electric motors. It is slippery and is an excellent lubricant. The ‘lead’ in pencils is a graphite/clay mix. Silicon is found as silicon dioxide and metal silicates, which together make up 75% of the Earth’s crust—sand, clay, asbestos, quartz and many gemstones contain silicon. It is the major component of glass. Mendeleev predicted the existence of germanium 15 years before its discovery, naming it ‘eka-silicon’. Germanium is used as the catalyst in fluorescent lights and its oxides are used in the production of lenses for optical instruments such as microscopes. Both silicon and germanium are semiconductors and are widely used in electronic components. Tin and lead are typical metals.
The transition metals include many of our most useful, colourful and valuable metals such as iron, copper, zinc, gold and silver. The transition metals have very similar properties: for example, the Period 4 metals iron, cobalt and nickel are all magnetic. All transition metals tend to be relatively hard and most have similar, high melting points.
Scandium, agent Sc-46! East German secret police (the Stasi) regularly sprayed opponents of the government with radioactive scandium, Sc-46. The unknowing dissidents were then traced with a Geiger counter strapped under the armpits of agents. Vibrations alerted the agent that their trace was nearby. The Stasi also used radioactive silver bullets that could be safely shot into the tyres of cars they wanted to track.
Prac 3 p. 35
UNIT
1. 5
The salts of transition elements are very colourful.
[ Questions ]
Worksheet 1.4 Changes in properties across the periodic table Worksheet 1.5 The periodic table
Checkpoint Group VIII: the noble gases 1 Describe the advantages of using helium and not hydrogen in airships. 2 Clarify what happens to the mass and density of the noble gases as we move down the group.
Group VII: the halogens 3 Clarify what happens to the melting points and boiling points of the halogens as we move down the group.
32
Fig 1.5.9
4 Identify which of the halogens is used as: a a disinfectant b a sedative c goitre control d a bleach e an anaesthetic
Group I: the alkali metals 5 Describe some typical reactions of the alkali metals.
6 Identify which of the alkali metals: a has a melting point of 98°C b is in caustic soda c is used as an air filter d would be the most reactive e would have the smallest atoms
Group II: the alkaline earths 7 Identify which of the alkaline earths: a would be closely related to potassium b is used as a ‘meal’ c is found in plaster d is used to protect iron from rusting e would be the least reactive
Group IV 8 These statements are about Group IV. Are they true or false? a The group contains both metals and non-metals. b All the elements in this group contain four electrons in their outer shell. c Diamond and graphite are forms of silicon. d Carbon is in all living things, but not in things that are dead. 9 Describe the main uses for: a diamond b graphite c silicon d germanium 10 State the percentage of diamonds that are valuable.
The transition metals 11 Identify three transition elements that: a are in Period 5 b are magnetic or can be made magnetic c are used for jewellery d are ‘silver’ grey in colour e have symbols from old Greek or Latin names
Think 12 Carbon could be classified as a semi-metal, not a non-metal. Explain.
UNIT
1. 5 Analyse 14 Identify which halogens would be solid, liquid or gas at these temperatures: a 20°C b 100°C c –199°C d 150°C 15 Carbon forms a compound, CH4. Predict the formula of compounds formed from hydrogen and the following Group IV elements: a silicon b germanium c tin d lead 16 Tin acts like a non-metal below 13°C. In 1913 Captain Robert Scott and two fellow explorers froze to death in Antarctica after they ran out of stored heating fuel. Propose why they unexpectedly ran out.
[ Extension ] Investigate 1 Investigate what goitre is and how it is treated. Write a set of guidelines for a person with goitre that could help them manage the condition. 2 Investigate what the different noble gases are used for. Make a summary of this information including pictures showing each gas in use. 3 Investigate what lead and tin are used for and why.
Skills 4 Research, collect the data needed and plot a line graph of: a melting point versus period number for the alkali metals b boiling point versus period number for the halogens
13 Carbon has been known for over 2000 years. Propose why it was found much earlier than most other non-metals.
33
>>>
Families of elements
UNIT
1. 5
[ Practical activities ] Halogen precipitates Aim To examine how halogen salts precipitate
Prac 1 Unit 1.5
WARNING: Lead nitrate is toxic. Do not get it on you. Wash your hands well after the prac, as toxic lead precipitates are produced and must be cleaned off.
Equipment Test-tube rack; 5 test tubes; filter funnel and 4 filter papers; beaker; wash bottle with water; disposable gloves; safety glasses; saturated lead nitrate solution; dropping bottles of saturated solutions of potassium fluoride, potassium chloride, potassium bromide and potassium iodide
Method 1 Quarter-fill a test tube with potassium fluoride solution. 2 Add a similar amount of potassium chloride, bromide and iodide solutions to the other test tubes.
4 Add a similar amount of lead nitrate to the remaining test tubes. 5 Record your observations. 6 Fold a filter paper and place in the funnel. Use a little water to keep the paper in place. Pour the material from the test tube into the paper, making sure not to overfill it. Collect the remaining solution (the filtrate) in the beaker and dispose of it in the container provided. Do this for each test tube. 7 Unfold the filter paper and allow it to dry.
3 Add 10 drops of lead nitrate solution to the first test tube. Making and filtering precipitates
Part 1: Test-tube rack
solutions of KF KCl KBr
Fig 1.5.10
Part 2: Folding filter paper KI
1
2
fold here fold here L ead N itr a t e
3
4
pull this single flap away from the other three form a cone
Questions 1 The solid formed in each case was a precipitate. Define ‘precipitate’. 2 Compare the compounds formed and list their similarities.
34
3 Compare how they were different. 4 The precipitates were lead fluoride, lead chloride, lead bromide and lead iodide. Draw conclusions about the halogen family from these results.
UNIT
1. 5 The alkaline earths Prac 2 Unit 1.5
Aim To examine the reactivity of the alkaline earth elements
Part A
Part B tongs
Equipment Crucible, lid and clay triangle, 2 test tubes and rack, Bunsen burner, tripod, bench mat, matches, safety glasses, distilled water, one 5 cm strip of magnesium, steel wool or emery paper, small sample of calcium
lit match
distilled water coil of Mg distilled water
Method PART A 1 Clean the magnesium strip with steel wool and then spiral it loosely around a pen. 2 Place the coil in a test tube and cover it with distilled water.
Ca
Bunsen burner Phenolphthalein
3 Watch very carefully over the next five minutes. Look for bubbles. 4 If nothing happens, heat gently over a yellow flame. 5 When finished add 1 drop of phenolphthalein to the solution. Record the colour.
Comparing alkaline earths
Fig. 1.5.11
PART B 1 Put about 5 cm of distilled water into a test tube. 2 Add a piece of calcium.
Group IV
3 Test the gas given off with a lit match.
Aim To examine family similarities in Group IV
4 Add one drop of phenolphthalein. 5 Record your observations.
Questions 1 Identify which alkaline earth is more reactive, Mg or Ca. 2 Describe what happens to reactivity as we move down Group II. 3 Assess whether Group II metals are more or less reactive than Group I.
Prac 3 Unit 1.5
elements
Equipment Samples of charcoal, graphite, silicon, lead, power pack or battery, leads with alligator clips, light
Method 1 Describe carefully the appearance of each sample. 2 Test whether each conducts electricity using the apparatus used in Prac 2 of Unit 1.2 (page 13).
Questions 1 Classify the Group IV elements as metals, non-metals or semi-metals. 2 Describe what happens to the properties of Group IV as we move down the group.
35
>>> Chapter review [ Thinking questions ]
[ Summary questions ] 1 Construct a simple outline of the periodic table, then use different colours to demonstrate the location of: a the noble gases c the semi-metals b the transition metals d the non-metals 2 Identify which groups these families are in: a halogens b inert gases Atom c alkaline earths 3 Describe the position of electrons in an atom and how many electrons each shell can hold. 4 Define what the period number and the group number represent.
Atomic number
Number of protons
32
Number of neutrons
Iodine
Atomic symbol
0 4
127 28
Number of electrons
16
9 74
59 28Ni
59
5 Distinguish five ways in which metals are different to non-metals.
12 Hydrogen and helium can be placed in a number of places in the periodic table. Explain.
6 Distinguish between a chlorine atom and a chloride ion.
13 Describe what happens to the size and weight of elements as we move down any group.
7 Identify the most likely charge of ions formed from an atom of: a five electrons d neon b 17 electrons e Group II c oxygen f Group V 8 True or false? a The mass number of an atom is the number of protons it has. b Mercury is a solid at room temperature. c There are millions of different types of atoms. d Group V atoms all have five electrons in their outer shell. e Period 4 atoms all have four shells in use. f An atom with an electronic configuration of 2,8,5 would be in Period 5, Group III. g Carbon dioxide is an element. h Air is a compound. i The element carbon is found in all living things. j In an atom the number of electrons equals the number of protons. k Ions are always charged. l Ions are formed when atoms lose or gain protons. m If an atom loses electrons it becomes a negative ion. n An atom that has gained three electrons would now be an ion of charge –3.
36
Mass number
1
Beryllium
Nickel
10 Explain which have the highest electronegativity: metals or non-metals. 11 Copy and complete the table.
Sulfur Hydrogen
9 Explain why elements of the same ‘family’ are always found in the same group.
14 Look back at the main scientists and their contributions to the understanding and development of the structure of the atom and the periodic table. Construct a table to summarise this information.
[ Interpreting questions ] 15 Determine how many p+, n and e– these atoms have. a
35Cl 17
b 31H c
197Au 79
16 Explain what happens if a potassium atom meets a fluorine atom in a chemical reaction. 17 The outer electrons control what the atom does in a chemical reaction. Analyse reasons why this is the case. 18 Carbon also forms a molecule CCl4. Predict the compounds that would form out of chlorine and the other Group IV elements. Worksheet 1.6 Periodic table crossword Worksheet 1.7 Sci-words
>>>
2
Chemical reactions Key focus area
>>> The nature and practice of science
identify reactants and products from word equations and chemical equations write word equations for simple chemical reactions
Outcomes
recognise when a chemical reaction is taking place
5.7.3, 5.2
By the end of this chapter you should be able to:
identify different reaction types, their reactants and products write formulas for simple compounds distinguish between acids and bases describe what indicators are and how they are used identify the approximate pH values of different acids and bases.
reaction has occurred?
2 We drink a lot of dihydrogen oxide. What is it really?
3 4 5 6 7
Is water a chemical? Name as many acids as you can. What is the chemical name of rust? How do antacids relieve indigestion? What pH in shampoos is considered ‘neutral’?
Pre quiz
1 How can we tell that a chemical
UNIT
>>>
context
2.1 Chemical reactions are occurring constantly inside us, around us, in the soil, in sea water, in the air and throughout the universe—absolutely everywhere! Some reactions, like fireworks, are quick and violent. Other reactions, like the reactions that occur in every cell in your body, are slower and more difficult to see. So how do we, as scientists, know whether or not a chemical reaction has taken place?
Fig 2.1.2
Melting is a physical change. Burning methane is a chemical change.
When methane burns, carbon dioxide and water are formed.
When ice melts no new substances form.
The substances present at the start of a reaction are called the reactants, and the new substances formed are called the products. We can write word equations to represent chemical reactions. These are written in the form: A+B→C+D reactants → products
Fig 2.1.1
Chemical reactions occur constantly in this nebula.
Signs of chemical change We say that a chemical reaction has occurred if at least one new substance has been formed. Burning methane gas is an example of chemical change because water and carbon dioxide are formed, and they weren’t present at the start of the reaction. This differs from a physical change, where no new substances are created. The melting of ice is an example of physical change. It is simply a change of state: solid water turns into liquid water.
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The arrow shows the direction of the reaction and means ‘react to form’. Thus the chemical equation above reads ‘Substances A and B react to form substances C and D’. Chemical equations are useful because they provide a quick and easy way to represent complex reactions. For example, the reaction of magnesium and copper oxide produces copper and magnesium oxide. This can be written as: magnesium +
copper oxide → reactants
copper
+ magnesium oxide
→ products
Using chemical symbols, this reaction is written: Mg + CuO → Cu + MgO reactants
→ products
UNIT
2.1
Iron is the main component of steel that makes up cars. Iron can react with oxygen to form iron(III) oxide—rust. The effects of this slow reaction can be very damaging.
Fig 2.1.4
The corrosion of iron or the burning of a match are examples of colour changes associated with reactions. Fig 2.1.3
The reaction of magnesium and copper oxide is spectacular.
In this case, the reactants are magnesium (Mg) and copper oxide (CuO). The products are copper (Cu) and magnesium oxide (MgO). Notice that the number of each type of atom is the same on each side of the equation. Atoms are not destroyed or created in chemical reactions. They just get rearranged. There are several signs that tell us whether or not a chemical reaction has occurred. A chemical reaction has definitely occurred if one or more of the following is observed: Carbon monoxide • There is a permanent poisoning colour change. Carbon monoxide (chemical • A gas is given off. formula CO) is a deadly gas • Energy is produced or emitted by cars. It is produced when carbon-based fuels like absorbed. petrol burn in a limited supply • A precipitate (solid) forms of oxygen. Haemoglobin is the from a solution. molecule in red blood cells • One metal deposits or that transports oxygen around your body. Carbon monoxide, forms on another.
Permanent colour change A permanent change in colour during a reaction is an indication that a chemical reaction has taken place.
A gas is given off If a reaction is taking place in solution (in a liquid), it is very easy to see a gas being produced because bubbling will be observed. With other reactions it can be more difficult to see the gas because most gases, like oxygen, hydrogen, nitrogen and carbon dioxide, are colourless and odourless. Figure 2.1.5 shows a reaction between limestone (calcium carbonate) and sulfuric acid that produces carbon dioxide gas. Prac 1 p. 43
The formation of a gas is a sign of chemical change.
Fig 2.1.5
which is odourless and colourless, is extremely toxic because it binds to haemoglobin 200 times more strongly than oxygen does. This leaves no space for the oxygen, so our cells quickly become starved of oxygen and die … and so do we!
39
What are chemical reactions and why do they happen? Energy is produced or absorbed Many reactions produce or absorb energy, usually in the form of heat. Imagine a reaction taking place in a test tube. If you feel the test tube as the reaction is taking place and it gets colder, then the reaction is absorbing heat energy from the surroundings. Reactions that absorb energy are called endothermic. If you feel the test tube and it gets warmer, the reaction is releasing heat energy to the surroundings. Reactions that produce energy are called exothermic. Endothermic: energy + reactants Exothermic:
reactants
→ →
products products + energy
Heat is generated when fossil fuels such as petrol, oil and coal are burnt. These are examples of exothermic reactions. The heat produced can be converted into other forms of energy and then used to do things like make cars move, produce electricity in power stations and heat your home. The burning of magnesium ribbon is an exothermic reaction that releases both heat and light energy. The burning of metals like magnesium is used to produce the amazing effects in fireworks. The equation for this reaction is: magnesium + oxygen → magnesium oxide + energy
>>> An example of an endothermic reaction is photosynthesis. The chlorophyll in plants absorbs energy from the Sun to make this important reaction occur. The overall chemical equation for this reaction is: carbon dioxide + water + energy 6CO2 + 6H2O + energy
Prac 2 p. 44
→ glucose + oxygen → C6H12O6 + 6O2
A precipitate forms A solution is made up of a solute (a substance that dissolves) and a solvent (the liquid that the solute dissolves in). For example, a solution of sodium chloride (table salt) is made up of solid sodium chloride dissolved in water. Solutions are clear, and sometimes coloured. When two solutions are mixed, a precipitate may form—an indication that a chemical reaction has occurred. A precipitate is an insoluble substance (a substance that does not dissolve) that forms when two clear solutions are mixed together. The precipitate is observed as cloudiness or solid particles sinking to the bottom of the test tube. Fig 2.1.7
Lead iodide precipitate is a distinctive yellow colour.
2Mg + O2 → 2MgO + energy
One metal deposits on another
Fig 2.1.6
40
Burning magnesium releases both heat and light energy.
When one metal deposits or settles on top of another metal, the reaction is known as a displacement reaction. Different metals have different degrees of reactivity. A basic rule is that a more reactive metal will displace a less reactive metal in solution. If you have a solution of a particular metal salt, and you place a solid piece of a more reactive metal in the
solution, a reaction will take place. The electrons from the more reactive metal will be transferred to the ions of the less reactive metal, which will become solid and deposit on the surface of the more reactive metal. Figure 2.1.8 shows what happens when a piece of zinc is placed in a solution of copper sulfate. Fig 2.1.8
Less reactive copper is displaced by more reactive zinc.
copper sulfate solution zinc ions form when zinc atoms give up electrons to copper ions solid zinc
2– Cu2+ SO4 Cu2+
SO2– 4 Zn2+
Cu2+
SO2– 4 SO2– 4
a coating of solid copper forms on the surface of the zinc as copper ions accept electrons to become copper atoms.
endothermic reactions. The burning of methane, the gas that comes out of the gas taps in the laboratory, is an exothermic reaction. We have to add a spark to start the reaction, but then it will just keep burning by itself. The equation for this spontaneous reaction is: methane + oxygen CH4 + 2O2
→ →
carbon dioxide + water + energy CO2 + 2H2O + energy
The products, carbon dioxide and water, have less stored energy than the reactants, so this reaction is likely to proceed as written. Notice the ‘2’ in front of the oxygen and water. These are put there to balance the equation. Because matter cannot be created or destroyed, there must be the same number and types of atoms on each side of the equation. This is achieved by putting whole numbers in front of the chemical formulas in the equation. At this stage, you don’t need to know how to balance equations. You will learn more about this in Science Focus 4. The hydrolysis (splitting up) of water doesn’t happen spontaneously. We have to pass an electric current through water to make this reaction happen. The equation for this reaction is:
→ 2H2O + energy →
water + energy
Why do chemical reactions occur?
UNIT
2.1
oxygen + hydrogen O2 + 2H2
Some reactions happen naturally. These are called spontaneous reactions. One example is the rusting of iron. Spontaneous reactions also include those that need a little help getting started, but then will keep going by themselves. For example, a sparkler lit for a birthday party needs a flame to get it going but then keeps burning until all of the chemicals have reacted. Other reactions need a continual energy input to keep them going, like the electrolysis of water, where an electric current is used to split water up into hydrogen and oxygen gas. These are called nonspontaneous reactions. So why do some reactions proceed with no help from us, while others are very difficult to start and keep going?
The energy content of substances The atoms in compounds are held together by chemical bonds. Energy is stored in these bonds, and the amount varies from substance to substance. Reactions are more likely to occur if the reactants have more stored energy than the products. This means that exothermic reactions are more likely to occur than
The hydrolysis of water produces twice as much hydrogen gas as oxygen gas. Why do you think that is?
Fig 2.1.9
41
What are chemical reactions and why do they happen? Both oxygen and hydrogen are diatomic gases. They can only exist as two atoms joined together to make a molecule. This is why they are written as O2 and H2
UNIT
2.1
rather than just O and H. The products, oxygen and hydrogen, have more stored energy than the reactants, so this reaction is not likely to proceed easily.
[ Questions ]
Checkpoint Signs of chemical change 1 Identify the five signs of chemical change. 2 Define the term ‘solution’. 3 Explain what is meant by ‘a solution is clear, but not always colourless’. 4 Describe how a precipitate forms.
Why do chemical reactions occur? 5 a Distinguish between a spontaneous and a non-spontaneous reaction. b Identify an example of each of the above types of reaction. 6 For each of the following reactions: a water + energy → hydrogen + oxygen b methane + oxygen → carbon dioxide + water + energy identify: i ii iii iv
the reactants the products whether the reaction is exothermic or endothermic whether the reactants or products contain more energy
b Solid purple iodine crystals are heated slightly and a purple cloud of iodine gas is observed. c When nitric acid is poured onto limestone, bubbling is seen. d Two colourless solutions at room temperature are mixed. After a minute, the temperature of the mixture is 60°C. e Ice is taken from the freezer and left on the bench. The temperature rises from 0°C to 20°C and the ice melts. f Yellow sulfur powder and iron filings are heated in a crucible. After heating, only a black solid remains. 10 If burning methane is a spontaneous reaction, explain why we have to light a match to make it burn. 11 It has been suggested that cars in the future might run by reacting hydrogen gas with oxygen gas (the reverse of the hydrolysis of water). Where would the energy to run the car come from? Would the reaction be spontaneous?
Analyse
Think
12 Chemical equations can be very useful. Explain two reasons why.
7 Classify the following as examples of chemical change or physical change. a cutting up cheese b making toast c burning gas d melting chocolate e freezing cordial f water evaporating g putting a soluble aspirin tablet in water
13 Construct word equations for the following reactions. a When copper is added to nitric acid, copper nitrate, nitrogen monoxide and water are formed. b If sulfuric acid is poured onto solid sodium carbonate, bubbles of carbon dioxide are produced, as well as water and sodium sulfate. c Magnesium burns easily in oxygen, producing magnesium oxide. d During photosynthesis, the Sun’s energy, carbon dioxide and water are used by green plants to produce glucose and oxygen. e An iron nail exposed to air and water will rust, forming hydrated iron oxide. f When solutions of lead nitrate and sodium iodide are mixed, a precipitate of yellow lead iodide is formed, as well as sodium nitrate in solution.
8 Describe three examples of chemical reactions that occur in your home. 9 For each of the following, identify whether a chemical change has occurred, and explain your answer. a A student mixes two unknown solutions together and notices a cloudiness forming.
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Surf
[ Extension ] Investigate 1 Cold packs are used for treating sporting injuries, without having to worry about carrying ice. They use an endothermic change to go very cold. a Investigate how a cold pack works, including whether it is a chemical or physical change. b Design an experiment to demonstrate how a cold pack works, and perform your experiment for the class. c Design a box that could be used to sell a cold pack. On the back should be instructions for the user, and information that explains how the pack works. d Predict whether a heat pack would be endothermic or exothermic. 2 Investigate how light sticks work and explain why a light stick cannot go forever.
UNIT
2.1
UNIT
2.1 3 Acid rain is causing significant damage to forests, monuments and historical buildings in certain parts of the world. Explore some information about acid rain by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 2, and clicking on the destinations button. a Research the chemical reactions that cause acid rain to form. b Research the chemical reactions that happen when acid rain reacts with buildings. c Assess the damage that acid rain has caused to the natural and built environment. d Write a letter to the government explaining the problems associated with acid rain. In your letter recommend action that should be taken to reduce the possible damage caused by acid rain.
[ Practical activities ] Signs of chemical change Aim To observe changes during chemical reactions Equipment
Prac 1 Unit 2.1
Solid copper carbonate, magnesium, dilute nitric acid, splint, matches, Bunsen burner, test-tube holder, test-tube rack, dilute sodium hydroxide, thermometer, dilute barium nitrate, dilute sodium sulfate, dilute copper sulfate, solid zinc, 5 test tubes (1 with stopper), lab coat, safety glasses
Note: 1.0 M is an appropriate concentration for these solutions, but anything between 1.0 M and 2.0 M would be suitable.
Method
2 Carefully heat a small amount of copper carbonate in a test tube. Ensure that the test tube is pointed away from people. Stop as soon as you see a colour change. Record your observations. 3 Add a small piece of magnesium to 2 cm of nitric acid in a test tube. Stopper the tube to collect some gas. Have your lab partner light a splint and place it near the mouth of the test tube. 4 Record the temperature of 2 cm of the nitric acid solution. Add 2 cm of sodium hydroxide solution and record the new temperature. 5 Place a small piece of zinc into 2 cm of dilute copper sulfate solution. Record your observations.
1 Copy the following results table into your book. Reaction number
Reactant(s)
1
Copper carbonate
2
Nitric acid and magnesium
3
Dilute barium nitrate and sodium sulfate
4
Dilute nitric acid and sodium hydroxide
5
Zinc and dilute copper sulfate
Questions Observations
Conclusion
1 Identify the gas formed in the reaction in step 2. 2 Predict what you think would happen if the zinc in the reaction in step 5 was replaced with silver.
43
What are chemical reactions and why do they happen?
>>> Fig 2.1.10
Light sticks: chemiluminescence Prac 2 Unit 2.1
Aim To investigate the effect of adding energy to a reaction
Equipment
light stick
light stick
2 x 250 mL beakers, ice, hot tap water, 2 light sticks (from scuba-diving store)
Method 1 Set up two beakers, one with a mixture of ice and water, the other with hot water. Your beakers should be filled to the 200 mL mark. 2 Activate your light sticks by bending them. This snaps the capsule inside and allows the chemicals to mix.
ice water
3 Place one light stick in ice and the other in hot water. 4 After a few minutes, take them out and compare the intensity of the light.
Questions 1 Compare the brightness of the light sticks. 2 Predict what would happen to an activated light stick if you put it into the freezer. 3 Discuss some uses for light sticks.
44
hot water
UNIT
context
2. 2 In the early days of chemistry, there was no system for the naming of compounds. Chemists used common names like bicarb of soda, quicklime, milk of magnesia, Epsom salts, spirits of salt, and laughing gas to describe compounds. As the number of named compounds increased it was obvious that if such common names were used, confusion would result. In 1787, in order to solve the problem, a scientist named Lavoisier established the principles for a systematic naming process.
Ionic compounds As you saw in Chapter 1, ions form when atoms gain or lose outer-shell electrons. Whereas atoms are neutral, ions are charged. If an atom loses electrons, then its ion is positive (there are more protons than electrons). If an atom gains electrons then the charge of its ion will be negative (there are more electrons than protons). Ionic compounds form when positive and negative ions attract each other and are linked together by electrostatic attraction—the attraction between opposite charges. These strong links are called ionic bonds. Ionic compounds are also called salts. In almost all cases the positive ion is a metal. When the ions come together to form compounds, they combine in a ratio that gives the compound a total charge of zero. There must be enough negative charges to balance the positive charges and vice versa. Sodium and chloride ions combine in a 1:1 ratio because sodium ions have a +1 charge and chloride ions have a –1 charge. Add these charges together: +1 + (–1) = 0. Thus, one of each ion join to give a compound with a total charge of zero. The formula is NaCl, and the name of this compound is sodium chloride. To name ionic compounds, simply follow these rules: • The positive ion is named first and the negative ion second.
There are, however, some familiar compounds that are always referred to by their common names. The systematic name for H2O, for example, is never used. What would you prefer to call it: dihydrogen monoxide or water? There are two types of compounds (ionic and covalent) that require naming, and different rules apply for naming each type.
sodium (2, 8, 1)
chlorine (2, 8, 7)
sodium ion (2, 8)
Na
Cl
Na+
chloride ion (2, 8, 8)
Cl–
–
+ An electron is transferred from sodium to chlorine. These positive and negative ions are attracted to each other and form a crystal where the ions are stacked to maximise attraction.
– + – +
+ –
– +
Na ++
– +
– +
–
The formation of sodium chloride
+ –
+ – + –
+
– +
–
+
Fig 2.2.1
• A simple positive ion takes its name from its parent element. For example, Na+ is called sodium. • A simple negative ion is named by taking the first part of the parent element’s name and adding the suffix -ide. Cl– was originally a chlorine atom but is now an ion and is given the new name chloride. Likewise, Br– (originally bromine) is called bromide, O2– (originally oxygen) is called oxide and N3– (originally nitrogen) is called nitride.
45
>>>
Naming compounds Positive ion and electron configuration
Negative ion and electron configuration
Formula
Name
Mg2+ (2,8)
Cl– (2,8,8)
MgCl2
Magnesium chloride
(2,8)
Na2O
Sodium oxide
(2,8,8)
Al2S3
Aluminium sulfide
Ca3N2
Calcium nitride
+
2–
Na (2,8) Al
3+
2+
Ca
O
2–
(2,8)
S
3–
(2,8,8)
N
(2,8)
Note that the charges of the ions are not included in compound formulas, but the numbers of each ion (the subscript numbers) are included. These subscript numbers indicate how many of each ion are in the formula. For instance, MgCl2 indicates that there are one magnesium ion and two chloride ions in the formula. No charges appear in the overall formula because, once they are balanced, there is zero charge.
Na+
Cl–
+
Na+
Fig 2.2.3
• Transition metals have a variety of ionic charges, but most form ions with a +2 charge. • If a metal has more than one common ion, the charge it takes is shown with Roman numerals. For example, copper(I) = Cu+, copper(II) = Cu2+, iron(II) = Fe2+, iron(III) = Fe3+. • The metals in Groups V and VI also have charges that can vary. These atoms lose electrons to get a noble gas electronic configuration.
Cl–
1 sodium ion joins with 1 chloride ion to form sodium chloride. Na+ + Cl– NaCl
Cl–
Mg2+ +
Cl–
Cl–
Mg2+
Cl–
1 magnesium ion joins with 2 chloride ions to form magnesium chloride. Mg2+
+
Fig 2.2.2
2Cl–
MgCl2
Formulas of ionic compounds must be balanced so that the net charge on the compound is zero.
Metal ions The formation of ions was covered in Chapter 1, and you will recall that: • Metals in Group I (the alkali metals) always form ions with a +1 charge. • Metals in Group II (the alkaline earth metals) always form ions with a +2 charge. • Metals in Group III always form ions with a +3 charge. • Metals in Group IV often have a +4 charge but can also have a charge of +2. Assume +2 unless you are told otherwise.
46
Non-metal ions From Chapter 1 you will remember that: • Elements in Group VII (the halogens) always form ions with a –1 charge. • Elements in Group VI always form ions with a –2 charge. • Elements in Group V always form Francium fluoride ions with a –3 charge. The most ionic • Non-metal elements in Group IV compound possible (carbon and silicon) may form is francium fluoride, because francium is the –4 ions. most reactive metal and • Elements in Group VIII (the noble fluorine is the most gases) either have full outer reactive non-metal. If these two elements ever electron shells or are happy with came together, the result eight electrons in their outer would be explosive shells. They are extremely stable indeed! and do not form ions.
These atoms gain electrons to get a noble gas electronic configuration.
Fig 2.2.4
e–e– e–e– e– e–– e–– e e
e–– e–– e e
Cl
e–e– e–e– e– e–– e– + e– e
e–– e–– e e
e–– e– + 2e– e
O
e– e–e– e–e–
e– e–e– e–
2, 8, 7
2, 8, 6
e–e– e–e– e–
e–e– e–e– e–
Cl–
e–– e–– e e
e–– e–– e e
Covalent compounds Covalent compounds form when atoms bond by sharing outer-shell electrons. They form when nonmetals come together. In these bonds, no electrons are transferred. Instead, atoms share pairs of electrons in order to gain a noble gas electron configuration. These links are called covalent bonds. Figure 2.2.5 shows how pairs of electrons are shared in an ammonia (NH3) molecule.
methane, CH4
O2–
e– e–e– e–e–
e– e–e– e–e–
2, 8, 8
2, 8, 8
UNIT
2.2
e– e– e– e–
H
water, H2O
H C
O
H
H
H
H
ammonia, NH3 H
Polyatomic ions or radicals Some ions are made up of more than one type of atom and are called polyatomic ions or radicals. These ions have special names. The table below shows some of the more common ones.
Ion name
Formula
Hydroxide
OH
Sulfate
SO4
Carbonate
CO3
Hydrogen carbonate
HCO3
Ammonium
NH4+
Nitrate
NO3
–
2– 2– –
–
When more than one polyatomic ion is required in a formula, brackets are used. For example, in sodium sulfate, Na2SO4, only one sulfate ion is needed to balance the charge so no brackets are needed. For aluminium sulfate, Al2(SO4)3, three sulfate ions are required so brackets are used.
N
H
H
These covalent compounds show atoms sharing electrons to gain noble gas electronic configurations.
Fig 2.2.5
The naming of covalent compounds is similar to ionic compounds, even though there are no ions present. The following rules apply: • The first element in the chemical formula is named first, using the element’s full name. • The second element in the formula is named as if it were a negative ion. Ionic or covalent? • Prefixes are used to show the Some compounds contain both ionic and numbers of atoms present (see the covalent bonding. table on following page). The ammonium ion • If the first element exists as a NH4+ is held together by covalent bonding (the single sharing of electrons). atom, no prefix is used. For However, when it joins example, to a negative ion like Cl–, the chloride ion, it CO2 is called carbon dioxide. forms an ionic bond.
Worksheet 2.1 Ionic compounds, names and formulas
47
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Naming compounds • To avoid awkward pronunciations, the final ‘o’ or ‘a’ of the prefix is often dropped when the element name begins with a vowel. For example, CO is called carbon monoxide, not carbon mono-oxide. Some examples of covalent compounds and their names are: • CO2 = carbon dioxide • CO = carbon monoxide • N2O5 = dinitrogen pentoxide • CCl4 = carbon tetrachloride • NH3 = nitrogen trihydride (commonly known as ammonia) • CH4 = carbon tetrahydride (commonly known as methane)
Number of atoms
Prefix
1
no prefix or mono-
2
di-
3
tri-
4
tetra-
5
pent-
6
hex-
7
hept-
8
oct-
9
non-
10
dec-
Some ionic and covalent compounds that you might know
UNIT
2.2
Fig 2.2.6
[ Questions ]
Checkpoint Ionic compounds 1 Explain what happens when a positive or negative ion is formed. 2 Identify what holds the ions together in ionic compounds. 3 Sodium is more stable as a +1 ion than as a neutral atom. Explain why this is the case.
48
Prac 1 p. 50
4 a Define the term ‘polyatomic ion’. b Identify an example of a polyatomic ion, naming the atoms found within it. 5 State the names of the following ionic compounds. a RbBr e NH4Cl b K2S f LiOH c BeO g Ag2CO3 d Na3N h ZnSO4
Covalent compounds 6 Explain how covalent compounds form. 7 State the names of following covalent compounds. a CO2 b N2O5 c SF6 d H2O2 e H2O
Think 8 Distinguish between ionic bonding and covalent bonding. 9 Metal elements always form positive ions. Explain why and give an example. 10 Using the periodic table on page 10, construct chemical formulas for: a sodium bromide b magnesium sulfide c calcium fluoride d lithium nitride e aluminium carbide 11 Construct formulas for these compounds containing polyatomic ions: a sodium sulfate b magnesium hydroxide c strontium carbonate d lithium nitrate e ammonium oxide 12 Construct formulas for the following and classify each as either ionic or covalent compounds. a iron(III) chloride b phosphorus trihydride c iron(II) chloride d copper(I) nitrate e oxygen dichloride f copper(II) nitrate
Analyse 13 Magnesium oxide has a higher melting point than sodium chloride. Analyse what this tells you about the strength of the attractive electrostatic forces between the ions in these compounds.
UNIT
2.2 15 Calculate the number of each type of atom in the following formulas. a (NH4)2SO4 b K2Cr2O7 c Ca(OH)2 16 When covalent molecular compounds melt, only the bonds between molecules are broken. The molecules themselves stay intact. Ammonia (NH3) has a melting point of –78°C, and dinitrogen monoxide (N2O) has a melting point of –91°C. Analyse what this tells you about the relative strength of bonds between the molecules in each sample. 17 Explain what would happen if there were no rules for naming chemicals.
[ Extension ] Create 1 Construct a board game that tests students’ knowledge of how compounds are named. You may use die or cards. The game must involve answering questions about formulas or the rules for writing them. Design a list of rules, bonuses and challenges for the game.
Investigate 2 Even though the noble gases are usually unreactive, some do form compounds under certain extreme conditions. Examine what compounds the noble gases form.
Surf 3 Fireworks were discussed in Chapter 1. Take your investigation further by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 2, and clicking on the destinations button. Construct information cards with pictures of the various firework colours on one side. On the other side include information about its composition, name, formula and ratios of the elements.
14 Calculate the total charge of: a four sodium ions b eight manganese(IV) ions c three nitride ions.
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Naming compounds
UNIT
2.2
[ Practical activity ] Action of heat on ionic and covalent compounds Aim To investigate the effect of heat on different
Prac 1 Unit 2.2
compounds
spatula
Equipment Solid samples of various ionic and covalent compounds that do not produce toxic fumes on heating (e.g. wax—candle or paraffin), graphite, sodium chloride, potassium nitrate, Bunsen burner, heat mat, metal spatulas, wooden pegs, safety glasses, lab coat
sample
Bunsen burner
Method 1 Draw up a suitable table to record your results. The table below is an example.
Substance
Ionic or covalent
heat-proof mat
Melts on heating?
Sodium chloride
Fig 2.2.7
Wax
Questions
Potassium nitrate
1 Write a paragraph summarising your results. 2 Take a small amount of your first sample on the metal spatula. Hold it in the hottest part of the Bunsen burner flame for no more than 5 seconds. 3 Record your results. 4 Thoroughly clean the spatula. Ask your teacher for an appropriate disposal method for the sample. 5 Repeat steps 2 to 4 for your other samples.
a) wax
Fig 2.2.8
50
b) rubber
Some covalent compounds
2 Explain your observations in terms of the strengths of bonds between ions or molecules. 3 Assess whether the following substances would have high or low melting points. a sulfur (covalent) b magnesium carbonate (ionic) c iodine (covalent) d lithium nitrate (ionic)
c) PVC plastic
UNIT
2. 3 context
Airbags
Even though each substance is unique, similar substances behave in a similar way in chemical reactions. This allows scientists to classify reactions into several general categories. In this unit we will investigate some of the main reaction types.
Combination reactions
Decomposition reactions Decomposition reactions are the opposite of combination reactions. One substance breaks down to form two or more new substances.
In combination reactions, two or more substances combine to form one new substance. These reactions have the general equation:
It’s hard to believe that a decomposition reaction saves lives every day! Inside the airbag is a chemical, sodium azide, which decomposes explosively into sodium and nitrogen when triggered. Amazingly, 100 grams of sodium azide forms about 56 litres of nitrogen in 0.03 seconds, which then inflates the airbag. The chemical equation for the reaction is: 2NaN3(s) → 2Na(s) + 3N2(g)
X + Y → XY
For example, carbon and oxygen can combine to form carbon dioxide: carbon + oxygen → carbon dioxide
Now that we know about naming, we can start to write the correct chemical equation as well as the word equation for each reaction. Hence, the above reaction can be written as: C + O2 → CO2
Fig 2.3.2
O2 is used instead of O by itself because the oxygen in the air around us exists as diatomic molecules. ‘Diatomic’ means that two oxygen atoms bond together to form a stable molecule.
The deployment of an airbag during a crash is caused by a decomposition reaction.
For substances that break down to form two new substances, the general equation can be written: XY
→X+Y
Examples are:
C
+
O
C
O C
+
Fig 2.3.1
O2
→ calcium oxide + carbon dioxide → CaO + CO2 magnesium hydroxide → magnesium oxide + water Mg(OH)2 → MgO + H2O calcium carbonate
O
CO2
One atom of carbon combines with one molecule of oxygen to form one molecule of carbon dioxide.
O
CaCO3
Precipitation reactions Precipitation reactions result in an insoluble solid (called a precipitate) being formed when two clear solutions are mixed. They can be written as: soluble salt A + soluble salt B → insoluble salt C + soluble salt D (the precipitate)
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Reaction types Sometimes in chemical reactions subscripts are used to show what state the substances are in. A small (s) shows that the substance is solid, (l) shows it is liquid and (g) a gas. The subscript (aq) is used to show aqueous solutions (from the Latin word aqua, meaning ‘water’). These are substances that are dissolved in water. A precipitate is a solid, insoluble substance and therefore it too has the subscript (s). Figure 2.3.3 shows the formation of silver chloride precipitate when solutions of the soluble salts silver nitrate and sodium chloride are mixed. The word and chemical equations for this reaction are:
→ silver chloride + sodium nitrate AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
The sodium and nitrate ions are left dissolved in solution. Solubility rules help us to work out which substance in the mixture is precipitating. For example, in the above reaction, it can’t possibly be sodium nitrate because all sodium salts are soluble and all nitrate salts are soluble. Solubility of common inorganic compounds in water Negative ions + (anions) Acetate CH3COO–
Positive ions (cations)
→
All
Soluble +
+
+
Alkali ions, Li , Na , K ,
All
silver nitrate + sodium chloride
Compounds with solubility:
+
+
Soluble
+
Rb , Cs , Fr
+
All
Ammonium ion NH4
All
Hydrogen ion H
Chloride Cl
–
+
Soluble
(aq)
2+
Ag , Pb , Hg ,
–
+
Bromide Br Iodide I
2+
Soluble
+
Low solubility
+
Cu , Tl
–
All others –
Alkali ions, H
Hydroxide OH
2+
2+
Soluble +
+
(aq), NH4 2+ +
,
Soluble
Sr , Ba , Ra , Tl All others –
Nitrate NO3
All Alkali ions, H
2–
All others
Carbonate CO3 Sulfate SO4 Sulfide S
2–
Soluble
3–
Phosphate PO4
2–
Low solubility
2+
2+
+
(aq),
+
NH4
Soluble Low solubility
2+
2+
2+
Ca , Sr , Ba , Pb , Ra
Low solubility
All others
Soluble
Alkali ions, H+(aq), NH4+,
Soluble
Be2+, Mg2+, Ca2+, Sr2+, 2+
2+
Ba , Ra
All others
Fig 2.3.3
Low solubility
Silver chloride precipitation forming a white cloud at the centre of the test tube
Prac 1 p. 55
Ba2+ NO3– NO3– Ba(NO3)2 solution Fig 2.3.4
52
+
Na+
Na+ SO42–
Na+
NO3–
NO3– NaNO3 solution with BaSO4 + Na precipitate
Ba SO4
Na2SO4 solution
Mixing solutions of barium nitrate and sodium sulfate produces a precipitate of barium sulfate.
Neutralisation reactions
Antacids
Neutralisation reactions occur when an acid is added to a base, forming water and other substances. A base is anything that can neutralise an acid, like metal hydroxides. These reactions can be written as acid + base → salt + water
Heartburn and indigestion are caused when there is more acid in your stomach than the amount normally present for digestion. Antacids work by neutralising this excess acid. They contain a non-toxic base such as magnesium hydroxide. This reacts with the excess hydrochloric acid in your stomach to form salt and water … and relief!
UNIT
2.3 Displacement reactions Different metals have different degrees of reactivity. Some metals give up their outer shell electrons very easily and so are very reactive. The alkali metals (Group 1) are the most reactive metals. Other metals, like gold and silver, are very unreactive. This means that they don’t give up their electrons as easily. The activity series of metals shown in Figure 2.3.6 lists the metals in order from most reactive to least reactive.
For example, hydrochloric + sodium sodium + water → chloride acid hydroxide HCl + NaOH
→ NaCl + H2O
K N a C a M g A l Z n Fe P b C u H g A g P t A u most reactive
least reactive
Acids, bases and salts will be explained in more detail in Unit 2.4. Fig 2.3.6
Combustion reactions A combustion reaction is simply burning a substance in oxygen, so O2 is always a reactant. The products will vary, depending on the substance that is burnt. Examples of combustion reactions are:
→ carbon dioxide + water C3H8 + 5O2 → 3CO2 + 4H2O magnesium + oxygen → magnesium oxide 2Mg + O2 → 2MgO propane + oxygen
How a bullet works A combustion reaction occurs when a bullet is fired. The combustion of the chemical propellant in the bullet case produces a gas which expands and forces the bullet out of the barrel at great speed.
You can see that the combustion of magnesium is also an example of a combination reaction. Reactions can sometimes fall into more than one general category. The combustion of a chemical propellant forces a bullet from a barrel.
Fig 2.3.5
The activity series of metals
When one metal deposits on (settles on top of) another, the reaction is known as a displacement reaction. Energy on the This means that if you have a solution move The reaction that occurs of a particular metal salt, and you in batteries to supply place a solid piece of a more reactive energy is a displacement metal in the solution, a reaction will reaction. The difference is that the electrons are take place. The electrons from the forced to flow through a more reactive metal will be transferred wire from the more to the ions of the less reactive metal, reactive metal to the less which will become solid and deposit reactive metal. This flow of electrons forms an on the surface of the more reactive electric current, which metal. The basic rule is that ‘a more can then be used to reactive metal will displace a less power things like torches and Discmans. reactive metal in solution’ or, in other words, ‘a less reactive metal in solution will deposit on a more reactive metal’ (turn back to Figure 2.1.8 for more information). Displacement reactions can be used to coat metals. For instance, if you wanted to coat a piece of zinc with copper, you could simply dip it into a solution of copper sulfate. The copper ions would accept electrons from the zinc atoms on the surface, because copper is less reactive than zinc. This reaction could be written as: zinc + copper sulfate → zinc sulfate + copper Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
This would not produce a very even coating, however. Industrial plating is carried out quite differently.
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Reaction types Electroplating is the name for the process that causes metal atoms to be deposited on the surface of a substance that acts as a conductor. By using electricity, non-spontaneous reactions can be Prac 2 made to produce decorative or useful surfaces. p. 56
UNIT
2.3
[ Questions ]
Checkpoint Combination reactions 1 Describe what a combination reaction is and give an example. 2 Oxygen is written as O2 in chemical reactions rather than just O. Explain why this is the case.
Decomposition reactions 3 Describe what a decomposition reaction is and give an example. 4 A gas is given off when calcium carbonate is heated. Identify this gas.
Fig 2.3.7
Solid copper (black) coats the zinc because the copper was replaced in solution by the more active zinc.
Precipitation reactions 5 Describe what observations may be made when a precipitation reaction occurs. 6 State the meaning of the subscripts (s), (l), (g) and (aq).
Neutralisation reactions 7 Describe what a neutralisation reaction is and give an example. 8 Identify the products formed when an acid is added to a metal hydroxide.
Combustion reactions 9 Describe what a combustion reaction is and give an example. 10 Identify an example of a chemical reaction that can be classified as two different reaction types.
Displacement reactions 11 Describe what a displacement reaction is and give an example. 12 Explain what the activity series shows.
Think
54
15 Predict the precipitate formed when these solutions are mixed: a silver nitrate and sodium chloride b mercury(I) nitrate and potassium iodide c calcium nitrate and lithium carbonate d barium nitrate and sodium sulfate 16 Construct word equations for the reactions in Question 15. 17 Explain how a displacement reaction occurs.
Analyse 18 Classify the following reactions. a Hydrogen peroxide breaks down into hydrogen and oxygen gas. b Phosphoric acid reacts with ammonia to form water and ammonium phosphate. c Magnesium when placed in zinc chloride solution causes zinc metal to form. d Sulphur reacts with iron to form iron sulphide. e Sodium burns in oxygen to form sodium oxide.
13 Choose two reactions in the previous questions and write word equations for these.
19 Choose two reactions in Question 18 and construct word equations for these.
14 Refer to the table of solubility rules on page 52. Assess which of the following substances would be soluble in water. a BaSO4 c CaCO3 b LiNO3 d MgCl2
20 Scientists have classified reactions into different types. Explain why this is useful. 21 Rules are often used in science. a Identify a set of rules in this unit. b Explain how these rules are helpful.
UNIT
2.3 [ Extension ] Investigate
Surf
1 a Research and explain the combustion reaction that drives a space shuttle. Use chemical equations in your answer. b Draw a diagram to illustrate how the shuttle engines work.
3 Complete some fun activities on the web that test your understanding of chemical reactions and equations by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 2, and clicking on the destinations button.
2 a Design an experiment to test whether the solubility of ionic compounds increases or decreases as the solutions get hotter. b Investigate and explain your results.
UNIT
2.3
DYO
[ Practical activities ]
Fig 2.3.8 step 1
step 2
step 3
Precipitation of unknowns Aim To identify an unknown solution using the solubility table
Prac 1 Unit 2.3
+
Equipment The table of solubility rules on page 52; unknown 0.1 M solutions labelled A, B, C, D, E—these are (not in order): sodium iodide, sodium chloride, sodium sulfate, sodium carbonate and sodium nitrate; 0.1 M solutions of silver, lead, calcium and barium nitrate; 20 semi-micro test tubes; Pasteur pipettes; lab coat; safety glasses; gloves Hint: Cu2+ ions are blue in aqueous solution. Lead iodide is bright yellow. Note: Solutions from this experiment must not be washed down the sink. They should be placed in a clearly marked waste bottle. Gloves must be worn at all times.
Method 1 Draw up a suitable table, similar to the one below, to record your results. Unknown A
Silver nitrate
Lead nitrate
Calcium nitrate
Barium nitrate
10 drops of unknown solution
Add 10 drops test solution and mix.
Check for cloudiness—hold it up to the light if not sure.
2 Put about 10 drops of unknown A into each of four semi-micro test tubes. 3 Add 10 drops of silver nitrate solution to the first, 10 drops of lead nitrate to the second, 10 drops of barium nitrate to the third, and 10 drops of magnesium nitrate to the fourth. Record your results. 4 Repeat steps 2 and 3 for each unknown solution. 5 Use the table of solubility rules to work out which solution is which.
B
Questions
C
1 Were any of your results inconclusive? If so, propose a reason.
D E
2 If you wanted to test a clear solution for the presence of lead, identify what you could add.
55
Reaction types
>>>
Electroplating
power source
AIM To investigate the displacement Prac 2 Unit 2.3
reaction associated with electroplating.
Equipment
6 V DC power source, 250 mL beaker, 2 insulated wires with crocodile clips on one end, 1 very thin 7 x 4 cm strip of copper metal (coiled copper wire may also be used), 1 stainless steel electrode, sandpaper, tongs, washbottle of distilled water, 1 M zinc sulfate solution, 2 M nitric acid, lab coat, safety glasses, gloves
Method
6 VOLTS DC
wire
copper
stainless steel
beaker
1 Clean the copper with the sandpaper. 2 Dip the copper in the acid and then rinse with distilled water. Don’t touch the part that will go in the solution. 3 Attach the copper to the negative terminal of the power source. Rest it in the beaker. 4 Put 150 mL of 1 M zinc sulfate solution in the beaker. 5 Attach the stainless steel electrode to the positive power terminal. Do not allow it to touch the copper terminal. 6 Turn the power on for about 3 minutes. 7 Remove the copper and rinse with distilled water.
Questions 1 Compare the appearance of the copper before and after. 2 Construct a word equation for the reaction that occurred. 3 Describe how you could coat the copper with nickel
56
1 M zinc sulfate solution
Fig 2.3.9
UNIT
context
2. 4 Many familiar substances can be classified as acids or bases. You can probably even name a few, like the acid in citrus fruits (citric acid) or the acid in vinegar (acetic acid). Can you name any bases? You’ve no doubt heard of ammonia, which is in many cleaning products. Did you know it was a base? So what makes a substance acidic or basic, anyway?
Strong or weak?
Acid burns With strong acids, the Sulfuric acid is a very hydrogen breaks away very good dehydrating agent; it removes water from easily. Weak acids tend to hold substances very easily. on to their hydrogen, and very It chars both paper and little hydrogen breaks away. sugar if it comes into contact with them. Strong acids are corrosive and It is this property that will destroy living tissue and makes sulfuric acid ‘eat through’ some surfaces. so damaging to living Hydrochloric acid, which tissue. Sulfuric acid used to be known as helps digestion of food in our oil of vitriol. stomachs, is a strong acid. The reason it doesn’t eat through the stomach lining is because the lining secretes protective mucus. Other examples of strong acids are nitric acid (HNO3) and sulfuric acid. Weak acids include vinegar and citric acid. Strong acids break apart completely in water, while weak acids tend to stay together.
strong acid—HCl hydrochloric acid
Fig 2.4.2
weak acid—CH3COOH acetic acid
CH3COOH
Fig 2.4.1
All of these common substances contain acids and bases.
H+ Cl–
Cl– H+
Acids contain the element hydrogen in combination with other non-metal elements. For example, hydrochloric acid has the formula HCl. It contains hydrogen in combination with chlorine. Sulfuric acid, H2SO4, contains hydrogen in combination with the sulfate ion (SO42–), which is made up of one sulfur and four oxygen atoms. When an acid is placed in water, the hydrogen breaks away from the other elements.
CH3COOH
H+
H+
Cl–
Acids H+
Cl–
H+ Cl–
Cl– H+
CH3COOH
CH3COOH CH3COO– CH3COOH
Some properties of acids: • Acids have a sour taste (don’t try this). • Acids turn blue litmus red. • Acids conduct electricity in aqueous (water) solution.
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Acids and bases Concentration Acids may also be dilute or concentrated. In science experiments we use a dilute acid solution of acid, which has very few acid particles (solute) in a relatively large volume of water (solvent). Concentrated solutions of acid have many acid particles dissolved in the solvent. Concentrated acid solutions are very dangerous, while dilute ones may be relatively harmless.
Sour wine In addition to its main ingredients of water, ethanol (alcohol), sugars, tannins and additives, wine also contains a variety of acids. These include tartaric, malic, lactic and succinic acids. The acidity level has to be controlled carefully. Too much and the wine acquires a nasty, sour taste. Too little and the wine will easily go ‘off’.
The uses of acids The acids that we eat and drink, like the citric acid in lemons and sherbet and the lactic acid in yoghurt, are both weak and dilute and so do not harm us. They are still strong enough to affect sensitive tissues, though, like lemon juice on a cut or in the eye. The table below shows some acids and the common uses of each. Acid
Common name
Acetylsalicylic acid
Aspirin
Pain reliever
Benzoic acid
Sorbic acid
Preservatives in foods
Ascorbic acid
Vitamin C
Vitamin supplement, antioxidant
Sulfuric acid
Battery acid
Common use
Car batteries, manufacturing fertilisers
4-chloro-2-methyl phenoxyacetic acid
MCPA
Hydrochloric acid
Spirit of salts
Brick cleaners, cleaning metals
Ethanoic (acetic) acid
Vinegar
Flavour and preserving food
The uses of bases Many household cleaners contain bases because they are excellent at dissolving oil and grease. Oven cleaners usually contain sodium hydroxide (NaOH), a strong base, because it reacts with oils to form soap, which then washes away easily. Bases include ionic compounds like hydroxides, oxides, carbonates and hydrogen carbonates. The table below shows some bases and their uses.
Base
Common name
Common use
Sodium hydroxide
Caustic soda
Making soaps, cleaning ovens
Calcium hydroxide
Slaked lime
Reducing acidity in soil
Ammonium hydroxide
‘Cleaning’ ammonia
Cleaning products
Sodium hydrogen carbonate
Baking soda, bicarbonate of soda
Cooking
Sodium carbonate
Washing soda, soda ash
Washing powders
Herbicide
Bases You can think of bases as the chemical opposite of acids. Bases react with acids to produce water and other substances. Any reaction of an acid with a base is called neutralisation.
Strong and weak Strong bases, like strong acids, attack living tissue and cause serious burns. They react differently to skin
58
than acids do, so while strong acids are corrosive, we say that strong bases are caustic. Bases that dissolve in water are called alkalis. Bases may also be weak, such as ammonia used for cleaning. Some properties of bases: • Bases taste bitter. • Bases have a soapy feel (remember, it is not advisable to touch chemicals). • Bases turn red litmus blue.
Acids and metals When an acid reacts with a metal, hydrogen gas and a salt are produced. A salt is an ionic compound containing the ions left over after reaction. The general reaction can be written as: acid + metal
→ salt + hydrogen
An example is hydrochloric + magnesium acid
→
magnesium + hydrogen chloride
2HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)
Note that a subscript ‘(g)’ is used to show a gas. This reaction is shown in Figure 2.4.3.
Hydrochloric acid reacting with magnesium to form a salt and hydrogen
our teeth, the toothpaste, which contains a base, neutralises the damaging acids left on our teeth by bacteria. Farmers can reverse the effects of acid rain on soil by adding the base calcium hydroxide. Indigestion caused by too much acid in the stomach can be relieved with antacids, which are just bases in solid or liquid form.
Fig 2.4.3
Hydrochloric acid is neutralised by sodium hydroxide, a strong base.
H+ Cl– H+
Most metals will react with acids. Some, like the Group 1 metals, react violently, while other metals, like lead, need hotter or more concentrated acid solutions to make them react. The table below shows the reactions between some acids and metals.
Cl–
H+
OH– water H20 Na+ Cl– OH–
HCl (aq)
+
OH– Na+
NaOH (aq)
Metal
Reaction equation
Salt produced
Nitric acid
Calcium
2HNO3(aq) + Ca(s) → H2(g) + Ca(NO3)2(aq)
Calcium nitrate
Sulfuric acid
Magnesium
H2SO4(aq) + Mg(s) → H2(g) + MgSO4(aq)
Magnesium sulfate
Hydrochloric acid
Iron
2HCl(aq) + Fe(s) → FeCl2(aq) + H2(g)
Iron(II) chloride
Na+ water H20
Cl–
Cl– Na+ Cl–
Na+ Na+
H2O (l) + NaCl (aq)
‘Houston, we have a problem’
The astronauts of the Apollo 13 space mission fac ed, among other things, a serious build-up of car bon dioxide on board the ir damaged spacecraft. The astronauts would quick ly have suffocated unles sa way could be found to reduce the CO levels 2 . By adapting lithium hyd roxide containers from the Lu nar Module they were abl e to keep the air breathabl e. Lithium hydroxide rea cts and removes carbon dioxide by producing lithium carbonate and water. This is a neutralisation reactio n.
Prac 1 p. 63
Neutralisation As stated earlier, a neutralisation reaction is when an acid reacts with a base. Water is always a product in neutralisation reactions, as is a salt: acid + base → salt + water
When the base used is a carbonate or a hydrogen carbonate, a third product, carbon dioxide, is observed as bubbles in the solution. Neutralisation reactions are very common. Every time we brush
Cl–
Na+
H+
Cl–
Fig 2.4.4
OH–
Na+
Acid
You can test for the hydrogen gas given off by using the ‘pop’ test. A spark in the presence of H2 causes a popping sound as the gas combines with the O2 in air to form water.
UNIT
2. 4
Fig 2.4.5
John Swigert holds one of the lithium hydroxide containers from the Lunar Module.
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Acids and bases Scanning electron microscope (SEM) image of the barbed sting of a honeybee. The acid is ejected from the red glands at the bottom of the image.
Fig 2.4.6
sulfuric acid + lithium oxide H2SO4(aq) + Li2O(s)
→ →
lithium sulfate + water Li2SO4(aq) + H2O(l)
Acids and carbonates Like the last two neutralisation reactions that we’ve looked at, the reaction of an acid with a carbonate produces a salt and water. It also produces a third product, carbon dioxide. The reaction of an acid with a hydrogen carbonate produces the same three things: acid + carbonate acid + hydrogen carbonate
→ salt + water + carbon dioxide → salt + water + carbon dioxide
Examples are:
Things that sting
Acids and hydroxides The general reaction equation for an acid combining with a hydroxide is: acid + hydroxide → salt + water
Some examples of dilute acids reacting with dilute hydroxide solutions are: hydrochloric + acid
sodium hydroxide
HCl(aq) + NaOH(aq) nitric acid + lithium hydroxide HNO3(aq) + LiOH(aq)
→
As everyone knows, worker bees can give you a very nasty sting. The painful sting is produced by the methanoic (formic) acid they inject. This is the same acid that puts the sting into bullants and greenheads. Other stinging creatures, like wasps and some jellyfish, inject a base into the skin of their victims. This can be neutralised by washing the wound with a weak acid like vinegar.
sodium + water chloride
→ NaCl(aq) + H2O(l) → lithium nitrate + water → LiNO3(aq) + H2O(l)
nitric + sodium acid carbonate 2HNO3(aq) + Na2CO3(s) hydrochloric + ammonium acid carbonate 2HCl(aq) + (NH4)2CO3(s) sodium sulfuric acid + hydrogen carbonate H2SO4(aq) + 2NaHCO3(s)
→
sodium + water + carbon nitrate dioxide
→ 2NaNO3(aq) + H2O(l) + CO2(g) →
ammonium + water + carbon chloride dioxide
→ 2NH4Cl(aq) + H2O(l) + CO2(g) →
sodium carbon sulfate + water + dioxide
→ Na2SO4(aq) + H2O(l) + CO2(g)
It is the carbon dioxide produced that often makes you burp after taking antacids. Baking powder is a mix of tartaric acid and sodium hydrogen carbonate (bicarb soda). When water is added, they dissolve and mix. This produces the carbon dioxide bubbles that make cakes rise. You can test for carbon dioxide by bubbling the gas through limewater. The limewater goes from
The above acids react in the same way as if the hydroxides were solids. The only difference is that the ‘(aq)’ subscript next to the hydroxide would be replaced by ‘(s)’. The subscript ‘(l)’ is always used for water to show it is a liquid.
Acids and oxides The general reaction of an acid with an oxide is: acid + oxide
→ salt + water
hydrochloric acid
lime water
Examples of dilute acids reacting with solid oxides are: hydrochloric + calcium acid oxide 2HCl(aq) + CaO(s)
60
→
calcium + water chloride
→
CaCl2(aq) + H2O(l)
calcium carbonate
Fig 2.4.7
Limewater test for the presence of carbon dioxide
clear to milky if carbon dioxide is present because of the formation of a calcium carbonate precipitate. Another test is that carbon dioxide will extinguish a lit match. Worksheet 2.2 A neutralisation reaction
Prac 2 p. 64
The pH scale
UNIT
2. 4 solution and thus only gives us a broad range of possible pH values. Other indicators are far more precise. Universal indicator is an example of this because it can undergo many colour changes and gives us a good estimation of the pH of a solution. You may have seen universal indicator used to check the pH of a swimming pool or spa. Figure 2.4.10 shows the colour changes of some other common indicators.
To describe how strong an acidic or basic substance is, we use the pH scale. At 25°C, the pH scale goes from 0 to 14, with acidic substances having pH less than 7, and basic substances having pH greater than 7. Strongly acidic substances have pH closer to 0. Very basic substances have pH closer to 14. A neutral substance is neither acidic nor basic and has a pH of 7.
neutral 6 7 8 9 pH
10
11 detergents
5
tap water pure water blood sea water baking soda
4
vinegar orange juice wine coffee
stomach acid
strong acids 0 1 2 3
Fig 2.4.8
strong bases 12 13 14 dishwashing powder
The pH scale (pH is short for ‘power of hydrogen’)
Blue litmus paper turns red when in contact with an acid. The juice of a lemon contains citric acid.
Fig 2.4.10
The colour changes of some indicators
pH
indicator
The pH is a measure of how much free hydrogen is present in a solution. If there is a lot, the pH is very low. If there is hardly any, the pH is higher. Every time you take a step along the pH scale, say from pH 3 to pH 4, the hydrogen present decreases by a factor of 10. Say you have 10 mL of a solution with a pH of 1. If you add 90 mL of water, the new volume will be 100 mL and you will have diluted the solution by a factor of 10. The pH of the new solution will be 2.
Fig 2.4.9
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 bromothymol yellow change blue blue litmus methyl orange phenolphthalein
red
change
blue
red-orangechange
yellow
colourless
change
pink deep
universal deep red red orange yellow green blue violet violet indicator 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Indicators Indicators are chemicals that are used to show the pH of a solution. Some indicators are not very precise and only tell us whether a solution is acidic or basic. Litmus, which is made from plants called lichens, is an example of this kind of indicator. It is red in acidic solution and blue in alkaline
Many plants, like beetroot, red cabbage, hydrangeas and hibiscus, produce dyes that can be used as indicators. Hydrangeas, for example, have blue flowers in acidic soil and pink flowers in alkaline soil.
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Acids and bases
Neutralisation 11 Describe some everyday examples of neutralisation.
1
2
deep red red
3
4
5
6
pH 7
12 a Identify some examples of stinging creatures. b Explain what can be done to neutralise the sting. c Explain why lifesaving clubs in New South Wales make available buckets of dilute vinegar when bluebottle jellyfish are being blown onshore. d Explain why vinegar would not relieve beestings. 8
9
10
11
12
red red orange green green blue blue orange violet yellow green blue
Colour changes of universal indicator with pH
13
14
violet
Fig 2.4.11
13 Copy and complete the following table to distinguish the reactants and products of the following reaction types. Reaction type
Example
Reactant(s)
Product(s)
(word equation and chemical formulas) Acid + metal Acid + hydroxide
Prac 3 p. 65
Prac 4 p. 65
Prac 5 p. 66
Prac 6 p. 66
Acid + oxide Acid + carbonate
Worksheet 2.3 pH levels of common drinks
UNIT
2. 4
The pH scale
[ Questions ]
Checkpoint Acids 1 Define the term ‘acid’. 2 Describe two properties of an acid. 3 Describe how sulfuric acid reacts with living tissue. 4 Identify three different acids and give their chemical formulas. 5 Identify the acid present in vinegar. Explain why it is a weak acid.
Bases 6 Define the term ‘base’. 7 Define the term ‘alkali’. 8 Describe two properties of a base.
Acids and metals 9 To non-chemists, ‘salt’ is sodium chloride, NaCl. Define what chemists mean by the term ‘ salt’. 10 Construct word equations for the reactions of the following metals with nitric acid: a aluminium c iron b zinc d lithium
62
14 Identify the approximate pH of: a a strong acid d a weak base b a weak acid e a strong base c pure water 15 Define the term ‘indicator’. 16 Identify an important use for an indicator. 17 At pH 8, identify the colour of: a universal indicator b red litmus c blue litmus
Think 18 Identify three fruits containing citric acid. 19 Distinguish between a dilute solution of nitric acid and a concentrated solution of nitric acid. 20 When sodium hydroxide reacts with fats, soap is produced. Explain why bases feel soapy to touch. 21 Describe how you could test for: a hydrogen gas b carbon dioxide gas 22 The normal pH in the mouth is about 6.5. The pH in the stomach is around 2 to 3. Explain why you get a burning sensation in the oesophagus, throat and mouth when you vomit.
23 Azaleas grow only in soil with pH greater than 7. a Select which substance should be added to basic soil to lower its pH. Choose either water, an acid or a base. b Explain your answer. 24 A certain food is found to be slightly acidic. It contains either hydrochloric acid or acetic acid. Evaluate which acid it is more likely to contain.
Analyse
30 Explain how classifying acids and bases can make science easier.
[ Extension ] Investigate 1 Many advertisements for shampoos and skin lotions mention their pH. a Research which pH is best for your skin and which is best for your hair. b Does the age of a person and their type of skin or hair change the answer to this question?
26 a Construct word equations for the following reactions. i hydrochloric acid + iron(II) hydrogen carbonate ii nitric acid + silver hydroxide iii sulfuric acid + barium oxide b Use the formulas given throughout this chapter to write the reactions as chemical equations. 27 Identify which acid and base you could combine to make these salts: a barium chloride b calcium nitrate c iron(III) sulfate
2 Sulfuric acid is one of the most important chemicals in the world. The sulfuric acid production of a country is said to be a good indicator of the state of its economy. Investigate what sulfuric acid is used for and analyse the reasons why sulfuric acid is a measure of the economy.
28 You are given 10 mL each of two solutions. Solution A has a pH of 2. Solution B has a pH of 4. Calculate how much water you would have to add to solution A to make its pH the same as that of solution B. This is a hard one!
UNIT
29 Evaluate the importance of acids and bases in our daily lives.
25 Identify the salt produced by each of the following neutralisation reactions. a nitric acid + strontium hydroxide b sulfuric acid + copper carbonate c hydrochloric acid + silver oxide d nitric acid + magnesium hydrogen carbonate
2. 4
3 Investigate some other acids that are used either in cooking or in medicine. This could include salicylic acid or tartaric acid, 4 The ideal pH of a swimming pool is around 7.2. At this pH, most bacteria and green algae can’t grow. Describe how pH levels of pools are tested, why they change and how the pH is kept at 7.2.
[ Practical activities ] Acids and metals
Hydrochloric acid
Aim To observe the reaction of an acid with a Prac 1 Unit 2.4
UNIT
2. 4
metal
Equipment
3 test tubes with stoppers, test-tube rack, matches, 100 mL beaker, small pieces of aluminium, magnesium, zinc, iron and tin, 0.1 M solutions of hydrochloric, sulfuric and acetic acids, lab coat, safety glasses
Sulfuric acid
Acetic acid
Aluminium Magnesium Zinc Iron Tin
Method 1 Copy the results table opposite into your book.
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Acids and bases
Fig 2.4.12
2 Pour 2 cm of hydrochloric acid into each test tube. 3 To the first test tube add one of the metals. If there is an obvious reaction, hold the stopper on the tube for about 15 seconds. Light a match and, removing the stopper quickly, hold the lit match to the mouth of the tube. Record your observations.
i
ii
iii
‘pop’
4 Repeat step 3 for the other metals. You do not have to repeat the gas test for every reaction. 5 Repeat steps 2–4 for the other acids.
Questions 1 Construct word equations for the reactions of the metals with one of the acids tested. 2 For the other two acids, identify the salts produced in each reaction.
Hold stopper on tube for 15 seconds.
3 From the speed of the reaction with each metal, arrange the metals tested in order from most active to least active.
A second person lights a match and holds it to the mouth of the tube as the stopper is removed.
A ‘pop’ indicates hydrogen is present.
Acids and metal carbonates Prac 2 Unit 2.4
Aim To observe the reaction of an acid with metal carbonates
Equipment 4 test tubes; test-tube rack; stopper; 100 mL beaker; matches; limewater; solid samples of sodium hydrogen carbonate, lithium carbonate, sodium carbonate and ammonium carbonate; spatula; 0.1 M solutions of nitric and hydrochloric acids; lab coat; safety glasses
Method
stopper
Test 1 If carbon dioxide is present, a lit match goes out.
1 You will be combining each acid with each solid. Draw up a suitable results table, similar to that used in Prac 1. 2 Add a small amount of each solid (about the tip of a spatula full) to four different test tubes. 3 Add 2 cm of nitric acid to the first tube and quickly stopper. Light a match and, removing the stopper quickly, put the lit match in the mouth of the tube. Record your observations. 4 Add 2 cm of nitric acid to the second tube and quickly stopper. Remove the stopper and add a small amount of limewater. Re-stopper the tube, but don’t let too much gas build up. Record your observations. 5 Add nitric acid to the other two tubes, but don’t stopper. Record your observations. 6 Repeat steps 2–5 using hydrochloric acid.
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match
Test 2 If carbon dioxide is present, limewater goes from clear to milky.
Fig 2.4.13
Questions 1 Construct word equations for all reactions. 2 Identify the salt in each equation by circling it. 3 Draw a diagram to explain how you could set up this experiment so that the gas produced bubbles through a separate beaker of limewater as it is produced.
Prac 3 Unit 2.4
Common indicators
4 Repeat steps 2 and 3 for the other indicators.
Aim To investigate the uses of various indicators in acidic and basic solutions
Questions
Equipment
0.1 M solutions of sodium hydroxide and hydrochloric acid, distilled water, 3 test tubes, test-tube rack, 3 x 100 mL beakers, liquid red and blue litmus, universal indicator, methyl orange, methyl red, bromothymol blue, phenolphthalein, lab coat, safety glasses
Method
UNIT
2. 4 1 Deduce why distilled water was used for this experiment, rather than tap water. 2 Summarise your results by writing a paragraph.
Colour in strong acid Colour in strong base Colour in neutral (hydrochloric acid) (sodium hydroxide) solution (water)
Red litmus
1 Copy the results table into your book.
Blue litmus
2 Using the beakers, pour 2 cm of acid into one test tube, 2 cm of sodium hydroxide (base) into another test tube, and 2 cm of distilled water into the third test tube.
Universal indicator
3 Add 3 drops of red litmus to each tube. Record your results.
Phenolphthalein
Methyl orange Methyl red
Fig 2.4.14
Natural indicators Aim To prepare and use natural indicators Prac 4 Unit 2.4
Equipment 0.1 M hydrochloric acid, 0.1 M sodium hydroxide, distilled water, pink or red flower petals, beetroot juice, tea bag, 3 x 100 mL beakers, filter paper cut into strips, Bunsen burner, heat mat, tripod, gauze, matches, 3 test tubes, test-tube rack, Pasteur pipettes, lab coat, safety glasses
red flower petals
beaker 50 mL water
pipette
indicator Bunsen burner
test-tube rack
tripod
Method 1 Gently boil 50 mL of water in a beaker combined with the flower petals until the water becomes strongly coloured, then remove from heat. 2 Place 20 mL of beetroot juice in another beaker.
heat-proof mat making flower petal indicator
hydrochloric sodium distilled acid chloride water
3 Boil 50 mL of water in another beaker and add a tea bag. 4 Using tongs, dip a strip of filter paper into each solution and lay them on paper towel to dry. 5 Place 2 cm of hydrochloric acid in a test tube, 2 cm of sodium hydroxide in a second test tube and 2 cm of distilled water in a third test tube.
Questions
6 Add about 10 drops of flower-petal water to each and record the colour of each solution.
2 Identify which of the three indicators was best. Explain your choice.
7 Clean the test tubes and repeat steps 5 and 6, first using beetroot juice, then tea.
3 How did the colours produced with the paper compare to the colours produced when using the liquid indicators?
8 Carefully dry the freshly made indicator paper over a Bunsen burner flame, being careful not to burn it.
4 Can you think of any other substances that might be natural indicators? If so, explain why you think they would work.
9 When dry, put a drop of acid on one end of each piece of paper, and a drop of base on the other end. Allow them to dry, then stick them in your book.
1 Propose a suitable conclusion for this experiment.
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Acids and bases
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Universal indicator
Testing household solutions
Aim To investigate the colour changes of Prac 5 Unit 2.4
universal indicator with increasing pH
Equipment
0.1 M hydrochloric acid, 1.0 M sodium hydroxide, distilled water, Pasteur pipette, 10 mL measuring cylinder, waterproof Texta, 14 large test tubes, universal indicator, lab coat, safety glasses
Method 1 Label your test tubes 1 to 14. 2 Place 10 mL of 0.1 M hydrochloric acid in test tube number 1.
Prac 6 Unit 2.4
Aim To test the pH of various household solutions Equipment
2 test tubes, test-tube rack, Pasteur pipettes, 2 watch-glasses, blue and red litmus paper, liquid universal indicator, distilled water, safety glasses, lab coat, a variety of household solutions including orange juice, soft drink, fresh and sour milk, vinegar. Solids may be used if dissolved in water first.
Method 1 Place 2 cm of solution into a test tube using a Pasteur pipette.
3 Using a pipette, transfer 1 mL of this solution to the measuring cylinder. Add 9 mL of distilled water and pour the mixture into test tube number 2. 4 Using a pipette, transfer 1 mL of the solution in tube 2 to the measuring cylinder. Add 9 mL of water and pour the mixture into test tube number 4. Continue this method up to tube number 6.
test-tube rack
test tubes
Pasteur pipette
5 Add 10 mL of distilled water to tube number 7. 6 Add 10 mL of 1.0 M sodium hydroxide to tube number 14. 7 Using a pipette, remove 1 mL of this solution, add 9 mL of water and pour the mixture into tube 13. Continue this method down to tube number 8.
test solution
red
blue
watch-glass
test solution + universal indicator
test solution + red litmus paper
test solution + blue litmus paper
8 Add 3 drops of indicator to each tube and sketch the result. The number of the tube is approximately the same as the pH.
Questions 1 On your sketch, indicate which tubes contain strong acids, weak acids, strong bases and weak bases. 2 Calculate the dilution factor between: a tubes 2 and 4 b tubes 10 and 11
Fig 2.4.15 2 If the colour of the solution is quite strong, add distilled water until it is faint. 3 Pipette a small amount of the solution onto each of two watch-glasses. Add red litmus paper to one and blue litmus paper to the other. Record your results. 4 Add 3 drops of universal indicator to the test tube and record the pH of the solution. 5 Clean the equipment and repeat the procedure for your other solutions.
Questions 1 Arrange your solutions in a list from most acidic to least acidic. 2 A brick cleaner is marked as highly corrosive. Identify where you think it would go on your list. 3 Explain why there is a difference in pH between fresh and sour milk.
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Chapter review [ Summary questions ] 1 Describe the observations you might make if a chemical reaction occurs. 2 Is rain a physical change or a chemical change? Discuss. 3 Is the melting of ice an endothermic or exothermic reaction? Discuss. 4 Identify the solvent and the main solute in sea water. 5 Explain why some metals are more reactive than others. 6 Construct formulas for: a lithium hydroxide b barium sulfate c aluminium bromide 7 Identify the systematic names of: a H2S b PF3 c SiO2
[ Thinking questions ] 8 Are the bonds between the atoms in H2O covalent or ionic? Explain. 9 Deduce what charge the ions of these metals have: a sodium b strontium c aluminium 10 Identify the names of these ions: a HCO3– b I– c S2– d NH4+ 11 Define the term ‘diatomic’. Give an example to illustrate your answer. 12 A clumsy student spills sulfuric acid on the lab floor. Identify the chemical you could add to the mess to neutralise the acid. 13 Identify an acid and a base commonly found around the home.
[ Interpreting questions ] 14 Identify the reaction type for each of the following equations: a lithium + chlorine → lithium chloride b sulfuric + barium → barium + carbon + water acid carbonate sulfate dioxide 15 State the type of reaction that could be used to coat a metal. 16 Identify what chemical is found in antacids. 17 Classify the following substances as acids or bases: a b c d e
NaOH Li2CO3 HCl MgO HNO3
18 Deduce the products of the following neutralisation reactions: a sodium carbonate + hydrochloric acid → b calcium hydroxide + nitric acid → 19 Identify what colour the following indicators would be at pH 4: a blue litmus b red litmus c universal indicator d methyl orange 20 You are given three unlabelled colourless solutions. You are told that one is pure water, one is a solution of hydrochloric acid and one is a solution of sodium hydroxide. You are also given some universal indicator which you can add to only one. Propose how you could identify each solution. 21 Scientists use a number of tools to make understanding science easier. Using examples from this chapter, explain how scientists have used the following tools. a classification b models c rules Worksheet 2.4 Chemical reactions crossword Worksheet 2.5 Sci-words
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Origin of the universe
3
Key focus area
5.5, 5.9.1, 5.9.3
Outcomes
>>> Current issues, research and development in science
By the end of this chapter you should be able to: describe the Doppler effect and explain how it gives us information about the movement of stars and galaxies explain the big bang and what occurred soon after it happened describe possible models of the universe identify and describe the main stages in the life of stars debate whether alien life forms exist and whether we should be trying to contact them
Pre quiz
discuss whether we will ever travel to the stars and, if so, how it may be done.
1 Why does an ambulance siren change its sound and pitch as it passes by?
2 The stars and galaxies are moving. True or false?
3 What was the ‘big bang’? 4 What is a black hole? 5 How long do you think it would take to get to our nearest star?
6 Do you think that alien life forms exist?
UNIT
context
3.1 It’s enough to make you go mad! Thinking about how the universe was formed leads to questions like ‘What was there before there was a universe—nothing?’, ‘What does nothing look like?’ and ‘How did something come from nothing?’ We can now give some answers to these questions. Through constant and ongoing scientific research, scientists have developed many theories about what the universe looks like now and what it was like at the beginning of it all.
The Doppler effect The universe is expanding. How have scientists determined this? The answer has something in common with a phenomenon that we hear whenever cars, ambulances and trains whiz past or an aeroplane flies overhead. Have you noticed that the sound they make changes from a high pitch to a lower pitch as they pass? Consider the sound waves coming from the siren of an approaching ambulance. The sound waves are produced by vibrations repeating themselves many times a second. Consider a sound vibration emitted in front of the ambulance as it approaches you. Because the ambulance is following this vibration, it is also ‘catching up’ to it a little. This means the waves in front of the ambulance are closer together
low pitch
Fig 3.1.1
and have a shorter wavelength. You will recall that such waves produce a higher-pitched sound. Conversely, a vibration emitted behind the ambulance gets further away from the ambulance because the ambulance is ‘running away’ from it. The sound behind the ambulance has a longer wavelength and hence a lower pitch. This change in wavelength and pitch is known as the Doppler effect after Christian Doppler, an Austrian physicist who described it in 1842. The Doppler effect also happens with light but there is a change in its colour instead of a change in pitch. When a light wave gets scrunched up or stretched, its wavelength changes and this changes its colour. The effect is only noticeable for incredibly fast-moving light sources, such as stars and galaxies. These emit a range of different light waves of various colours, which we call a spectrum. One way of observing a spectrum is to pass light through a prism so the different colours are separated as light bends or refracts. Fig 3.1.2
A prism, like a spectrometer, refracts light and separates it into its spectrum.
high pitch
Sound waves of different wavelengths are produced when the source of the sound moves.
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The expanding universe Scientists use a device called a spectrometer to view the various colours or spectrum of a light source. Atoms in the atmosphere of stars absorb Prac 1 some of the light of a galaxy’s spectrum, p. 72 producing dark lines within it. The American astronomer Edwin Hubble studied the positions of these dark lines within the spectrum of light emitted by a star or galaxy and deduced whether they are moving towards or away from us, and at what speed. Stars that are moving away exhibit a spectrum whose dark lines are moved towards the red end of visible light (light of longer wavelength) while those that are moving towards us have a spectrum whose dark lines are shifted towards the blue end (longer wavelength). It turns out that most stars are moving away at a great rate, with their spectrum moving towards the red end of the light spectrum. We call this effect the red shift. This is comparable to what we hear as an ambulance moves away from us. The faster it goes, the deeper its siren will sound: the siren has a ‘low pitch shift’.
>>> The fact that most galaxies are moving away from us at an enormous rate suggests that the universe is expanding, just as all the raisins in a cake that is being baked move further apart as the cake ‘rises’, or dots on a party balloon Prac 2 become increasingly separated as the p. 72 balloon is inflated.
past
present
The universe is expanding.
Fig 3.1.4
Backwards in time Imagine taking a video from high above a football stadium, just as the final Earth star at fixed siren goes in the NRL grand final. distance from Earth People will start to leave in all directions through numerous exits, spreading through the surrounding carparks, then suburbs, as they travel away. If you were to watch a few star moving away—spectrum ‘red shifted’ star moving Earth minutes of the end of the video, you away from Earth could probably work out roughly where the people lived. If you were then to run the video backwards, to the very beginning, you could see where each person sat at the grand final. star moving towards us—spectrum ‘blue shifted’ This is similar to how scientists have come up with the currently Light waves from stars and galaxies moving Fig 3.1.3 favoured theory of the universe. By imagining all the away from us are ‘red-shifted’. stars and matter in the universe ‘going backwards’, In 1929 Hubble reported that the distant stars and they believe that all the matter in the universe must galaxies were receding from us, and that the further have once been much closer together—so close that it away they were, the faster they were going. This is once all fitted inside a pinhead, before exploding out now known as Hubble’s law. in what scientists call ‘the big bang’. star neither moving towards or away from us
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You may be wondering: ‘What was there before the big bang?’ or ‘Why did it blow up?’. The answer you are likely to get from most scientists specialising in the big bang is: ‘The question has no meaning
UNIT
3.1
UNIT
3.1 because, before the big bang, time and space did not exist’. This answer means more like: ‘I don’t know’—it seems that this is just the ultimate impossible question!
[ Questions ]
Checkpoint
10 Construct a sketch of a spectrum and, below it, sketch a spectrum that is ‘blue-shifted’ compared to the first.
The Doppler effect 1 A car with its horn blaring approaches and passes you. Describe the change in pitch you hear. 2 Identify two more examples of the Doppler effect that involve sound. 3 Identify whether a short or long wavelength would produce a sound of: a high pitch b low, deep pitch 4 Describe the effect that a change in wavelength may have on light. 5 Explain how light may be separated into different colours. 6 State Hubble’s law.
11 State whether the density of the universe just after the big bang was high or low. Justify your answer. 12 Construct a question about the origin of the universe that is impossible to answer. 13 Identify two scientists and describe their contributions to the understanding of the formation of the universe.
[ Extension ] Investigate
Backwards in time 7 Explain how scientists conclude that all the matter in the universe was once packed closer together. 8 Identify the currently favoured theory of the formation of the universe.
Think 9 Copy the diagram below. Demonstrate how the sound waves behind the jet would appear, by adding lines to show them. Fig 3.1.5
1 Research more about the Hubble Space Telescope. Gather information about: a Hubble’s involvement in space research b what the space telescope does c where it is d what Hubble’s constant is In small groups, present your information to the class in a five-minute presentation. 2 Investigate the relationship between a sonic boom and the Doppler effect. Construct a diagram to explain your findings.
Create
sound waves
3 Investigate how a spectrometer works. Construct a model of a spectrometer and an accompanying instruction leaflet.
Surf 4 Explore the Doppler effect in action by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.
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The expanding universe
UNIT
3.1 Prac 1 Unit 3.1
[ Practical activities ] Using a spectroscope
A balloon universe
Aim To observe the spectrum of white and
Aim To investigate the theory of an expanding universe
coloured light
Prac 2 Unit 3.1
Equipment A spectroscope
Equipment A balloon and a pen for marking dots on the balloon Fig 3.1.7
Method Fig 3.1.6
1 Mark several galaxies on an uninflated balloon. Circle one ‘galaxy’. This represents the Milky Way. 2 Blow the balloon up gradually, noting the movement of the ‘galaxies’.
WARNING: Do not aim the spectroscope directly at the Sun.
Questions 1 Use a spectroscope to study the spectrum of light from a light globe or from a window. 2 Sketch what you see. 3 Use your spectroscope to view coloured light from a light box containing a coloured slide or ‘filter’. Again, sketch what you see.
Questions 1 What were the differences between the spectrum of white light and the coloured light? 2 Construct a diagram to show how a prism can separate white light into colours.
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1 How did the other galaxies move compared to the Milky Way? 2 Predict how your answer to Question 1 would have changed if you had circled a different galaxy. 3 Evaluate how our position in the universe affects the observations we make. 4 Assess whether the balloon actually has a centre about which it is expanding.
UNIT
context
3.2 After much research, scientists are reasonably confident of their version of the history of the universe back to about 14 billion years ago —a fraction of a second after the big bang. Before that, temperatures were so extreme that the laws of physics, as they are currently known, break down and do not apply. Thanks to the work of physicists and astronomers we can take an imaginary journey through time from the big bang to the present. We can even predict what the future of the universe may be.
The first few minutes
The most famous equation of all
After a second of existence, the universe had cooled to ‘only’ 10 billion degrees Celsius, and after three minutes had a temperature of 1 billion degrees. At this temperature, particles called quarks began to clump together in groups of three to form protons and neutrons. A proton is the centre or nucleus of the simplest atom—hydrogen. Single protons and single neutrons also combine to form another form of hydrogen called deuterium. These in turn combine to form helium. The formation of chemical elements had begun! Calculations based on conditions just after the big bang predict that these simple elements should have formed in the proportion 77% hydrogen and 23% helium. Current-day analysis of matter in the universe supports these calculations.
ion,
Einstein’s famous equat The big bang theory states E = mc 2, is known by many that the universe exploded people, but do they really in all directions from a understand what each letter means? The E stands for single point (called a energy, m stands for mass singularity) containing an (in kilograms) and c stands enormous and incredibly for the speed of light, equal to 300 000 000 metres per concentrated amount of second. Under extreme energy. At the instant of conditions involving tiny creation, the universe must particles, such as those just have been unbelievably hot, after the big bang, energy be converted to mass, may with energy being converted or mass converted to energy. to matter and antimatter. Initially, the universe expanded relatively slowly, then, within a fraction of a second, inflated suddenly to become 100 million billion billion times bigger, filled with a variety of particles of matter and antimatter in an environment at 100 trillion trillion degrees Celsius. When a particle of matter and antimatter meet, they annihilate each other, releasing a burst of light energy called a photon. For example, electrons are particles of matter, and are annihilated by their antimatter equivalents, positrons. Luckily for us, after all the annihilations, a ‘small’ excess of matter was left over. These ‘leftovers’ became the building blocks of the universe as we know it today.
Fig 3.2.1
From the big bang to our present solar system
The fog clears The early universe was a foggy, opaque place containing energy in the form of radiation such as X-rays and light. Eventually, 300 000 years after the big bang, the continuing expansion of the universe
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The big bang had dropped its temperature to 3000°C. This resulted in electrons slowing down enough to be captured by hydrogen and helium nuclei to form new types of atoms or elements. As more and more particles combined to form new elements, the fog cleared. As the universe expanded further, radiation took the form of heat, radio waves and microwaves.
Afterglow In 1965 physicists Arno Penzias and Robert Wilson set out to detect radio waves coming from the halo of our Milky Way galaxy. They were confused by a signal that showed no change during day or night, or even at different times of the year. The signal was also very similar in all directions. After suspecting interference from everything from the cities on Earth to pigeondroppings on their antenna, they realised that the signal was the afterglow of the creation of the universe—they received the Nobel prize for their discovery!
Fig 3.2.3
A ‘heat’ photograph of the universe obtained by the COBE satellite. Hotter regions are shown in red, and cooler ones in blue.
This image shows that the universe was not the same throughout, but that matter had begun to clump together to form the seeds (shown as blue) from which galaxies would be born.
Galaxies, stars and planets About a billion years after the big bang, swirling clouds of gas compacted to form the first galaxies. It is thought that invisible so-called ‘dark matter’, largely made of subatomic particles left over from the big bang, is responsible for the drawing together of gas clouds. Within these galaxies, clouds of gas collapsed even more to give birth to the first stars, made of hydrogen and helium. Rings of gas and dust orbiting stars may condense to form young planets or planetesimals, which in turn attract more matter and increase in size to form planets. The Carina nebula showing clouds of dust and gas that may give birth to small star clusters or young planets.
These men—Arno Penzias (left) and Robert Wilson (right)—made one of the greatest discoveries of all time by detecting background radiation left over from the very beginning of the universe.
Fig 3.2.2
In 1992, the COBE (Cosmic Background Explorer) satellite, described as the ultimate thermometer, mapped this background radiation and produced an image of the universe at age 300 000 years, shown in Figure 3.2.3.
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Fig 3.2.4
UNIT
3.2 Open universe If our universe has a low enough mass, it will keep on expanding forever but at a decreasing rate. Eventually the stars and galaxies would cease to shine, and it would be a dark and very cold place. This model of the universe is called the open universe.
Closed universe
At the centre of this spiral galaxy are older yellow and red stars. The outer spiral arms are bluer due to the ongoing formation of young blue stars. The arms are also very rich in interstellar dust, seen as dark areas, which may form planets around individual stars.
Fig 3.2.5
Worksheet 3.1 Big bang to present
If our universe has a high enough mass, expansion will eventually stop. Gravitational attraction between matter will then pull it all closer together, just as the Earth’s gravity pulls objects closer to the centre of the Earth. The universe would contract into a smaller and smaller space. Eventually all matter would become superheated and atoms would disintegrate in a reversal of the big bang. Black holes would join together and suck in more and more matter until a final ‘big crunch’ packed everything into a single black hole. Perhaps then there would be another big bang and the cycle would continue.
Flat universe The flat universe model states that the universe will eventually stop expanding, but never reverse.
Accelerating universe
The future Can the universe keep on expanding forever? Did the initial big bang provide enough energy for this to happen? Scientists have trouble answering these questions. The best they can do is to present a number of theories.
UNIT
3.2
[ Questions ]
Recent observations and research indicate that the expansion of the universe may not be slowing due to gravitational forces. It may actually be expanding more and more rapidly due to a mysterious cosmological force some call ‘dark energy’ that overrides gravity. The existence of dark energy would complicate each of the above theories. Scientists have a long way to go before understanding the current state of the universe, and our ability to predict how it may be in the future is nowhere near complete!
Checkpoint The first few minutes 1 State how old the universe is thought to be. 2 Identify the time when the young universe suddenly inflated. 3 Matter and antimatter didn’t totally destroy each other after the big bang. Explain why it is lucky that this didn’t occur. 4 Identify what particles grouped into threes to form protons and neutrons. 5 a State the proportion of hydrogen in the universe. b Explain why hydrogen is the most common element.
6 Describe what is in a hydrogen nucleus.
The fog clears 7 Explain why the early universe was opaque. 8 Describe the effect on the ‘fog’ of the continuing expansion of the universe.
Afterglow 9 Penzias and Wilson detected evidence for the big bang. Clarify the evidence they collected. 10 State what the acronym COBE stands for.
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The big bang Galaxies, stars and planets 11 Explain how galaxies and stars are formed. 12 Explain how ‘baby planets’ become bigger.
The future 13 Outline the four main theories about the future of our universe. 14 Evaluate which theory you think is most likely to represent our future.
Think 15 a State when the first atoms began to form. b Explain why this did not happen earlier. 16 List some different types of radiation. 17 If matter in the early universe was spread completely evenly, instead of in uneven clumps, predict what would not have formed.
Analyse 18 Construct a time line showing the temperature of the universe at various key stages (not necessarily to scale). You will find the temperatures throughout Unit 3.2. 19 Another theory of the universe, called the ‘steady state’ theory, says that the universe has basically always been how it is now, with old galaxies dying and new ones being born. Assess whether you think this is more or less likely than the big bang theory. Justify your answer.
>>> [ Extension ] Investigate 1 a Examine the contribution made by others to the big bang theory. People to investigate could include Walter Adams, Ralph Alpher and Robert Dicke. b Produce an information card to display your findings. 2 Investigate the different possible ‘shapes of space’ —closed, flat and open. Present your findings in a short written report. 3 Investigate other theories of the origin of the universe or suggest your own. Have a class debate to discuss for and against the big bang theory. Different student roles may include: speakers for each team, timekeeper, chairperson and adjudicators.
Surf 4 Explore the history and timeline of the universe by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.
Create 5 Produce a poster summarising the development of the universe after the big bang to our present day.
20 Construct a flow chart to outline the steps and time periods of the main features of the big bang theory from the beginning to present day.
This side on view of a galaxy was taken by the Hubble space telescope.
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Fig 3.5.2
UNIT
context
3. 3 The stars we see in the night sky have not always been there. Stars are born and die all the time. In fact, because of the huge distances involved and the time it takes for their light to get to us, some of the stars that we see may have died millions of years ago! Let’s now live NGC 1999 ‘the life of a star’. New Gene
Birth of a star Stars are born in a dense cloud of gas and dust found in the spiral arms of galaxies. The raw ingredients of a star are called a nebula. The star actually forms when dense regions in these clouds collapse under their own gravity. The nebula’s gas and dust come closer together,
ral Catalogue (NGC) is the basic reference list of all star clusters, nebulas and galaxies. It was compiled in 1888 by Danish astronomer Johan Dreyer, who based his work on earlier lists made by William and Caroline Herschel. The NGC 1999 nebula in Figure 3.3.1 is illuminated by a very young star that is still surrounded by leftover material from its formation. It lies close to the Orion Nebula, about 1500 light years from our Milky Way.
forming a protostar. As more material is packed into the protostar, the centre gets hotter and hotter until conditions are suitable for nuclear reactions to begin. In these reactions, atoms of hydrogen are fused together to form helium, with vast amounts of heat and light energy given out. At this stage, a main sequence star, like our Sun, is formed. Fig 3.3.2
A protostar about 250 000 years after it began to form
Death of a star
New stars are produced in nebulae. This photo shows nebula NGC 1999 in the constellation of Orion.
Fig 3.3.1
Stars have a limited amount of fuel (hydrogen), which eventually runs out. Those like our Sun will last for around 10 billion years before this happens. Amazing transformations then take place, depending on how big the star is. A star with a mass of one Sun will start to use helium as a fuel, producing carbon in the process. It also begins burning hydrogen in its atmosphere and, in so doing, expands up to 100 times its original diameter to become a red giant. When this eventually happens to our Sun (in around 4 billion years) the inner planets will be engulfed by the Sun, and the Earth will be roasted to a cinder. Outer layers of the star and the carbon within them are blown away to form clouds in space which may form new stars and planets—so in a sense, we are all made
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The life of a star from leftover material from other stars! Without the pressure produced by nuclear reactions, the remaining centre collapses under its own gravity to form a small, very dense core called a white dwarf. A teaspoon of matter from a white dwarf would have a mass of about 3 tonnes (or 3000 kg). For comparison, a teaspoon of matter from our Sun would have a mass of 2.1 grams.
A star before and after exploding to become a supernova
Fig 3.3.4
Pulsars A pulsar is a rapidly rotating neutron star with a strong magnetic field. A pulsar emits radio waves that sweep across space as it rotates, a little like a moving searchlight. A special type of telescope (called a radio telescope) detects each burst of radio waves as a pulse.
Fig 3.3.3
Optical image of stars in interstellar gas and dust. The star Antares (bottom left) is a red supergiant. It is several hundred times the diameter of the Sun and several thousand times the Sun’s brightness.
A star with a mass ten times that of the Sun uses up its fuel supply much more rapidly over a period of about 30 million years and becomes a blue supergiant, before further expanding to form a red supergiant. The inner core collapses in less than a second, causing a huge explosion called a supernova. This explosion blasts matter into space and shines for about a month with the intensity of billions of stars. It is in supernovae that elements such as gold, silver and iron are formed. The remains of the star form what is called a neutron star, having a mass three times the Sun but with a diameter of only 20 kilometres. A teaspoon of matter from a neutron star would have a mass of a billion tonnes!
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rotating neutron star
beam of radio waves
Fig 3.3.5
The beam from a pulsar may be detected as it sweeps past the Earth.
Black holes
The first black hole
The first black hole was If a star is massive enough, it detected in 1971 in the collapses even more than a Cygnus constellation, and neutron star to form a black hole— was named Cygnus X-1. an object so dense that anything After its X-rays were detected, scientists close by will be drawn into it by noticed that a nearby star, its overpowering gravity. A black a supergiant, was orbiting hole’s gravity is so strong that even the X-ray source. They calculated that the X-ray light cannot escape! Black holes source must be around distort the space around them, and ten times heavier than our can often suck nearby matter into Sun, so it could not be a normal star or a neutron them, including other stars. As star. By a process of matter swirls into the black hole it elimination, the X-ray becomes incredibly hot and emits source must be a black hole. tell-tale X-rays. Because black holes cannot be seen directly, scientists detect them by observing X-ray emissions and the behaviour of nearby stars.
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3.3
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3.3 Evidence suggests that a massive black hole with a mass of about 2.6 million times that of the Sun lies at the centre of our own Milky Way Galaxy. Worksheet 3.2 The HR diagram A black hole near a companion star
Fig 3.3.6
gas from companion star
swirling gas heated to 100 million ºC due to frictional effects x-rays
[ Questions ]
Checkpoint Birth of a star 1 Define the term ‘nebula’. 2 Identify the main fuel in stars.
Death of a star 3 Arrange these stages of our Sun’s life in order from its earliest stage: red giant, burns hydrogen, white dwarf, burns helium 4 Compare what would happen to our Sun during its lifetime with a star ten times more massive.
Pulsars and black holes 5 Define the term ‘pulsar’. 6 Explain what a black hole is and how it is formed. 7 Nobody has ever seen a black hole. Propose some reasons why and explain how we know they exist.
Think 8 Deduce how the carbon and other elements in our bodies originally came from the stars. 9 Arrange these stages in order from the earliest stage, for a star with a mass of ten times that of our Sun: supernova, red supergiant, neutron star, blue supergiant. 10 Predict whether or not you could lift a sugar-sized grain of matter from a neutron star. 11 Predict what would happen if a black hole were at the centre of our own galaxy, the Milky Way.
[ Extension ] Investigate 1 Investigate how Jocelyn Bell Burnell discovered pulsars in 1967. Write a short account of this event. 2 Research one of the following features of the universe: • neutron star • pulsars • quasar • supernova • asteroids • meteors • black hole • comets • nova • the Milky Way galaxy a Define what the feature is. b Describe the feature and obtain a diagram or photo of it. c Compile your work and other students’ into a booklet. Give the booklet a title such as ‘My Pocket Guide to the Universe’.
Surf 3 Explore amazing images of the universe by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.
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context
3. 4 If all the atoms making up our bodies and our planet resulted from a chain of events starting with the big bang, then maybe there are other beings on other planets orbiting other stars, all formed from the big bang too. NASA and other space agencies have spent billions of dollars looking for signs of extraterrestrial life, but so far have had
Mars attacks! Mars is where Martians come from … well that’s what science fiction writers like to suggest! When astronomers first began to use telescopes to study the planets, they found what appeared to be great channels crisscrossing the surface of Mars. Although we now believe these are dried up natural water channels and one very large canyon, early astronomers thought that they were canals like those in Venice, built by the obviously very civilised and technologically advanced inhabitants of Mars. None of the other planets seemed to have canals like these, so aliens had to come from Mars and not the other planets.
How to make contact? Travelling at the speed of the Voyager I space probe it would take 80 000 years to reach the nearest star and search for extraterrestrial life on any orbiting planet. This is obviously not viable, so how can we search for ET (extraterrestial) life? The only way is to send out messages at the fastest speed available to us—the speed of light.
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little success! There are, however, plenty of stories of spaceships visiting Earth and of extraterrestrial visitors. Many people believe that other beings do exist. Earlier speculation about the existence of little green Martians may seem fanciful. But with over 200 billion stars in our Milky Way galaxy alone, the odds are that there are planets capable of supporting life. A scene of life on the Moon, alleged to have been observed by John Herschel through his telescope. It was a journalist’s fabrication.
Fig 3.4.1
Electromagnetic radiation such as lasers and radio waves travels at the speed of light—considerably faster than any spacecraft—and offers a way to detect life elsewhere in the universe, either by sending or receiving messages. Television and radio transmissions are being emitted continuously from Earth with the hope that intelligent life elsewhere will tune in to these. To increase our chances of making contact,
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3. 4 SETI Pythagorean pines
The plaque carried by the spacecraft Pioneers 10 and 11 into deep space. A hydrogen molecule appears at the top, and the radiating lines show the bearings of the nearest pulsars.
Fig 3.4.2
scientists broadcast in the microwave range of frequencies, since background interference is less in that channel. We have started looking for signals only recently, so the main hope may be to receive a message from an intelligent race that has been sending for a long time. Who knows? Perhaps we have received a message, but are not advanced enough to recognise it. numbers 1 to 10 in binary
One idea suggested for attracting the attention of extraterrestrials is to plant square forests of pines around a field of wheat in the shape of a right-angled triangle, providing a gigantic demonstration of Pythagoras’s theorem that would be visible from space. This states that the square of the longest side of a rightangled triangle is equal to the other two sides squared and then added 2 2 2 together (a + b = c ).
SETI stands for ‘Search for Extra Terrestrial Intelligence’. ‘Terrestrial’ means ‘of the Earth’ and ‘extra’ in this context means ‘outside’. The SETI Institute is situated in Silicon Valley, California. The southern hemisphere part of SETI, named Project Phoenix, involves the Parkes radio telescope in New South Wales.
The Project Phoenix team also visit the Arechibo telescope in Puerto Rico (the largest telescope in the world) twice each year. Computers monitor over a thousand stars and millions of radio channels simultaneously, as no one knows what frequency a likely ET would use.
SETI politics Searching for extraterrestrial life has not always been popular with bureaucrats and politicians due to the large sums of money required and the slim chances of success. When US politicians pulled the plug on early SETI funding, it prompted pro-SETI press to ask, ‘Is there any intelligent life in Washington?’.
atomic numbers of important elements proportion of elements in our DNA
Fig 3.4.4
The biggest radio telescope in the world—the Arechibo radio telescope in Puerto Rico, Central America
DNA double helix world population human solar system (Earth moved up slightly) outline of radio dish
Fig 3.4.3
This is the message that was beamed from the Arechibo radio telescope towards globular cluster M13 in 1974. A series of 1670 on/off pulses was used, as 1679 is the product of two prime numbers (23 and 73), giving an ET receiving the message a hint to arrange it into rows of 23 pictures, with 73 rows in total.
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Are we alone? For and against There are those who think that attempting to make contact with extraterrestrials is fraught with danger. Their concerns are perhaps best summed up by the famous astrophysicist Stephen Hawking, who is quoted as saying, ‘On balance, I would rather not encounter a superior civilisation. They might wipe us out’.
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3. 4
Worksheet 3.3 Future civilisations
[ Questions ]
Checkpoint How to make contact? 1 Explain why space travel is not the best way to search for extraterrestrial life in our lifetime. 2 Explain why microwaves are preferred to radio waves of other frequencies when sending messages into space. 3 Clarify what the section at the bottom of the Pioneer plaque indicates.
SETI 4 Define the acronym SETI. 5 Discuss why politicians were unsupportive of early SETI programs. 6 Identify two radio telescopes used by the SETI team. 7 Even if SETI detects signals from an advanced civilisation, the civilisation may not exist. Explain how this can be.
Think 8 Propose what the heading for this unit, ‘Are we alone?’ really means. 9 Propose at least two reasons why the plaque attached to the Pioneer 10 and Pioneer 11 space probes may have offended some people. 10 A group called SOOT (Switch Off Our Transmitters) has been proposed by a biologist who thinks we may be at risk from advanced civilisations. Analyse why switching off our transmitters would not guarantee our safety.
Analyse 11 If only one in every fifty of the stars in the Milky Way contained an Earth-like planet, calculate how many such planets our galaxy would contain. Assume there are 2 billion stars in the Milky Way. 12 Propose your opinion about the chances of extraterrestrial life existing.
Create 13 Construct a clear diagram for a space probe plaque showing who you are and where you live on Earth.
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Dan Werthimer of project Serendip (another SETI search) puts forward the counter-argument that the not-so-peaceful advanced civilisations are likely to have blown themselves up before contacting us. What do you think?
[ Extension ]
UFOs and spaceships UFO is an acronym for unidentified flying object. It applies to anything in the sky that cannot be identified, whether is a strange light, a strange weather phenomenon or a stray weather balloon that doesn’t show up on radar. Although a UFO could be an alien spaceship, it is more likely to be something else!
Investigate 1 Investigate the SETI project. a Find out details of its operation, what has been discovered so far and who the ‘father of SETI’ was. b Present your findings to the class in a presentation of your choice. 2 The movie Contact starred Jodie Foster as an astronomer who discovers signals from extraterrestrial intelligence and later makes contact. This character is rumoured to be based on a real-life SETI researcher, Jill Tarter. Research Jill’s contributions to the SETI program. 3 Examine the technical details of the Arechibo or Parkes radio telescopes. Investigate how they operate and what they are used for.
Action 4 Run a class debate on the topic: ‘Aliens do exist and we should try to make contact with them’.
Surf 5 Find out more about the SETI project by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.
Creative writing Prepare for contact! You are in charge of the IETRT (International Extra Terrestrial Response Team), and must come up with a protocol for dealing with Earth’s response to the first contact with extraterrestrial intelligence. What steps should Earth follow? How should the public be handled? Who should be involved in a meeting or reply? Construct a report or essay dealing with a hypothetical situation.
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3. 5 context
Fuel shortage
Space travel is currently incredibly expensive (it has been estimated that it costs $50 000 per kilogram to place objects into orbit), but perhaps in the future, space travel will be accessible to all of us. At present we can only travel quite slowly, and so covering the phenomenal distances involved in reaching another planet—let alone another star or galaxy—takes an extremely long time. If we are to travel deep into space we will need to develop The first space new methods of propulsion. tourist This is another area of ongoing This honour went to American billionaire scientific research.
Long-distance space travel
Dennis Tito, who paid the Russian space program US$40 million for the privilege— equivalent to seven per cent of their annual budget. Tito blasted off in a Soyuz rocket in April 2001 for the International Space Station on a resupply mission. This was despite initial protests from the US space agency, who were concerned about safety and protecting their multibillion dollar investment.
There are several major obstacles to long-distance space travel. For a start, the distances are staggering. The closest star (Alpha Centauri) is 4.3 light years away. The next closest is Barnard’s star at 6.0 light years.The closest star in the Southern Cross is 88 light years away and the centre of the Milky Way is 38 000 light years. A light year is the distance that light travels in one year. Since light travels at 300 000 kilometres every second, a light year is a long, long, long way! If we could travel at the speed of light it would take 38 000 years to reach the centre of our galaxy. Reaching the closest galaxy outside the Milky Way (the Sagittarius Dwarf Elliptical galaxy) would take 80 000 years, the Large Magellanic Cloud 179 000 years and the Andromeda Galaxy 2 000 000 years! These times show the problems facing scientists as they try to find solutions to space travel. Current scientific belief is that nothing can travel faster than light.
Current spacecraft must carry large amounts of chemical propellant. The space shuttle’s mass at lift-off is 95% fuel and only 5% shuttle. The most efficient rocket would need to carry fuel weighing more than all the mass in the entire universe to reach Alpha Centauri!
The Voyager I space probe left our solar system travelling at 55 000 kilometres per hour. It would take 80 000 years to reach Alpha Centauri, and that’s without the extra mass of human occupants and their requirements. This is also a one-way trip. Perhaps we need to find a way to put humans into suspended animation and awake them on reaching their destination. Worksheet 3.4 Time travel
New rocket technology If we are to reduce travel time to the stars, scientists will need to develop new spaceships that approach the speed of light, and develop new ideas for rocket propulsion. Some proposals are outlined below.
Antimatter Atoms of antimatter consist of a negative nucleus surrounded by positive electrons (the opposite
Computer artwork of an antimatter drive spaceship
Fig 3.5.1
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Future space travel charges to normal matter). When antimatter and matter combine, both are destroyed, and huge amounts of energy are released. Future spaceships may use antimatter and matter stored in separate tanks to provide energy for propulsion, though some major problems will have to be overcome first. One of these is how to obtain enough antimatter—less than a billionth of a gram has been produced so far!
equal to about 3.5 newtons per square kilometre for objects in near-Earth orbit. American Robert Forward suggested aiming a powerful laser mounted on an orbiting satellite at sails on a spacecraft to accelerate it to one-fifth the speed of light.
Collect fuel as you go Space is not completely empty—it contains some stray atoms and subatomic particles. Less fuel would need to be carried if these particles could be collected and used as fuel by the spacecraft as it moves. One idea involves using a funnel-shaped magnetic field to collect particles.
Ion drives Ion-drive engines work in a similar manner to conventional rockets, but emit a stream of fastermoving, positively charged xenon ions (an ion is a charged atom). Unlike conventional exhaust propulsion, ion engines emit a very small amount of mass, and take a much longer time to accelerate a craft, though they are more efficient and reach much greater speeds eventually. NASA has been working on prototypes of ion-drive engines with a view to using them on future missions. Fig 3.5.2
Nuclear bombs Car engines work using a series of controlled petrol, diesel or gas explosions. Why couldn’t a spacecraft do the same but with nuclear explosions? One suggestion, called Project Orion, involves using several nuclear explosions every second to push a giant plate attached to a spacecraft. Such an engine may be capable of producing speeds of up to one-tenth the speed of light.
Change the rules? Mars mission’s measly mass Scientists have suggested that one-millionth of a gram of antimatter would be enough to power a mission to Mars.
Laser drive Light exerts pressure on anything it strikes, but the effect is normally not noticeable because it is so small and is overwhelmed by other factors such as air resistance. In space, however, light’s pressure may be more noticeable. Large ‘solar sails’ may be used to take advantage of the pressure exerted by sunlight,
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An artist’s impression of a solar sail spaceship passing Jupiter and one of its moons, Europa
When Captain James Kirk of the science fiction series Star Trek underwent one of his starship exams, one of the tests was a computer simulation involving an emergency situation. The simulation was programmed so there was no solution—and hence it was impossible to pass the exam. Kirk did, however, pass the exam! How? By reprogramming the simulation, or, in other words, changing or expanding the rules. Perhaps the solution to long-distance space travel will be found when we discover more advanced rules governing how the universe works. Here are a few that are currently being researched.
Warp engines Captain Kirk’s Enterprise starship was able to travel faster than light, powered by a fictional warp-drive. This inspired Mexican physicist Miguel Alcubierre,
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3. 5 who proposed that, rather than change the speed of a spacecraft, we may learn how to change or warp the fabric of space and time. Distances behind the spacecraft would need to be expanded, with the distances shrinking in front. The fictional USS Enterprise is capable of warp speed.
wormhole
SPA
Fig 3.5.3
Earth
CE
TIM E
FA BR IC
4.4 Alpha ligh tye Centauri ars
Fig 3.5.4
Perhaps wormholes in space can be found or created, and used to reach distant stars almost instantly.
Unlocking the mystery of gravity Wormholes Another idea, proposed by American physicist Kip Thorne, concerns so-called wormholes in space. Maybe we can discover how to use these ‘shortcuts’ to reach places we had previously only been able to imagine getting to by other routes. If you don’t quite ‘get’ these ideas about warp drives and wormholes, don’t worry—neither does anybody else at the moment!
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3. 5
[ Questions ]
Checkpoint Long-distance space travel
We now know that it’s not just the Sun and planets that attract objects. All masses attract all other masses but the effect is noticeable only if one or more of the objects are very large. Some scientists believe that one day we will learn to control this gravitational force and hence revolutionise transport. Though some of the above ideas may seem far-fetched, it’s worth remembering that many things we take for granted today, such as aircraft, nuclear energy, silicon chips, Internet and satellite communication, video and DVD players, were once unheard of. The future may bring all kinds of breakthroughs that today we can only dream about.
New rocket technology
1 Estimate how much it would currently cost to place 100 kilograms into orbit around the Earth.
5 Estimate how long it would take to reach Alpha Centauri, which is 4.3 light years away, using a nuclear-bomb engine.
2 Identify the first space tourist and how much it cost to be aboard.
6 Trying to store antimatter in a tank would cause a major problem. Explain what this problem is.
3 Calculate approximately how many lifetimes it would take to reach Alpha Centauri travelling at the speed of the Voyager I space probe. 4 Discuss how putting people into suspended animation could save energy on a long-distance space voyage.
Change the rules? 7 Propose some potential dangers of using a wormhole for space travel. 8 Assess whether you think scientists will be able to control gravity and revolutionise space travel.
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Future space travel
Think
Analyse
9 Describe how a volleyball game would be different on the Moon, where gravity is only one-sixth that on Earth. 10 For a long time humans have been interested in reaching other stars. Propose why this is so. 11 Propose some of the advantages of colonies in space for the human race, world government and private industry. 12 Identify an example (besides those mentioned at the end of this unit) of something that seemed impossible long ago, but is possible today.
13 Explain why ion-drive engines must neutralise the emitted ions in the exhaust. 14 The thrust of an ion engine is nowhere near enough to lift a spacecraft from Earth and through its atmosphere. Propose how an ion engine spacecraft could be used. 15 Predict some problems that may arise in developing and using Project Orion. 16 Imagine a laser drive spacecraft powered by a laser on Earth or in Earth orbit. Describe some difficulties that may arise as the craft gets a very long way away. 17 Construct a diagram or series of diagrams to explain how a warp drive may work.
[ Extension ] Investigate
Surf
1 Construct a spreadsheet to calculate how long it would take to reach the various planets in our solar system as well as selected objects outside it, travelling at the speeds given for each propulsion system throughout this unit.
6 Explore space travel at present and future directions by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button.
2 Investigate and explain another proposed new method of powering spacecraft for long flights (e.g. fusion engines). Alternatively, invent your own. 3 Review a science fiction video (e.g. one of the Star Trek movies, Mission to Mars, Galaxy Quest) and assess the scientific correctness of information and the plausibility of the technology in it.
Create 4 Construct a model of a future space station. Remember, it must contain all the features required to keep people alive and healthy for a very long time.
DYO
5 Imagine yourself as a travel agent who markets holidays around the universe. Design a travel brochure or advertising campaign to sell a destination to Earthlings. Include descriptions and photos of the sights to be seen there, how you will get there and an account of the conditions and environment there.
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Creative writing Living in space 1 Write an account of life aboard a space station. In your account, explain how you overcome some of the problems associated with zero gravity and its associated loss of muscle tone and bone density. 2 How would life be different if long-distance space travel were cheap and virtually instantaneous?
Science focus: International space station Prescribed focus area: Current issues, research and development A quest to explore space Humans have long dreamed of living in space and this fascination has led to a belief that one day people would live aboard space stations. Living in space enables scientists to explore and collect information free from gravity and the atmosphere. Experiments can be performed in space that are impossible on the surface of Earth. With all these possibilities, and the innate desire of humans to explore, the dream of building a space station has become a reality.
A global effort: the International Space Station In 1984 America announced plans to build a permanent space station named Freedom. More countries quickly became involved and the International Space Station, or ISS for short, is now being constructed. Modules produced on Earth are carried into orbit. Stage 1, consisting of the Russian
This module of the ISS is the Japanese Experimental Module (JEM). It is designed for scientific research and has an external platform for space environment experiments. It will take three shuttle missions to assemble the JEM in space.
Fig SF3.1
control module (called Zarya) and the American connecting section (called Unity) were launched on 20 November and 3 December 1998 respectively and later docked to form the nucleus of the station. Over 40 missions involving the space shuttle and Russian Soyuz and Proton rockets will be required during construction of the ISS, as well as around 1000 hours of spacewalks or EVA (extra-vehicular activity). One such spacewalk, the first by an Australian, was made by Andy Thomas in March 2001 when he assisted with some wiring and construction jobs after arriving at the ISS via the space shuttle Discovery. The ISS will look like this when it is completed.
Fig SF3.2
The construction of the ISS has been slower than expected, but despite setbacks, the human occupation has been ongoing. A couple of civilians have even paid to have the opportunity spend time on the ISS. While onboard, the long-term occupants are involved in setting up and maintaining the equipment, and conducting scientific experiments. In the weightless environment created by the microgravity of their
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Fig SF3.4
Fig SF3.3
Astronaut James Voss performs an experiment in the Destiny laboratory.
This photo of the ISS taken from a departing shuttle shows the structure in 2004.
orbit, to stop their muscles and bones deteriorating the occupants exercise on special equipment to keep the skeleton and muscles healthy.
ISS Fact file
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Countries involved
United States, Russia, Japan, Canada, Brazil, and eleven countries of the European space agency (Belgium, Denmark, France, Germany, Italy, The Netherlands, Norway, Spain, Sweden, Switzerland, The United Kingdom)
Dimensions
Length 110 m, width 80 m, mass 460 tonnes, volume 1200 cubic metres (pressurised)
Orbit
Altitude 407 km (average) at an angle of 51.6° to the equator
Orbital speed
3000 kilometres per hour
Power source
4000 square metres of solar panels generating 20 kilowatts
Oxygen source
Russian Elektron generator will make oxygen by splitting water into oxygen and hydrogen, supplemented by solid fuel oxygen generation (SFOG) cartridges as required. External oxygen tanks will be fitted in latter stages of construction.
Heating
More than enough is provided by on-board electronic equipment. Excess heat is vented to outer space.
Escape vehicle
Soyuz capsule capable of transporting three people
Research and the ISS NASA is currently working on more efficient ways to transport supplies and people to the ISS. The ISS will also be used to study the effects of microgravity or weightlessness, and extended space flights on humans. The ISS will be used by governments, industry and educational organisations for research in various fields including life science, medical research, earth science and engineering. Past space technologies that have been developed commercially include Velcro (now used as a quick way of attaching objects, e.g. doing up shoes) and Kevlar, which is used to make bullet-proof vests.
Gravity affects the way crystals form on Earth, leading to small imperfections, but in microgravity almost perfect crystals can be made. Applications of such crystals may lead to faster computers or more effective medicines. Tissue cultures of human cells grow more quickly in space, and studies in microgravity may lead to breakthroughs in this field. Microgravity also allows scientists to better study combustion, as gravity no longer forms convection currents which disturb a flame. Perhaps research in space will discover a method of burning which produces less pollution.
[ Student activities ] 1 a Research the construction of the ISS and the components that will slowly be assembled. b Produce a chart to demonstrate the countries involved, and the role they will play, in the construction of the ISS. 2 a Research the qualifications and training required to be an astronaut. b Construct a resume for yourself as if you were an astronaut. 3 a In small groups, discuss the advantages and disadvantages of building space stations and record your findings. b Gather information on some of the costs associated with carrying payloads into space. c Discuss reasons why a global effort is required if missions like building the ISS are to be successful. d Evaluate the importance of building the ISS. 4 Write a submission to NASA outlining some space research you wish astronauts on the ISS to conduct for you. a Outline the reasons you chose your area of research. b Describe details of the experiments you would like to be carried out. In this experiment 750 material samples are being placed outside the ISS for 18 months to collect information about how the materials weather the space environment.
Fig SF3.5
5 Civilian tourists have paid large amounts of money to visit the ISS. This is one way that some of the expense involved in building the ISS can be recovered. Imagine you are the person responsible for advertising a scientific holiday on the ISS. Design a postcard which describes some of the scientific experiences that a visitor can have.
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>>> Chapter review [ Summary questions ] 1 Copy the following and modify any incorrect statements so they become true. a A Formula One car’s screaming engine changes pitch from high to low as it races past your position in the grandstand. b Only sound can undergo a Doppler effect. c Stars moving towards us may have a spectrum shift towards the red end. d Hubble’s law states that stars further away from us are moving faster than those closer to us. e The universe is contracting. 2 Explain what is meant by ‘the big bang’. 3 Identify the first two, and most abundant, elements in the universe.
[ Thinking questions ]
10 Describe the tell-tale signs of a black hole. 11 Describe an area of space research: a that may be conducted in space b that is conducted from Earth 12 List several proposed new methods of propulsion, in order (in your opinion) from most likely to very unlikely. 13 Select two scientists mentioned in this chapter and summarise their contributions to our understanding of the universe.
[ Interpreting questions ] 14 Analyse why scientists think there must be ‘dark matter’ in the universe. 15 Assess why lines are drawn showing pulsars on the plaque on the Pioneer space probes. 16 Define the meaning of the E and the T in SETI.
4 Describe how the temperature of the early universe compares with the current temperature.
17 Explain why many radio frequencies are checked for ET signals.
5 Predict what would happen if a positron met an electron.
18 You are making a phone call to a friend. Demonstrate something that would represent interference.
6 State when the ‘fog’ of the early universe cleared. 7 Calculate how long it would take to travel to our nearest star (Alpha Centauri, 4.3 light years away) and back travelling at: a the speed of light b the speed of the Voyager spacecraft 8 Identify what type of celestial objects are known as ‘star nurseries’.
hydrogen runs out
'adult' star of 10 solar masses or more
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9 Copy and complete the flow chart below for the life of a large star.
19 Discuss arguments for and against continuing the search for extraterrestrial life. Worksheet 3.5 Origins of the universe crossword Worksheet 3.6 Sci-words
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4
Light Key focus area
>>> The applications and uses of science
explain how some optical illusions are due to refraction and reflection identify situations where lenses and curved mirrors are used
Outcomes
explain what is meant by the terms ‘absorption’, ‘refraction’, ‘reflection’ and ‘scattering of light’
5.3, 5.6.4
By the end of this chapter you should be able to:
construct ray diagrams to predict the size, location and type of images identify the colours of the visible spectrum predict the colours seen when light passes through the atmosphere or falls on different-coloured objects.
bright only when lights shine on them?
2 Why does there often appear to be water lying on bitumen roads on hot days?
3 Why do cameras, microscopes and our eyes need lenses?
4 Why do shops often have curved mirrors high up on the wall?
5 Unless you are under water, it is very difficult to spear a fish. Why?
6 Why is the sky blue? 7 When mixed, yellow and blue make green. True or false?
Pre quiz
1 Why do reflectors on a bike appear
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4.1 We see objects when light enters our eye and an image is formed on the retina. Light can reach the eye in many ways. The light travels directly to our eye if we look straight at a luminous object like a light bulb. If we look away from the bulb, light will more than likely still reach our eye by reflecting from the many surfaces and objects in the room. Sometimes the light enters our eye after it has passed through a transparent substance such as water or glass. Light is bent as it passes through different substances. This bending of light is called refraction. Refraction is
Refraction Refraction is the bending of a light ray as it passes into a different substance. Figure 4.1.1 shows how a light ray is bent as it travels through a glass block. Some dotted lines have been drawn on the photo. Each dotted line is called a normal. A normal is a line drawn perpendicular (at 90°) to the boundary between the two substances. The light ray bends towards the normal on entering the glass, and away from the normal on leaving it. Some reflection also occurs at the edge of the glass.
responsible for making the depth of a swimming pool look less than it really is and some really odd effects when we look through a glass of water. It also splits light into the colours of the rainbow, and makes it difficult to spear a fish under water.
Experiments have shown that light slows down as it passes from air into glass. It also bends towards the normal. Glass is an example of a substance that has a higher refractive index than air. We also say that glass has a higher optical density than air. Other substances with optical densities higher than air are water, clear perspex and diamond. When light travels from one substance into another of lower optical density (e.g. from glass to air), the opposite happens—it speeds up and bends away from the normal. There is one exception, and that is when light hits ‘head-on’, perpendicular to the Prac 1 boundary. The light does not bend but its p. 97 speed still changes. Light travelling from one substance into another of greater optical density may be compared to a car passing from a region that allows fast travel (such as a bitumen surface) to one that slows the vehicle down (such as sand). Fig 4.1.2
A car slows down and its path bends towards the normal as it drives into sand from bitumen. normal
bitumen
sand
Fig 4.1.1
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Refraction in a glass block. Note that a dotted line called a normal has been superimposed on the photograph.
Refraction explains why objects immersed in water appear bent when viewed from air.
UNIT
4.1 The rear lenses that make up a car’s stoplights use refraction to ensure light is bent up or down to avoid a strong beam of direct light dazzling other motorists. Worksheet 4.1 Snell’s law
Depth illusions Refraction is also responsible for another illusion in which water appears shallower than it really is. This is evident when you look into a swimming pool, as shown in Figure 4.1.5. We say the apparent depth is less than the actual depth. Fig 4.1.5
Refraction causes the ‘bending’ of the ruler.
Prac 2 p. 98
Refraction makes it difficult to judge depth.
Fig 4.1.3
You may be wondering why the ruler in Figure 4.1.3 is bent away from the normal instead of towards the normal like the ray in Figure 4.1.1. Light from the lower part of the ruler is travelling into a region of lower optical density (air), and so has been bent away from the normal. The image in the water is actually an illusion—an image our brain constructs based on where light from the lower part of the ruler appears to come from. It assumes that the light travelled in a perfectly straight line, even though it didn’t.
air water apparent depth real depth image of point point
Total internal reflection Light doesn’t always refract when it hits a boundary between substances. When light travels from a more optically dense substance into a less optically dense
light bulb
air
ray skims surface
concave mirror
glass total internal reflection
red perspex
Fig 4.1.4
A car stoplight in action. Notice how light is refracted towards the normal on entering the perspex, and away from the normal on leaving it.
equal angles
critical angle
light source
For total internal reflection to occur, light must be travelling into a substance of lower optical density and must strike at an angle greater than the critical angle of incidence.
Fig 4.1.6
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Bending light one (say from glass into air), it sometimes reflects instead! The light is unable to escape from the substance it’s in. This phenomenon is known as total internal reflection, and happens when the angle between the light ray and the normal is greater than the critical angle. The critical angle is formed when the light ray travels along the boundary between the two substances. Reflectors used on bikes and cars are shaped at the back to ensure the angle of incoming light is always greater than the critical angle. This allows the light from the car behind to be reflected back, making the reflector appear to be shining bright red. A red bike reflector in action
light from a car behind
Optical fibres Optical fibres use total internal reflection to trap light within a thin, flexible strand.
Fig 4.1.7
total internal reflection
Optical fibres are used in decorative lights and in communication.
plastic sheath
Fig 4.1.9
inner core
outer layer
total internal reflection
Fig 4.1.10 Fig 4.1.8
Air at different temperatures refracts light differently, causing two types of mirage.
real cloud
Optical fibres use multiple total internal reflections to transmit light.
cool air warm air bent rays travelling through cool and warm air
mirage cloud
warm air mirage island cool air real island
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Mirages Cool air and warm air have different optical densities. Light will therefore bend as it moves into air of a different temperature. If the temperature (and optical density) varies gradually, light can be bent so that it follows a curved path. It then creates another image known as a mirage. When the sky is the object of the mirage, the land will appear as a lake or sheet of water.
Optical fibres are used in endoscopes. These flexible tubes contain optical fibres and can be passed via the mouth into the digestive system to provide doctors with images (magnified around four times) of the stomach and intestinal lining. Tumours that would otherwise be impossible to treat may be destroyed
UNIT
4.1 by laser light sent down an optic fibre cable inserted nearby. A recent invention, the endomicroscope, produces images of body cells magnified 2000 times. Optical fibres are also increasingly being used instead of copper wire to transmit data and communications because they are thinner, cheaper, more durable and can carry more information. They also have increased data security and are not affected by electromagnetic radiation. Fibre optic networks now connect all of Australia’s major cities.
UNIT
4.1
[ Questions ]
Checkpoint Fig 4.1.11
Refraction
An endoscope being used during surgery
1 Define the term ‘refraction’. 2 Identify an example of where refraction occurs. 3 The refractive index of a substance can be used to predict which way a light ray will refract and by how much. Identify another term that can also be used to predict the bending of light by a substance.
Depth illusions 4 Copy the diagram in Figure 4.1.12. Use a ruler to draw light rays to explain why the stone appears higher than it really is.
Think 7 Explain how a bike reflector can reflect light if it doesn’t contain a mirror. 8 Describe what happens when a light ray that is travelling through glass gets to the end of the glass and strikes the air at an angle: a less than the critical angle b greater than the critical angle 9 Describe how a scratch on the outside of an optical fibre might cause problems. 10 Optical fibres have a number of protective layers coating and wrapping them. Explain their purpose. 11 Propose why an endoscope contains several optical fibres rather than one. 12 Your stomach does not contain a light source, so deduce how a doctor could see inside it using an endoscope. 13 Identify a device that converts the following into an electrical signal. a sound b light c an e-mail
Fig 4.1.12
Total internal reflection 5 Define ‘total internal reflection’. 6 State the advantages of using optical fibre instead of copper wire for communications.
14 Identify a device that converts an electrical signal into: a sound b light c a printed page 15 A mirage is created because of refraction even though the light only travels through air and never enters a new substance. Describe how this can occur. >>
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Bending light
Analyse 16 a Copy the diagrams in Figure 4.1.13 into your workbook. b Draw a normal wherever the light rays enter a new substance. c Demonstrate what will happen to the rays as they enter and exit from the substances by continuing the ray through the shape and out the other side. Fig 4.1.13
18 Fibre optic technology offers many advantages when used in medical applications. a Describe how optical fibre may be used in medical applications. b Identify the traditional medical techniques that optical fibres might replace. c Evaluate the benefits of fibre optic technology to medicine.
Skills 19 The table below lists the refractive indices of several substances.
b
a
a Construct a bar or column graph for these values. b Identify which of the substances listed bends light coming from air the most.
c
air
air
glass
glass
water air water
d
Substance
Refractive index
Air
1.00
Water
1.33
Glass
1.52
Diamond
2.42
Perspex
1.49
e perspex air glass air
17 Use Figure 4.1.5 to deduce the direction in which the girl should aim her spear to hit the fish (assumed to be stationary) in Figure 4.1.14.
20 When light travels from a substance with a lower refractive index to one with a higher refractive index (e.g. from air to water), it slows down and bends towards the normal. When light travels from one substance into another of lower refractive index (e.g. from water to air), the opposite happens. Use the table of refractive indices in Question 19 to predict which way light will bend when travelling from: a water to glass b glass to diamond c perspex to glass
A B C
D
fish as seen by girl with spear
Fig 4.1.14
96
UNIT
4.1 [ Extension ] Investigate 1 As shown in Figure 4.1.15, place a coin in a bowl and have a glass of water within reach. Look at the coin and move your head until it just moves out of view. Slowly add water to the bowl and observe the coin. Describe and explain your observations. 2 Investigate fibre optics. Find out: a how a fibre optic cable is made b some further medical applications of fibre optics Present your findings to the class. 3 Explore refraction further by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button.
UNIT
4.1
Fig 4.1.15
[ Practical activities ]
Fig 4.1.16
Measuring angles of refraction Prac 1 Unit 4.1
light box single slit slide
Aim To investigate the relationship between the angle of incidence and the angle of refraction
angle of incidence
Equipment A light box and single slit slide, 12 volt power source, sheet of paper, ruler, polar graph paper (or protractor or Mathomat), semicircular slab of Perspex boundary line
Method
normal
1 Assemble the apparatus as shown.
angle of refraction
2 Ensure an initial angle of incidence of 10°. Use two dots or crosses to mark each part of the light path and measure the angle of refraction. Record your results in a table like the one shown here, including your results for the following angles of incidence: 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°.
Angle of incidence Angle of refraction Amount of bending 0°
0°
0°
Questions 1 Explain why the semicircular slab is a convenient shape to use. 2 Analyse how the angle of incidence affects the degree of bending of light. 3 Construct a graph of angle of incidence versus angle of refraction for Perspex (and water if this was also tested).
3 If time permits, replace the Perspex slab with a semicircular, water-filled dish and repeat the experiment.
4 Assess how the graph would be different if a semicircular diamond was used instead. Diamond is more optically dense than Perspex.
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Bending light
Fig 4.1.17
Apparent depth Aim To investigate how refraction causes depth Prac 2 Unit 4.1
illusions
Equipment White paper with several parallel lines drawn on it, glass block, a pin in a cork
Method glass block
1 Place the glass block on a piece of paper with some parallel lines drawn on it. 2 Hold the cork containing the pin against the block so it lines up with one of the parallel lines.
parallel lines
3 Move the pin up or down the block until it appears to be at the same depth as the parallel line it is lined up with. You have found the correct position if the pin and line move together when you move your head from side to side. 4 Measure the depth of the pin below the top of the block. This is the apparent depth of the glass block. 5 Measure the height of the block above the paper. This is the real depth of the glass block.
Questions 1 Calculate the refractive index of the block by dividing the real depth by the apparent depth. 2 Predict how the apparent depth would change if the block were replaced with water.
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view from above apparent depth pin
real depth
pin
Move head back and forwards. Pin and line should move together when the pin is at the correct position.
UNIT
context
4.2 Lenses are some of the best-known applications of refraction and are commonly used in optical instruments. Our eyes have lenses and they too use refraction to focus the light, allowing us to see an image. Mirrors do not refract light but reflect it instead. We look in the mirror every morning to see a sleepy but clear reflection. Other smooth surfaces can do this too. Some very strange images, however, can be formed if we look instead into curved mirrors like those found at amusement parks.
Light rays often need to be controlled and focused to produce images in optical instruments such as microscopes, cameras and binoculars, and to change the focus for people wearing contact lenses or glasses. We can control and focus light by using lenses and curved mirrors.
Types of lenses There are two main types of lenses: • convex lenses—these curve outwards and are fatter in the middle • concave lenses—these curve inwards (a little like a cave) and are thinner in the middle.
What’s in a name? The word ‘lens’ means ‘lentil’ in Latin. Lentil seeds have the same shape as small convex lenses.
When describing lenses and drawing rays of light, scientists use special rules which are shown in Figure 4.2.2. The main rules featured in Figure 4.2.2 are: • In a convex lens, an incoming Various types of convex and concave lenses Fig 4.2.1 ray parallel to the principal axis is refracted through the principal focus (F). • In a concave lens, an incoming ray parallel to the principal axis is refracted so that it appears to come from the principal focus (F). bi-concave planoconvexobi-convex planoconcavoconcave concave convex convex • The distance from the plane of the lens (centre line of the Convex lenses Concave lenses lens) to F is called the focal length of the lens.
plane of lens principal focus F
parallel rays of light
Ben’s bifocals Bifocal lenses are div ided into two sections tha t bend light by different amou nts. Benjamin Franklin, fam ous for flying a key dangli ng from a kite during an electr ical storm, invented them.
principal axis
plane of lens
principal focus F principal axis
focal length Convex lens
parallel rays of light
focal length Convcave lens
Key features of lenses
Fig 4.2.2
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Lenses and curved mirrors Eye for an eye • A ray passing through the The ciliary muscles stretch and relax the jelly-like lens centre of either type of in the human eye so it gets lens is unaffected. thinner or thicker. Its • As with all images, rays curvature thus changes, of light that come from a allowing us to focus on objects at different distances. part of the object come together again at that same part of the image. The greater the curvature of a lens, the more it bends light and hence the shorter the focal length.
Image type and location
The shape of a lens can affect its focal length.
Fig 4.2.3
weak lens
long focal length strong lens
Prac 1 p. 106
The above rules, when incorporated into a scale drawing, can be used to determine the position, size and type of an image produced by a lens. These scale short focal drawings are called ray tracing diagrams. length Convex lenses produce two different A real image is formed by a convex lens when the object is beyond the focus. Fig 4.2.4 types of images, depending on where the object is located. Ray tracing diagram What you see • If the object is at a screen distance greater than the focal length of the lens, a real focus image is formed. focus object real image real A real image can image be projected onto a focus screen or even onto film, which will object then permanently record the image. See Figure 4.2.4. • If the object is at a distance less than Ray tracing diagram What you see the focal length of the lens, a virtual image is formed. virtual virtual image image This image can’t be projected onto a object screen. See Figure focus focus 4.2.5. Concave lenses produce only virtual eye traces rays back to form a virtual image images. See Figure 4.2.6. Fig 4.2.5
100
A virtual image is formed by a convex lens when the object is inside the focus. This is how a simple magnifying glass works.
Ray tracing diagram
What you see
eye traces rays back to form a virtual image
object
UNIT
4.2 virtual image object
focus virtual image
Fig 4.2.6
Virtual image formation in a concave lens
Images produced by the lenses are sometimes upside down or bigger or smaller than the original object. Scientists use the following terms to describe images: • upright—the same way up as the original object • inverted—upside down compared with the original object • enlarged—bigger than the original object • diminished—smaller than the original object • magnified—image size divided by object size (e.g. a magnification of 5 means that the image is five times bigger than the object).
Optical instruments Lenses are the key components in several optical instruments.
Telescopes
Telescopes make small, distant objects appear larger. By itself, a single lens will only produce smaller images of objects a long way away. The stars and the Moon would appear even smaller! In order to produce a magnified image of such objects, two lenses are used. The objective lens in a telescope produces a real, inverted image just inside the focus of a second Finding the focal length lens, called the eyepiece lens. The image produced by Rays coming into a lens from a distant object are the first lens now acts as the object for the second almost parallel and form an image very close to the lens. Because the first image is inside the focus of the focus. We can then measure the distance from lens second lens, the second image (the one seen by the to image to determine the focal telescope user) is virtual and enlarged compared to length of the lens. the first one (see Figure 4.2.8). The thinner the first lens (objective lens), the Worksheet 4.2 Ray tracing for lenses Prac 2 Prac 3 larger the first image. But thin lenses have longer p. 107 p. 108 focal lengths—this is why telescopes are long An image of a distant object can be used to find instruments. A telescope is focused by adjusting the the approximate focal length of a convex lens. Fig 4.2.7 distance between the two lenses. The image produced by a simple telescope is approximate focal length distant object upside down, but this is almost parallel rays convex lens usually not important when viewing objects such as planets and stars.
real, inverted image
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Lenses and curved mirrors Binoculars
Fig 4.2.8
A telescope produces an image of an image.
Binoculars do the same job as a telescope, although virtual image formed by eyepiece lens here we need the image to convex eyepiece be the right way up. This is lens (thick) telescope important—for example, can you imagine viewing sports F where everything was upside down? Binoculars consist of convex objective two telescopes but they use real image formed lens (thin) triangular prisms to redirect by objective lens light and ensure images are upright. The ‘bouncing’ of the light path due to total internal reflection has objective the added advantage of having lens ray from object an instrument shorter than a conventional telescope.
total internal reflection
prisms
Microscopes Microscopes make small objects appear much larger. A microscope, like a telescope, produces images in several stages. Light may be reflected from a mirror through a condenser. If a condenser is present it sits below the stage and directs focused light through the specimen. The light then passes through an objective lens to form a real image inside the focal length of an eyepiece lens. The eyepiece lens then magnifies the first image to produce a final virtual image.
eyepiece lens
focus knob
Fig 4.2.9
Prac 4 p. 108
Binoculars consist of a pair of compact telescopes.
Prac 5 p. 108
Curved mirrors In Science Focus 1 we looked at plane mirrors and how reflections occurred. Curved mirrors can also reflect light. There are two main types of curved mirrors: concave and convex.
Concave mirrors Concave mirrors produce an enlarged (magnified) virtual image of an object placed close to the mirror. This is shown in Figure 4.2.11. They are very useful when shaving or applying makeup or when dentists need a close-up view of tooth decay. A compound microscope
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Fig 4.2.10
If an object is held at a large distance from a concave mirror, a real, inverted image is produced. See Figure 4.2.12. When an object is a very large distance from a concave mirror but directly in front of it, a very small, real image is produced at a point known as the ‘focus’. See Figure 4.2.13.
UNIT
4.2 concave mirror
upright, enlarged virtual image object
concave mirror
virtual image
side view object close to a i Image formation in a concave mirror when the object is close to the mirror
Fig 4.2.11
concave mirror
Slide projector The slide projector contains a concave mirror to reflect light from a bulb through condenser lenses which concentrate light to pass it through a slide placed just outside the focal length of a projection lens.
inverted, real image
object object further away from mirror
Fig 4.2.12
Image formation in a concave mirror when the object is further away from the mirror
The image of a distant object will form at the focus of the concave mirror.
focus
light from distant object
real image concave mirror side view
Fig 4.2.13
The projection lens then produces a magnified, real image on a screen. See Figure 4.2.14.
Convex mirrors
image of distant object
slide concave mirror
condenser
projection lens
lamp
image on screen
Fig 4.2.14
A slide projector produces an enlarged, real inverted image.
Convex mirrors gather rays of light from a wide area to produce a smaller virtual image behind the mirror. See Figure 4.2.15. Convex mirrors are useful when a wide view is needed. They are used in shops for security across the whole store, at dangerous intersections where vision is difficult, and in some car rearvision mirrors to give a wider view of what is behind the car. See Figure 4.2.16.
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Lenses and curved mirrors
Prac 6 p. 109
Worksheet 4.3 Ray tracing for mirrors
virtual image side view
Fig 4.2.15
A convex mirror produces only virtual, smaller images.
Fig 4.2.17 Fig 4.2.18 a
A convex mirror produces a wider view than a flat mirror.
F
Fig 4.2.16
F
b
UNIT
4.2
[ Questions ]
Checkpoint Types of lenses 1 Copy the lenses in Figure 4.2.17 and identify each as concave or convex by labelling them. 2 The terms ‘diverging’ (moving apart) and ‘converging’ (coming together) may be used to describe lenses. Identify which term applies to: a a convex lens b a concave lens
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F
F
3 Copy and complete the ray tracing diagrams in Figure 4.2.18 to demonstrate the path taken by the light rays.
Image type and location 4 Copy the following and modify any incorrect statements so they become true. a Real images formed by convex lenses are always bigger than the original object. b Virtual images formed by convex lenses are always bigger than the original object.
c Concave lenses can form only virtual images. d Images in a concave lens are always the right way up. e Real images in a concave lens are always the right way up.
Optical instruments
18 To see an object clearly, an image of it must be formed on the retina (the back inside surface of the eye). Propose what sort of lens may be used in spectacles or contact lenses to correct each vision defect shown below. Illustrate your answer with a diagram.
UNIT
4.2
5 Identify two optical instruments that probably contain lenses. 6 Deduce what problems would occur if binoculars did not contain triangular prisms.
a
retina
Curved mirrors
distant object
7 Identify the two main types of curved mirror and sketch each one, indicating the mirrored side in both cases. 8 A curved mirror produces a large upright image when held close to an object. Identify the type of mirror it is likely to be.
shortsightedness
eye b
longsightedness retina close object
Think 9 Use ray tracing to explain how the thickness of a lens affects: a the focal length of the lens b the size of the image 10 Use ray tracing to describe what happens to the image when a distant object is brought closer to (but not closer than the focal length of): a a convex lens b a concave lens 11 A camper is using a magnifying glass to set a piece of paper on fire. Deduce what type of lens is being used and what the ‘hot spot’ on the paper is an image of. 12 Justify why a slide must be placed upside down in a slide projector. 13 At the movies we see real images, not virtual ones. Assess how you can tell. 14 Identify which type of mirror would be best for use: a at a dangerous intersection b by a dentist
eye
Fig 4.2.19 19 Describe how a lens or mirror could be used to start a fire.
Skills 20 Calculate the magnification in each case for images produced by various lenses:
Object height
Image height
2 cm
6 cm
5 cm
20 cm
25 mm
5 mm
16 mm
4 mm
8 cm
160 mm
Analyse 15 A convex lens can produce an enlarged image of an insect. Analyse why it can’t produce an enlarged image of the Moon. 16 You have two lenses—one thick and one thin—at your disposal to build a telescope. Propose which one you should use for the eyepiece, and which one for the objective lens. 17 Compare telescopes and binoculars by listing the things that are: a similar b different
[ Extension ] Investigate 1 Investigate the history of an optical instrument such as the telescope or camera. Include the following information: a who invented it and when b what improvements have been made over the years and by whom >>
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Lenses and curved mirrors
Fig 4.2.20
c a diagram of the first instrument developed and a diagram of a modern version of this instrument— include a discussion of some of the differences or improvements between the original and modern versions of the instrument Present your information in a written report. 2 Investigate one type of sight defect such as longsightedness, short-sightedness, cataracts, night blindness or colour blindness. Find out the following information: a what causes the defect b the symptoms displayed (include diagrams if applicable) c any treatment(s) available to control or cure the defect Present your information as an information leaflet that may be found in a doctor’s surgery.
Action 3 Investigate the magnification produced by a water drop lens using different-sized drops.
UNIT
4.2
DYO
[ Practical activities ] Lenses and a light box
Prac 1 Unit 4.2
Aim To investigate the refraction of light through various lenses Equipment
4 Does it matter if a lens is hollow on the inside? Will curved surfaces with nothing (but air) in between have the same effect as a solid lens? Examine these questions by designing your own experiment.
DYO
Surf 5 Explore how some optical instruments (such as the telescope, microscope, binoculars and cameras) work by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button.
A light box, multiple-slit slide, 12 volt power supply, light box lenses set, sheet of paper.
Method 1 Adjust the light box (using the knob on top) to produce a wide beam of light with parallel edges on a piece of paper.
ray box
2 Direct a wide beam of light through a lens shape with no slide inserted in the light box. 3 Now use the slide with multiple slits to direct several parallel beams of light through the lens. Use a pencil to mark parts of the light paths.
lens
4 Remove the lens and light box from the paper and rule the complete light paths. 5 Repeat steps 1 to 4 for several different lenses, including concave lenses. (Use a new piece of paper in each case.)
Fig 4.2.21
Questions 1 Describe in words the effect of: a a convex lens b a concave lens 2 Compare the light path through a wide convex lens with that through a thin one.
106
3 Identify whether there are any individual light rays that are not bent by the lens in each case. 4 What were the focal lengths of the lenses you used? Construct a trace or sketch of each lens and write the focal length under each one.
UNIT
4.2 Images in a convex lens Aim To investigate the image formed by different Prac 2 Unit 4.2
convex lenses
Equipment A convex lens, white card or screen, plasticine or lens holder, metre ruler, candle or small globe with power supply Fig 4.2.22
Method 1 Determine the focal length of your lens by using it to form an image of a window 5 metres or more away on your card/screen. Measure the distance of the image/screen from the lens—this is the focal length. 2 Use your apparatus to obtain the sharpest possible image on the screen with the candle or lamp more than two focal lengths from the lens. A darkened room will help. 3 Copy the table below, and record your measurements. 4 Repeat for the other positions in the table.
Questions 1 Describe what happened as the object was brought closer to the lens. 2 Summarise the circumstances in which: a a real image (on a screen) is obtained b a virtual image (one that cannot be ‘caught’ on a screen) is obtained c no image is obtained 3 If time permits, repeat for a convex lens of different focal length.
Convex lens focal length: ________ cm Object Diagram
Description of position
Image Distance from lens (cm)
Distance from lens (cm)
Description (e.g. larger/smaller, inverted/upright)
Object more than two focal lengths from lens
Object two focal lengths from lens
Object between one and two focal lengths from lens Object less than one focal length from lens (i.e. object inside the focal length) Object exactly at the focus (one focal length from lens)
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Lenses and curved mirrors
Images in a concave lens Aim To investigate the image formed by different Prac 3 Unit 4.2
concave lenses
Equipment A concave lens, card or screen, candle or light globe and power source
Method
Questions 1 Assess whether it is possible to form a real image (one that may be ‘caught’ on a screen) using a concave lens. 2 Explain how the image changes as the object-to-lens distance is varied.
1 Using the equipment provided, attempt to capture an image produced by a concave lens on a screen. 2 Study the effect of moving the object closer to the lens, then away from the lens.
Telescopes and microscopes Prac 4 Unit 4.2
Aim To investigate how telescopes and microscopes form images
Equipment Two convex lenses—one thin (e.g. focal length 25 cm) and one thick (e.g. focal length 5 cm), cardboard, scissors, tracing paper or other translucent material (e.g. thin plastic from a shopping bag), lamp, small object to view
Method Part A: The telescope 1 Construct and assemble the apparatus as shown in Figure 4.2.23.
2 Place the object a large distance (say, 1 metre) from the objective lens, and move the eyepiece lens and screen to obtain the sharpest possible image looking through the eyepiece lens. Note the size of the image compared with the object. 3 While looking through the eyepiece lens and observing the image, remove the screen. You should still see the image! Think about why. Part B: The microscope 1 Now move the object close to the lens (but not closer than the focal length). 2 Adjust the position of the lenses to obtain an image that is larger than the object.
Questions objective lens
1 Distinguish between a telescope and a microscope. 2 Describe how the removal of the screen changes the image in part A (step 3) above.
translucent screen
Constructing a field telescope Prac 5 Unit 4.2
eyepiece lens DYO
Fig 4.2.23
108
Construct a more readily portable telescope using cardboard tubes. Use it to focus on objects various distances away. Investigate the effect of replacing the eyepiece with a concave lens.
UNIT
4.2 Curved mirrors Prac 6 Unit 4.2
Aim To investigate the images formed by convex and concave mirrors Equipment A convex and a concave mirror, a candle, a screen
Method PART A: Concave mirror 1 Arrange the apparatus as shown in Figure 4.2.24. 2 Move the screen until you obtain a clear image of the candle. 3 Investigate the different images produced with the candle at different distances from the mirror. Is there a position where it is impossible to obtain an image on the screen? Can you see a virtual image in the mirror? PART B: Convex mirror 1 Hold the mirror at arm’s length and look at your image. 2 Gradually move the mirror towards you, noting any changes in the image as you do so.
Questions 1 Explain what happens to the image as an object is brought closer to: a a concave mirror b a convex mirror 2 Identify which type(s) of image are possible in each type of mirror.
screen
image
concave mirror
plasticine candle (object)
Fig 4.2.24
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UNIT
context
4.3 Have you ever wondered why the sky is blue, sunsets are red and rainbows are many colours? Isaac Newton was also puzzled by these questions. In 1665 he conducted an experiment using triangular prisms to split a
Dispersion When a thin beam of white light is refracted by a triangular prism, it may be split into the colours of the rainbow. Isaac Newton first described this in 1665 when he was a student at Cambridge University in England. This effect is known as dispersion, and the colours of light produced are called the visible spectrum.
Roy G Who? One way of remembering the colours of the visible spectrum is imagining that the first letter of each colour is part of a name—this forms the mnemonic Roy G Biv.
thin beam of white light into the colours of the rainbow. This experiment established the basic ideas that we now use to explain the many phenomena of light. We can use these ideas to explain the colours we see when looking at objects, the sky, theatre lighting or printed photographs.
Multicoloured cars The multicoloured effect sometimes seen in car paint is achieved by reflecting light through a five-layered flake made of transparent metal oxides. It creates a rainbow effect that changes according to the light source and viewing angle, and the shape of the car panel.
Although the spectrum is made from an infinite number of merged colours, Newton liked the idea of seven main colours—red, orange, yellow, green, blue, indigo and violet. This was probably because he was interested in mysticism and seven was, in Newton’s time, a highly symbolic number for Christians. It has been argued that indigo was included to ‘make up the numbers’ to seven, as most people find it Prac 1 p. 115 hard to tell blue and indigo apart.
Blue skies and red sunsets Blue skies and red sunsets are caused not by refraction of sunlight, but by another phenomenon known as scattering in which molecules of gas and dust particles in the atmosphere alter the direction of light rays. Blue light is scattered more than the other colours of the spectrum, and the scattered blue rays seen against the dark background of space causes the sky to appear blue. At sunrise and sunset, when sunlight travels further through the atmosphere, almost all of the blue rays are scattered and the light that reaches us is mainly red or orange.
Teacher demonstration Milky sky
A triangular prism splits white light into the colours of the rainbow.
110
Fig 4.3.1
Your teacher may demonstrate scattering of a light beam by a beaker of water with a few drops of milk added to produce blue and red effects of sunset.
Rainbows Small droplets of water behave like tiny prisms in the sky. Sparkling Sometimes the colours will diamonds reach our eyes after refracting ond sparkles due diam A and undergoing total internal to light undergoing reflection. As can be seen in multiple total internal Figure 4.3.2, droplets higher in reflections. In fact, a ond is shaped to diam the sky refract red to our eyes, maximise these while green and blue go reflections. At each overhead. In drops lower in the reflection, light is rsed, with some dispe sky, blue light is refracted and colours eventually reflected to our eyes, but green making it out of the and red light bend lower down, stone to reach our eyes. missing our eyes. The overall effect is that we see a primary rainbow—a band in the sky with red at the top and blue at the bottom.
white light
raindrop
white light
light from Sun
millions of colours. We say red, blue and green are primary colours, because they can be combined in various proportions to form all other colours. A magnified view of a television screen reveals lots of tiny coloured spots called phosphors.
Fig 4.3.3
Another way of adding colours involves coloured beams of light. Where all three primary colours combine, white light is produced. This is the opposite to the splitting of light. Where just two primary colours overlap, secondary colours—cyan, magenta and yellow —are produced.
raindrop
light from Sun
primary rainbow
Fig 4.3.2
UNIT
4.3
secondary rainbow
How primary and secondary rainbows are formed. Note that the colours are reversed in the secondary rainbow.
Sometimes a less intense secondary rainbow can be seen above a primary one. Light reaches our eyes from a secondary rainbow after two internal reflections inside each raindrop. This has the effect of reversing the colours so the bottom band is red.
Colour addition If you look closely at a television screen, you’ll see lots of tiny spots coloured red, blue and green by special chemicals called phosphors. These spots are made to glow in various combinations by electron beams inside the television. Our eyes merge the glowing spots and we perceive pictures containing
blue magenta cyan white red yellow green
Fig 4.3.4
Overlapping light beams demonstrate colour addition.
111
>>>
Colour People sometimes incorrectly believe that yellow is a primary colour, but they are probably thinking of mixing paint, not light. Prac 2 This will be discussed later in this unit. p. 115 Two colours of light that mix to make white light are called complementary colours. Red and cyan are complementary colours, as are green and magenta. Blue and yellow form another pair.
white light
white light red light reflected (all other colours absorbed) object appears red
blue light reflected (all other colours absorbed) object appears blue red light
Colour subtraction One way of removing colours from a beam of light is to use a filter. A filter is really just a slide containing coloured cellophane or plastic that allows only light of a certain colour to pass through it. For example, a red filter allows only red light to pass through it—all other colours are absorbed or ‘trapped’ by the chemical dye in the filter. Filters allow light only of a particular colour to pass through them.
red light reflected object appears red red light
yellow light red light reflected (green absorbed) object appears red
no light reflected object appears black
Fig 4.3.6
Coloured objects absorb some colours and reflect others.
Fig 4.3.5
red filter red transmitted
white light
Prac 3 p. 116
Colourful chameleons
blue filter white light
Chameleon lizards, native to Madagascar and Eastern Africa, are able to change colour. They do this in response to temperature changes and stress levels or to blend in with their environment. Pigment movement in special skin cells called chromatophores controls the colours produced.
blue transmitted blue filter
red light
no light transmitted (you would perceive black) green filter
yellow light
green transmitted
Seeing colours Colour subtraction or absorption also occurs when we look at coloured objects. When we see a red T-shirt, it’s because white light from the Sun or a ceiling light hits it and reflects red light to our eyes. The red T-shirt absorbs all other colours. Some peculiar effects can be observed when coloured objects are viewed in coloured (rather than white) light. Some of these are explained below. To simplify explanations, consider white light to be made up of red, blue and green light only.
112
Fig 4.3.7
Chameleons can change colour.
Mixing pigments Pigments are finely spread-out solid particles of colour found in substances like paint and ink. These behave quite differently to light. For example, blue and yellow light mix to make white light, but blue and yellow paint mix to make green paint. We normally view objects in white light that is a mixture of red, orange, blue, green, indigo and violet
(ROYGBIV). Paints are not perfect colours and usually reflect and absorb groups of these colours. For example: • Blue paint absorbs red, orange and yellow light (ROY), but reflects green, blue, indigo and violet (GBIV). • Yellow paint absorbs blue, indigo and violet (BIV) and reflects red, orange, yellow and green (ROYG). • A mixture of blue and yellow absorbs all colours that both individual colours do (red, orange, yellow, blue, indigo and violet (ROYBIV)), leaving only green (G) reflected, so the mixture appears green. Remember in art classes when all the paints you were using eventually got mixed, and you were left with a murky dark colour? This is because most colours were absorbed by the mixture, leaving very little to be reflected. Colour absorption in pigments
Fig 4.3.8
red absorbed cyan
green absorbed magenta
yellow
UNIT
4.3
magenta blue red black cyan green yellow
Fig 4.3.9
Mixing paints
Cyan, magenta and yellow are sometimes referred to as the primary colours of pigments. Secondary colour combinations give us a range of colours that can then be printed. For example, to produce red on a printed page, magenta and yellow are combined. The magenta subtracts green and the yellow subtracts blue, leaving only red. Many desktop publishing programs can produce so-called colour separation files—four single-colour images that are transferred to plastic film used in the printing process. These images are used to control when C, Y, M or K is printed.
blue absorbed full colour photograph or electronic image file
Printing The secondary colours of light—cyan, magenta and yellow—are very important in the printing process, such as that used to print the colours in this book. They are used because they each subtract one of the primary colours. Black is also used to provide contrast and variety in shades. This set of secondary colours, together with black, is known as CYMK. The last letter in the word ‘black’, K, stands for black.
colour separations
Colour photography Photographic film consists of three layers which each react with a different primary colour to produce three superimposed images when the film is exposed after a picture is taken. When the film is developed, each of these images is replaced with a secondary colour dye using chemical reactions to make a colour negative. When the final photo is produced, the negative filters out various colours to leave the correct ones for each part of the picture.
used to make printing plates C
Y
M
K
printing printed page
Cyan, yellow, magenta and black (CMYK) are important colours in the printing process, where tiny dots of each combine to produce the colours we see in the final image.
Fig 4.3.10
113
>>>
Colour
UNIT
4.3
[ Questions ]
Checkpoint Dispersion 1 Identify what Isaac Newton used to split light into several colours. 2 a List the colours of the visible spectrum. b Construct a sentence that helps you remember the colours in order.
Blue skies and red sunsets 3 a Identify the effect where atoms in the atmosphere spread light. b Identify which colour light does this the most. 4 Explain why sunrises and sunsets are red or orange in colour.
11 Identify the colour you would see when paints of the following colours are mixed. a cyan and magenta b yellow and cyan c cyan, magenta and yellow
Printing 12 Identify the colours important to the printing process. 13 Identify the colour pigments that would be mixed to produce red on a printed page.
Think 14 Diagram A below shows a ray of red light passing through a glass object. Identify which diagram (A, B, C or D) best shows a ray of blue light passing through the same object.
Rainbows 5 Describe what happens inside water droplets to cause a rainbow. 6 Explain how you can tell whether a rainbow is a primary or secondary one.
Colour addition
A
B
C
D
7 Identify the: a primary colours of light b secondary colours of light 8 Explain what complementary colours are. 9 Identify the complementary colour for: a green light b cyan light 15 Explain how a television screen produces colour images.
Colour subtraction 10 Copy and complete the following light filter diagrams. Fig 4.3.11 a white light G b blue light G c cyan light G
114
Fig 4.3.12
16 Propose what happens to the light energy that is absorbed by a filter. 17 Assess why K, not B, is used for black in the CYMK colour system. 18 Explain why there are three layers in photographic film and developing paper. 19 A stack of coloured blocks appears as shown here in white light.
magenta
green
red
Construct a diagram and label the colour of each block when viewed in: a blue light b yellow light
Fig 4.3.13
UNIT
4.3 [ Extension ] Investigate 1 Investigate more about how electron beams are controlled to strike just the right spots on a colour television screen. 2 Investigate how colour inkjet or laser printers work. Summarise your findings in a flow chart. 3 Research in detail the process of colour printing or photography from film to print. Present the information in a poster, including diagrams to outline the steps.
Action 4 Construct one or more colour wheels and study the effect of ‘mixing’ various colours in different proportions. Summarise your findings in a table.
Fig 4.3.14 DYO
Worksheet 4.4 Colour-mixing wheels
UNIT
4.3
5 Construct a crossword that provides a summary of the information you have learnt about colour.
[ Practical activities ] Dispersion: splitting white light Aim To disperse a beam of white light into
Prac 1 Unit 4.3
the spectrum
Equipment
Triangular glass or Perspex prism, light box and power supply, slide with single slit, white paper
Method 1 Alter the position of the light box and prism to obtain a clear spectrum.
3 Use any other light box accessories available to try to recombine the colours into a single white ray.
Questions 1 Identify the colour that refracts: a the most b the least 2 Propose how it may be possible to recombine colours separated by a prism.
2 Mark the ray path and position of each colour within the dispersed beam. Fig 4.3.15
Mixing colours
light box
Aim To investigate the mixing of coloured light Prac 2 Unit 4.3
red slide (filter)
using various combinations of coloured filters blue slide (filter)
Equipment Light box and power supply, a variety of coloured slides, white paper
Method 1 Place a red and a blue slide in the light box and use a side mirror to combine the coloured beams. Note the resulting colour in a table like the one below, and try various colour combinations. >>
reflecting door white paper
115
>>>
Colour Warning: Do not leave filters in the light box too long or they may be damaged.
2 Use the light box to combine three colours and record your results.
Copy the table and record each result. Slide A
Slide B
Red
Blue
Red
Green
Blue
Green
Red
Cyan
Green
Magenta
Blue
Yellow
Result
Slide A
Slide B
Slide C
Red
Blue
Green
Cyan
Magenta
Yellow
Result
Questions 1 Identify which combinations produced white light. What do you call such combinations? 2 The white produced was probably not quite white but was a little ‘off’. Propose why some of the results may not have been ‘perfect’.
Seeing things in a different light Aim To investigate the colour of objects when Prac 3 Unit 4.3
Questions
viewed under different-coloured lights
Light box and power supply, a variety of coloured slides, a variety of coloured cards
1 Identify which colour light needs to shine on a red card so that it appears: a red b black or very dark
Note: The slides and cards should be labelled with their colour.
2 Identify examples where an object appeared quite different to its actual colour.
Method
3 It is important to label each card with its colour. Explain why this is the case.
Equipment
1 Check that each slide and card has its colour written on it. 2 Use a light box and coloured slides to shine coloured light onto various coloured cards and record the appearance of the card in each case in a table like the one below.
4 Theoretically, several combinations should have resulted in cards appearing to be pitch black. Assess why you may have seen dark colours instead.
Appearance of coloured cards in coloured light Card colour Red
Light colour
Red Blue Green Cyan Magenta Yellow
116
Blue
Green
Cyan
Magenta
Yellow
Chapter review [ Summary questions ] 1 Copy and complete: When a light ray travelling in air strikes a glass boundary, it bends ________ the normal. The speed of the ray in the glass is ________ than it is in air. 2 True or false? a Light always bends when it enters a different substance. b Images can be caused by reflection or refraction. c Light can bend due to refraction within the one substance. d Light passing from water to air will bend towards the normal. e The apparent depth of a swimming pool is less than the real depth.
6 Identify the complementary colour to: a red b magenta 7 Identify the type of image produced when an object is close to: a a concave mirror b a convex mirror 8 Describe three situations in which different types of mirrors are used and why.
[ Thinking questions ] 9 Identify which of the following lenses are: a concave b convex
3 State two uses of optical fibres. 4 Construct ray diagrams by copying and completing the light ray in each diagram below.
a
b
c
a
air
water
d b
air
e f
water
c
glass water
5 a Copy the following sentence, modifying it to correct any mistakes. Light travelling along inside an optical fibre undergoes several total internal refractions. b Describe at least two uses for optical fibres. c Outline how each use you have described may benefit society.
10 Construct a diagram to demonstrate how ‘ray’ tracing can be used to find a real image in: a a concave lens b a convex lens 11 Describe the image type (real or virtual), size (enlarged or diminished) and orientation (inverted or upright) when a candle is placed: a 20 cm in front of a convex lens of focal length 10 cm b 100 cm in front of a convex lens of focal length 10 cm c 5 cm in front of a convex lens of focal length 10 cm d 5 cm in front of a concave lens of focal length 10 cm
>> 117
>>> 12 Identify the two lenses in a basic telescope or microscope. 13 Describe how lenses and/or mirrors are used in the following technological developments: a microscope b security mirror in a shop c binoculars d slide projector
17 Identify how many total internal reflections occur inside a drop of water that helps form: a a primary rainbow b a secondary rainbow 18 Analyse why red sunsets can sometimes be more impressive when there is more dust or pollution in the air than usual. 19 Copy and complete the following diagrams involving filters.
[ Interpreting questions ] c
a
14 Identify an optical device that produces: a real images for viewing b virtual images for viewing
white light
15 Copy and colour each of the following colour combination diagrams. b
a
yellow light
blue filter
d
magenta light
b
cyan filter
white light
red filter
blue filter
green filter
magenta blue
green
red
Light
yellow
20 Describe the appearance of: a a green flag viewed in blue light b a blue flag viewed in red light c a cyan flag viewed in green light
cyan
Pigments
16 Assess which colour light in each pair below refracts the most. a red or orange b blue or green c yellow or violet
118
21 A printer combines hundreds of tiny cyan dots with a similar number of yellow dots in one region of a page. Deduce what colour that part of the page will appear. 22 A fruit shop places a red light above a basket of lemons. Deduce what colour the lemons will appear to customers. Worksheet 4.5 Light crossword Worksheet 4.6 Sci-words
>>>
5
The fragile
crust
Key focus area
>>> The implications of science for society and the environment
identify what happens at the boundaries of tectonic plates explain what causes movement in the molten rock below the Earth’s surface and how that influences what is happening on the crust above
Outcomes
recall evidence that suggests the crust of the Earth is moving
5.4, 5.9.2, 5.9.4
By the end of this chapter you should be able to:
explain why earthquakes occur and describe the different seismic waves they cause describe the different types of volcanoes describe how faults, folds and volcanoes mould the crust of the Earth describe how fossils form use fossils and other remains as a method of dating rocks.
apart, yet could be suburbs of each other some day. How?
3 Australia doesn’t get many earthquakes or volcanoes but New Zealand does. Why?
4 Why do people live near active volcanoes when they are so dangerous?
5 What is the biggest mountain on Earth and why is it in the Pacific Ocean?
6 What are plastic rocks?
Pre quiz
1 Australia is moving northwards. True or false? 2 Los Angeles and San Francisco are 1200 km
>>>
UNIT
context
5.1 If you look at a map of the world, it appears that some coastlines could fit neatly together. Francis Bacon first noticed it in 1620: the eastern coast of America had just been mapped and seemed to fit the coasts of Africa and Europe like pieces in a jigsaw. This observation seems to suggest something amazing—that these continents were once joined and have since moved apart!
The evidence Wegener used in forming his theory included: • Two hundred million year old fossils of the same fern-like plant (Glossopteris) and Triassic reptiles were found across the southern continents, as shown in Figure 5.1.2. They all seem to have started on a single continent, then were taken around the world when it split and the pieces drifted apart.
Continents that move! In 1915 Alfred Wegener proposed a radical theory. He suggested that there was once a supercontinent called Pangaea, which split to form the continents. These then drifted into their current positions. Although Wegener had lots of evidence to support his ideas about drifting continents, geologists did not take his work seriously, since Wegener was not a trained geologist but an astronomer and meteorologist.
Cynognathus Africa
India
Lystrosaurus
South America Australia
Antarctica
Mesosaurus Glossopteris
The migration of Triassic reptiles could have happened only if the continents were joined. The reptiles could not possibly swim the large distances between the continents and the spores (seeds) of ancient ferns could not survive in the sea.
Fig 5.1.1
120
Alfred Wegener
Fig 5.1.2
• The structure and rock composition of mountains in eastern North America can be matched to those of mountains across north-western Europe, as shown in Figure 5.1.3. Likewise, Africa seems to be matched with South America.
Greenland Iceland North America Atlantic ocean
Fig 5.1.3
Europe
The mountain ranges in eastern North America and north-western Europe can be matched in detail for structure and rock composition.
The continents seem to have shifted so that these mini-magnets point in mismatched directions. If the continents Prac 1 are put together, however, they all point p. 124 in the same direction, as shown in Figure 5.1.4. It was later suggested that Pangaea split first into two smaller supercontinents, Gondwana (comprising Australia, Antarctica, South America, Africa and India) and Laurasia (North America, Europe and most of Asia) before breaking again. The idea didn’t catch on at the time, however, since it was generally thought that the Earth was solid rock. How could continents move across solid rock, and what pushed them? The magnetic alignments of ancient igneous rocks are scattered. If the continents are joined, the magnetic poles all point to the same spot.
N
N
The man from Snowy River ‘He hails from Snowy River, up by Kosciusko’s side, where the hills are twice as steep and twice as rough.’ The Snowy River valley in New South Wales/Victoria was partly formed by a 15 km long glacier. Had the ‘man’ lived in the Ice Age he would have needed a snowboard instead of a horse! The closest we get to a glacier in Australia now are am 30-metre deep snow patches on Mt Twyn in New South Wales. These patches are thick and heavy enough to compact to a density of about 80% that of ice.
UNIT
5.1
Fig 5.1.4
common pole (roughly where Hawaii is now)
N
N
Evidence from below! • Ancient glaciers have left valleys and debris across many continents, including some now too warm to produce glaciers. These continents seem to have moved from a colder climate. • Coal has been found above the Arctic Circle. Coal comes from decomposed plants and it is far too cold there now for plants to grow. These regions seem to have shifted from one with a warmer climate where plants could grow. • As lava from a volcano cools, it adopts the magnetism of the Earth at that moment. Three hundred million year old magnetic rocks in South and North America have been found with their north poles pointed in different directions.
During World War II, the military needed accurate maps of the seabed and they also needed to find underwater reserves of fossil fuels to assist the war effort. Using the newly developed technology of sonar, some surprising results were found: • Huge underwater volcanic mountain ranges run down the centre of the oceans, the longest being the Mid-Atlantic Ridge with a length of 65 000 km. • The ages of the rocks of the ocean floor vary from brand new to 200 million years old, far younger than the rock of the continents. • Incredibly deep ocean trenches exist, the deepest being over 11 km deep. • The rock of the continents is less dense than that of the ocean floor and seems to ‘float’ on it.
121
>>>
Plate tectonics • The rocks of the ocean floor have magnetic ‘stripes’, parallel with the underwater ridges. The magnetic field of the Earth has changed many times in its history, with the north pole becoming south and vice versa. The stripes show this reversal and indicate that the youngest rock is next to the ridges and the oldest next to the trenches. The magnetic stripes of the ocean floor south of Australia are shown in Figure 5.1.5. Magnetic stripes show that the rocks of the ocean floor vary in age and are moving away from a mid-ocean ridge.
Fig 5.1.5
Floating plates You should remember from Science Focus 1 that the Earth is made of layers. We live on the crust, which varies in thickness from about 11 km under the ocean to an average of about 33 km under the continents. Fig 5.1.7
The inner structure of the Earth (not to scale) Lithosphere p (crust and upper mantle)
Crust 11–70 km thick
Mantle
Australia
oldest ocean rock
2900 km
Tasman Sea Solid
new rock mid-ocean ridge new rock Key:
Inner core
Core
5100 km
6378 km
N
rocks have rocks have N plate movement oldest ocean rock Antarctica
All this evidence suggests that the new crust is born at mid-ocean ridges The molten rock cools as it hits the water, builds new mountains and pushes old ones out of their way. The ocean floor acts like a conveyer belt, carrying everything towards the trenches. volcanic activity (island arc)
rising magma
Fig 5.1.6
122
oceanic crust
oceanic ridge
direction of movement of magma
ocean sediment trench
continental plate
melting mantle rising magma
continental crust
The ocean floor is like a conveyor belt dragging new rock from mid-ocean ridges into the ocean trenches.
Next is the 2900 km thick mantle. The mantle is unusual in that the upper mantle is solid, very much like the crust. The upper mantle and crust form a rigid layer of rock called the lithosphere. Below the lithosphere is a narrow, mobile layer of fluid-like rock called the asthenosphere. The rock here is under extreme heat and pressure and behaves like a sludgy, slow-moving liquid. The rigid slabs of lithosphere, called tectonic plates, float on the slowly moving asthenosphere. The continents sit on the plates and move with them. Imagine the asthenosphere as a bowl of thick, hot soup and the tectonic plates as pieces of toast floating on the soup. The toast will move whenever the soup is stirred. Some pieces will crash against each other, some will ride on top of others, and others will sink. The idea of moving plates is called the Theory of Plate Tectonics and was first developed in 1962 by the American Harry Hess. This theory was not accepted in the old Soviet Union, because that country (of which Russia was the main part) is located far from any plate boundary. Soviet geologists at that time believed instead that the continents were stationary and affected only by vertical movements of
the Earth’s crust. Another alternative theory (the expanding Earth model) was proposed by the Australian geologist S. Warren Carey. This model suggests that the Earth was much smaller 200 million years ago, and that it has since expanded to its present size, with the current increase in radius being 3 to 4 mm per year. The model easily accounted for the break-up of Pangaea, the movement of the plates and the spreading of the ocean floor, but failed to explain the ocean trenches. Although scientists now agree that the plates are moving, nobody is quite sure why. Many
Antarctica The rocks of east Antarctica are 4 billion years old, which means they are among the oldest known rocks on earth. Antarctica’s fossil record is similar to Australia’s and includes dinosaurs, amphibians and marsupials from when the two continents were joined. Australia began to separate from Antarctica about 85 million years ago. Complete separation occurred about 30 million years ago. They are still moving apart at the rate of 7 cm a year.
UNIT
5. 1
[ Questions ]
Checkpoint Continents that move! 1 Outline five pieces of evidence that suggest the continents were once joined. 2 Identify the land masses thought to have made up: a Gondwana b Laurasia
Evidence from below! 3 List five surprising facts discovered when the ocean floor was first mapped. 4 Identify the locations of the oldest and youngest rocks on the ocean floor.
Floating plates 5 Define the following terms: a tectonic plate b mantle c crust 6 State how thick the crust is. 7 Explain the Theory of Plate Tectonics.
hypotheses have been proposed. Some involve the pulling by the plates where they go into a trench, others the pushing at the spreading oceanic ridge, and some put it all down to tidal forces. The most commonly accepted theory is convection currents. Hot air and liquids rise and so does hot molten rock. Likewise, ‘cool’ rock drops. Heat from deep within the Earth causes the molten rock of the mantle to move upwards. When this hot mantle rock comes into contact with the relatively cold crust, it cools and sinks. Convection currents in the mantle are the result. Prac 2 p. 125
UNIT
5.1
Prac 3 p. 126
Think 9 Copy the following and modify any incorrect statements so they become true. a Triassic reptiles could have swum the distances required to populate different continents. b There are similar mountain ranges in the USA and Africa, and also in Europe and South America. c Continents that do not have glaciers now have always been too warm to have them. d Coal deposits above the Arctic Circle suggest that the land floated there from warmer climates. e The rock of the ocean floor and that of the continents are the same age. f Continental rock is denser than the rock of the ocean floor. g Magnetic stripes on the ocean floor suggest that new rock is made along mid-ocean ridges. 10 Temperatures along the ridges are higher than elsewhere in the ocean. Propose why. 11 Draw a diagram to illustrate the convection currents in an oven. 12 Explain what keeps the mantle from cooling down and becoming solid. 13 Assess what would happen to the plates if the asthenosphere below them cooled and became solid. 14 Plate tectonics explain why Australia once had glaciers but doesn’t have any now. Propose another possible reason for this phenomenon.
8 Discuss what causes convection currents and identify where they are thought to occur.
123
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Plate tectonics Plate
[ Extension ] Investigate
N
1 The plate on which Australia sits is moving northward at about 5 cm per year. Calculate how far will it move in an average lifetime.
M ap o f
P lan
the et Spla
tt e r
N
2 a Investigate what one or more of these people contributed to the development of the theories of continental drift and plate tectonics. Alexander Du Toit Arthur Holmes Abraham Ortelius Eduard Seuss Antonio Snider-Pellegrini Frank Taylor Alfred Wegener b Imagine you are the person you have researched. Construct a letter to send to the Geological Society of Australia explaining what you have discovered. 3 The expanding Earth theory is an alternative to the theory of plate tectonics.
N
a Use this theory to explain how the continents split and moved apart. b Investigate more about this theory and the works of Carey, O.C. Hilgenberg and H.G. Owen. 4 Examine what sonar is and how it measures depth. Illustrate your findings with examples. N
The planet Splatter Aim To reconstruct a supercontinent Prac 1 Unit 5.1
Equipment
Key
A4 photocopy of the map in Figure 5.1.8 or photocopy of worksheet 5.1
N
Worksheet 5.1 The planet Splatter
Splattonians think that the continents on their planet move and were once the supercontinent Squidgewana. Evidence comes from shape, magnetic fields and fossil remains of the golden splattered slug and the squidgian tinea fern.
direction of north pole of ancient magnetic rocks fossil remains of golden splatted slug fossil remains of squidgian tinea fern
Method 1 Cut out the continents and arrange them to rebuild Squidgewana. 2 Stick the map in your workbook.
N
UNIT
5. 1 [ Practical activities ]
Map of the planet Splatter
Fig. 5.1.8
Questions 1 Explain how each piece of evidence suggests that a supercontinent once existed. 2 Determine whether there are any other ways the supercontinent could be arranged.
124
UNIT
5.1 Convection currents Aim To investigate the movement of Prac 2 Unit 5.1
convection currents
Equipment
Large (500 mL or 1000 mL) beaker, potassium permanganate, tweezers, hot plate or Bunsen burner, bench mat, tripod, gauze mat, plastic bag, ice
Method PART A: Hot convection 1 Three-quarter fill the beaker with cold water.
PART B: Cold convection 1 Three-quarter fill the beaker with cold water. 2 Put some ice in the plastic bag. 3 Use the tweezers to hold a crystal at the top of the beaker, just below the bag of ice. 4 Draw what happens.
2 With the tweezers drop a single crystal into the centre of the beaker.
Questions
3 Gently heat the beaker on the hot plate or over the Bunsen burner.
1 Explain what causes convection currents.
4 Carefully observe and draw the motion of the purple stain.
Part A
2 Use a diagram to clarify what a ‘hot’ current does. 3 Identify the direction of a ‘cold’ current.
Part B
beaker
plastic bag of ice
tweezers to hold crystal hot plate
beaker of cold water
crystal potassium permanganate
Fig 5.1.9
Hot and cold convection currents
125
>>>
Plate tectonics Future Earth Prac 3 Unit 5.1
Aim To predict possible future changes to the position of the Earth’s continents
3 Lay all the sheets on top of each other to reproduce the current map of the world.
Equipment
4 Move each transparency 1 cm in the direction of the arrows.
Map of tectonic plates, A4 sheet of paper, 6 overhead transparencies, overhead transparency pen or marker, sticky tape, photocopy of worksheet 5.2
5 Trace the new shape of the continents. Transfer the diagram to your workbook. 6 Move the transparencies 1 cm more and re-trace.
Worksheet 5.2 Future Earth
7 Do this three more times, so that you have a series of ‘maps’.
Method 1 There are seven main tectonic plates. Trace the African plate and Africa onto a piece of A4 paper and tape it to the desk. Trace the other plates and continents onto overhead transparencies, one plate per sheet. 2 On each sheet draw a large arrow pointing in the direction the plate is moving. Predicting a new world
8 Mountain chains will form when a continent hits another. Mark them and give them a name. 9 Name any new seas or oceans formed.
Questions Fig 5.1.10
1 In this prac each plate moved at the same speed. Assess whether this is accurate in reality. 2 Predict what will happen to these bodies of water in the future: a the Mediterranean Sea b the Atlantic Ocean c the Red Sea
A4 sheet with tracing of Africa
overhead transparencies with plates, continents
3 Propose the likely positions of these cities in the future: a Darwin b Tokyo c Hong Kong d Los Angeles e Rome 4 Propose what you would expect to happen to the climate of New South Wales in the future. 5 Compare your maps with those produced by scientists by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button.
shift the sheets 1 cm in the directions of the arrows
126
UNIT
context
5. 2 The tectonic plates move at about the rate at which our fingernails grow. For this movement to continue, new crust must be made and old crust destroyed. All this action happens at the edges or boundaries of the plates and creates the basic landscape of our world, including its volcanoes and earthquakes.
• Collision boundaries are where one plate collides with another. These are destructive boundaries since rock is melted here and is returned to the mantle for recycling. • Transform or scraping boundaries are where plates scrape along each other. They are conservative boundaries since they conserve rock. They do not create or destroy it.
Plate boundaries
A broken scab: spreading plates
There are three types of plate boundaries: • Spreading boundaries are where plates move apart. They are also known as constructive boundaries since new rock is being made on the ocean floor.
Mapping of the ocean floor shows that some plates are moving apart at a rate of up to 20 cm a year. A weakened line (called a fault) in the crust causes a huge crack or rift valley to form and hot liquid magma forces its way up from the mantle to fill it.
North American plate
Eurasian plate
Caribbean plate Philippine plate
African plate
Cocos plate
Pacific plate
Indian–Australian plate
South American plate
N W
Nazca plate E
S collision boundaries spreading boundaries
movement not known transform boundaries
main movement directions
Tectonic plates and their boundaries: split, bang and scrape
Fig 5.2.1
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At the edges The magma cools and solidifies as it hits the water, and creates underwater mountain ranges like those observed in the Atlantic and Pacific Oceans. This is brand new oceanic lithosphere. Older rocks crack and are squeezed out of the way as more magma moves upwards. New magma then fills the crack and the process repeats itself. It’s like a wound: a scab begins to repair the wound but any stress cracks it, allowing blood to ooze again. The scab then needs to re-form. Most rift valleys are under water but a few are on the surface. The largest is the East African Rift Valley, which is filled in parts with lakes like Lake Victoria, and in other parts with huge volcanoes like Mt Kilimanjaro. Other rift valleys pass through the
Dead Sea (at 400 metres below sea level, the lowest point on Earth not under an ocean) and the Sea of Galilee (209 metres below sea level). This rift valley continues into the Red Sea, indicating that it will widen and become an ocean in the future. Fire and ice! Another rift valley is Although a relatively small island, Iceland gradually splitting Prac 1 produces more than p. 132 Iceland in two. one-fifth
of the total lava output from all volcanoes around the Earth! It is located on a spreading boundary and is where the Mid-Atlantic Ridge is exposed as land.
Sea of Galilee The Helgafjell volcano in Iceland began its life in 1973.
Fig 5.2.3
Going under: subduction zones
Dead Sea
Fig 5.2.2
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The Sea of Galilee, Dead Sea and Gulf of Aqaba all lie in a giant rift valley that joins with the Red Sea.
If new oceanic lithosphere is made at the mid-ocean ridges, where does the old material end up? As the oceanic plates move away from the mid-ocean ridges they collide with other oceanic plates or with continental plates. Continental plates can also hit other continental plates. Each collision creates something different. The rock of the oceanic plates is denser than the plates that the continents sit on. When they hit, the heavier oceanic plate is forced under the continental plate at an angle of 20° to 60° to the surface. This angled dive is called a subduction zone. Meanwhile the upper plate gets crushed, thickens and forms folded mountains along its edge. By the time the ocean plate has reached a depth of about 200 km it has melted and becomes part of the asthenosphere once more. Worksheet 5.3 Where are the ocean trenches?
Fig 5.2.4
Volcanoes and trenches come from collisions between an oceanic plate and a continental plate.
ocean trench
Going up: island chains If an oceanic plate hits another oceanic plate and their densities are the same, the fastest plate sinks in the collision. Once again a subduction zone is created. The upper plate gets thicker and volcanoes form, some of which push out of the water to form islands and island chains. Examples are the islands of Japan, Indonesia, the Philippines, the Caribbean and the Aleutians.
volcano
magma ocean plate
earthquakes
continental plate
subduction zone
The two plates do not slide easily over each other due to friction between them. When they do slip, it’s sudden and an earthquake results. The friction also generates heat, which produces magma along the top of the oceanic plate as it submerges. The magma will try to force its way back to the surface, perhaps to burst out as a ridge of volcanoes. The Andes Mountains were formed in this way. Parallel to them is the Peru–Chile trench. Ocean trenches form where the oceanic plate drops below the continental plate. Although some of these trenches are filled with sediment, many are incredibly deep.
ocean trench
Fig 5.2.5
island arc
subduction zone active volcano rising magma
ocean plate
Really deep!
Prac 2 p. 133
When an oceanic plate meets another oceanic plate, a chain of islands forms.
UNIT
5.2
The Mariana Trench in the western Pacific y was discovered in 1951 by the British surve of depth a With . ship Challenger 11 033 metres it is more than six times deeper than the Grand Canyon in the USA. Mt Everest could easily sit in it, leaving plenty of room for Mt Kosciusko to fit in as of well! In January 1960 Dr Jacques Piccard USA the of h Wals ld Switzerland and Lt Dona took the US Navy bathyscaphe Trieste to a depth of 10 915 metres in the trench.
ocean plate
earthquakes melting
Really big mountains When two continental plates collide, they crumple and fold. Intense heat from the collision also melts some rock and forms a solid ‘mountain root’ that resists weathering. The Himalayas are the tallest mountains on Earth, with Mt Everest the biggest at 8854 metres. These were formed when the plate that carries India collided head-on with the plate that carries the bulk of Asia.
Climb Mt Everest now!
No dinosaur ever climbed Mt Everest, because it did not exist when they were alive. The collision of plates is still happening and is raising the Himalayas about 1 cm a yea r. Current mountaineers now need to climb half a metre more than the first successful climbers, Sir Edmund Hillary and Tenzing Norgay, in 195 3. Every year the peak gets talle r, so don’t wait: do it now!
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At the edges Both plates have similar densities and neither can push the other underneath. Instead the plates crumple, fold and push up.
mountains
Plates that scrape Plates scrape along each other along a transform boundary. These don’t make mountains or volcanoes but do produce lots of earthquakes, some very strong. Although most of these boundaries are under water, some are on land. The most important of these is the San Andreas fault, which runs 1300 km through California USA, directly under San Francisco and close to Los Angeles. The coastline of California slips 5 cm along it every year, moving Los Angeles north and closer to San Francisco.
continental plate continental plate
Massive folded mountains form when continent collides with continent.
Fig 5.2.6
Worksheet 5.4 Where do quakes happen? Worksheet 5.5 Volcanoes: where are they?
UNIT
5.2
[ Questions ]
Checkpoint Plate boundaries 1 a Identify the three types of plate boundaries. b Describe what happens to the plates at each boundary.
A broken scab: spreading plates 2 A mid-ocean ridge can be compared to a scab. Explain why.
Fig 5.2.7
Going under: subduction zones 3 Describe what happens in a subduction zone. 4 Determine which is more likely to sink when the two hit each other. a the fast or the slow plate b the heavy or the light plate c the continental plate or the oceanic plate 5 The Himalayas have a ‘mountain root’. Explain what this means and how it formed.
Plates that scrape 6 Describe what occurs at a transform boundary.
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The San Andreas Fault has nearly separated Point Reyes from the rest of California. It is an example of a transform fault.
Think 7 Describe boundaries which: a are conservative b are destructive c are constructive d have subduction zones e form rift valleys f dive into the mantle g cause trenches h cause huge, folded mountains i have only sideways movement j form island chains k form mountains
8 Identify the type of boundary on which these places are situated: a Iceland b the San Andreas fault c Mt Everest d Mt Kilimanjaro e Lake Victoria f the Dead Sea 9 Illustrate the following with a labelled diagram. a spreading plate boundaries b oceanic plate meets continental plate c oceanic plate meets oceanic plate d continental plate meets continental plate e transform plate boundaries 10 Construct a four-frame cartoon to demonstrate the development of the: a Himalayas b Indonesian islands c Mid-Pacific Ridge d Andes 11 Identify the two plates that created the: a Himalayas b Andes c Mid-Atlantic Ridge d Caribbean islands e Japan f Mariana Trench g San Andreas fault h Dead Sea 12 A plate often gets thicker when another plate is forced under it. Explain why.
Skills 13 a The Himalayas are growing about 1 cm per year. Calculate how much they will grow in an average lifetime. b Calculate how long it will take for them to grow a further: i 10 m ii 100 m iii 1 km
UNIT
5.2 [ Extension ] Investigate 1 Using an atlas, locate the following places and information on the map. a East African Rift. Use the map to find the geological features that lie on it. b Jordan Rift Valley. Find what lies along it and what connects it with the East African Rift. c Iceland. Find information about its eruptions and earthquakes, and how Icelanders make use of its volcanic nature. d The island chains that make up Japan, Indonesia, the Philippines, the Caribbean and the Aleutians. 2 ‘Black smokers’ are found on mid-ocean trenches. Find out what they are.
Surf 3 Explore animations of colliding plates by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button.
Creative writing Tell them where to stick it! A new type of power station has been developed: only ten are needed to supply all the electricity needs of the whole world! But they are safe only if they are not disturbed. The United Nations will build them but it needs your advice about where to put them. No more than two can be located on any one continent, and they must be close to large population centres. You must be convincing, because California, Japan, Iceland, Indonesia and New Zealand all want them. Give reasons for your ten choices.
14 Currently the Red Sea is about 240 km wide and widening at about 20 cm per year. Calculate the time it will take for it to become the same width as the: a Mediterranean Sea (about 500 km) b Atlantic Ocean (6100 km) c Pacific Ocean (14 000 km)
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At the edges
UNIT
5.2
[ Practical activities ] Plates that separate
Prac 1 Unit 5.2
Aim To model the mid-ocean spreading of tectonic plates Equipment A3 sheet of paper, coloured pencils or highlighters, scissors, sticky tape, pegs tape
Method 1 Push two desks together. 2 Cut the sheet of paper lengthwise and tape the pieces together to make a long strip.
colour each 5 cm strip as it emerges peg
peg
3 Fold and push both free ends of the paper up through the gap between the desks. 4 As the paper emerges from the gap, brush it down with your hand so that the paper follows the bench top. 5 As each 5 cm emerges, colour or decorate each new strip of paper.
push paper up
Modelling spreading plates
Fig. 5.2.8
Questions 1 Explain how this activity relates to the spreading at the mid-ocean ridges. 2 Identify what in your model represents each of the following: a ocean floor or plate b the water c the lava flow d gravity e mid-ocean ridge f the magnetic strips found in rocks parallel to the mid-ocean ridges
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3 Describe what you noticed about the height of the paper as it emerged from the gap compared to the paper further out. 4 Identify which of the strips you coloured would be the ‘oldest’ rock and which the ‘youngest’ rock. 5 Identify which of these strips would be the first to be ‘swallowed’ by an ocean trench.
UNIT
5.2 Colliding plates Prac 2 Unit 5.2
Aim To model what happens when two tectonic plates collide Equipment A stack of about 30 A4 pages (recycle: use scrap paper!), textbook
Method 1 Split the stack of A4 paper into two smaller stacks of about fifteen sheets each. 2 Place each on the desk and slide them slowly into one another.
3 Observe what happens to the layers as they collide. Repeat four times to confirm your observations. Sketch what usually happened. 4 Now hold the end of one stack to keep it still. Push the other stack into it. Observe which layer climbs on top of the other. Repeat for confirmation and draw what happened. 5 Finally, place a textbook on the desk and push a stack of thirty sheets into it. Observe which goes under.
Questions 1 Compare the above tests with plate tectonics. 2 The stack of paper had obvious layers. Assess whether rock has layers, and if so explain why.
Test 1
Test 2 keep this stack still
Test 3
Fig 5.2.9
3 State which tests simulated the following collisions. a a continental plate with another continental plate b an oceanic plate with another oceanic plate c an oceanic plate with a continental plate 4 Identify a place on Earth where each of these collision types occurs.
Modelling plate collisions
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UNIT
context
5. 3 We have seen that tectonic plates separate, collide and scrape over each other. None of this movement is smooth, because the plates must build pressure to overcome the incredible friction forces that causes them to ‘stick’. The plates are constantly trying to move, so the release of pressure is frequent. More than one million earthquakes occur per year, although most are so small or so remote that they are not noticed and cause little damage.
Now imagine bending a branch. It bends fairly easily up to a point, then suddenly snaps. The vibrations you feel through your hands are the release of the stored energy in the branch. This is what happens with an earthquake. The pressure release is sudden, explosive and often catastrophic. Major earthquakes can destroy buildings, roads, services and lives. In the process they also devastate the community they hit, making many homeless and destroying the economic structure of the community.
The epicentre is the point on the Earth’s surface that is directly above the focus and will suffer the most damage.
epicentre focus
R and L waves (surface waves) surface of earth
P and S waves (body waves) Fig 5.3.1
Damage caused by the 1989 Newcastle earthquake
Focus and epicentre The focus of an earthquake is the point where it begins. It is where the plates slip and is on a fault line usually at the plate edges. The focus can be very close to the surface or can be as deep as 200 km, the depth at which the oceanic plate finally melts into the asthenosphere. The size of an earthquake does not depend on the focus depth.
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Fleas cause earthquakes! In the earthquake-prone Kamchatka peninsula in Siberia, an old tale has the god Tuli riding with the Earth on a sled being pulled by flea-ridden dogs. When they stop and scratch, the Earth shakes!
The focus is where the earthquake starts. Seismic waves spread from here to the epicentre and beyond.
Fig 5.3.2
Seismic waves Earthquakes release energy in the form of vibrations, called seismic waves, which travel through and around Earth. An instrument called a seismometer detects all these waves. The recorded seismograph gives the time delay of the arrival of each different wave type as well as an indication of their energy.
behave in the up-down motion of water waves that we are used to. Sound is another example of a longitudinal wave. P waves can travel through both solid and liquid rock and subject the rocks to an alternating push-pull motion, hitting the surface with an P waves up-and-down motion. P and S begin S waves waves S waves are slower than P and are arriving surface arrive waves the next to be recorded. They are arrive transverse waves and have an up-down P and S and surface waves time movement just like water waves. S waves travel only through solid rock. A typical seismograph, showing P, S and Fig 5.3.3 Molten rock blocks them. S waves hit the surface with surface waves a shaking or side-to-side motion. The greater the energy, the higher the amplitude (width of the squiggle) of the trace on the seismogram. Seismic waves can be split into two categories: The speeds of P and S waves depend on what they • body waves—these travel through the body of the are travelling through. The denser the rock, the faster Earth and can be either primary (P) or they go. The waves change speed as they pass into secondary (S) rock of different density, and also change direction. • surface waves—these travel on the This is called refraction and happens to all types of surface of the Earth and are either Prac 1 waves as they change speed on passing from one p. 141 Rayleigh (R) or Love (L). material to another. Water waves do it and so do light and sound waves. When an earthquake happens, The Earth’s surface is seismometers around the world record pushed and pulled. all the waves that reach them. When all the seismographs are analysed, a The Earth’s pattern showing the spread of waves surface is is produced. shaken.
UNIT
5.3
Earthquake shadows
rock vibration
movement of primary wave
rock vibration movement of secondary wave
A longitudinal or compression wave
Fig 5.3.4
A transverse wave
Deliberately creating earthquakes Geologists searching for minerals and fossil fuels often create ‘mini-earthquakes’ with explosives. A seismograph shows the shock waves produced and gives information on thickness, density and position of different rock layers. This will hopefully pinpoint materials worth mining.
Body waves: P and S
Body waves Primary waves move fastest and are the first to be recorded. They are an example of longitudinal or compression waves that push and pull and do not
The bending of the waves and the fact that S waves will not travel through liquids causes some seismographs to record different combinations of body waves. Figure 5.3.5 shows how this happens.
Prac 2 p. 142
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Earthquakes • There is an area directly opposite the epicentre of an earthquake where S waves are not recorded. The outer core is blocking the S waves. Why? It must be liquid rock since S waves cannot travel through liquid. • The paths of S and P waves are not straight. They are bent or refracted by the changes in density and temperature of the different layers of the Earth. This causes two ‘shadow zones’, as shown in Figure 5.3.5, where neither P nor S waves are recorded. Refraction of P and S waves and ‘shadows’ where they do not arrive epicentre of quake
Fig 5.3.5
both P and S waves arrive
shadow zone— no P or S waves
The graph in Figure 5.3.6 indicates that if the S wave arrives 8.6 minutes after the P wave, the epicentre is 7000 km away. Worksheet 5.6 Earthquake epicentres
For an exact location, seismometer readings need to be gathered from three different locations. By subtracting the time of arrival of the P wave from the time of the S wave, the time difference can be found. The distance from each seismometer to the epicentre is found by using the graph in Figure 5.3.6. Circles can then be drawn from the location of each seismometer using this distance as the radius. The epicentre is where the three circles intersect. Prac 3 p. 142
P waves only— no S waves
An old tale has the Moon made from green cheese. Moon rock brought back from the Apollo missions of the 1970s looks like rock but it does have some cheese-like properties! Speeds of seismic waves in moon rock range from 1.2 km/s to 1.84 km/s, comparing well with those found in cheese: Muenster cheese has the lowest seismic speed at 1.57 km/s and Swiss cheese has the highest at 2.12 km/s. In contrast, Earth rocks have speeds of 4.9 km/s to 5.9 km/s.
Locating the epicentre: Newcastle is hit.
Fig 5.3.7 both P and S waves arrive
A cheesy moon?
shadow zone— no P or S waves Adelaide
h min s 10:32:09 P 10:31:45
10:34:15 S 10:33:25
Melbourne
Finding the epicentre
Brisbane
P and S waves arrive at seismometers at different times. Their speeds are well known and the distance from the epicentre can be calculated from the difference in time between their arrivals.
Distance from earthquake (kilometres)
Fig 5.3.6
136
Brisbane
10:32:16
Newcastle Sydney
Adelaide
The difference between the arrival times of P and S waves tells us how far away the earthquake is. 0
8000
10:31:06
500 km
Melbourne
7000 6000
Surface waves
5000 4000 3000 2000 1000 0 0
8.6 minutes 2 4 6 8 10 Difference in arrival times of P and S waves (minutes)
Rayleigh (R) and Love (L) waves travel around the Earth, not through it. They have further to go than P and S waves and arrive after them. They are more dangerous than P and S waves, however, because their effect on the surface is more severe. Their energy radiates from the epicentre like ripples on a pond from where a stone has been dropped.
R waves are rolling waves, like breakers at a surf beach. They are the slowest but often the largest and most destructive. L waves are the fastest surface wave and have a side-to-side motion, like a moving snake. Figure 5.3.8 shows the dramatic effects of R and L surface waves. Fig 5.3.8
Rayleigh and Love waves are very dangerous and travel across the surface.
in the size of the earthquake and a 30 times increase in the energy released by it. This means that an earthquake of magnitude 8 is ten times the size of an earthquake of magnitude 7 and has thirty times its energy. Any earthquake above 7 on the Richter scale must be considered dangerous since major damage can be expected. Luckily, such serious earthquakes are rare. Fig 5.3.9
The location of major Australian earthquakes
Rayleigh wave
UNIT
5.3
Darwin 1979 1929
1964 1978
1906
1970
Alice Springs Bundaberg Simpson Desert 1972 1938 1918 Gayndah 1873 1937 1941 1935 Meeberrie 1941 Brisbane Geraldton 1885 Cadoux 1979 Picton Newcastle Adelaide Perth Meckering 1968 1989 1973 1954 Warooka 1902 Sydney Dalton Canberra 1949 Beachport 1897 Berridale 1959 1920 Melbourne Warnambool 1903
Carnarvon 1965
Love wave
Hobart
Worksheet 5.7 Comparing P and S waves
Measuring earthquakes Richter and Mercalli Scientists can use seismographs to estimate the energy of an earthquake at its epicentre. An earthquake’s strength is measured on a scale devised by American Charles Richter in 1935. It is an open-ended scale that starts at 0. No known earthquake has ever exceeded 9 on the scale. On the Richter scale an increase of one unit represents a 10 times increase
The Richter scale gives no indication of the damage caused by an earthquake. Damage depends on the The worst ever location of the epicentre, Earthquakes were first environment of the region, recorded in China around 1000 BC. density of population, The most devastating construction and design of the happened in 1556 at buildings and the length of Hsian where most of the people had dug time of the earthquake. The cave-like homes into Mercalli scale gives a better the hills. These indication of the earthquake’s collapsed, burying them alive. Landslides, floods, effects because it is based on lakes, famine and actual observations. Guiseppe disease claimed more. Mercalli developed the A total of 830 000 are Mercalli scale in the 1890s thought to have died. before seismometers were in use. It measures the intensity of the earthquake rather than its magnitude. Worksheet 5.8 The Mercalli earthquake scale
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Earthquakes a
Richter 2–3 Mercalli I–II
Fig 5.3.10
b
Richter 4–5 Mercalli IV–V
c
Richter 5–6 Mercalli VI
d
Richter 6–7 Mercalli VII–VIII
Richter 7–8 Mercalli IX–X
Earthquake damage levels a Very feeble—noticed only by sensitive people b Moderate—felt by people who are moving about c Strong—slight damage to buildings d Destructive—chimneys fall e Disastrous—many buildings are destroyed
Damage caused
Richter Mercalli
Average number per year
Felt by seismographs only
1–2
I
More than 500 000
Felt by very few people
2–3
I–II
100 000 to 500 000
Felt by people in tall buildings; hanging objects swing, some damage
3–4
II–III
10 000 to 100 000
Felt and heard by most; parked cars rock, crockery rattles, walls crack
4–5
IV–V
1000 to 10 000
Felt by all; some panic, furniture moves, difficult to walk
5–6
VI
200 to 1000
Some panic, difficult to stand; chimneys and some buildings collapse; cracks in the ground
6–7
VII–VIII
20 to 200
General panic; deep cracks in the ground, most buildings collapse, rail lines twist, dams break
7–8
IX–X
10 to 20
Total destruction; few buildings survive, valleys fill with mud from landslides and flood
8–9
XI–XII
0 to 10
In 1906 San Francisco was hit by a earthquake estimated at 8.3 on the Richter scale. Sixty per cent of the damaged city (520 city blocks!) was then burnt to the ground in the days that followed.
Tsunami
Other earthquake nasties Aftershocks Large earthquakes have the power to move large slabs of crust and rock around. These slabs take some time to settle and cause smaller earthquakes called aftershocks. Although these are usually smaller than the first earthquake, they can be extremely dangerous, particularly if buildings were made unstable by the first earthquake.
Fire Gas pipes can easily be broken in an earthquake. One spark or flame can turn the wreckage of a large earthquake into a furnace.
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e
Animals predicting earthquakes? In China in 1975, animals began to act strangely. Snakes left their burrows as if in fear and dogs barked wildly at nothing. Authorities thought the animals could sense an earthquake approaching. They warned that a major earthquake would occur in the next six months. Townsfolk were evacuated to the country. Soon after, an earthquake did occur, but because of the precautions few died. Another earthquake struck two years later, killing 240 000 people. Would you trust the animals?
An earthquake with its epicentre under the ocean floor can cause a wave to be formed. Although it may start at only 2 metres high, it travels at incredible speeds and increases dramatically in height as it enters shallow water. This wave is called a tsunami (pronounced soon-army). Tsunamis can travel at 800 km/h and reach heights of 35 metres when they hit land, crashing onto the shore and sweeping everything out of their path. People in low-lying areas receive little warning because the first waves caused by the earthquake are no bigger than normal surf. The first real warning is that water rapidly gets sucked out to sea, with the main wave crashing in soon after. The sea can then die down. Survivors often move in to help search for victims and can be swept away by another large wave that follows up to an hour later.
In 1998 an underwater earthquake of 7 on the Richter scale caused a 15-metre high wave to hit the north coast of Papua New Guinea, killing an estimated 3000 people. On an even larger scale, a tsunami which hit Japan in 1892 killed 27 000 people.
Fig 5.3.12
The number of hours taken for the 1964 Alaskan tsunami to cross the Pacific Ocean
safe area Japan safe area
Australia
UNIT
5.3
safe area
New Zealand
Alaska 1 Canada 2 3 4 USA 5 6 Mexico 7 8 9 10 South 11 America 12 13 14 15 16 17 18 19 20
Worksheet 5.9 Earthquake statistics
Fig 5.3.11
UNIT
5.3
Damage in the sea port due to the 1964 Alaskan tsunami
Worksheet 5.10 Tsunami statistics
[ Questions ]
Checkpoint Focus and epicentre 1 Explain why friction exists at plate boundaries. 2 Use friction to explain what causes an earthquake.
Seismic waves 3 Identify the main types of seismic waves.
Body waves 4 Identify examples of: a a longitudinal wave b a transverse wave
Earthquake shadows 5 Define the term ‘refraction’. 6 Describe what causes refraction of P and S waves. 7 Outline the evidence that suggests that the Earth’s core is liquid.
Finding the epicentre 8 Distinguish between the epicentre and the focus of an earthquake. 9 Identify the maximum depth the focus can be below the surface.
Surface waves 10 a Contrast L waves and R waves. b Draw diagrams to demonstrate the action of L and R waves.
Measuring earthquakes 11 List two reasons why most earthquakes are not felt. 12 At what value on the Richter scale would you call an earthquake ‘serious’? Explain why you chose this number.
Other earthquake nasties 13 Describe what aftershocks are and what causes them. 14 Aftershocks are often more dangerous than the first earthquake. Explain why this is the case. 15 Explain what causes a tsunami to form. 16 There are almost no video or photographs anywhere of tsunamis. Propose an explanation for this.
Think 17 Australia has few earthquakes, yet our neighbours Papua New Guinea and New Zealand have lots. Use the Theory of Plate Tectonics to explain why.
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Earthquakes
Analyse
18 Distinguish between: a body and surface waves b a longitudinal and a transverse wave 19 Determine which of the seismic waves, P, S, R or L: a are the most dangerous b are up-down waves c are compression waves d pass through the Earth e are the fastest f are the last to arrive g are like surf h travel like a snake i cannot travel through liquid 20 Copy the following and modify any incorrect statements so they become true. a Aftershocks are huge waves caused by earthquakes. b An earthquake of strength 5 on the Richter scale is double the strength of a 4. c Earthquakes are caused by plates slipping. d The focus of an earthquake is the exact point where an earthquake starts. e Tsunamis are huge when in deep water. 21 A tremor is an earthquake that can be felt but does little damage. State what its value would probably be on both the Richter and Mercalli scales. 22 Superquakes are ones that are more than 8 on the Richter scale. a Evaluate the damage that can be expected when superquakes hit b State how often they occur per year. 23 Illustrate the damage that can be expected for each level of the Mercalli and the Richter scales with a series of sketches.
Arrival time of P waves (h:min:s)
Arrival time of S waves (h:min:s)
10:24:00
10:32:00
04:48:20
04:52:50
2:55:21
3:01:21
7:37:03
7.42:33
14:08:34
14:11:46
20:21:02
20:25:50
24 Illustrate what happens to a slinky spring if the following waves move down it: a longitudinal wave b transverse wave 25 Calculate the distance from the epicentre if the time between the P and S waves arriving is: a 4.0 minutes b 2.2 minutes c 3.5 minutes d 8.1 minutes 26 Explain where you would need to be for the P and S waves to arrive at the same time. 27 Explain what a single seismograph tells us about an earthquake. 28 Calculate the length of time between the arrival of the P and S waves if the epicentre is this far away: a 6000 km c 3300 km b 1500 km d 900 km 29 Demonstrate with a diagram how S waves change an up-down movement in the rock into a side-to-side movement of the surface.
Skills 30 Complete the information about a number of earthquakes given in the table below. To calculate column 4, convert the seconds into a decimal by dividing by 60.
Time difference (min:s)
Time (min)
4:30
30 ÷ 60 = 0.5 so time is 4.5 min
05:45:10 11:34:30
140
Distance of epicentre (km)
5.0 6:30
08:12:56
2500
15:21:04
5800
[ Extension ]
b Japanese traditional architecture is designed to withstand frequent earthquakes. Investigate why this type of architecture is ideal for an earthquake-prone country.
Investigate 1 The most devastating earthquake in recent times in Australia was in Newcastle, NSW in 1989. Imagine you were part of a team of analysts called in after the earthquake to assess the area. Present your findings about its strength, damage and injury/death toll in an official written report to be sent to the government. 2 a In groups, research how engineers and architects design buildings to withstand earthquakes.
UNIT
5. 3
UNIT
5.3 3 Examine what you should do if an earthquake hits. Present your findings in an illustrated poster.
Surf 4 Explore animations of seismic activities and pictures of earthquake zones by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools , selecting chapter 5 and clicking on the destinations button.
[ Practical activities ]
Making waves
Fig 5.3.13
Slinky springs Prac 1 Unit 5.3
Aim To model the movement of P and S waves
move hand side to side
Equipment
waves
paper
Slinky spring, dense smaller-diameter slinky, string, paper, sticky tape
keep hand stationary
Method 1 Tape a small piece of paper to the slinky. PART A: Transverse waves 1 Lie the slinky along the floor. Hold the spring at both ends, stretching it lightly. One person should hold their end still at all times.
stick small sheet of paper to spring
move hand in and out waves
2 Move one end sideways so that a ripple-like wave moves down the spring.
spring
3 Construct a diagram showing the movement of the paper and in which direction it moves down the spring.
paper
keep hand stationary
4 Test bigger and smaller waves. Compare their speeds and ‘height’ or amplitude. PART B: Longitudinal waves 1 Quickly move one end of the spring in and out about 30 cm. A compression should move down the spring. Describe what happened to the paper. PART C: Waves in different densities 1 Attach the heavy, smaller slinky to the bigger one and repeat the above experiments. Compare your observations on speed and size when the wave travels from big to small diameters and vice versa. 2 Repeat, but attach a piece of string instead of the smaller-diameter spring.
Questions 1 Identify the direction of movement of the paper in the slinky when: a a transverse moved along it b a longitudinal wave moved along it 2 Imagine you are an ant standing on the piece of paper in each case. Describe what you would feel. 3 Identify which part of the experiment (A, B or C) best represents: a a P wave b an S wave c an L wave
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Earthquakes
Building a seismometer Aim To construct a working model of a seismometer Prac 2 Unit 5.3
Equipment Retort stands, bossheads and clamps, springs, heavy weight, adhesive tape, felt pen
spring
paper
Method 1 Construct the contraption shown in Figure 5.3.14. 2 Slowly pull the paper while creating ‘earthquakes’ by thumping the bench on top and at the end.
weight
Questions
tape felt pen touching paper
1 Identify which movements caused the seismographs to work. 2 Explain why the graph didn’t stop after the earthquake did.
Fig 5.3.14
Locating the epicentre
Modelling a seismograph
Aim To locate the epicentre of an earthquake Prac 3 Unit 5.3
Equipment
5 The epicentre is the point or small area where the circles intersect.
Compass, ruler, photocopy of worksheet 5.11 Worksheet 5.11 Locating the epicentre
Questions
Method
1 Locate the epicentre of the earthquake.
1 Calculate the difference in time between the arrival of the P and S waves for each seismograph.
2 Locate its focus.
2 Use the graphs in Figure 5.3.6 to find the distance the epicentre is away from each location.
3 Calculate the time between the arrival of the P and S waves in Broome.
3 Paste the photocopy supplied into your workbook.
4 Check an atlas to locate the town most likely to be affected by the earthquake.
4 Use a compass to draw three circles on it with radii equivalent to these distances.
Find the epicentre.
15:06:47
Cairns
Broome
15:07:41
Alice Springs Brisbane
h min s 15:13:11 P
Perth 15:17:47
Adelaide
S
0
142
1000 km
Sydney Canberra Melbourne 15:10:37
Hobart
15:13:49
Fig 5.3.15
UNIT
context
5. 4 What could cause a noise so loud that it could be heard clearly 5000 km away and was painful to people 50 km from it? What could completely destroy an island and produce waves 40 metres high that would travel inland for 16 km and kill 36 000 people?
The cause of this disaster was a small volcanic island called Krakatoa, located west of Java. It erupted in 1883 and caused the largest explosion ever experienced in the recorded history of humans.
Mt St Helens in the USA was dormant for 123 years until it erupted violently in 1980, blowing 400 metres off its top and killing 57 people.
In the 120 years since Krakatoa destroyed itself, pressure from below has steadily built a new island of Krakatoa. The new island (pictured here) has small, regular eruptions.
Fig 5.4.1
Volcanoes everywhere Dead or alive? All volcanoes can be classified as either active or dormant. Active volcanoes erupt regularly. Dormant volcanoes are ‘sleeping’—volcanic activity is still present but they have lasted 20–5000 years without an eruption. Dead volcanoes are those that cannot erupt. They are often classified as extinct and have had no eruptions for the last 25 000 years.
There are about 1500 potentially active volcanoes around the world with some erupting each day. Eruptions are often not noticed, however, as many of these active volcanoes lie under water, their eruptions producing about three-quarters of the total lava erupting from volcanoes each year. There are no active volcanoes in Australia. Mt Gambier in South Australia last erupted about 4600 years ago and can probably be said to be extinct. A long period of inactivity does not always mean that a volcano is extinct, however:
The ash cloud from the 1980 eruption of Mt St Helens, USA. The Mt St Helens blast ripped the trees from all the surrounding hills and devastated more than 400 square kilometres.
Fig 5.4.2
Just like a pimple! Most volcanoes occur at the edges of Volcanoes in space At 24 km high and with a the tectonic plates. Pressure from gases base spanning a distance in the mantle squeezes the molten rock equal to that from Sydney upwards. The surface of the Earth can to Melbourne, the largest swell like a big pimple until it cannot volcano in the solar system so far found is take any more pressure. It then Olympus Mons on Mars. explodes with lava, ash and steam bursting through the surface. Eruptions may come from a single vent, or from a group of vents. Others take place from long cracks called fissures. Worksheet 5.12 Volcano
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Volcanoes
Colour of lava
Temperature
White
Above 1150°C
Yellow
1000–1150°C
Orange
900–1000°C
Red
500–900°C
Black
Less than 500°C
Volcanic material
Fig 5.4.3
Hot lava and ash spurts from this erupting volcano. You can use the table at right to determine the temperature of the lava.
Most volcanoes just release clouds of steam, gas (called fume) and ‘smoke’, which is actually made up of fine rock dust or ash and rock. Magma is molten rock that forms in a magma chamber deep under the surface. A cutaway view of a volcano showing various volcanic material during an eruption.
dust, ash, steam and gases
volcanic bombs lava central vent layers of lava and ash from past eruptions side vent
Earth’s crust Earth’s crust
magma chamber
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Fig 5.4.4
Lava flowing from a volcano
Fig 5.4.5
It is lighter than the surrounding rock because it is full of gas. The pressure pushes it up until it bursts out from a vent. What emerges is called lava. This is made up of magma and gases such as hydrogen sulfide (rotten egg gas) and steam. Lava flows down the volcano at speeds of less than 10 km/h and will later cool to form solid rock. Hot volcanic ash, steam and gases form a fast-moving (often 200 km/h) cloud that can reach incredible heights. Krakatoa’s cloud is estimated to have reached a height of 80 km! The ash is carried by the winds and eventually settles back to Earth as a thick blanket. The ash from the 1994 eruption of Mt Tavurvur in Papua New Guinea crushed the nearby town of Rabaul. In 79 AD the people of Pompeii, Italy, suffocated on the ash from Mt Vesuvius and were then buried by it! Ash from Mt St Helens landed up Unexpected to 500 km away. turbulence Rain often then turns the ash into a lahar, a river of mud that can devastate anything downstream from it. Volcanic ash can also travel the planet in the jet-stream winds that exist 30 km up. Here the ash blocks the Sun, making the planet cooler and producing spectacular sunsets. Ash from the 1991 eruption of
UNIT
5. 4
In 1982 a British Airways Boeing 747 en route from Kuala Lumpur to Perth flew through an ash cloud from the eruption of Mt Galunggung in Java. The dust jammed all four engines and the aircraft dropped without any power for many minutes before they could be re-started. Volcanic ash is not visible to radar so the pilots had little warning.
Fig 5.4.6
Ash from Mt Pinatubo in the Phillipines blocked the Sun for many days in 1991.
Mt Pinatubo in the Philippines is thought to have blocked 4% of the sunlight reaching Earth that year and the dust from Krakatoa changed the colour of the sky in England, 10 000 km away! Gas explosions can destroy parts of the volcano itself, with large pieces blown out as solid rock, called volcanic bombs. Volcanic bombs also form when hot lava is thrown into the air, landing great distances from the crater. The rock can also block the vent until the gases build enough pressure to clear it once Prac 1 more with another large p. 147 explosion.
Why live next door to a volcano? Across the world about 500 million people live uncomfortably close to active volcanoes. Why? Volcanic materials break down to form some of the most fertile soil on Earth and farming it can give good crops with plenty to eat and market. Living near an active volcano is obviously risky but it is often the only livelihood available. For this reason vulcanologists are constantly trying to to predict future eruptions of the world’s active volcanoes.
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Volcanoes
UNIT
5. 4
[ Questions ]
Checkpoint Volcanoes everywhere 1 State the number of volcanoes in the world and how many of them are active. 2 State what Krakatoa was, is now, and why it is famous. 3 Explain why erupting volcanoes are sometimes not able to be seen. 4 State the location of an Australian volcano that is probably extinct.
Just like a pimple! 5 Distinguish between a fissure and a vent. 6 Explain why volcanoes are more likely to be found at the edges of tectonic plates than in the middle of them.
Volcanic material 7 Identify five different volcanic products. 8 a Explain why volcanic ash clouds rise. b Identify three different situations in which volcanic ash can be dangerous. 9 Define the following terms: a lava d fume b the magma chamber e jet stream c lahar 10 Identify what a volcanic bomb is and three ways it can form.
Think 11 Copy the following and modify any incorrect statements so they become true. a Lava is not the same as magma. b A dormant volcano is a live volcano. c Volcanic ash moves more slowly than lava. d White lava is hotter than red. e Ash clouds do not travel far. 12 Identify what causes the smell that is always around volcanoes and hot springs. 13 The edge around the Pacific is often called the ‘Ring of Fire’. Propose a reason for this. 14 Justify why volcanic areas are also areas of great earthquake activity. 15 The sound of the Krakatoa explosion took four hours to travel 5000 km across the Indian Ocean. From this information calculate the speed of sound. (Remember: speed = distance/time.)
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[ Extension ] Investigate 1 Examine where Krakatoa (or Pulau Rakata) is located. On a copy of the map, draw the 5000 km radius circle in which its eruption could be heard. 2 The word ‘volcano’ comes from the Roman god Vulcan. Research some information about him and where he was supposed to live. 3 Use a scale of 1 cm : 1000 m to construct a diagram of: a Centrepoint tower (305 m) b Mt Everest (8848 m) c the ash cloud of Krakatoa d the height at which commercial aircraft fly (10 000 m) Hint: You will not be able to do this in your workbook! 4 Construct a time line of major eruptions in the last century. 5 Research one major volcanic eruption. Imagine yourself as a reporter and present your findings in a newspaper article. Try to find: a the date of the eruption b what warnings there were that an eruption was coming c the type of volcanic products the volcano expelled d the damage it caused
Surf 6 Explore photos and information about volcanic eruptions by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button.
Creative writing Mt Bigbang Mt Bigbang is going to erupt in the next day or two. You are a seismologist who is to make a speech to a group of technicians staying in the area of Mt Bigbang to monitor the eruption. Your speech must explain to them what: a dangers they may encounter b volcanic products might be coming their way c precautions they should take.
UNIT
5. 4
[ Practical activity ] Volcanic clouds
Method
Aim To investigate the formation of volcanic Prac 1 Unit 5.4
UNIT
5. 4
clouds
1 Three-quarter fill the large beaker or container with cold water. 2 Put 2–3 drops of food dye in the 100 mL flask.
Equipment Large beaker, pneumatic trough or transparent jar, 100 mL flask, rubber stopper with hole, food dye Modelling hot volcanic ash rising
Fig 5.4.7
pneumatic trough or large beaker
3 Fill the flask to the very top with hot water (the hotter the better, but take care). 4 Seal the flask with the stopper. 5 Place your finger over the hole and lower the flask carefully into the container of cold water until it is completely submerged. 6 Carefully remove your finger and observe the motion of the hot coloured water.
Questions 1 Construct a diagram of what you saw.
cold water hot green coloured water
2 State whether hot water rises or falls when it mixes with cold water. 3 Identify what the coloured and clear waters represent in this model of a volcano. 4 Predict what you think would happen when hot ash from a volcano mixes with cold air. 5 Propose a likely reason why this happens.
Volcanic activity
Fig 5.4.8
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UNIT
context
5. 5 The crust is built up in layers. The oldest rock is the deepest and the youngest rock and sediment from erosion are on the very top. These layers were originally flat and horizontal but have since been cracked and
folded by plate movement and punctured by volcanoes. Weathering and erosion further shape the landscape to form the land we live on today.
Normal and reverse faults
Faulty landscaping! Faults are fractures in the Earth’s crust caused by the extreme forces from the slow movement of rock in the asthenosphere. Faults can be: • normal • reverse • transcurrent.
These faults are roughly vertical and are formed by forces pulling the crust apart (normal fault) or by compressing the crust (reverse fault). Movement along them is roughly up-down, creating a fault scarp. If the rock is hard and weathering slow, a cliff will form. If the rock is soft, erosion will wear it down to a gentle rise. Fig 5.5.2
Faults are fractures along lines of weakness in the Earth’s crust. The arrows show likely movement.
Normal faults can erode into different landscapes depending on how hard the rock is.
Fig 5.5.1
hard rock
normal fault
soft rock
reverse fault
transcurrent fault
148
Sometimes two faults allow a block of rock to thrust up to form a horst or sink down to form graben or rift valleys. The Spencer and St Vincent gulfs in South Australia are examples of horst and graben (in these cases filled with water). Erosion sometimes moulds them into parallel mountain ranges, as seen in Figure 5.5.3.
horst horst
graben
to buckle and fold without breaking (scientists call this plastic behaviour). It can be folded to build mountain ranges or hills. The folded rock can form an arch (called an anticline) or a trough (a syncline) or may even fold over another fold (an overfold).
weathers to
graben graben
Fig 5.5.3
UNIT
5.5
Horsts and graben are blocks of rock with faults on two sides. The rocks of the European alps have undergone intense folding due to the collision of continental plates.
Transcurrent faults These faults are horizontal and movement along them is in a sideways direction. No mountains are formed but the movement shatters rock along the fault. Smaller rock is easier to weather than larger rock, so heavy erosion creates troughs that often fill with water to form lakes and inlets.
Fig 5.5.5
Loch Ness
anticline
overfold
syncline A transcurrent fault nearly splits Scotland in two. It is partly filled with water and includes the very deep and mysterious lake, Loch Ness.
Fig 5.5.4
Folding When continental plates collide, the rock of the Earth’s crust is subjected to extreme pressure both horizontally and vertically. Under these conditions rock acts like plasticine and begins
Fig 5.5.6
Synclines, anticlines and overfolds can occur when rock buckles under intense pressure and high temperature.
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Landscaping the crust Erosion can wear away exposed soft rock or can level the folded layers. When new sediments are laid down on top of these old and eroded folds, an unconformity is created, as shown Prac 1 p. 154 in Figure 5.5.7.
Fig 5.5.7
On edge! Uluru (formerly known as Ayres Rock) is the massive tip of a fold formed when layers of sandstone were folded 300 million years ago. The folding was so severe that the layers are 80° to the horizontal.
Cinder cones are very common and relatively small, rarely exceeding 300 metres in height. These are piles of hot rock and cinders that spewed out of the vent, only to fall back around it.
Erosion exposes layers of folded rock and allows new layers to be laid on top.
erosion of folds
Mt Kilauea in Hawaii is a cinder cone. The helicopter gives an idea of the size of the volcano and the lava flow. new rock unconformity old rock
Volcanic landscapes
Tourist drives to top of world’s tallest mountain! Mauna Loa on the island of Hawaii rises 9169 metres directly from the ocean floor and thus is a much higher mountain than Mt Everest at 8848 metres. Only 4169 metres of Mauna Loa is above water, however, and it has a road all the way to the top!
Volcanic mountains can be built in three different ways. The biggest form well away from the boundaries of the tectonic plates and are what vulcanologists call shield cones. These get bigger every time an eruption takes place, with lava cooling as it slowly slides down its sides. The slopes are very gentle and the volcano resembles a shield lying on the ground. Their eruptions are rarely life threatening but large lava flows do destroy property and agricultural lands. Mauna Loa on Hawaii is an active shield volcano.
Volcanoes formed above the subduction zones at the edges of tectonic plates are called composite cones. These erupt with explosive force because the magma is too thick to allow the easy escape of volcanic gases. It’s like putting your thumb over an opened bottle of soft drink and shaking it. The release of the magma is the same—violent and messy. They include the ‘typical’ volcanoes of Mt Fuji (Japan), Mt St Helens (USA) and Prac 2 Mt Vesuvius (Italy). p. 155
Mt Fuji, a composite volcano
150
Fig 5.5.8
Blacksmiths make lava! In ancient Greece it was thought that the god of fire, Hephaestus, lived under Mt Etna in Sicily. Here he made weapons for the gods. When he hammered the red-hot iron, fire flicked out of the volcano above. The ancient Romans had their god Vulcan living under the island of Vulcano.
Fig 5.5.9
Plugs and other intrusions Magma is filled with gases and will always try to force its way up. Sometimes it breaks the surface to explode from a volcanic vent. Magma often cools before it gets to the surface, sometimes in the vent of a dying volcano. Over the years the softer rocks of the walls erode away, leaving a volcanic plug where the vent once stood. If the magma cools below the surface it is called an igneous intrusion. Each igneous intrusion depends on where it eventually cools. Some different types are: • dykes • sills • batholith • laccolith.
Magma does not always get to the surface before it cools and solidifies.
UNIT
5.5 Fig 5.5.10
volcano lava extrusive igneous rock
dyke sill magma
intrusive igneous rock
Moving volcanoes Volcanoes are usually located at the weak edges of tectonic plates. Some are nowhere near an edge, however: these volcanoes are directly over hot spots or plumes. Although there is no obvious weakness in the plate above it, the magma has so much pressure that it can force its way through. The islands of Hawaii lie 3200 km from the nearest plate boundary. Underwater volcanoes formed over a hot spot, eventually rising above sea level to form islands. All are different ages. In the west is Kauai, the oldest at 5.5 million years. The youngest is the ‘big island’ of Hawaii itself, which began building 700 000 years ago and is still being extended by lava flows from the continually erupting Mt Kilauea. Although the hot spot never changes position, the plate above does, carrying the islands to the west. Hawaii is directly over the hot spot now and will eventually move on, too. An underwater volcano called Loihi is already forming east of Hawaii and will become the newest island in the chain. The Australian territories of Heard Island and Lord Howe Island were once located over hot spots. An active hotspot is at longitude 40°S, passing under Victoria, Bass Strait, Tasmania and the Tasman Sea.
Fig 5.5.11
Hawaii’s islands are moving west with the plate.
Kauai (5 million years old)
Oahu (2.5 to 4 million years old)
Maui (750 000 to 1 million years old)
Hawaii (brand new to 700 000 years old)
Pacific plate moves hot spot
Luckily, its activity is confined to minor earthquakes with epicentres east of Flinders Island. A few hotspots are on land, the largest being Yellowstone National Park in the USA. Here the magma boils underground water that then forces its way to the surface as geysers, steaming lakes and mud pools.
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Landscaping the crust A geyser
Fig 5.5.12
of fossil fuels. Fossil fuels are actually plant and animal matter that decomposed to form a tar-like compound called kerogen. This needs to be ‘cooked’ for some millions of years to form other compounds called hydrocarbons, which are the actual energy store in the fuel. The intense pressures and heat at the weak spots may provide just the right ‘cooking’ conditions to do the job. Weak spots may also provide a more porous or sponge-like rock for oil to be squeezed into. Ore deposits are also associated with magma bodies that have solidified, causing the metallic minerals to form rich mineral veins. As the global population rises and industrialisation increases, the world’s demand for minerals and energy will grow enormously. This will require an improved knowledge of the relationship between plate tectonics and natural resources.
Volcanic landscapes 6 Construct diagrams of shield, cinder and composite volcanoes.
Treasure from below Many natural resources of energy and minerals are found near present or past plate boundaries. Fossil fuels (oil, coal and natural gas) are usually found near weaknesses in the crust. Plate boundaries, smaller faults, folds, hot spots and even the craters of extinct volcanoes have all been found to have stores
UNIT
5.5
7 The Glasshouse Mountains in Queensland are volcanic plugs. Construct a series of diagrams to demonstrate how they formed.
Moving volcanoes 8 Outline evidence that indicates that the Hawaiian Islands are moving westwards. 9 Illustrate with a diagram how hot-spot islands can move and how their volcanoes die.
[ Questions ]
Checkpoint Faulty landscaping! 1 Identify the three basic types of faults. 2 Fault scarps are often very rounded and not sharp like cliffs. Explain why. 3 Horst and graben exist along the mid-ocean ridges, where new crust is being made. Explain why.
Folding 4 State the properties of something that shows plastic behaviour. 5 Describe what conditions are needed to make rock act in a plastic way.
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Plugs and other intrusions
Treasure from below 10 Australians use the natural gas stored deep under Bass Strait. Identify what weakness in the Earth’s crust may have contributed to this gas being available here. 11 Propose two possible reasons why fossil fuels are found at weak spots in the crust.
Think 12 Use diagrams to distinguish between: a a normal and a transcurrent fault b a fault and a fold c a syncline and an anticline d kerogen and hydrocarbons
13 Distinguish between: a a plug and a dyke b a shield and a cinder cone volcano c horst and graben
a
A B C D E F G
14 Assess the conditions needed for volcanoes to form away from plate boundaries.
H
15 Illustrate how Uluru could have formed from a fold. 16 New Zealand has huge mountains in its South Island and active volcanoes in the North Island. Propose how these features were formed.
UNIT
5.5
I J
K
b A B
Analyse 17 Identify and label the faults, anticlines, synclines and unconformities in the landforms in Figure 5.5.13.
C D
Fig 5.5.13
18 Arrange the names of the different layers and features shown in Figure 5.5.13 in the order in which they occurred.
Creative writing
[ Extension ] Investigate 1 Hot spots can produce basalt plains instead of mountains. Research how they form and where they are located. 2 Examine the islands of Hawaii. a Trace a map of Hawaii. b On each island, locate the volcanoes and label them as active or dead. c Indicate where Loihi is likely to be and where future islands may form. 3 Investigate the natural gas reserves of Bass Strait. What else is found there, how is it tapped and what processing is needed?
Surf 4 Explore animations of the different types of faults by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button.
Darwin, an outer suburb of Hong Kong! All the tectonic plates are moving faster than ever before! What would have taken millions of years is now happening in a single day! Australia’s north-west coast is heading for the underbelly of China: Darwin and Hong Kong are to join! You are the information officer for the State Emergency Services and have the job of providing information to the citizens of Darwin. You must: • explain why the plates are shifting • describe what the climate will do • describe what events can be expected before the collision • describe what will happen once the continents collide • supply a list of relatively safe cities in Australia and overseas to evacuate to. Write it as information sheets, a Powerpoint presentation or a script for a TV announcement. Be imaginative, but base all descriptions on what you know about tectonic plates and their boundaries.
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Landscaping the crust
UNIT
5.5
[ Practical activities ] Faults and folds Aim To model faults and folds in
Prac 1 Unit 5.5
a
the land
Equipment Plasticine in four colours, a rolling pin, fine wire or a hacksaw blade
c
Method 1 Roll the plasticine flat into 1 cm layers. 2 Make a layered ‘cake’ with the plasticine.
b
3 Copy the table below into your workbook. 4 Model each feature shown in the table. To make faults, cut the cake in the direction of the arrows with the hacksaw, or hold the wire tightly with two hands and cut down through it.
d
Making faults, folds and erosion
Geological feature Syncline (downward fold)
Anticline (upwards fold)
What to build
Before erosion
After erosion
Aerial view after erosion
Fig. 5.5.14
5 Once again use the hacksaw blade or wire to cut in the direction shown by the arrows in each diagram. This is our ‘erosion’. 6 For each feature, draw a cross-section or side view after ‘erosion’. Colour the layers appropriately. 7 Look down on the feature as if you are travelling over it in an aircraft. Draw what you see.
Overfold
Questions 1 Identify which geological feature created these layers when seen from the air. Normal fault
Transcurrent fault
Horst and graben
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Fig 5.5.15
UNIT
5.5 Shaping volcanoes Prac 2 Unit 5.5
Aim To examine the angle of repose of different types of volcanoes Equipment
Funnel, retort stand, bosshead and clamp, 1 sheet of graph paper, ruler with millimetre markings, materials such as fine sand, coarse sand, flour, fine blue metal screenings, candles (old stumps will do), matches, protractor, access to a scientific calculator When material piles up into a cone, the angle that the side makes with the horizontal is called the angle of repose.
Method
retort stand
PART A 1 Set up the funnel as shown in Figure 5.5.16.
graph paper
2 Place your finger over the end of the funnel and fill with fine dry sand. Remove your finger quickly and let the sand run out. 3 Measure the height of the mound. Use the graph paper to estimate the diameter of its base. Calculate its radius.
candle
4 Construct a scale diagram of the side-view (crosssection) of the mound. 5 Use a protractor to measure the angle that the sand makes with the horizontal.
graph paper
6 Another way is to use trigonometry. Follow these steps: a On your calculator, divide the height by its radius. The answer should be less than 1. b Push the tan–1 button (push the inverse or shift button first!). c The answer is the angle of repose of the sand.
height
7 Put the angle on your diagram. 8 Repeat the experiment and calculations for the other samples of sand, flour and blue metal screenings. 9 Make bigger ‘volcanoes’ using two funnel-loads of material and calculate the angle of repose for each.
angle of repose
radius
Fig 5.5.16
Questions
PART B 1 Repeat the experiment but make the cone with melted candle wax. Drip a small amount of wax onto the graph paper and allow it to cool.
2 Arrange the materials in order from smallest to largest angle of repose.
2 Drip more and more wax, allowing it to cool each time.
3 Assess why the angles might differ between materials.
3 Calculate the angle of repose of the wax.
4 State whether bigger ‘volcanoes’ have different angles to smaller ‘volcanoes’ of the same material.
1 Explain what type of volcano you built in parts A and B.
5 Design and test a model for a composite volcano. DYO
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context
5. 6 How old is the Earth? How has it changed over time? For centuries, people have tried to answer these questions. Seventeenth century biblical records suggested that the Earth was created at around 4004 BC. Growth rings in trees may be used to trace back further than this, but, more recently, other methods have been used to estimate the ages of rocks in the Earth’s crust.
Fossils Palaeontologists study fossils to add to our knowledge of Earth’s history. A fossil is evidence of past life found in a rock or other material. This evidence may be the remains of a plant or animal, or an impression such as a footprint. In rare cases, a complete animal may be preserved—for example, an insect trapped in amber (sap from a plant), or a woolly mammoth preserved in frozen Siberian soil. Fossils can be created when the remains of an animal or plant are covered by sediments (dust, sand or mud) and become part of the sedimentary rock that is formed. Most remains are crushed or decay too quickly for them to be preserved. Sometimes, however, they are preserved as shells or skeletons, as moulds, or as
Fig 5.6.1
156
The bones of an Icthyosaurus have been replaced by minerals to form this fossil.
Wrong end! quartz, limestone or even opal ‘models’ of them. The general steps in the formation of fossils are shown in Figure 5.6.2. Generally, the lower the layer, the older the fossils. Fossils that lived over a comparatively short period of time and were widespread are called index fossils, and can help determine the age of a layer of rock. Fig 5.6.2
In 1870, dinosaur hunter Edward Drinker-Cope wrote a report about a plesiosaur—what we know today as a long-necked, short-tailed dinosaur. Cope made an embarrassing error, however—he put the head at the wrong end, to construct a short-necked, long-tailed dinosaur.
Fossil formation
a An ammonite dies and falls to the bottom of the sea where it is covered by sediments and protected from being eaten by other animals. The soft parts of its body decay, leaving just the shell.
b More and more sediment covers and squeezes the shell. The shell may remain or be replaced with minerals such as quartz or limestone that seep into it in solution before the original shell dissolves.
c After millions of years, movement in the Earth’s crust may thrust the layer of sedimentary rock containing the fossil upwards to form part of a mountain range.
d Weathering and erosion may eventually wear away some of the rock to expose part of the fossil. Fossils are often found in road cuttings or quarries.
For example, the presence of different species of ammonite can be used to date various layers of rock around the world to within a million years or so. The presence of more primitive ammonites indicates that a region is older than one containing more evolved ammonites. Prac 1 p. 161
Fig 5.6.3
First anima
l life
h n and Swedis An Australia d un fo 02 in 20 research team ilar to those m si fossil tracks or worms in left by corals the Sterling om sandstone fr uth t 400 km so Ranges abou cks ro e es Th . th east of Per to to date back are believed and on lli bi 2 1. between s. This would 2 billion year twice as old ils ss make the fo lly accepted as the genera animal life r fo e scientific ag on Earth.
Fossil tracks in sandstone dated to 1.2 billion to 2 billion years
Fig 5.6.5
UNIT
5.6
Ammonite fossils that formed about 100 millions years ago
Radioactive dating Rocks contain radioactive substances that gradually change or decay into other substances over a long period of time. For example, uranium is a radioactive substance found in many rocks, and slowly changes into lead over time. By comparing the amount of uranium and lead in a rock, the age of the rock may be determined. This type of radioactive dating is used to determine the ages of fossils more than 100 million years old. Using this technique, tiny sand grains found in Western Australia have been estimated to be 4.25 billion years old. A radioactive form of carbon found in plants and animals may also be used to date Prac 2 fossils less than 70 000 years old. p. 162
The geological time scale
Fig 5.6.4
A human fossil plaster cast—this unfortunate person died under a layer of volcanic ash after Mount Vesuvius erupted in 79 AD.
Scientists now believe the Earth to be about 4.5 billion years old. If the complete history of the Earth were condensed into a year, modern humans (Homo sapiens) would have appeared only in the last five minutes of the year. It is no wonder there is still much to be learned about the past! Despite this, rocks and fossil records have enabled scientists to piece together a history of the Earth in various stages, called eras. Each era is divided into periods.
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Geological time
Era
Period
Millions of years ago (mya)
Cenozoic (recent life)
Quaternary
0—2
Humans (Homo sapiens)
Tertiary
2–65
Mammals and birds become dominant after extinction of the dinosaurs.
Mesozoic (middle life)
Cretaceous
65–144
Final period for dinosaurs. Small mammals, flowering plants. Tyrannosaurus lived around 65–68 mya.
Jurassic
144–208
Plant-eating dinosaurs abundant, flying reptiles, first birds. Apatosaurus (formerly Brontosaurus) lived around 150–156 mya.
Triassic
208–248
Dinosaurs. Tiny mammals.
Permian
248–290
Modern insects. New mountains, deserts.
Carboniferous
290–362
Reptiles evolve from amphibians.
Devonian
362–408
Many types of fish, first land animals, amphibians, tree-sized land plants.
Silurian
408–438
Early simple land plants, first insects.
Ordovician
438–505
Fish, corals, molluscs.
Cambrian
505–570
Worm-like creatures, first vertebrates—eel-like animals, animals with shells (e.g. trilobites)
Precambrian
570–2700
Single-celled animals, early sea plants, fungi.
Archaeozoic (primitive life)
2700–3500
First signs of life—algae and bacteria.
Azoic (without life)
3500–4600
No life. Earth still cooling after its creation.
Palaeozoic (ancient life)
Proterozoic (earlier life)
Life/comments
Many of the animals that evolved over the ages no longer exist—dinosaurs are perhaps the most famous example. There have been several times when mass extinctions have occurred in a relatively short space of time, allowing other species to emerge and
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dominate their environment. For example, around 250 million years ago, the trilobites died out and crustaceans became abundant—today there are over 30 000 species of crustaceans. One, the horseshoe crab, bears some resemblance to the trilobite.
This trilobite fossil is 5 cm long and between 250 and 400 million years old.
UNIT
5. 6
UNIT
5.6 Fig 5.6.6
[ Questions ]
Fig 5.6.7
The horseshoe crab of today is thought to be a distant relative of the trilobite.
Checkpoint Fossils
7 List the periods that make up the Mesozoic era.
1 Identify how trees can be used to trace back through time.
8 Propose two reasons why a species may become extinct.
2 Define the term ‘fossil’.
Think
3 Copy the following statements into your workbook, modifying any incorrect statements so they are true. a A dinosaur footprint is not a fossil. b Minerals may replace the shell or bone of an animal to make a fossil. c Soft-bodied animals are less likely to form fossils than animals with shells or skeletons. d Fossils are found only under oceans or other bodies of water. e Generally speaking, lower layers of rock in a region contain older fossils. f Fossils of complete animals do not exist.
Radioactive dating 4 Identify what uranium changes into over time. 5 a Identify which radioactive substance may be used to date plant and animal fossils. b Evaluate whether it could be used to date a 100 000 year old fossil.
The geological time scale 6 Arrange the following eras in order, starting with the most recent: Palaeozoic, Archaeozoic, Cenozoic, Azoic.
9 Identify an example of an index fossil. 10 State how old scientists currently believe the Earth to be. 11 Copy and complete this table.
Period
Span
(millions of years) 12 Identify the period in which: Quaternary 2 a reptiles evolved Tertiary 63 b Tyrannosaurus lived c land plants appeared d bacteria evolved from a ‘chemical soup’ in the oceans e birds appeared f plant-eating dinosaurs had their heyday g fish appeared on Earth h sea plants appeared i flying reptiles first existed j dinosaurs last lived. >>
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Geological time
13 a Demonstrate the first three eras and the periods they contain on a scaled time line. b Use arrows to indicate the reign of the dinosaurs and when humans appeared. c Explain why would it be difficult to extend the time line to include the Precambrian era. 14 Older fossils can sometimes be found in rock above newer fossils. Justify how this can be. 15 Rock containing fossils of sea life can be found in areas far from the ocean. Assess how this can happen. 16 In the year 79 AD, Mount Vesuvius erupted, burying the cities of Herculaneum and Pompeii under molten rock and mud flows. Lava hardened around the human and dog victims. When the bodies rotted away they left human-and dog-shaped spaces, which were later discovered. Propose a method that would produce accurate models of these victims.
Analyse 17 Assess what may have happened long ago to produce the tracks in Figure 5.6.8.
[ Extension ] Investigate 1 a Research one famous palaeontologist such as Mary Anning, Edward Drinker Cope, Othniel Charles Marsh or current day dinosaur hunters such as Patricia Vickers-Rich. b Prepare a profile about them, including dates and their contribution to science. 2 Examine different fossils. Sketch several and indicate when the original animals or plants lived. 3 a Research what is meant by the term ‘ice age’. Find out when they occurred. b Watch the movie Ice Age and evaluate whether the conditions shown are accurate. 4 The diprotodon and giant short-faced kangaroo are two examples of Australian megafauna that lived between 40 000 and 1 600 000 years ago. a Investigate these and/or other Australian megafauna. b Explain some of the theories as to why these animals became extinct.
Fig 5.6.8
Fig 5.6.9
At three metres long and two metres tall, the diprotodon was the largest marsupial that ever lived.
Surf 5 Explore an ever-changing Australia from 110 million years ago to the present and beyond by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button.
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UNIT
5. 6
[ Practical activities ] Dinosaur fossils Aim To make a fossil of a dinosaur
Prac 1 Unit 5.6
UNIT
5.6
Equipment Clay or plasticine (to make a mould), a pin, a probe or blunt pencil, tracing paper or photocopy of the skeleton below, rolling pin or piece of dowel, cardboard or shoe box lid, plaster mix, water
Method 1 Trace the skeleton shown in Figure 5.6.10 (your teacher may provide a photocopy).
2 Roll out a layer of plasticine about half a centimetre thick, large enough for a copy of the skeleton. 3 Transfer a copy of the skeleton to the plasticine by pushing a pin through the copy at key points to mark the shape and use a probe to form an impression of the skeleton. 4 Place the plasticine in a shallow cardboard tray or shoe box lid that is at least 3 cm deep. 5 Mix up a thick plaster paste, fill the impression with it and allow it to dry overnight. 6 Carefully remove the cast of the ‘fossil’.
Fig 5.6.10
Questions 1 If this was a real fossil, propose what you would use to replace the plasticine/plaster mix. 2 You have actually made two types of artificial fossil. Describe each one. 3 Identify an example of something more likely to make each type of fossil.
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Geological time
‘Radioactive’ cubes
Chapter review
Aim To model the radioactive decay of uranium Prac 2 Unit 5.6
Equipment 50 or more small wooden cubes, with one face marked (e.g. with a dot), a cup, graph paper
Method 1 Make sure one face of each cube has a distinctive mark (e.g. a dot or a ‘6’). 2 Imagine that each cube represents an atom of radioactive uranium. These atoms emit invisible particles as they change into lead. Shake the ‘uranium’ cubes in a cup and tip them carefully onto a desk. 3 Cubes that land with the distinctive face uppermost are said to have ‘decayed’ into lead. Remove these from the pile and put them to one side. Count how many ‘uranium’ cubes are left (e.g. subtract the number of ‘lead’ cubes that were removed). 4 Collect the remaining ‘uranium’ cubes and repeat steps 2 and 3 until no ‘uranium’ cubes remain.
Questions
Number of ‘atoms’ remaining
1 Plot a graph showing the amount of ‘uranium atoms’ left after each toss. Draw a smooth curve like the one in Figure 5.6.11 through the middle of the group of plotted points. This is called a ‘curve of best fit’.
1 Explain why the Earth’s plates are like toast on soup. 2 Pangaea is Greek for ‘all the lands’. Justify why this is a good name for the original supercontinent and identify the names of its ‘babies’. 3 Describe how magnetism in rocks suggests that: a the continents were once joined b the ocean floor is spreading 4 Define the theory of plate tectonics. 5 Distinguish between the theory of continental drift and the theory of plate tectonics. 6 Describe how convection pushes tectonic plates around. 7 Earthquakes occur mainly at plate boundaries. Explain why. 8 State at what depth the subduction zone is completely molten and returns to the asthenosphere. 9 Identify the waves detected by a seismometer and in what order they will be detected. 10 Construct a drawing of a transverse wave. 11 Identify which seismic waves produce these motions at the Earth’s surface: a side-to-side b up-down c rolling 12 Describe three different ways in which mountain ranges can form. 13 Distinguish between a fault and a fold. 14 True or false?
Number of tosses
Fig 5.6.11 2 Use your curve of best fit to determine the number of tosses taken for the original amount of ‘uranium’ to halve. This is called the ‘half-life’. 3 Compare the half-life for your experiment with that obtained by other groups. 4 Try to find out the half-life of real radioactive uranium.
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[ Summary questions ]
a The mantle is where most volcanic and earthquake activity occurs. b The crust is thickest under the continents. c Scientists who study earthquakes are called seismologists. d A seismograph shows where an earthquake is. e A tsunami is a wave caused when the epicentre is under the ocean. f Magma rises because it is full of gas. g A dead volcano will never erupt again. 15 a Identify which types of animals are more likely to form fossils. b Explain why this is the case. 16 State what scientists measure to tell the approximate age of a rock.
17 Identify which eras occurred in the following periods. a Silurian b Cambrian c Tertiary d Jurassic 18 Identify a life form that existed in each of the following times: a Devonian b Archaeozoic c Quaternary
[ Thinking questions ] 19 Assess why the mysteries of the ocean floor weren’t discovered until the late twentieth century. 20 A map of the world in the future will be different to the one we know now. Explain how. 21 a Analyse how the upper mantle can be solid but still able to move. b Identify other substances that are like this.
[ Interpreting questions ] 28 Explain why the temperature near the ceiling of a room is always hotter than that at floor level. 29 Assess why magma rises. 30 P and S waves are refracted. Illustrate what this means. 31 Propose why the sides of a cinder cone are steeper than those of a shield volcano. 32 Use a diagram to explain why: a the Mediterranean Sea is being slowly squeezed shut b the Atlantic ocean is getting wider c the Himalayan mountains are getting higher 33 Explain why volcanic ash rises in the atmosphere. 34 Describe any volcanic material visible in the picture below.
22 The ocean floor has been likened to a conveyer belt. Assess why. 23 Identify where on Earth the longest mountain ridge and the highest mountain ridge are. 24 Analyse how density affects the movement of plates. 25 Propose an easy way of remembering what P, S, R and L waves do. 26 Explain how slipping plates: a cause earthquakes b often allow volcanoes to appear 27 Explain what magma is and why it gets squeezed to the surface.
Fig 5.6.13
Worksheet 5.13 The fragile crust crossword Worksheet 5.14 Sci-words
Fig 5.6.12
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Reproduction Key focus areas
>>> The applications and uses of science >>> Current issues in research and
5.3, 5.5, 5.8.1, 5.8.4
Outcomes
development in science
By the end of this chapter you should be able to: explain why reproduction is constantly taking place within and around us describe asexual reproduction, and give examples of organisms that reproduce in this way describe sexual reproduction and identify the sex cells that are needed for organisms to reproduce label the organs of the male and female reproductive systems and describe their function outline the changes that occur during puberty outline the main stages in the growth of a baby during pregnancy describe what can influence the development of a baby in the womb list various methods of contraception and assess their effectiveness
Pre quiz
list common sexually transmitted diseases, their symptoms and possible treatment.
1 How many parents are needed for reproduction?
2 3 4 5
What is a hermaphrodite? Why don’t clones all look identical? Why do we have belly buttons? How many sperm does a man release when he ejaculates?
6 Name as many sexually transmitted diseases as you can.
6
UNIT
context
6.1 The only way a species can survive is if more individuals of the same species are constantly being produced. Reproduction is a chain of events that leads to the creation of new individuals. Not all living things or organisms reproduce in the same way. There are two types of reproduction: asexual and sexual.
Asexual reproduction Asexual reproduction requires only one individual organism or parent. Although this might seem strange, it is happening right now within your own body! All body cells reproduce in this way, during growth or to repair damage. Many plants reproduce this way too. In asexual reproduction, there is no need for two types of sex cells. Instead, new cells are formed by older ones called parent cells splitting to make two identical copies, called daughter cells. Because the new organism is made from cells from only one parent, little variation is introduced into the new organism. Organisms produced this way are sometimes called clones. Clones may not always look exactly the same—for example, two cloned trees may look different because of the environment they live in.
Fig 6.1.1
These mushrooms were produced by asexual reproduction, so they look very similar to each other and the parent plant.
Genes and DNA The nucleus of every cell in an Asexual reproduction is useful if: organism contains long, thin threads called chromosomes. • the environment is constant, the These determine what a cell organism is suited to it and there does. Chromosomes are made is no advantage in changing up of many small sections • the species is rare and there is called genes, which consist of DNA (deoxyribonucleic acid). not much chance of meeting an This amazing chemical is able organism of the same type and to copy itself and pass on of the opposite sex instructions to new cells. Genes determine every • the organism can’t move much. characteristic of living things. Sometimes change happens If you have blue eyes, it is when cell division fails to produce because your chromosomes carry the gene for blue eyes. exact copies of cells. The offspring Every cell in your body will then exhibit a new and contains all the instructions unexpected characteristic. This needed to build every part of is called a mutation. you, but only a few instructions are used in each cell.
Mutants in Sydney! All Granny Smith apple trees can be traced back to a seedling that appeared in an orchard in Sydney in the nineteenth century. The seedling, the result of a mutation, was then cloned. There are now millions of Granny Smith apple trees worldwide, all derived from the original tree. In a similar way, all navel orange trees are the result of a mutation causing the first tree to appear in Brazil in 1870.
All Granny Smith apple trees are clones of a single tree that appeared in Sydney due to a genetic mutation.
Prac 1 p. 171
Fig 6.1.2
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Types of reproduction
>>>
Types of asexual reproduction include fission, budding, spores and fragmentation followed by regeneration.
Fission Fission produces new cells that are identical to the parent cell. The parent cell simply grows and then divides across the Deadly bacteria middle, causing a split or Because bacteria can reproduce so quickly by fissure. This is how most fission, some types can bacteria reproduce. Some kill a human within other single-celled organisms, hours of infection. The including some types of algae bacteria that cause food poisoning can kill a and fungi, also reproduce by healthy adult in less than fission. Reproduction can occur 24 hours. very quickly by fission. In ideal conditions—plenty of food and the right temperature—a single bacteria cell could ‘breed’ over a million new cells in hours. This is why some foods ‘go off’ very quickly.
Fig 6.1.4
Spores Some organisms have special structures called spore vessels. Inside these structures the reproductive cells (or spores) form. Spores are released from time to time and can be spread by air, water or other living things. When the spores reach a suitable environment, they grow and form a new organism. Many fungi, mosses, ferns and algae use spores to Prac 2 p. 171 reproduce. Fig 6.1.5
Fig 6.1.3
Bacteria divide by fission—this cell is about to divide.
Budding Budding is a type of uneven fission. When the parent cell divides, one part, the mother cell, is much larger than the other, the bud cell. The buds later form buds of their own. Organisms that reproduce by budding include yeasts and many cnidarians (coral, jellyfish and anemones; see Science Focus 1, Chapter 6).
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Scanning electron microscope image of budding yeast cells. Yeast is important in food production, particularly bread and alcoholic beverages.
Imperfect fungi Although most fungi reproduce asexually, some reproduce sexually and are known as ‘imperfect fungi’. Ringworm in humans is not a worm at all, but an ‘imperfect fungus’.
This fern will release millions of spores into the air.
Fragmentation and regeneration Fragmentation occurs when pieces break off from an organism. Each of these parts can then regenerate into a new organism. This can happen in starfish, earthworms, mushrooms and many flowering plants. When plants reproduce by this method, it is known as vegetative reproduction or vegetative propagation.
Fig 6.1.7
The offspring of sexual reproduction are quite different from each other and their parents.
UNIT
6.1
Gametes This starfish is lucky—a new arm is regenerating at its centre, to replace one that has been lost. The broken-off arm can also regenerate as a new individual.
Fig 6.1.6
The sex cells or gametes produced by males are called sperm, and move about using a tail called a flagellum (plural: flagella). Sperm are mature male sex cells or gametes.
Fig 6.1.8
Sexual reproduction Sexual reproduction requires two different sex cells in order to begin. These cells may come from an individual organism (as in many plants and some animals) or from two parents of different sex. The two sex cells, called gametes, fuse together to form a new cell called a zygote, which then divides over and over to form a new organism. A plants or animal that has both male and female reproductive organs and produces both types of sex cells is called a hermaphrodite. If organisms of a species are too similar, a small change in the environment could mean that all will die. If there is a lot of variance within a species, it is much more likely that some of them will be able to survive unfavourable conditions. This is why sexual reproduction tends to take place in environments where conditions are varied or possibly unfavourable for future survival. The offspring of asexual reproduction are very similar to the parent, but the offspring of sexual reproduction are quite different from their parents.
The gametes produced by females are larger and are called ova (singular: ovum) or eggs. Eggs carry a store of food to nourish them. They do not have flagella and so do not move about of their own accord. The release of an ovum in the female is called ovulation.
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Types of reproduction
stigma the female style part of ovary the flower ovule
anther filament
stamen—the male part of the flower
petal
sepal
A scanning electron microscope image of a female egg or ovum
Do you find my stomach attractive? Male camels perform a clumsy dance to attract a mate. During the dance the male sometimes regurgitates one of its two stomachs, which then hangs frothing from its mouth to tempt the female!
Fig 6.1.9 Fig 6.1.10
Animals signal their readiness for mating in different ways. Some females make certain calls or sounds that tell the male they are ready to mate. Some birds display brightly coloured plumage or perform a dance to initiate mating. Mammals release chemicals called pheromones to stimulate the opposite sex.
Fertilisation Fertilisation is when two gametes The preying mantis successfully join ntis is believed The female praying ma together to form a to tempt the cal mi che a e ret to sec zygote. For fertilisation t he’d better bu , her h male to mate wit al for the usu un t no is It to occur, the gametes t! ou watch g mating. rin du le ma female to eat the must be released at the same time, properly formed and fully developed, and the environment must be just right.
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Fig 6.1.11
Many flowers contain both male and female parts— they are hermaphrodites.
Plants cannot deliberately move closer together to cause fertilisation, so they rely on the wind or insects to transfer pollen from the anthers to the stigma. This is called pollination. Selfpollination is when pollen Parthenogenesis from an anther is transferred to the stigma on the same flower. Cross-pollination is when pollen is transferred from one flower to another flower on a different Prac 3 p. 171 plant. Worksheet 6.1 Strange plant sex
pollen transfer
Sex and plants Many plants reproduce sexually, using flowers which may contain both female and male parts. The female gametes are produced in the plant’s ovaries, inside structures called ovules. Each ovule contains one female gamete. Male gametes are produced in the flower’s anthers and are found inside pollen grains.
nectary
Cross-pollination
In certain animals, an egg cell can become a new individual without ever being fertilised by sperm. This is called parthenogenesis. In aphids, unfertilised eggs all become females. In honeybees, only males result from parthenogenesis. Desert whiptail lizards only reproduce by parthenogenesis, so the entire species is female!
Fertilisation in animals may be external (outside the body) or internal (inside the body). After internal fertilisation, the zygote may develop inside the female or can be laid as an egg. Fig 6.1.12
Fish fertilise many eggs at once because only a few will survive to maturity.
female
A male approaches a female, who is attracted to his red belly.
The male leads the female to the nest.
The female lays her eggs after being tapped on the tail by the male.
The female leaves the nest after being bitten by the male. The male goes in and sheds sperm over the eggs.
6.1 UNIT
male
[ Questions ]
Checkpoint
Development of the embryo Zygotes continue to divide to form a bundle of cells called an embryo. If the embryo receives sufficient nourishment and is not harmed by environmental factors (like a hungry predator), it will grow to become a fully developed organism. Some organisms lay a large number of eggs at one time, but only a few will survive to adulthood. Other organisms have only one offspring at a time. Generally, organisms that do not provide much parental care fertilise many eggs at once. In contrast, organisms that provide a lot of parental care fertilise as little as one egg at a time.
Elephants provide a lot of care for their young and so have only one baby at a time.
UNIT
6.1
Fig 6.1.13
Asexual reproduction 7 Define ‘fertilisation’.
1 a Identify three types of asexual reproduction. b Distinguish between them.
8 Explain what a hermaphrodite is.
2 Match the following organisms to the type of asexual reproduction they use:
9 Draw a diagram of an egg and a sperm. Explain why an ovum cannot move around like sperm can.
Bacteria Yeast Ferns Starfish
Fragmentation and regeneration Budding Fission Spores
3 Describe the characteristics of spores that enable them to be spread by air, water and other organisms. 4 Explain how you think spores might be spread by other organisms. 5 Define ‘vegetative propagation’ and give an example of how it might happen.
Sexual reproduction 6 Sexual reproduction is the better method of reproduction in a varied environment. Explain why.
10 State the two types of gametes and identify where each is produced. 11 Describe what things are necessary to bring about successful fertilisation. 12 Copy the following, modifying any incorrect statements so they are true. a The release of an ovum by the female is called pregnancy. b All fertilised eggs survive to maturity. 13 Explain why nectar is located deep inside the lower part of the flower and below the anthers. 14 Compare the advantages and disadvantages of internal and external fertilisation.
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169
Types of reproduction
Think 15 Copy the following, modifying any incorrect statements so they are true. a In asexual reproduction, two parents are needed. b Fission is a type of sexual reproduction. c If the daughter cell is identical to the parent cell, a mutation has occurred. 16 Do clones always look exactly the same as their parents? Explain. 17 Evaluate the advantage of reproducing by spores, compared with budding. 18 If organisms such as earthworms and mushrooms can regenerate lost body parts, propose why they eventually die. 19 If bacteria reproduce easily in humans, propose which temperature suits them best. 20 New plants are often made by taking a ‘cutting’, a small piece of the original which is then placed in soil until it forms roots. a Explain why reproduction does not always need two parents. b Explain what type of asexual reproduction this is an example of. 21 Many plants can reproduce both sexually and asexually. Explain why this is an advantage. 22 Many insect-pollinated plants are brightly coloured and have flowers that contain a sweet sugary solution called nectar. Explain how features such as this help reproduction of these plants. 23 Explain why it is best if kangaroos have only one offspring at a time.
>>> 29 Fish do not provide much care to their young. Explain why it is beneficial that they fertilise many eggs at once. 30 The overuse of pesticides has greatly affected reproduction in plants pollinated (fertilised) by insects. Explain why.
[ Extension ] Create 1 Construct a crossword to summarise sexual and asexual reproduction. Include definitions and specific examples of the different types of reproduction.
Investigate 2 a Use information about weather, water and food availability and health care to predict which countries of the world might have: i a high rate of pregnancy ii few babies dying in their first year iii a high rate of women dying in childbirth b Explain your answers. c Investigate whether your predictions were correct. d In small groups discuss your findings and analyse the importance of research. 3 a Research how common the occurrence of twins is in the general population. b Investigate how twins occur and construct an informative poster to show this. Differentiate between identical and non-identical twins.
24 Define parthenogenesis.
Action Analyse 25 Describe an advantage of asexual reproduction over sexual reproduction. 26 Two trees have exactly the same genes. One is growing in far north Queensland, and the other in southern Tasmania. They look quite different from each other. Explain why. 27 Cloning human cells can help in making replacement body parts, like skin for burns victims. If cloning is so useful, propose reasons why so many people are against it. 28 If a bacterial cell divides once every five minutes for an hour, calculate how many cells will be present at the end of: a 10 minutes c 1 hour b 30 minutes d 1 day
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4 a Investigate how vegetative propagation is used in agriculture. b Choose one example of this and design an experiment or demonstration to show how it is done. c Perform your experiment or demonstration.
DYO
Surf Complete the following activities by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button. 5 Explore the parts of a flower and how flowers reproduce. 6 Examine an introduction to DNA structure and function.
UNIT
6.1
[ Practical activities ] Asexual reproduction in plants
Prac 1 Unit 6.1
UNIT
6.1
Aim To examine asexual reproduction in plants
Examination of spores Aim To examine spores using a stereomicroscope Prac 2 Unit 6.1
Equipment An onion and a potato with eyes, knife Note: Many other things could be substituted for the onion and potato, such as strawberry runners, Chinese willow stem cuttings or orchid bulbs.
Equipment Stereomicroscope, fern leaf with visible spores, tweezers, filter paper
Method 1 Place your leaf under the microscope and examine the spore vessels. Draw a section of the leaf and describe in words what you see. 2 Use the tweezers to break open some of the spore vessels onto the piece of filter paper. Examine these under the microscope and describe them.
Questions 1 Describe how easy it was to break open the spore vessels. 2 Predict how many spores you think were in each spore vessel. 3 Describe how easily you think the fern spores could be spread. 4 Identify some ways in which the spores will be spread.
Flower dissection Aim To examine the reproductive parts of a flower Fig 6.1.14
Method 1 Cut the onion in half lengthways.
Prac 3 Unit 6.1
Equipment Dissecting instruments, large flower, hand lens
Method
2 Draw the onion, labelling the parts shown in the diagram above.
1 Examine your flower. How many petals and anthers does it have?
3 Draw the potato. Identify the buds.
2 Carefully cut the flower so you can see all the parts.
Questions 1 The buds of an onion can become new individuals. Explain why this is an example of asexual reproduction. 2 If the ‘eye’ of a potato is a bud, predict what might happen if you cut out a potato eye and planted it.
3 Draw the flower and label the different parts. 4 Use two different-coloured pencils or highlighters to colour the male and female parts of the flower. 5 Examine the flower with your hand lens and note any unusual features.
Questions 1 Predict whether you think your flower would have been capable of self-fertilisation. 2 a Examine the flower of a different plant. b Compare the differences and similarities. 3 State whether these flowers reproduce by sexual or asexual reproduction.
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UNIT
6. 2 context
The human population
The reproductive system makes the continuation of life possible. From adolescence onwards, humans feel a strong sexual drive. This instinct to reproduce is driven by hormones produced in our reproductive system. We need to understand how this system works and how it affects our bodies as we grow and develop.
The male reproductive system Sperm are produced in the two testes. The testes are located in a sac called the scrotum, which hangs outside the body. This keeps the testes cooler than the normal body temperature of 37°C. The cooler temperature allows maximum sperm production. The testes also secrete the male hormone testosterone.
The human population has grown enormously as nutrition, hygiene and medicines have improved. We have greater life expectancies than ever before. As little as 100 years ago, many women died in childbirth and many children did not survive infancy. We now face the problem of trying to control our evergrowing population, as the Earth cannot sustain unlimited numbers of humans. China has introduced a one-child per couple policy in an attempt to curb its population growth.
Most of each testis is made up of tiny, tightly coiled tubes called seminiferous tubules. Many hundreds of millions of sperm are formed in these tubes each day, but they take several weeks to reach maturity. Once formed, the sperm are moved along the tubes by cilia—hair-like structures attached to the walls of the tubes, which beat back and forth. The sperm are stored in another part of the testis, in a group of coiled tubes called the epididymis. It is here that they become fully developed and start to ‘swim’ in fluid released from the walls of the tubes. Fig 6.2.1
The human male reproductive system
kidney ureter
vertebral column
bladder ureter
prostate gland seminal vesicle
epididymis
urethra penis
sperm duct (vas deferens)
bowel
bladder pubic hair
prostate gland rectum
pubic bone sperm duct (vas deferens) urethra erectile tissue penis
anus epididymis testis
glans
testis foreskin scrotum
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scrotum
Each testis is connected to the urethra by the sperm duct or vas deferens. The urethra is the tube that runs along the length of the male sex organ, the penis. This tube also connects to the bladder and is used to empty it of urine. As the sperm travel from the sperm duct to the penis, they pass by glands that add more fluid to the mixture. The major glands are the prostate, seminal vesicle and Cowper’s glands. This mixture of fluid and sperm is called semen. Although both semen and urine pass along the urethra, it is not possible for both to pass through at the same time.
Follicles Before puberty, the surface of women’s ovaries are unscarred. From puberty onwards, every time a follicle develops, it appears on the surface of an ovary. When the egg bursts from it, the follicle is left behind and leaves a scar. By middle age, women’s ovaries are dotted with many of these scars.
Fig 6.2.3
The release of eggs and hormones from the ovary occurs in a cycle called the menstrual cycle. At the start of every menstrual cycle (day 1), an immature egg, contained in a small sac of cells called a follicle, starts to develop. The follicle and egg get bigger until about day 14 of the cycle, when the egg becomes mature. The egg then
UNIT
6.2
Every month a new scar is formed on the ovary, due to follicle formation. These pictures show the ovary of a 3-year-old girl and a 27-year-old woman.
The female reproductive system Ova (eggs) are produced by the two ovaries, which also produce female hormones, mainly oestrogen and progesterone. Whereas males constantly produce new sperm throughout their lives, all of the female’s eggs are formed in her ovaries before birth. A human female newborn has about 500 000 eggs in each ovary, but only a few hundred of these ever become fully formed. Worksheet 6.2 Male and female reproductive organs
Fig 6.2.2
The reproductive system of a human female
vertebral column ureter fallopian tube (oviduct) ovary uterine wall
uterus
cervix vagina
bladder urethra
fallopian tube (oviduct) ovary uterus (womb) bladder pubic hair pubic bone uretha clitoris labia
cervix rectum anus vagina vulva
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Human reproductive systems
Puberty
bursts from the follicle into the ovary cavity. From here, the egg moves into the fallopian tube or oviduct, moved along by cilia Menstruation and muscular contractions. While many mammals While the egg is in the have special hormonal cycles, only primates fallopian tube, it is capable of menstruate. In other being fertilised. It stays there for mammals, the unused about seven or eight days during lining of the uterus is each menstrual cycle, after broken down and reabsorbed by the body. which it travels to the uterus The reproductive cycle regardless of whether it has been in these animals is fertilised or not. called an oestrus cycle rather than a From the start of every menstrual cycle. menstrual cycle, the lining of the uterus becomes thicker with an increased blood supply, in preparation for receiving the fertilised egg. If the egg has been fertilised, it implants in the wall of the uterus and starts to develop. A change in hormones tells the body to keep the uterine lining, so menstruation does not occur. The female is then said to be pregnant. Menstruation is the shedding of the uterine lining. It is also known as a period and occurs when the egg is unfertilised on about day 25 of the cycle. The lining of the uterus consists of blood, mucus and cell debris. After many cycles, no more eggs are released. This is called menopause and commonly occurs in humans between the ages of forty and fifty.
Puberty is the time when males and females reach sexual maturity. Puberty can start at different ages, but usually no earlier than 10 years of age. It is normally over by 17 years of age. Before puberty, the reproductive organs are present, but are not fully developed or functional.
Changes in males at puberty
facial hair deeper voice
muscle development
penis longer and wider
growth spurt
Worksheet 6.3 Fertility and temperature
Fig 6.2.4
before puberty
Changes in the lining of the uterus
Days
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uterus vagina
Ovulation
cervix
Egg-preparation stage Menstruation and follicle development
2
4
Preparation of the uterus
Follicular phase— one follicle dominates
6
8
after puberty
Changes in males at puberty
The menstrual cycle
Events
sperm production begins
underarm and pubic hair
10
12
Preparation of uterus. Corpus luteum forms and then degenerates
14
16
18
20
22
24
26
28
Fig 6.2.5
The hormone testosterone begins to be secreted by the testes from the start of puberty and causes many changes. Testosterone stimulates the development of the genital organs and secondary sexual characteristics such as facial hair, pubic, underarm, leg and chest hair, increased muscle mass and bone structure and a lower voice. The testes develop and begin sperm production.
UNIT
6.2 Changes in females at puberty The major female hormone is oestrogen, which causes maturing of the eggs and makes the lining of the uterus thicken with blood. Oestrogen is also responsible for the outward changes seen in females at puberty. Like males, females experience a growth spurt around the time of puberty. Breasts and buttocks develop and hips become wider, the reproductive organs grow and mature, pubic hair and underarm hair develop. At some stage, menstruation begins. This first period is called the menarche.
UNIT
6.2
growth spurt breasts develop
underarm and pubic hair
menstruation begins
hips widen, buttocks grow
[ Questions ]
Checkpoint The male reproductive system before puberty
1 Identify the parts labelled a–e in Figure 6.2.7.
Fig 6.2.6
after puberty
Changes in females at puberty
The female reproductive system 5 Identify the parts labelled a–e in Figure 6.2.8. Fig 6.2.8
a
b c d e
a b c d
Fig 6.2.7
e
2 Explain why the testes are located outside the male body. 3 State what semen is made up of. 4 Identify the major glands of the male reproductive system.
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Human reproductive systems
6 State the number of eggs present in an ovary at birth and how many become fully formed. 7 Describe what regulates the menstrual cycle. 8 Explain how the body knows not to menstruate when pregnancy occurs. 10 Identify when menopause occurs. 11 Identify where in the female body the egg is fertilised.
Puberty
Height (cm)
9 Describe what the lining of the uterus consists of.
12 Define ‘puberty’. 13 State two changes that occur in females and two that occur in males at puberty.
Think 14 a Identify the major male and female hormones. b Where possible state what each hormone does in the body.
190 180 170 160 150 140 130 120 110 100 90 80 70 60 50
boys
girls
2
4
6
8 10 12 Age (years)
14
16
18 19
15 State the name for the first period. 16 Adult males can father healthy children at any age. Explain why adult females cannot give birth at any age. 17 Puberty is often delayed in elite athletes. Explain what this indicates. 18 Explain how a woman’s ovaries become scarred with time.
Skills 19 The graph above shows the average heights of boys and girls. Use it to answer the following questions.
Average heights for boys and girls
Fig. 6.2.9
a State the average height of an 8-year-old boy. b State the average height of an 11-year-old girl. c According to this graph, state the ages that puberty occurs between. d ‘Boys are taller than girls.’ Assess whether this statement is true, false or a bit of both. Explain your reasons.
[ Extension ] Action 1 Construct a life-sized outline of a girl and a boy on a large sheet of butcher paper. a Draw and label all the parts of the reproductive systems. b Label the changes that occur to each during puberty.
Investigate 2 a Investigate how the reproductive systems of a platypus and a kangaroo differ from that of a human. 3 a Research the rate of population growth in several countries. Which country has the highest rate and why? Which has the lowest and why?
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b In order to control its population growth, China has introduced a one child per couple policy. More male than female babies are surviving in China under this policy. Investigate why this is occurring. c Evaluate the one child policy and decide whether you agree with it or not.
Surf 4 Explore the human reproductive systems and the body’s changes during puberty by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button.
UNIT
context
6.3 The first cell of a new baby is formed when the egg and sperm fuse together during fertilisation. This one cell goes through an amazing nine months of growth to become a human baby. During this time the cell grows and divides to form all the different organs
Copulation and fertilisation Sperm are brought into contact with the female egg through sexual intercourse, sometimes called copulation. The penis becomes erect when the male is sexually aroused, and is inserted into the female’s vagina. Semen is pushed (ejaculated) into the vagina. A male will normally release several hundred million sperm in this process. Once inside the vagina, the sperm ‘swim’ towards the fallopian tubes. Only a few hundred will make it as far as the egg. The others will die.
and structures of the body. We will now follow the reproductive process from fertilisation to the birth of a new baby. This time is known as the gestation period.
If an egg is encountered, the sperm will surround it, although only one sperm will eventually fertilise it. After one sperm has entered the egg, the surface of the egg changes to stop any more getting in. Any sperm left outside the egg will eventually die, although they can live for up to two days in the female—so it is possible for women to become pregnant two days after sexual intercourse!
Alternatives to tube-tying
Many sperm may reach the egg, but only one penetrates the surface.
Fig 6.3.1
If women want to stop any chance of pregnancy, they can have an operation that is done under general anaesthetic which involves cutting or cauterising (burning shut) the fallopian tubes. However, sometimes this is not successful. A new coil, called STOP, has been developed. It is inserted under local anaesthetic and ‘plugs’ the fallopian tubes. Reports from trials are very promising— 100% success rate with no side effects.
Twins Fraternal twins result when two separate eggs are fertilised. They are the most common type of twins and don’t look any more alike than any two brothers or sisters. Identical twins result when a single fertilised egg splits in two. Because these twins come from the same egg and sperm, they are genetically identical. Some scientists believe that a third type may be possible. Half-identical twins could be conceived if the mother’s egg splits before fertilisation and each half is then fertilised by a different sperm. This could explain why some fraternal twins look so alike.
Contraception Most animals mate only to reproduce. Humans are unusual because we also mate for pleasure. To prevent unwanted pregnancies, contraception is used. Most methods of contraception are used by women, but some are used by men, including a contraceptive pill similar to that taken by many women. Some types of contraception are listed in the table overleaf.
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From gamete to birth
Name
How it works
Advantages
Disadvantages
Failure rate
The pill
Consists of hormones which stop ovulation. A pill is taken at the same time each day for 21 days, followed by 7 days’ break.
Easy to use, and can protect against problems like cervical cancer. May make periods lighter and improve acne.
Shouldn’t be used by smokers or people with circulatory problems as there is a risk of blood clots.
Low if taken as directed, but vomiting, diarrhoea and some antibiotics can reduce its effectiveness. This risk is reduced with some newer types of pill.
Condom
Rubber sheath that fits over the penis and stops semen entering the vagina
No side effects, although rare allergic reactions do occur. May protect against many sexually transmitted diseases.
Reduced sensation and spontaneity
If the condom is of high quality and is used properly, the failure rate is low. Actual failure rate is higher due to unskilled use and tearing of low-quality condoms.
Cap and diaphragm
Rubber devices that fit over the cervix. They stop sperm from entering the uterus.
Few side effects
Reduced spontaneity. Increased risk of bladder infections
Low, especially if used with a spermicide (chemical that kills sperm). They should be replaced yearly and inspected regularly for holes or cracks.
IUD (intra-uterine device)
This is fitted by a doctor and sits inside the uterus for up to eight years. Stops sperm entering the uterus.
Once inserted, no further maintenance is required.
Can result in infection and heavier, painful periods. It offers no protection from sexually transmitted diseases
Low
Contraception in history Up until this time, all required nutrients have come from the original egg. Now that more nutrients are required, the blastocyst buries itself in the lining of the uterus and starts to absorb nourishment from it. This is called implantation. The blastocyst produces a hormone that keeps the lining of the uterus thick and prevents menstruation. Fig 6.3.2
Many contraceptive options have been made available through scientific research.
How a zygote becomes a baby After the zygote has formed in the fallopian tube, it begins a five-day journey to the uterus. Along the way, the zygote divides several times to form new cells. By the time it reaches the uterus, it has become a clump of up to 80 cells, called the morula. In the uterus the cells continue to divide, forming a fluidfilled ball called a blastocyst.
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The history of birth control methods ranges from the deadly to the truly bizarre. Women once placed cow dung mixed with honey, or dried fish mixed with lemon, inside the vagina as a means of birth control. These things were supposed to kill sperm, but they could also cause serious infections and death for the women. Condoms were once made of snakeskin, sheepgut or linen, and were washed after use.
This sequence—from fertilisation to implantation—takes around a week to complete.
Fig 6.3.3 zygote
morula fertilisation blastocyst glands
uterus ovum
blood vessels muscle Structure of uterus lining (endometrium)
As the cells in the blastocyst multiply, they start to move around and become different from each other. In about eight Pregnancy tests weeks, the beginnings of all the A missed period can mean pregnancy, but the major body systems will form only definite sign is the and the heart will begin presence of a special beating. For these eight weeks, hormone produced by the developing individual is the blastocyst. This hormone is present in a known as an embryo. pregnant woman’s blood After eight weeks, the and urine, and is what embryo becomes a foetus. The over-the-counter pregnancy tests detect. foetus is protected by a pool of amniotic fluid, surrounded by the amniotic membrane. Oxygen and nutrients come from the placenta via the umbilical cord.
period of dividing zygote, implantation and beginning embryo 1
2
usually not susceptible to teratogens
Inside the pregnant woman
Fig 6.3.4
placental villi (surface over 11 metres)
UNIT
6.3 amnion (amniotic membrane)
umbilical cord
amniotic fluid
38 week foetus endometrium (uterus wall)
plug of mucus blocking cervical canal
embryonic period, weeks
foetal period, weeks
full term
indicates common site of action of teratogen 3
4
5
6
7
8
9
16
20–36
38
40
brain central nervous system
heart
palate
heart eye
eye
arm leg
ear
ear
Teeth
external genitalia central nervous system
heart
arms eyes legs teeth palate external genitalia ear
prenatal death
major structural abnormalities
physiological defects and minor structural abnormalities
Development in gestation
Approximately 280 days (close to nine months) after fertilisation, birth occurs. The cervix relaxes or dilates to let the baby through. The membrane around the baby splits and amniotic fluid rushes out of the woman’s vagina. This is called the ‘breaking of the waters’. The uterus contracts strongly at regular intervals. This is known as labour. Eventually, the
Fig 6.3.5
baby is pushed out head-first. After the birth, the placenta is delivered and the umbilical cord is cut. Your belly button marks the place where your umbilical cord was once attached. The baby starts to breathe air for the first time as it is born. Crying helps to clear fluid from its lungs.
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From gamete to birth The mother’s health in pregnancy While the foetus is developing, its health is almost entirely dependent on the health of the mother. The pregnant woman must pay close attention to her lifestyle and nutrition in order to give the foetus the Ancient viruses greatest chance of g young that develop Havin developing normally. It is inside the female’s body especially vulnerable as an offers many advantages. embryo, when the body The young are protected, they can get rid of wastes systems start developing.
Tests during pregnancy Ultrasound scanning can detect things like the heartbeat, how many foetuses are present, how old the foetus is and if there are any obvious problems or defects. It is possible to tell the sex of the child from about the sixth month. Ultrasound image of a baby
It is normal and desirable for women to gain 9 to 13 kilograms in pregnancy. Pregnant women don’t need to eat too much more than usual, but it is important that all the nutritional needs of the developing baby are met. One important nutrient is folate. It is recommended that women take 0.5 mg of folate per day at least one month before pregnancy and for the first trimester (first three months of pregnancy). This level is easily obtained through diet, and so supplements are normally not necessary. Folate prevents 70% of neural tube (spinal) defects. These are problems that occur as the nervous system is forming. Spinal defects occur in about
A blood test is taken to measure the level of alphafetoprotein in the mother’s blood. A high level of this substance indicates problems and further tests will be carried out. An amniocentesis can be performed at 15 to 17 weeks of pregnancy to detect abnormalities. Guided by ultrasound, a needle is inserted through the
a Amniocentesis b Chorionic villus sampling
b
a
spinal needle ultrasound scanner
uterine wall placenta amniotic fluid
Fig 6.3.6
easily and they have a constant, plentiful supply of nutrients and oxygen. Mammals that carry live young can do so because of the development of the placenta. Researchers believe that the development of the placenta first came about through a viral infection of our ancestors some 120 million years ago. The genes for these viruses can now be found in the DNA of all mammals and are active during foetal development.
Nutrition
Fig 6.3.7
one in 500 pregnancies. The pregnant woman’s reserves and intake of iron and calcium must be enough not only for her own needs but also for those of the foetus.
pubic bone amniotic fluid
bladder cannula speculum vagina
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UNIT
6.3 Drugs
Career profile Medical imaging technologist Medical imaging technologists operate X-ray and other imaging equipment in the diagnosis, monitoring and management of various medical conditions. In the field of reproduction they work with ultrasound in particular. •
• • •
• • •
Medical imaging technologists can be involved in: determining which imaging techniques would be most appropriate to provide information for the doctor. This could include X-ray, ultrasound or other methods. explaining procedures to patients operating imaging equipment checking imaging results to determine whether further views are required. A good medical imaging technologist is able to: work accurately communicate well with others apply the scientific method in solving problems.
Because the new baby’s blood supply is linked to its mother’s, anything taken in by the mother Thalidomide has the potential to cause harm Thalidomide was to the baby. introduced in 1957 and in wide use until the was Research has consistently early 1960s. It was shown that women who hailed as a wonder drug, smoke, drink or do both during a sedative that combated morning sickness and pregnancy are more likely provided a sound night’s to produce children who are sleep. Because morning mentally and/or physically sickness strikes in the first trimester, this is defective than women who don’t most women were when smoke or drink. Children of these taking it. However, the mothers are also more likely to embryo is very die during their first week of life. vulnerable at this stage and the results of Smoking affects the circulation thalidomide were of blood to the baby, and the devastating. It caused children of smokers are more terrible malformations (often shortened or likely to be underweight and have absent arms and legs) reduced mental abilities than the and many deaths. In the children of non-smokers. 1990s, thalidomide was found to be effective in Other substances that cause treating the severe harm include: weight loss that occurs • hallucinogens (e.g. LSD)— in patients with diseases such as AIDS, there is a risk of miscarriage culosis (TB) and tuber and deformities leprosy. Thalidomide has • heroin—the foetus can become also recently shown addicted promise as a treatment for cancer. • cortisone—can cause deformities • antibiotics—may cause problems. These are not the only substances that can cause negative effects. It is best to avoid taking any drug— legal or illegal—during pregnancy unless it is advised by a doctor.
Other considerations A medical imaging technologist performing an ultrasound scan
Fig. 6.3.8
abdomen and a sample of amniotic fluid is removed. Although a fairly safe procedure, it does carry a small risk of injury to the foetus. Chorionic villus sampling can be used between 10 and 12 weeks of pregnancy. In this procedure, a sample of placental material is taken. Like amniocentesis, this method carries a small risk for the foetus.
Diseases like rubella (German measles) can cause enormous deformities in the child if contracted by a pregnant woman in the first trimester. Toxoplasmosis can cause damage to the eyes and nervous system of the foetus. Any negative emotions experienced by the mother will also affect her body systems and hence the foetus. Emphasis should be on reducing anxiety and stress wherever possible. No heavy exercise should be undertaken in the first trimester. Worksheet 6.4 Stages of pregnancy
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From gamete to birth
UNIT
6.3
[ Questions ]
Checkpoint Copulation and fertilisation 1 Define ‘copulation’. 2 State the number of sperm released in one ejaculation. 3 State the number of sperm that penetrate the egg. 4 a Identify the two types of twins. b Explain how each are produced. 5 a Identify two different types of contraception from the table on page 178. b Compare the advantages and disadvantages of each type.
b Vasectomies do not always work. Explain why this is the case. 21 Many people are now choosing home births rather than hospital births. State one advantage and one disadvantage of each. 22 Explain what would happen if menstruation occurred after implantation. 23 A woman is expecting a baby in February. a Propose what tests you recommend she has and when. b Predict when you think she knew she was pregnant. c Describe how she could have found out. 24 A caesarean is often required when birth will be difficult. Research what it is and how it relates to the Emperor of ancient Rome.
How a zygote becomes a baby 6 Differentiate between a zygote, a morula and a blastocyst. 7 Identify the most dangerous time of pregnancy in terms of potential harm to the developing baby. 8 Describe how the foetus is protected inside the mother. 9 Explain why the foetus does not drown in the amniotic fluid. 10 When a baby is first born, the bones of the skull aren’t joined. Explain why this is helpful for the birthing process. 11 A woman knows she is about to give birth when her waters break. Explain what this means.
The mother’s health in pregnancy 12 Identify four things that can harm the embryo/foetus.
Investigate 1 a Investigate more about what an imaging technologist does. It may be possible to interview one at a local hospital or clinic. b Imagine you are a medical imaging technologist. Construct a diary entry for a typical day, explaining the patients you met and the tests you performed.
15 Smoking constricts blood vessels and causes circulation problems. Explain how this could affect the foetus.
2 The rhesus factor can cause miscarriage during pregnancy. a Investigate what this is and how it affects the mother and foetus. b Describe how the problem is avoided using medical treatment. c Present your information in a way that can be understood by a person who has just become pregnant.
16 Explain why it is good to hear a newborn cry loudly.
Surf
13 Describe two tests that can be performed to find out if there is anything wrong with the foetus while it is still in the womb. 14 Explain why folate is important during pregnancy.
Think
17 Explain what toxoplasmosis can cause. 18 It is especially important that a pregnant woman does no heavy exercise in the first trimester. Explain why. 19 Draw a diagram to demonstrate how amniocentesis is performed.
Analyse 20 Men sometimes have vasectomies when they don’t want any more children. a Identify the tube that is cut to stop any sperm entering the vagina.
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[ Extension ]
3 Explore an animated journey through the first nine months of pregnancy by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button.
UNIT
context
6. 4 Our reproductive systems are vulnerable to many problems. These problems can include: • diseases that are passed from person to person by sexual contact. These are called sexually transmitted diseases (STDs), but were once called venereal diseases (VD). • other diseases that are not ‘caught’. For example, prostate cancer affects many males, and breast cancer is common in females. Regular tests can detect these cancers early, which increases the person’s chance of survival.
• other problems, including painful periods and ovarian cysts. These can also occur when the reproductive system does not work properly. • infertility, where the male or female reproductive system does not work properly. This makes pregnancy difficult or impossible to achieve. Some of these problems can be fixed or cured, while others are still being researched to understand their causes and effects.
Sexually transmitted diseases While AIDS is the most feared and life-threatening sexually transmitted disease, there are many others that can cause serious illness. Most are treatable, but can leave permanent damage. The best cure is prevention. The only way to be completely safe is to avoid all sexual contact. If you do choose to have sex, the use of condoms can greatly reduce the chances of becoming infected with some diseases. Other forms of contraception give little or no protection from STDs.
If you notice any unusual symptoms, you should see a doctor as soon as possible. The longer an infection is left in your system, the more damage it can do and the harder it becomes to treat. Some diseases can be asymptomatic (without symptoms). Chlamydia has few symptoms and can cause infertility. Syphilis is potentially deadly and begins with sores called chancres. All symptoms soon disappear, however, and victims may incorrectly think they are ‘cured’. Regular check-ups can identify any problems early.
STDs through history King Henry VIII is thought to have suffered from advanced syphilis. The infection is likely to have affected his brain and slowly made him ‘go mad’. Early treatment of some STDs involved taking mercury-based medicines. Unfortunately, these led to brain damage. Infections in the urethra in men (gonorrhoea, chlamydia) were sometimes treated by inserting red-hot rods into the penis to burn and kill the offending infection!
Disease
How is it spread?
Symptoms
Treatment
AIDS (viral, caused by HIV)
Sexual contact, exchange of body fluids (e.g. blood, semen)
Flu-like symptoms shortly after infection, then often nothing for years. Eventually breaks immune system down and results in many infections
No cure. Some drugs can slow the disease.
Herpes (viral)
Contact with active sore
Causes sores on mouth or genital region. Fever, itching
No cure. Some drugs can reduce the symptoms.
Gonorrhoea (bacterial)
Oral, genital, anal sex
May have no symptoms or can cause painful urination and a yellowish discharge in both men and women. Can cause infertility.
Antibiotics
Syphilis (bacterial)
Sexual contact or mouth. Enters through any break in skin.
Open, painless sore (chancre). If left untreated, can then develop a rash and finally infection of body organs.
Antibiotics, as long as it has not progressed too far
Chlamydia (bacterial)
Sexual contact
No symptoms or may have painful urination and discharge. Can cause infertility.
Antibiotics
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Reproductive problems
Fig 6.4.2
The steps in IVF treatment—there are many variations on this basic technique.
The eggs are collected by a needle or laparoscope and put in a salt solution.
The eggs are mixed with sperm, left overnight and checked to see if they have been fertilised.
Drugs are given so that more than one egg matures.
The fertilised eggs are incubated for a couple of days and then implanted in the woman’s uterus.
Fig 6.4.1
This engraving from the seventeenth century shows a patient with syphilis undergoing a treatment with powder. Fortunately, better treatments are available today. Many people used to go mad from the disease.
Infertility Both men and women can be infertile—unable to have children. It may be caused by an infection, or by radiation, or the cause may be unknown. Some people come to accept this situation, or choose to adopt. For those who wish to have their own child, there are other options available.
In-vitro fertilisation In-vitro literally means ‘in glass’. In-vitro fertilisation, or IVF, means that fertilisation takes place outside the woman’s body. Various medications are used to stimulate the ovaries so that they produce many eggs at once, rather than the usual one at a time. These eggs are then retrieved from the ovary. The eggs are placed in a salt solution at body temperature (37°C) until they are ready to be fertilised. Fresh sperm are added to each
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egg and allowed to incubate overnight. The next day, each egg is examined to check whether it has been fertilised. The fertilised eggs are then allowed to develop for another couple of days in the laboratory. Usually several embryos are transferred at once through a small tube into the uterus. While the transfer of multiple embryos increases the chance of success, it also increases the chance of multiple foetuses developing. Fig 6.4.3
Low sperm counts inherited Men with low sperm counts or sperm that do not swim properly are able to become fathers using an IVF technique where a sperm is injected directly into the egg. Sons born through this technique often inherit their father’s infertility problems, however.
IVF frequently results in multiple pregnancies.
Multiple births Non-identical twins normally happen in about 1 in 80 births and identical twins happen in 1 in 250 births. The chances of having triplets or quadruplets are much smaller. In some areas, up to 50% of babies conceived through IVF are twins or triplets. Women’s bodies are not designed to carry more than one child at a time, and so multiple pregnancies pose serious risks to the mother and the developing foetuses.
UNIT
6. 4 Career profile Medical practitioner Medical practitioners diagnose physical and mental illness, disorders and injuries, and prescribe treatments and medication to restore good health. Many specialise in different fields related to reproduction, including: • obstetrician/gynaecologist—provides medical care before, during and after childbirth • paediatrician—diagnoses and treats diseases of children from birth to early adolescence. • • • • • •
A good medical practitioner is able to: relate to and enjoy working with people listen to others carefully demonstrate good communication skills apply logical and scientific thought to a problem make observations and draw conclusions based on this information display a high degree of motivation and self-discipline.
UNIT
6. 4
Paediatrician checking the health of a baby
Fig. 6.4.4
[ Questions ]
Checkpoint Sexually transmitted diseases
11 Identify one part of the male reproductive system commonly affected by cancer.
1 In your own words define ‘sexual contact’.
12 Identify one part of the female reproductive system commonly affected by cancer.
2 Describe how you can protect yourself from sexually transmitted diseases.
13 Evaluate the importance of regular check-ups if you have multiple sex partners.
3 Describe how gonorrhoea is spread and how is it treated.
14 IVF is very time-consuming. Explain why.
Infertility 4 Identify two things that can cause infertility. 5 Define ‘asymptomatic’. 6 Define ‘chancre’.
15 Describe three things a pregnant woman could do to help her child to be born healthy.
Analyse
7 Explain why IVF often results in multiple pregnancies.
16 The rate of adoption is going down. Analyse whether this is related to IVF.
Think
17 Write a paragraph to summarise the basic steps in IVF.
8 Explain why it may be dangerous for a woman to proceed with a multiple pregnancy. 9 Sometimes herpes is passed to a new baby as it is being born. Explain how this occurs. 10 Infertility is more likely to occur in older people. Explain why.
18 State three reasons why the number of new cases of most sexually transmitted diseases is increasing in many countries despite contraception being used more widely. 19 Evaluate the importance of contraception to society.
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Reproductive problems
[ Extension ]
Chapter review
Investigate 1 Research toxic shock syndrome. a What is this condition? b Why are tampons no longer likely to cause toxic shock? c Outline some alternatives to using tampons. 2 Design a poster promoting safer sex. What is it and why is it important?
[ Summary questions ] 1 List the types of asexual reproduction and state an example of each type. 2 Arrange these terms in order: foetus, zygote, fertilisation, implantation, embryo, gametes. 3 Look at the following diagram and label parts a–e.
3 Pap smears can detect cervical cancer. Research how this test works. 4 Research other reproductive problems not discussed here. For example, how do ovarian cysts arise and how are they treated? Present your findings as a leaflet to be placed in a medical centre. 5 Investigate a sexually transmitted disease and outline: a the signs and symptoms b how the disease is spread c how the spread of the disease can be controlled d how widespread the disease is e any cures or treatments f current research into this disease. Select a way to present your information by negotiating with your teacher.
a d b
e
c
Fig 6.4.5
4 Identify the type of reproduction that requires only one parent and produces offspring identical to the parent. 5 State how long gestation takes in humans. Give your answer in days and months. 6 Identify where fertilisation takes place in humans. 7 Describe the conditions needed for maximum sperm production. 8 Discuss one advantage of asexual reproduction. 9 State one advantage of the young developing in the mother’s body.
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10 Match each of the following reproduction terms with its correct definition.
Terms
Definitions
Ova
a Ring of muscle separating uterus and vagina
Ovaries
c Male sex organs that make sperm cells
Ovulation
d The male sex cell
Oviduct
e Area where sperm cells are stored
Uterus
f Consists of seminal fluid and sperm
Cervix
g The process of releasing an ovum once a month
Vagina
h Area where the embryo implants and grows
Sperm
I The female sex cell
Testes
j Nourishes and activates sperm cells
Scrotum
k The passageway for menstrual flow and birth of a baby. Sperm is also deposited here.
Epididymis
l Tube that ‘catches’ the ovum
Seminal fluid Semen
m Passes through the penis. Urine and sperm pass through this tube. n Pocket of skin that holds the testes o Female sex organ that produces ova
[ Thinking questions ]
[ Interpreting questions ]
11 List the changes that testosterone causes in males at puberty.
20 Assess how mutations can sometimes lead to permanent improvements in a species.
12 Describe how two types of asexual reproduction occur.
21 Complete the following table to compare flower and human parts.
13 Describe one contraceptive method, including how effective it is and why. 14 List three things a mother-to-be could do that would harm a growing foetus.
Flower part
15 Explain how you can protect yourself against herpes.
Anther
16 Propose how the risk of multiple pregnancies by IVF can be reduced.
Ovary
17 a Construct a labelled diagram of a flower. b Construct a table to summarise the flower parts and their function. c Explain the term ‘pollination’.
Ovule
18 Identify possible career paths in the area of reproduction and associated technologies. 19 Outline the scientific skills that would be useful for a career as a medical imaging technologist.
Human part
Comparable function Production of male sex cells
Ovary Sperm
Male sex cell
Male sex cells deposited here
22 Distinguish between asexual and sexual reproduction. 23 Outline the role of cell division in multicellular organisms in: a growth b repair c reproduction Worksheet 6.5 Reproduction crossword Worksheet 6.6 Sci-words
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Energy in ecosystems
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7
Key focus area
5.3, 5.10, 5.1 1
Outcomes
>>> The implications of science for society and the environment By the end of this chapter you should be able to: distinguish between the living and non-living parts of your environment distinguish between organic and inorganic substances construct simple food chains construct simple energy flow diagrams for an ecosystem track water through the water cycle describe the carbon and nitrogen cycles describe how humans can interfere with the water, carbon and nitrogen cycles
Pre quiz
list examples of renewable and non-renewable energy sources, stating their advantages and disadvantages
1 Which nuclear reaction do you witness daily? 2 There are more insects and small animals than big ones on Earth. Why?
3 What will you choose to boil a kettle— peanuts or cashews?
4 Why does the venus flytrap plant eat bugs? 5 You are getting energy from the Sun when you eat a sausage. How can this be?
6 Petrol is a fossil fuel. What does this mean when it doesn’t appear to have any fossils in it?
7 Can poo be used for energy?
UNIT
context
7.1 The planet Earth flourishes with a rich variety and abundance of plant and animal life. Each living organism has its own particular energy requirements and therefore will only be found in areas that meet its needs. Plants get their energy from light from the Sun. Animals eat plants, or animals that once ate plants. The energy absorbed by plants from sunlight therefore passes directly or indirectly to animals and up through the food chain. Whatever organism we study, the ultimate source of energy is the Sun.
What is energy?
into the insect (a primary or first order consumer), which then provides energy for the frog (a secondary or second order consumer). The frog is a source of energy for the snake (tertiary or third order consumer), which in turn provides energy for the kookaburra (fourth order consumer). In this food chain, the kookaburra is the highest order consumer, as it is unlikely that anything else will be able to catch and eat it. If by chance a dingo or some other animal caught it, that animal would be considered a fifth order consumer. Fig 7.1.2
The third link in the food chain—a snake eats a frog.
Energy is the ability to do work and is measured in joules (J). Organisms require energy for the ‘work’ of living. This work includes growth, reproduction, respiration, repair of body tissues and digestion. What supplies the energy for these processes? Consider the simple food chain in Figure 7.1.1. This can be written as: green plant → insect → frog → snake → kookaburra
In this food chain, we can see that the energy from the green plant (biologists call this a producer) goes
Fig 7.1.1
A diagram of a food chain in an Australian ecosystem. The arrows point in the direction the ‘food’ is travelling.
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Energy for life In the example, the food source for each of the consumers in the chain is obvious—but what provided the energy for the plant to grow? The answer is the Sun. Apart from a few specialised bacteria that use chemicals and volcanic heat as their energy source, the Sun is the initial source of energy for all other organisms. It provides the foundation upon which most food chains are built.
Life without light Not all life on Earth depends on sunlight. In 1977, scientists from the Woods Hole Oceanographic Institution found a number of places deep in the Pacific Ocean where huge tubeworms, crustaceans and octopods all survived on chemosynthetic bacteria. With no sunlight able to penetrate these depths, these specialised bacteria used the compound hydrogen sulfide from surrounding rocks as their energy source.
Conservation of energy All energy is conserved within an ecosystem. The Law of Conservation of Energy states that energy is neither created nor destroyed, but instead converts from one form into another. Energy conversions begin in the Sun, where a reaction called nuclear fusion converts nuclear energy into massive quantities of heat energy and light energy. Plants Energy are able to trap the Sun’s light conversions energy and use it as the power In one hour, the Sun source for food production within produces more energy ly earth other their cells—that is, they convert than all our resources combined can light energy into chemical energy. provide in one year! Organisms that produce food in this Cars are very inefficient way are referred to as producers or when converting energy. s joule autotrophs. All other organisms rely Out of every 100 of chemical energy on the energy stored by plants to stored in petrol, only meet their energy needs. Organisms about 20 joules is used that eat plants are referred to as car! in moving the consumers or heterotrophs.
A one-way flow Within an ecosystem, energy flows in one direction only. Producers and consumers rely daily on the light energy from the Sun to drive the process of photosynthesis. Consider the energy flow in the food chain in Figure 7.1.1. Starting with the Sun as the initial energy source, the energy flow could be written: nuclear energy
→
light energy
(from the Sun) (from the Sun)
190
→
chemical energy
→
chemical energy
(made by producers) (eaten by consumers)
The transfer of energy from one organism to the next is not 100% complete. Consider the first two organisms in the food chain shown in Figure 7.1.1. • The insect eats the plant’s molecules. • The plant’s molecules are digested—large molecules are broken down into smaller ones. This process uses some energy while making other energy available. • The chemical energy and the smaller molecules are now available to the insect for its own requirements. • Unused molecules, and the chemical energy holding them together, are excreted as waste products. These are then used by other organisms in the ecosystem, such as decomposers that break down waste. The insect now contains the chemical energy of the plant. This energy is then used for the many functions the organism must perform to stay alive or to continue its species. • Some will be used as the insect moves around in search of food or a mate, or perhaps to evade a predator. This type of energy, the energy of movement, is called kinetic energy. • Some insects also produce sounds to communicate with each other. The initial chemical energy provided by the plant has become kinetic energy that is observable as sound. • Much of the chemical energy passing into the kookaburra in our food chain will be converted into heat energy that will keep its body temperature constant. Animals that maintain a constant body temperature are said to be endothermic. The body temperatures of the insect, frog and snake, however, depend on the temperature of their external environment. Such animals are described as ectothermic. • Whatever energy is left over after these processes will be used to grow new cells. This energy is effectively ‘stored’ and passes on to the next level of the food chain when the animal is eaten. The energy that the organism converts into sound, heat and movement is released directly into the environment and cannot be used by the next organism in the chain. This energy is essentially ‘lost’ from the food chain, leaving as little as 5–20% of the total energy to be passed on to the next level of the food chain.
UNIT
7.1 If the total number of plants in a particular ecosystem were counted, we would find an enormous number. We would expect to find a smaller number of herbivores eating those plants and an even smaller number of carnivores eating the herbivores. In any ecosystem the number of individuals at each level decreases as we move from the producers up to the higher orders of consumers. Another way to illustrate this aspect of a food chain would be to consider the dry weight of the organisms involved at each level. By comparing the dry weight of the organisms at each level in the food chain, we find that as each level increases, the weight of organisms sustained by the previous level decreases. Regardless of which way we measure the organisms at each level, a food pyramid is formed. The food pyramid also shows that the total amount of energy at each level decreases.
The food we eat provides the energy we require for the activities and functions we need to survive—heat to keep our bodies at a constant 37°C, energy for growth and repair of body tissues, and energy to move.
Fig 7.1.3 5 dingoes 10 kangaroos
Conservation of matter In the food chain in Figure 7.1.1, it is obvious that energy is not the only thing being transferred from one organism to the next—matter is also being transferred. While most of this material is used directly by the next organism for its own growth and survival, some is lost to the environment in the form of waste products. In 1789, the French scientist Antoine Lavoisier proposed one of the most fundamental laws of science—that atoms are not created or destroyed during chemical reactions, just rearranged. Known as the Law of Conservation of Mass, this law states that atoms can be recycled, allowing them to be used again and again in a variety of different structures.
Food pyramids How does the inefficient transfer of matter and energy affect the ecosystem? In order to understand the answer to this more clearly, consider this summarised food chain: producers (plants) → herbivores → carnivores
more than 1 million blades of grass
200 kg dingoes 1000 kg kangaroos 10 t grass
Fig 7.1.4
If we were to gather all the producers, herbivores and consumers in a food chain, and represent either their numbers or their dry weight diagrammatically, we would expect a pyramid-shaped diagram.
Worksheet 7.1 Food chains and food webs
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Energy for life
UNIT
7.1
[ Questions ]
Checkpoint What is energy? 1 Define and give examples of the following terms: a producer b consumer 2 Distinguish between a first order consumer and a second order consumer. 3 Consider the following food chain: algae → water snail → small fish → large fish → kookaburra
a Identify the producer. b List the first, second, third and fourth order consumers in this chain. c Explain what the direction of the arrows indicates.
The conservation of energy 4 Explain the Law of Conservation of Energy. 5 Identify three types of energy. 6 Identify energy conversions that take place in: a the Sun b a producer
A one-way flow 7 List two examples of an animal that is a ectothermic b endothermic 8 Describe how energy is ‘lost’ from your own body. 9 Look at the food chain in Figure 7.1.1. Of the organisms listed, determine which one receives the highest percentage of its energy from the plant. Explain your answer.
The conservation of matter 10 Explain the Law of Conservation of Mass.
Think 14 Distinguish between the flow of energy in an ecosystem and the flow of matter in an ecosystem, describing any similarities and differences. 15 Plants are often referred to as producers. Do you think this is an appropriate name? Explain your answer. 16 Construct a food chain, including yourself as one of its organisms. a Are you a consumer or a producer? b Are you the last organism in the chain? c Can you think of an organism that feeds on you? 17 If we included the dingo in the food chain in Figure 7.1.1, it would be considered a fifth order consumer. Propose a sixth order consumer in this chain. 18 Assess what would happen to all the consumers in the food chain in Question 16 if the Sun’s light were blocked for: a a week b a year 19 Construct a food chain you might find in your own backyard or local park.
Analyse 20 Describe how energy is ‘lost’ from a family pet. 21 Analyse how your answer to Question 20 depends on the type of pet you own. 22 In the graph in Figure 7.1.5, which line do you think would best represent a snake, and which line would best represent a kookaburra? Use the terms ‘endothermic’ and ‘ectothermic’ to explain your choice. Fig 7.1.5
Food pyramids
13 Construct a food pyramid for the following food chain: seaweed → small crab → lobster → octopus
a Include an estimate of the number of organisms at each level. b Show with arrows where energy is ‘lost’. c Label the producer. d Label each consumer and its order.
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Body temperature (ºC)
11 Define the term ‘inefficient’. 12 State whether there would be more carnivores or more herbivores in a food pyramid.
6 a.m.
A B
12 p.m.
6 p.m. Time
12 a.m.
UNIT
7.1 23 Discuss the advantage of a kookaburra having more than one food source (e.g. snakes and fish). 24 Construct an energy flow diagram for the food chain in Question 3. Does this flow diagram differ from the one given for the food chain in Figure 7.1.1? Explain.
[ Extension ] Investigate
For each biome:
1 Examine five different samples of one of the following: • breakfast cereals • ice creams • packaged foods (such as pies or pasties) • bread. For each sample you investigate: a Record the energy content. b Explain how it is different from the other samples. c State the unit for the energy content listed on each pack. d Identify which would be the best food choice for someone who sits down all day, compared to someone who spends the day doing hard manual labour. Explain your reasoning.
i Construct a diagram for each food chain/web, and name the producers, herbivores and carnivores. ii Compare its features with those of the other biomes, noting any similiarities. iii Create a game in which individual cards have a picture of the different organisms in the food chain/web. Also include ‘arrow’ cards and cards with the words ‘producer’, ‘herbivore’ and ‘carnivore’. During the game the cards should be arranged into the correct food chain or web. Develop the game and scoring rules.
Creative writing
Create
Alien food web
2 You will remember from Science Focus 2 that a biome is an area of similar climatic conditions. Within each biome are a number of different ecosystems and food chains. Research one such food chain or web that you might find in: a an arctic biome b a desert biome c a marine biome d a grassland biome
You are a ‘bioscientist’ on the spaceship Endeavour. You have just received the first samples of life from a planet you are orbiting, and it is your task to arrange them into a series of inter-linked food chains—that is, a food web. Before you begin this task, describe the features of the planet you are orbiting. Does it have one or more suns? What is the temperature like? What about the atmosphere, water, soil types present? How will these factors influence the organisms that live there? Draw and describe six alien life forms that live there, including both plants and animals. Give the reasoning behind their order in the food chain and label them as either producers, first, second or third order consumers, or decomposers. What features, if any, do they share with their Earth counterparts?
Penguins live in an Artic biome.
Fig 7.1.6
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Science focus: Bioaccumulation Prescribed focus area: The implications of science for society and the environment Pesticides and herbicides In order to supply enough food for an increasing human population, agricultural practice has changed. Large-scale farming has become more common, with huge amounts of land devoted to growing crops. These crops have been a readily available source of food for many insects and pests. The use of fertilisers and ploughing of the land has also encouraged weeds to grow among the crops, using the valuable nutrients in the soil. Both weeds and animal pests are known as competitors, as they try to use the same space or to eat the growing crops. Humans have developed a range of strategies and chemicals to control these competitors, and therefore improve crop growth. These chemicals, called herbicides and pesticides, have never existed before and are being released into the environment. Herbicides kill pest plants or weeds, while pesticides kill animal and insect pests. Some of these chemicals were considered wonderful as they promised to kill the pests while having minimal impact on the health of the natural environment. But this has turned out not to be true in most cases.
Chemicals entering the food chain With the widespread use of herbicides and pesticides, many chemicals have become part of the natural food chains. The chemicals are absorbed by plants and small animals. When these plants and animals are consumed by other animals, the chemicals are also consumed and passed up the food chain. Chemicals also wash into rivers, lakes and the ocean, where they are absorbed by algae. The algae are consumed by aquatic animals and again the chemicals are passed up the food chain. Many of the household chemicals we use end up in the environment and enter the food chain.
Fig SF7.2
Bioaccumulation
In order to control weeds and animal pests, crops are often sprayed with pesticides and herbicides.
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Fig SF7.1
Bioaccumulation is the process of organisms accumulating (building up) higher and higher levels of these chemicals in their bodies. These chemicals become more concentrated in organisms as we move up a food chain. Because energy is lost in each step along the food chain, animals have to eat a lot of plants or other animals in order to meet all their energy requirements. Animals at the top of the food chain must consume very large amounts of other organisms, and so more and more chemicals become concentrated in their tissues.
Fig SF7.3
The huge amounts of chemicals used in agriculture, and the various chemical wastes released by industry into the environment have produced many unexpected and undesirable consequences for animals and plants. These include: • the deaths of many large sea mammals such as dolphins and whales, which is thought to be related to bioaccumulation • the thinning of egg shells of birds such as the American eagle, leading to this animal becoming endangered • increased rates of cancer, disease and deformities in humans
The concentration of chemicals in a food chain is shown by this energy pyramid.
2 dolphins
Less organisms at each level but a higher concentration of toxic chemical
500 large fish Energy loss 20 000 medium fish
200 000 small fish
1 000 000 algae Chemical
The brown dots represent a chemical added to crops. There are two food chains shown. The arrows show the direction of movement of chemicals and the flow of energy through the food chains. Food chain 1: Directly from the crop 1
This begins with the crop being eaten by a first order consumer (a small beetle). The small beetles have small amounts of the chemical in their tissues. 2 & 3 The small beetles are then eaten by both the wasps and the small animals. The small animals eat a large number of the wasps and the beetles. This causes more of the chemical to accumulate slowly in their tissues. 4 The bird of prey (e.g. an eagle or a hawk) eats the small animals. The levels of the chemical have become more and more concentrated in each level of the food chain.
4
3
Food chain 2: Indirectly from agricultural run-off into waterways 2 1
5 1 2 3
After the run-off from crops reaches the ocean: 1 Small microbes (plankton) or algae take up the chemicals from the water as they build their cells. 2 Small fish and other animals feed on the plankton and algae. 3 Many of these small fish are eaten by larger fish. 4 Large fish eat these fish. 5 Top predators, such as dolphins, eat the largest fish and slowly accumulate large amounts of the chemical in their tissues.
4
Bioaccumulation of chemicals in the food chain
Fig SF7.4
195
• increased rates of death and disease in many animals, especially the top predators, such as polar bears.
Fig SF7.5
A scientist is milking this tranquillised polar bear to test for pesticides. Although pesticides are not used in the Arctic, they are still found there.
[ Student activities ] 1 The chemical known as DDT was once considered the most useful chemical ever invented. But these hopes proved false and DDT was banned in the United States after it was discovered that a by-product from DDT was accumulating in the tissues of the bald eagle, the US national bird. The DDT was affecting the eggs being laid by the eagles, causing the shells to be so thin-walled and brittle that they rarely lasted long enough for the chick to be born. Even after the banning of DDT use in the United States and many other countries, it is still produced and supplied to developing countries, particularly to combat the malaria mosquito. a Investigate the uses of DDT and problems that have arisen as DDT by-products have accumulated in food chains. b Discuss these problems in a group, and propose reasons why DDT is still being used in some countries. 2 a Using your knowledge of how bioaccumulation occurs in food chains, describe some of the things people need to consider when using chemicals in the environment and when choosing foods to eat.
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DDT was once thought safe and was sprayed on people at the beach and throughout neighbourhoods to control mosquitoes.
Fig SF7.6
b Evaluate the use of pesticides and herbicides. Are they worth using in spite of the problems they cause? 3 The problem of chemicals being found in the food we eat has become of increasing concern, yet many people are still unaware of the potential problems that can arise if chemicals start to accumulate through food chains. a Research the possible hazards of bioaccumulation. Find examples to help you demonstrate the problems it can cause. b Design a poster to demonstrate the hazards of bioaccumulation. Your poster should be displayed at school and should allow all students to easily understand the process. 4 Organic farming uses a natural approach that avoids the use of chemicals in growing food. a Investigate some organic farming practices. b As a group set up a vegetable garden and design an experiment to test the effectiveness of an organic farming technique. Compare it to a technique that uses chemical control. Try to answer such questions as: Which technique produces the largest crop? Which is healthier? Which is easier? c Evaluate your results and make recommendations for improving your experiment.
UNIT
context
7. 2 Although it seems impossible, the water you showered in today could have once been part of a glacier on Mount Everest! Some atoms in your body could even have once been part of a great scientist like Marie Curie or the warrior Genghis Khan! How can this be? Every day, atoms are recycled through the
Two types of matter In an ecosystem, matter can take an unimaginable number of forms: the petals of a rose, precious stones embedded in rock, the hard exoskeleton of a cicada, the wax in your ear. Everything around us is made of matter. All matter is made up of atoms—but while the same atoms are present in many different structures, each structure has its own specific combination and arrangement of atoms. At first glance you might think that the legs of a cockroach and the hairs on your head are very different. In fact, they are built from cells made from the same basic atoms: carbon, oxygen, hydrogen and nitrogen. The only difference is that they are arranged in a different way.
Fig 7.2.1
A close-up look at the structure of a rose petal and the structure of a butterfly’s wing. In spite of the obvious differences, the atoms that make up the two are basically the same.
ecosystem—used again and again in the structural components of plants and animals. It is possible, therefore, that the atoms that were once part of a long extinct dinosaur may now be somewhere in your own body. We can only imagine where they will be 100 years from now.
All living things have one vital thing in common— they are all made from matter that contains carbon atoms. The skin, muscles and bones that make up animals contain carbon atoms, as do the bark and leaves that make up plants. Matter that contains carbon atoms is called organic matter. All other matter is referred to as inorganic matter and includes all the non-living components of the ecosystem. Rocks, minerals, most of the gases found in air and water are all examples of inorganic matter. Both organic and inorganic matter are recycled through an ecosystem and form a series of ‘cycles’. Some cycles are simple (e.g. the carbon cycle), while others are more complex (e.g. the nitrogen cycle). All cycles rely on the flow of atoms between the biotic (living) and the abiotic (non-living) environment. In healthy ecosystems, this flow remains balanced.
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Recycling in nature One bad apple
H
H
C
C
H
H
Fig 7.2.2
Ethene is an organic compound released by many fruits as they ripen. When apples are bruised or damaged, they release more than the usual amount of ethene, which causes other fruits near to them to ripen more rapidly. Thus one bad apple can spoil a whole bag!
The structure of the organic compound ethene, a naturally occurring chemical produced when fruits ripen. It is hoped that one day this substance can be used as the initial building block from which synthetic fuel can be made.
The water cycle Compound count More than 2 million organic compounds have been discovered so far—and this e number is increasing by mor than 100 000 each year.
Because water, H2O, contains only hydrogen and oxygen atoms it is classified as an inorganic compound. Of all the water on Earth, almost 98% is found in the salt water of the oceans. Of the remaining 2%, some is
found in the form of atmospheric water vapour and as permanent ice deposits in various parts of the Earth. Less Raining cannons than 1% is available as fresh It was observed that it water to the organisms that live would often rain after on the Earth. It is only because battles in which cannon fire was heavy. This was water is recycled that life on due to the release of our planet has been able to millions of tiny carbon exist for millions of years. particles as the cannons were fired. Each of these The Sun is the only source particles acted as a of energy that powers the nucleus around which a essential process that we know raindrop would form. This principle is used as the water cycle. Heat energy today in a technique from the Sun causes water called ‘cloud seeding’. molecules to evaporate from: Planes release a • moist soil surfaces multitude of tiny crystals as they fly through • living organisms such as clouds, causing it to rain. plants (by transpiration) and animals (sweat) • lakes, rivers and oceans. Of these, evaporation from the oceans provides most of the water vapour present in our atmosphere. Carried by air currents, The water cycle
Fig 7.2.3
condensation precipitation rain evaporation from lakes, rivers, ocean transpiration from vegetation
dunes run off soakage weathe red la (perme yers able)
solid rock (impermeable)
198
beach
fresh water lake salt water
ocean basin
much of the water vapour Interesting water facts falls as either rain or snow • 75–80% of the Earth’s surface when it reaches land. This is covered in water. water seeps down through • The human body is soil and porous rock until it approximately 60–70% water. reaches a layer of non• Stanislao Cannizzaro established the formula for porous rock which stops the water as H2O in 1860. water sinking any lower. • As the salt content of water The soil and rock increases, the boiling point immediately above this increases. becomes saturated with • As the salt content of water increases, the freezing point water. This saturated layer is decreases. known as the water table. Eventually the water finds its way back to the sea, allowing the cycle to continue.
The carbon cycle
Prac 1 p. 202
Prac 2 p. 203
Carbon is found in all living things and in all things that once lived but have since died. It is present in carbohydrates, lipids and proteins— the building blocks of living tissue. It is also found in our atmosphere, combined with two oxygen atoms to form the gas carbon dioxide—CO2. It is the movement of carbon atoms between the living and the non-living environment that we call ‘the carbon cycle’. In our biosphere, green plants inhabit the terrestrial (or land) ecosystem, and algae inhabit the aquatic (or water) ecosystem. Both green plants and algae obtain the carbon atoms they need from the carbon dioxide in the atmosphere. Land plants take up the carbon dioxide directly from the atmosphere through tiny pores in their leaves called stomata, while aquatic algae absorb carbon dioxide, dissolved in the water surrounding them, over their entire surface. Once inside the plant, the carbon atoms do not remain joined to the oxygen atoms. During photosynthesis, the carbon Interesting carbon facts atoms detach from their • 75 billion tonnes of carbon are turned into carbohydrates oxygen atoms and rearrange each year via the process of to form glucose. Glucose is photosynthesis. used for energy or further • 500 billion tonnes of carbon rearranged into cellulose is stored in the sea. (a structural component in • 700 billion tonnes of carbon is stored in the atmosphere. plant cell walls) and starch (an energy store).
UNIT
7.2 sunlight
CO2 H2O carbon dioxide + water (6CO2 + 6H2O)
light
energy
glucose + oxygen (C6H12O6 + 6O2)
H2O H2O
Fig 7.2.4
Photosynthesis is driven by energy from the Sun. It is the process that provides the foundation for most of life on Earth.
Atmospheric carbon enters the ecosystem through the process of photosynthesis. How is it then distributed among all the organisms that live there? Digestion! Herbivores eat and digest plant matter, using the carbon and other elements contained within the plant to provide for their own energy and growth requirements. Higher order consumers are usually carnivores (meat eaters) and rely on digestion to convert the carbon obtained from eating animal tissue into a form they can use. Omnivores, which eat both meat and plants, convert carbon from both sources. A perentie is a desert biome dweller. Here one is feeding on a small wallaby—‘wallaby atoms’ are soon to become ‘perentie atoms’!
Purple bacteria Halobacteria (salt-loving bacteria) live in water seven times saltier than sea water. Although these bacteria are photosynthetic, they do not use chlorophyll, the green photosynthetic pigment of green plants. Instead they use retinal, the pigment found in the vertebrate eye that enables us to see. For this reason, halobacteria appear purple, not green.
Fig 7.2.5
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Recycling in nature If photosynthesis and digestion distribute carbon atoms among the organisms within an ecosystem, how are they returned to the atmosphere? There are several methods, including: • the release of carbon dioxide back into the atmosphere via respiration, which can be summarised as: sugar + oxygen → water + carbon dioxide + energy
Sugar is broken down to provide energy for the organism’s needs. Carbon dioxide and water are waste products that are released back into the ecosystem. • the return of carbon to the ecosystem through animal wastes (faeces and urine) • the decomposition of dead plants and animals and animal wastes by the action of decomposers (bacteria, fungi and worms) in the How is a fungus soil. Decomposers also like an iceberg? undergo respiration, The part of a fungus that returning carbon you see above the ground is called the dioxide to the ‘fruiting body’. This is atmosphere. the reproductive The production and structure of the fungus and varies greatly in consumption of carbon colour, size and shape dioxide and oxygen are from species to species. linked through the processes Fungi are similar to icebergs: the largest of photosynthesis and proportion of their respiration. In the past, the structure, the thread-like levels of carbon dioxide and structures called hyphae, oxygen in the atmosphere lies below the visible surface.
Killer burp On 21 August 1986, the have been relatively constant, with waters of Lake Nyos in oxygen at approximately 20% and Cameroon released a carbon dioxide at 0.04%. The massive ‘burp’ of carbon dioxide gas, suffocating balance of carbon dioxide and almost 2000 people. oxygen levels has recently been upset, however, due to: • large-scale felling of rainforest trees • increased production of carbon dioxide by industry • increased burning of fossils fuels such as petrol. Burning fossil fuels releases carbon into the air.
Photosynthesis removes CO2 from the atmosphere
easees ease phe e phere
Animals gain carbon by eating plants H2O or other animals. H2O Dead organisms and their wastes are Dead organisms can form fossil fuels decomposed by fungi and bacteria. in the Earth's crust – coal, oil and gas. They also release CO2 back into the atmosphere.
The carbon cycle is a relatively simple cycle, with carbon atoms moving between the abiotic and biotic environments. Sunlight is the driving force behind it all.
This imbalance has contributed to what is referred to as the enhanced greenhouse effect, and is discussed in detail in Science Focus 4.
The nitrogen cycle
Fig 7.2.6
200
The common mushroom is one of an estimated 250 000 species of fungi. Although they vary greatly, each plays an important role in the decomposition of dead organic matter.
Fig 7.2.7
Meat-eating plants Carnivorous plants have a unique way of getting nitrogen—they eat it! The pitcher plant, found on Cape York Peninsula, contains enzymes similar to those found in the stomachs of vertebrate animals. It obtains nitrogen by dissolving the insects that fall into it.
Nitrogen is found in the atmosphere as a colourless and odourless gas, N2, which makes up about 78% of the air around us. Most organisms cannot use nitrogen when it is in its atmospheric, N2, form. Before it can be used it needs to undergo a process called nitrogen fixation. Most of this happens during lightening strikes, where the electrical energy from the storm converts atmospheric nitrogen into various useful nitrogen compounds.
One group of those compounds is the nitrates (containing the nitrate ion NO3–). These dissolve in rain droplets and fall onto the Earth’s surface, and are taken up by the roots of plants. Once inside the plant, nitrogen plays an essential part in the formation of amino acids (the building blocks of protein) and nucleic acids (the building blocks of genetic material). These nitrogen compounds are then consumed by animals when the plants are eaten. The animals now have a source of nitrogen from which they can produce their own proteins and nucleic acids.
Fix
ing nitrogen The Earth experiences an average of 16 000 000 thunderstorms eac million tonnes of nitrog h year. One hundred en enters the soil in thi s way. Although only fixed nitrogen, a few a small source of bacteria also perform this essential functio • the nitrogen-fixing n. These include: and soil-living Azobac ter • Rhizobium, which lives in root nodules on leguminous plants (su clover) and some wa ch as peas and ttles • Frankia, which live s in the root nodules of plants of the Casua These three bacteria rina genus. use atmospheric nitrog en directly, convertin g it into forms that can then be used by animals and other pla nts. Much of this nitrogen is returned to the eco system as ammonia, urine and faeces, or wh present in animal en dead organic matter converted back into nit decomposes. This am rates by nitrifying ba monia is cteria that are natura soil. Another type of lly present in the bacteria, the denitrif ying bacteria, conver t these nitrates back into atmospheric nitrog en gas.
Worksheet 7.2 Too big for our boots!
Fig 7.7.8
The nitrogen cycle is complex, as it involves the interaction of many different organisms in the ecosystem.
Atmospheric Nitrogen is converted to nitrates and dissolved in raindrops
Atmospheric nitrogen in soil spaces is converted by bacteria in root nodules into proteins which are was Sci 3 the figplant used by
Dead organisms and their wastes are decomposed by fungi and bacteria. Nitrogen is released back into the soil as nitrates.
Soil
UNIT
Atmospheric nitrogen
Nitrates used by plants
7.2
UNIT
7.2
De-nitrifying bacteria in soil convert nitrates into atmospheric nitrogen.
[ Questions ]
Checkpoint Two types of matter 1 Identify the two groups into which we classify all matter. 2 List two examples of each type of matter you identified in Question 1. 3 a Define the terms ‘biotic’ and ‘abiotic’.
b Classify each of the following as a biotic or abiotic feature of the environment: water, leaf, soil, air, algae, bacteria, rock, grass, cloud, human.
The water cycle 4 Describe the water cycle. 5 Define the following terms: a condensation
b evaporation
c precipitation
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Recycling in nature
The carbon cycle 6 Draw a diagram to illustrate the basic conversions that occur in the carbon cycle. 7 Identify where, and in what form, carbon enters a plant. 8 a Identify the process whereby plants convert carbon dioxide and water into the sugar known as glucose. b Identify the source of the energy for the above process. 9 a Identify an important gaseous product of the process described in Question 8. b Explain why this by-product is important.
[ Extension ] Investigate 1 Research the phosphorous cycle and the effect that fertilisers have on the environment. Include a diagram in a short written report of your findings. 2 Investigate how coal is formed. Explain how the carbon in coal is eventually released back into the environment. Illustrate your short report with a ‘carbon-cycle’ that shows the important conversions.
The nitrogen cycle 10 Is nitrogen, N2, an organic or inorganic compound? Justify your answer. 11 Draw a diagram to illustrate the main conversions that occur in the nitrogen cycle. 12 Identify two acids in the human body that require nitrogen. Explain why these acids are important. 13 State the form in which nitrogen exists in: a the atmosphere b the soil c urine and faeces
Think 14 Deduce whether the following statements are true or false: a Nitrogen and carbon atoms move between the abiotic environment and the biotic environment. b Most living organisms need water. c The nitrogen cycle, the carbon cycle and the water cycle all support the Law of Conservation of Matter. d Bacteria play an essential role in the continuation of life. 15 Describe what lightning does in the nitrogen cycle. 16 List three different bacteria that can fix nitrogen.
Create 3 Imagine that you are a carbon atom. Describe what you have been doing for the past 100 years. What interesting things have you been a part of, and where do you think you will go next? Construct a diagram of your life cycle so far. 4 a Use an old fish tank or large glass jar to construct a terrarium to simulate the DYO water cycle. b Place labels on the outside of the tank to explain what is occurring in each part of the tank in relation to the water cycle. 5 Use a computer program such as Flash to construct an animation of the carbon, nitrogen or water cycle.
Surf 6 Explore the informative and interactive animations of the carbon and water cycles by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7 and clicking on the destinations button.
17 Distinguish between the different types of bacteria involved in the nitrogen cycle.
Analyse 18 What would happen if all the decomposers on the Earth suddenly disappeared? Explain your reasoning.
UNIT
7.2 202
[ Practical activities ] Testing for water Aim To test for the presence of water in
Prac 1 Unit 7.2
different liquids
Equipment Cobalt chloride paper, anhydrous copper(II) sulfate, watchglass, pipette, paper towels, various liquids (tap water, methylated spirits, salt water, sucrose solution, acetic acid (2M)), unknown liquids X, Y and Z
Measuring the boiling point of water
Method There are two simple tests that determine whether a liquid contains water. • Test 1: When water is added to anhydrous cobalt(II) chloride paper, it turns the paper from blue to pink. • Test 2: When water is added to anhydrous copper(II) sulfate, it turns from white to blue. Note: The term ‘anhydrous’ means ‘without water’. 1 Drop a small amount of water on a small piece of anhydrous cobalt(II) chloride paper and a small sample of anhydrous copper(II) sulfate. Verify that each changes colour according to test 1 and test 2 listed above. 2 Copy the table below into your notebooks.
Prac 2 Unit 7.2
UNIT
7.2 Aim To measure the boiling point of various samples of salt water
Equipment Bunsen burner and mat, tripod, matches, tongs, four 250 mL beakers, distilled water, salt, tablespoon, thermometer able to record temperatures higher than 100°C
Method 1 Copy the table below into your notebook. Liquid
Boiling temperature
Beaker 1 (distilled water)
Liquid tested
Copper(II) sulfate
Cobalt chloride paper
Beaker 2 (1 tablespoon salt) Beaker 3 (2 tablespoons salt)
Tap water Beaker 4 (3 tablespoons salt) Methylated spirits Salt water Sucrose solution Acetic acid Unknown X Unknown Y Unknown Z
3 Place one spatula of anhydrous copper(II) sulfate on a watch-glass. 4 Add 5–10 drops of tap water and record any colour change. Record your results. 5 Wash and dry the watch-glass thoroughly. 6 Place a piece of cobalt(II) chloride paper on the cleaned watch-glass.
2 Set up the Bunsen burner, the mat and the tripod. Light the burner. 3 Label the beakers 1 to 4. Add 200 mL of distilled water to each. 4 Heat the water in beaker 1 until it boils. Measure the temperature and record the result. (Note: Place the thermometer in the water while it is still cold and heat it gradually. Allow it to cool down a little between tests.) 5 Using tongs, remove beaker 1 and place it to one side. 6 Place beaker 2 on the tripod. Add 1 tablespoon of salt and stir until the salt has dissolved. Continue heating until the water boils. Measure the temperature and record the result. 7 Using tongs, remove beaker 2 and place it to one side.
7 Add one drop of tap water and record any colour change. Again, wash and dry the watch-glass thoroughly.
8 Repeat steps 6 and 7 with beakers 3 and 4.
8 Repeat steps 3–7, replacing the tap water with each of the solutions listed above.
Questions
9 Record your results.
Questions 1 Apart from a colour change, describe what else happens when water is added to anhydrous copper(II) sulfate.
1 Construct a line graph to show the relationship between the amount of salt dissolved in water (on the horizontal axis) and the temperature at which the water boiled (vertical axis). 2 Propose a reason for the results you observed.
3 Identify which of the unknown liquids contained water.
3 Antifreeze is a salty solution that is often put in car radiators to stop the water from freezing in very cold weather. It is also very useful in stopping radiators from boiling in hot weather. Analyse why.
4 Assess the importance of washing and drying the watchglass thoroughly between each test.
4 Analyse this statement: ‘Impurities in water increase its boiling point’.
2 Identify which of the known liquids contained some water.
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UNIT
context
7. 3 Individual humans have similar energy requirements to other mammals of comparable size. As a population, however, we have developed enormous energy requirements. In many countries, people have come to rely on all kinds of luxuries. Although inventions such as televisions, cars and air conditioners make our lives more pleasant, they are not really essential to life. A lot of energy is used in producing and running them. It is these non-essentials that have caused an energy crisis and an imbalance in the
Earth’s ecology. The future of the human race will be determined by what we do about our production and use of energy.
Energy sources are classified as non-renewable or renewable.
coal flue gas cooling water steam reheat air condensate
to station switchyard
detail of separation firing vapour burner feed water
economiser
steam from reheater steam to reheater
degenerator
reheater super heater
steam from super heater
coal bunker boiler
separator
turbo generator
chimney
burners rotary air heater air
precipitator boiler feed pump
circulating water pump
204
coal conveyor from open cut
gas
natural draught cooling tower
Fig 7.3.1
main burner
condensate pump
LP HP heater heater
pulveriser
water from separator
air intake FD fan
air supply duct
ID fan
ash removal to ash settling pond
Coal power stations pollute when they are operational. Their waste products are often toxic and environmentally destructive.
Non-renewable energy sources Energy sources that cannot be replaced are referred to as non-renewable. These energy sources include: • fossil fuels such as coal, gas, crude oil and its products petrol, diesel, kerosene and aviation fuel • uranium and other nuclear fuels used in nuclear power plants.
UNIT
7.3 There’s a dinosaur in my car! Fossil fuels are really just prehistoric plants, animals and algae that died millions of years ago. So when the family car is next filled, it is very possible that some dinosaur is being pumped in!
Fossil fuels Fossil fuels form when dead organic matter is not decomposed. This most often occurs in bogs and swamps. Oxygen is scarce in the mud at the bottom, making it impossible for decomposers to break down dead matter that has fallen there. More mud and silt slowly deposits on top, until the dead matter is eventually covered with dirt. Intense pressure and heat from movement in the surrounding earth over millions of years compresses and ‘cooks’ the matter first into coal, and then into crude oil and gas. While the burning of these fossil fuels provides large amounts of energy, it also releases large quantities of pollutants, particularly the greenhouse gas carbon dioxide, CO2. Also, once fossil fuels have been used, they cannot be used again.
Fossil fuels such as crude oil and natural gas can be extracted from under the oceans.
Fig 7.3.2
Fig 7.3.3
Prehistoric life provided the coal, crude oil and gas that we use today. Once these fuels run out, we will have no more. The original source of such energy is the Sun.
Uranium When uranium atoms are bombarded with neutrons, they often split, releasing more neutrons and enormous amounts of energy. So much energy, in fact, that splitting just one uranium atom releases 26 million times more energy than the burning of one molecule of natural gas! This process is referred to as nuclear fission. After World War II, nuclear reactors were built in the hope that fission would produce enough energy to meet the world’s increasing needs. Problems soon arose, however, the most pressing being how to dispose of the dangerous waste products. Radioactive waste can cause cell damage in living organisms and lead to cancer. Many methods of storing nuclear waste have been tried in the past but all are only short-term solutions. The waste can remain radioactive for many thousands of years, but some of these methods have failed after only a few decades. Scientists are currently considering ‘injecting’ waste deep underground into stable beds of a rock called shale, effectively trapping it far beneath the Earth’s surface. These measures are temporary, however—none of the nuclear waste produced in the United States over the past 45 years has yet been permanently disposed of! You will learn more about nuclear energy in Science Focus 4.
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Human intervention: energy crisis! Renewable energy sources Because of the rapid increase in use of fossil fuels, and the ecological impact of this, there is a very real need to find and use alternative and renewable sources of energy. Renewable energy comes from sources that can be used over and over again with minimal impact on the environment. Renewable forms of energy include: • energy from the Sun • energy from the vast quantities of heat stored within the Earth • energy from the action of wind • energy from water—the action of waves, currents or tides, the falling of water due to gravity, or differences in salt content • ‘green energy’—energy derived from wood and other plant matter (sometimes called biomass).
>>> Solar cells The solar cell, or photovoltaic cell, was first developed for the NASA space program and has been used to provide power for satellites and space probes. Solar cells convert light energy into electrical energy. In California, USA, a solar power station has 2000 mirrors positioned to reflect sunlight onto a receiving tower. It generates 10 megawatts of power each day. The computerised mirrors follow the Sun’s path during the course of the day.
Fig 7.3.4
Energy from the Sun Green plants use the Sun’s energy to power their own food production. Some animals use sunlight to regulate their body temperatures. In contrast, humans tend to waste it, rarely using it as a primary source of heat and only sometimes as a source of electrical production. This energy is free and non-polluting, a bonus especially for developing countries that lie near the equator.
Solar ponds In a shallow pool, sunlight passes through the water and is absorbed by the base and sides of the pool, gradually warming them. Water that is in contact with the sides and base slowly gets warmer too. Warm water rises and cool water drops, causing convection currents throughout the pond. These continue until the temperature of the pond is uniform throughout. If salt is added to the water, however, the warm water does not rise, but stays warm at the bottom of the pond. Water pipes running along the bottom of the pond can be used as a way to heat fresh water passing through the pipes. The temperature of the water at the bottom of a solar pond can be as high as 107°C—hot enough to turn special turbines to generate electricity. This method is used in Israel to generate a small percentage of that country’s electrical needs by exploiting the extreme saltiness of the Dead Sea.
206
Fig 7.3.5
A solar-powered telephone exchange—ideal for isolated places such as the Australian outback, where communities are scattered over a vast area and the cost of installing power lines would be too high.
They are extremely useful in remote areas because they have no moving parts to service and require no fuel except sunlight. Solar cells are being used more and more in items as diverse as electronic toys, calculators and solar hot water heaters. Unfortunately the process used for the production of solar cells is not energy efficient and also produces pollution. Solar panels are also not very energy efficient and much research is going into improving their performance. Recent research has led to the development of a ‘solar concentrator’—the Winston tube. This instrument concentrates light to intensities similar to that of the Sun’s surface, generating enormous quantities of cheap, non-polluting energy. It has been suggested that by 2010 the Winston tube may be in widespread use in many countries where light is plentiful.
mirror lens can be raised or lowered to control light
reflecting mirrors
the intense light produced by the Winston tube could be used to destroy toxic chemicals
water and carbon dioxide
Named after its American inventor, the Winston tube offers hope for large-scale energy production with little or no pollution.
magma very close to their surface because they lie on fault lines in the Earth’s crust. They are able to use this Hot dry rock geothermal energy to produce One cubic kilometre of electricity: water is pumped hot granite at 2500°C has the stored energy of into the ground, where it is 40 million barrels of oil. heated by the molten rock Australia has large until it boils and produces areas of granite of this temperature at 3 to steam. The steam is tapped 5 kilometres below and turns turbines that the surface. produce electricity. Although this system appears to be ideal, there are some disadvantages: • Only countries near fault lines have easy access to molten rocks beneath the surface. • When water is extracted from or pumped into rocks, underground pressures change, leading to increased likelihood of earthquakes and rock cracking. • Geothermal energy produces a number of gaseous pollutants, particularly carbon dioxide, hydrogen sulfide, sulfur dioxide and methane. Improved technology has greatly reduced the impact of these substances on the environment, however, and the overall effect is less damaging than other sources of energy production.
UNIT
7.3
dangerous chemical waste
Fig 7.3.6
generator building pump house cold water down hot water up
Energy from within the Earth The Earth’s crust is an incredible insulator. Desert animals have long taken advantage of this fact by digging burrows 20–30 centimetres Ring of fire below the surface, where the Most of the planet’s temperature is lower. Without the 850 active volcanoes are the crust, heat from the Earth’s molten in a region called Ring of Fire—around interior would have devastating the edges of the Pacific consequences for life on the Ocean. Within this ring surface. The surface would be as some countries such New Zealand are taking ‘baked’ from below as well as from advantage of geothermal the Sun above. Some countries, power. such as New Zealand, have hot
water heats up hot rocks
Geothermal energy is used in areas where active volcanoes and lava flows are present, or where water heated by deeply buried rocks makes its way to the surface. Water can be pumped down into the ground to be heated by the hot rocks, then pumped back out again.
Fig 7.3.7
207
Human intervention: energy crisis! Tallest geyser The pressure of a geyser Geothermal energy in all its builds up when forms currently produces more underground water is than 7000 megawatts of boiled by underground electricity per year—about 0.15% magma. Currently, the tallest geyser in the of the world’s energy needs. world is the Steamboat At the moment, Australia Geyser in Yellowstone makes only limited use of National Park, blasting water up to 115 metres geothermal energy production. into the sky. The Mulka Cattle Station in South Australia has used it since 1987, and the Garden East Apartments (also in South Australia) have been operational since 1994. Funding has also been provided for a pilot plant in the Hunter Valley, New South Wales. In contrast, New Zealand meets up to 75% of its energy needs through geothermal sources. Other countries using this form of energy production include the United States, the Philippines, Iceland, Russia, Mexico, Italy and Japan.
>>> Energy from the wind Have you ever wondered where the wind comes from? Global winds are the result of hot air rising over the equatorial regions. This process creates a space into which cooler air from the poles rushes. We call this movement of air ‘wind’. Sailing boats and windmills have used wind energy for thousands of years. More recently, windmills have been redesigned using modern materials and technology, greatly increasing their efficiency. Now called wind turbine generators, they convert the energy of wind movement into electricity. This electricity is used directly to do mechanical work, or fed directly into the electricity grid, or it can be stored in batteries for later use. Factors that influence the amount of electrical energy produced include: • the wind speed. The power supplied by the wind turbine generators depends on the wind Is this the future? speed cubed. Thus when the wind speed doubles, the power produced increases eightfold. • the length of the blades. The power supplied is related to the length of the blades squared. This means that when the blade length is doubled, the power is quadrupled. Australia’s first electricity grid connected to a wind farm is located at Crookwell in New South Wales,
Fig 7.3.8
208
Steam rising from a geothermal power plant
From the traditional to the modern: old and new windmills. Wind turbines can now produce enough energy to be considered a viable energy source for the twenty-first century.
Helgoland, an island in the North Sea, combines solar and wind energy, together with heat energy from the sea and a little diesel oil in order to meet its energy needs. A solar-, diesel- or wind-powered heat pump extracts the heat and salt from sea water, giving the islanders not only power to heat their homes, but a supply of fresh water to drink!
Fig 7.3.9
where eight turbines generate 4.8 MW (megawatts) of power. At Blayney, west of Bathurst, New South Wales, 15 turbines generate 10 MW of power. This is enough power for 7000 homes and replaces older technologies that would have produced 16 000 tonnes of carbon dioxide emissions annually. The largest single wind generator is on Kooragang Island, Newcastle, New South Wales. In the future, it is highly probable that wind farming will become a major industry along Australia’s vast coast, with small towns and villages becoming almost totally self-sufficient in their energy production.
Talbingo Reservoir and Tumut 3 hydroelectric power station in the Snowy Mountains
Fig 7.3.10
UNIT
7.3
Energy from water Water provides the backdrop for all life on our planet, and can be used to provide us with energy in a number of ways.
Hydroelectricity Gravity pulls water downhill until it reaches the lowest possible point—the sea. The gravitational potential energy it contains can be harnessed by passing it through turbines to generate electricity. Electricity produced in this manner is referred to as hydroelectricity. There are two ways we can maximise the amount of electricity produced. • Make a small volume of water fall from a great height—the Alps of Europe and the Rocky Mountains, USA, are ideal for this. • Make a large volume of water fall from a much smaller height—dams built on the Amazon River (Brazil), the Nile (Egypt and Sudan) and the Yangtze River (China) all use this method. The largest hydroelectric scheme in Australia is the Snowy Mountains Scheme in New South Wales, which generates almost 3800 MW (megawatts) of power. Consisting of 16 dams and 145 km of tunnels, this series of seven power stations provides 50% of Australia’s hydropower. A further 30% comes from Tasmania. The advantages of this form of energy production are that it uses a renewable source of energy and is pollution free. It can also respond quickly to demand during peaks of energy consumption. There are some disadvantages, however. The construction of dams, and the water they hold, results in large loss of land, and destruction of both natural habitat and towns. As the water is no longer freely moving, the oxygen content falls, and the quality of the dam water reduces to the point where it is often unable to sustain normal fish populations.
Using water currents, tides, waves and salinity Modern technology has given us four ways to produce electrical energy from sea water. 1 Warm water currents in the sea can be harnessed through ocean thermal energy conversion (OTEC) schemes. Warm ocean water is pumped through a pipeline and is used to heat fresh water to boiling point. The steam produced generates electricity. The method is particularly suitable for tropical lands, but is very expensive. 2 Osmosis is the movement of water from a weak solution (having low salinity, like fresh water) to a stronger solution (with a higher salinity, like sea water) through a semipermeable membrane. This membrane allows some molecules to pass through it (in this case water), but prevents the movement of other particles (salt). Japanese scientists have used osmotic pressure to generate large quantities of pollution-free energy. A disadvantage of this form of energy production is that it is available only to countries that have fresh-water rivers flowing into the sea, Prac 1 where there will be large differences in p. 213 salt concentration. 3 A system of wave energy generators is being developed by both Britain and Japan. Waves are forced into a narrow gully, causing the air above them to rise and fall. This moving air passes through a turbine to produce electricity. Because this method relies on situating a power station on
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Human intervention: energy crisis!
Wells turbine turns in same direction irrespective of airflow direction incoming wave forces air out of OWC
Fig 7.3.11
An oscillating wave column (OWC) generates energy by using ocean waves. The waves push air past a turbine, causing it to spin.
rocky cliffs, it has had limited use. Britain is also developing a form of wave generator that floats on the ocean surface. 4 The daily movement of the tides is the only known renewable resource that is totally predictable. The basic engineering behind tidal power generation is relatively simple and is usually achieved by placing a barrier across a bay’s entrance so that the incoming tide turns a turbine. At the maximum height of the tide, the water flow is blocked until the tide is low. The stored water is then released again, turning a turbine to produce electricity. The amount of energy generated is related to the size of the tides. Only a few countries have large enough tides to currently use this technology. The northern coast of Western Australia near Broome would be ideal for this technology, although currently there is little need for it due to the small local population.
Biomass Biomass is the term used to describe organic material that has recently died and which can be used to generate energy. It includes everything from wood from fallen trees or industrial processes to the faeces from humans and animals. The energy that is stored in biomass is referred to as bioenergy, and is usually lost to the environment in the form of heat.
210
Comfy compost Looking for a nice warm place to hide out in the winter? Try curling up in the middle of a haystack! If you can’t find a haystack, climb into the compost bin! Both of these examples of biomass release large amounts of heat energy as their material decomposes into its elementary molecules.
retreating wave sucks air back into OWC
The conversion of biomass into bioenergy is, in effect, the process of photosynthesis in reverse. Although the carbon contained in the biomass is converted into carbon dioxide and is released back into the atmosphere, the total amount of carbon dioxide present in the ecosystem does not change. How is this possible? Because the carbon dioxide that is released is equivalent to the amount absorbed by the plant as it was growing.
Energy from timber and agricultural wastes Biomass can be used directly by burning it. Wood can be burnt for heating and cooking but, although it is a renewable resource, it takes Macadamia nut power time for timber to grow. We are A power plant in also using timber faster than it Queensland is producing can grow. For this reason, many 9.5 gigawatts of countries are now choosing to renewable energy per year by using waste plant fast-growing trees that are macadamia nut shells. suitable for coppicing. Coppicing This displaces some harvests only the tree canopy 9500 tonnes of greenhouse gases. and does not kill the tree. Every few years the shoots that have sprouted from the stump can be harvested again. During this time, the roots of thetrees also assist in keeping the soil together to reduce erosion. Indirect use of biomass involves converting it into a suitable fuel that is then used as an energy source. This most commonly occurs with agricultural crops such as sugar cane, corn, rice and wheat, and oil-bearing crops such as sunflowers. Waste products from their harvesting are processed into fuels such as ethanol and biodiesel. Prac 2 p. 214
Energy from industrial and household waste With the increased production of pre-packed and pre-cooked foods, the commercial food industry produces vast quantities of both solid and liquid wastes. These wastes include peelings, pulp, filter sludges and fibrous wastes, together with the water from the washing and blanching of food products. These wastes contain dissolved organic matter, including sugars and starches, and have the potential to produce ethanol when combined with certain anaerobic bacteria. Of the total household waste collected each day, more than 80% is biomass, and of this 46% is organic matter (food scraps and garden waste), 24% is paper, and the remainder is an assortment of plastic materials. This type of waste can be converted into energy directly, by burning, or it can be ‘digested’ by anaerobic bacteria in Source landfill gas plants to produce biogas (methane and carbon dioxide), which can Coal then be used to generate heat and power.
Conservation: the most important ‘fuel’ of all There is one fuel we have not considered yet, and it is possibly the most important of all. It is the ‘fuel’ of conservation: for every joule of energy we do not use, there is one less joule of energy that needs to be produced. If each of us makes an effort to use less energy, then the energy requirements of our cities will be reduced, resulting in less pollution and our resources lasting longer. The Australian Government has a number of subsidies and grants for the development of energy conservation technologies. For example, biofuel producers will receive $37 million in subsidies to help reach the government’s goal of 350 megalitres of renewable fuel production by 2010.
In many developing countries, the manure from cows, camels and other animals is shaped into ‘pancakes’ or ‘bricks’, dried and stored. It is then burned to provide heat mainly for cooking. Animal and human wastes can also be converted to biogas using anaerobic bacteria. The table opposite shows the advantages and disadvantages of r! we po the energy sources Pig f Pigs can only use hal available in the food they eat—the Australia. half is lost as other waste. This waste has k been used at Berryban ere Pig Farm at Winderm near Ballarat, Victoria. Electricity is generated on the site from the breakdown of pig effluent into biogas.
Advantages
Disadvantages
Large Australian reserves Easily mined Low cost Provides export income
Non-renewable Causes greater pollution than oil and natural gas
Oil
Limited Australian reserves Easily transported Many uses
Non-renewable Limited world supplies Causes pollution
Natural gas
Limited Australian reserves Efficient source of domestic heat
Non-renewable Causes pollution, although less than coal and oil
Nuclear
Large Australian reserves High energy output per unit mass of fuel Low accident rate Provides export income
Non-renewable Radioactive waste disposal Security risks
Solar
Renewable Low running costs Efficient heating Causes little pollution
Dependent on weather Large collectors needed
Hydro
Renewable Causes little pollution Low running costs
Dependent on weather Dam destroys local habitat
Wind
Renewable Causes little pollution Low running costs
Dependent on weather Low energy output
Tidal/wave
Renewable Causes little pollution Low running costs
Dependent on tides/waves Restricted sites
Biomass
Renewable Biogas uses wastes
Limited rate of supply Low energy output per unit mass of fuel
Worksheet 7.3 Energy in the community
Energy from animal and human waste
UNIT
7.3
(wood, biogas, etc.)
211
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Human intervention: energy crisis!
UNIT
7.3
[ Questions ]
Checkpoint
Think
Energy sources
17 Describe how fossil fuels are produced.
1 a Identify how energy resources are classified into two major types. b List examples of each type.
5 List three ways we use energy from the Sun.
18 Copy the following, modifying any incorrect statements so they are true. a Splitting atoms to generate energy is called nuclear fusion. b Geothermal power is a source of energy that can be used worldwide. c Hydroelectricity is the electricity produced by harvesting falling water. d Global winds arise from cold air blowing in from the polar ice caps.
6 State the two major benefits of using the Sun as an energy source.
19 Assess why the base and sides of solar ponds are painted a dark colour.
2 Define the term ‘fossil fuel’. 3 Define the term ‘nuclear fission’ and explain why some think it is a desirable energy source. 4 Discuss two disadvantages of nuclear energy.
Energy from the Sun
Energy from within the Earth 7 Define the term ‘geothermal energy’. 8 Describe how geothermal energy is used to produce electricity. 9 Discuss two disadvantages of geothermal energy.
Energy from the wind 10 State the benefits of using wind-powered electricity generators.
20 Your friend cannot understand why coal and gas are called ‘fossil fuels’. Explain to him why these terms are being used correctly. 21 The oil fields of the Middle East lie under hot and dry deserts. In prehistoric times would you expect these areas to be the deserts they are now, or warm and wet swamps and shallow lakes? Justify your reasoning.
Analyse
11 a Propose a likely meaning for the term ‘wind farming’. b Discuss the advantages and disadvantages of this form of energy production.
22 Consider this statement: ‘The most valuable energy source is conservation’. Do you agree or disagree? Justify your reasoning.
Energy from water
23 List as many ways as you can in which you can help conserve resources.
12 a List the various ways in which water can be used to generate electricity. b Select two of these ways and describe how the energy in the water is used to generate electricity. 13 Define the term ‘osmosis’.
Biomass 14 Define the term ‘biomass’. 15 Explain two ways in which biomass can be used to supply energy.
24 Explain in your own words why the conversion of biomass into bioenergy can be considered ‘the process of photosynthesis in reverse’. 25 a Copy and complete the table below to summarise any five energy sources in this unit. b Consider the energy sources you have summarised and evaluate their potential as future energy sources.
Conservation: the most important ‘fuel’ of all 16 Explain how conservation of energy benefits society.
Name of energy source
212
Description of how energy is produced
Advantages
Disadvantages
UNIT
7.3 [ Extension ] Investigate 1 Design an energy poster. You could include a number of different methods of energy production, or you might look at one specific method in more detail. Include: a whether this is a renewable or non-renewable resource b the advantages and disadvantages of this type of energy source c the requirements for this type of energy source d which countries can use this method of energy production e whether or not it has already been employed as an energy source, and if so, how successful it has been. 2 Research more about the work being done by Australian company Energy Developments in using energy from landfill sites.
Action 3 a Construct a list of the energy wastage in your home. Are lights left on in empty rooms? Do you leave the water running while you clean your teeth? Do taps drip? Do you recycle paper, PET plastics and glass? Does your home have a compost bin? Is your home adequately insulated? How can you improve the energy usage in your home?
UNIT
7.3
Surf Complete the following activities by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7 and and clicking on the destinations button. 5 Explore some Australian environmental issues and State-specific environmental problems. 6 a Examine how to save water, and study environmentally friendly designs for a home. b Design an environmentally friendly house using the information provided. Create an architectural plan of the house, including the environmentally friendly features.
[ Practical activities ] Checking out osmosis
Prac 1 Unit 7.3
b Design a plan of attack on energy wastage, including at least ten points that can be improved upon. 4 Visit your local council and examine what is being done in your community to conserve resources. Does it have ‘green waste’, glass, PET plastic and paper collection? What happens to them after they are picked up?
Aim To observe the movement of water across a semipermeable membrane Equipment Three 10 cm lengths of dialysis tubing, 3 large beakers, distilled water, salt water (two different concentrations), stopwatch
Method 1 Tie a knot in the bottom of each length of dialysis tubing. 2 Label the tubes A, B and C. 3 Fill tube A to three-quarters full with distilled water, and tie off the top with a rubber band. Leave about 3 cm of space at the top of the tubing.
4 Fill tube B to three-quarters full with the lowest concentration of salt water, and tie off the top as before. 5 Place each tube into a beaker of distilled water— the tube should be almost completely immersed. 6 You will find that the volume of liquid in tube B will increase as the water moves into the tube to try and balance the salinity. Using a stopwatch, time how long this process takes. 7 As you did with tubes A and B, fill tube C to three-quarters full with the highest concentration of salt water. 8 Place tube C into a beaker of distilled water and time how long it takes for the tube to become full. 9 Record your results in a table similar to the one overleaf.
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Human intervention: energy crisis! Fig 7.3.12
Peanut power Aim To release the chemical potential energy in
Tube A distilled water
Tube C salt water— high concentration
Tube B salt water— low concentration
Prac 2 Unit 7.3
a peanut
Equipment
Peanut and other nuts such as macadamia, cashews, pecan or walnuts; a cork; large needle; tripod; 100 mL beaker; thermometer; water
Method 1 Carefully push the eye end of a large needle into the smaller end of the cork. 2 Very carefully and gently push the needle into a peanut. If you push too hard the peanut will split. 3 Add 30 mL of water to the beaker. 4 Place the thermometer in the water and record the temperature. 5 Carefully set the peanut alight and place it under the beaker.
distilled water
6 Allow the peanut to burn until it goes out. 7 Record the maximum water temperature reached. 8 Repeat the experiment with different types of nuts. Tube A
Tube B
Tube C
Tick to indicate a movement of water Time taken for water to fill tube
Questions 1 Construct a diagram of the experiment, labelling all parts. 2 Describe how the appearance of the dialysis tubing has changed. Have all tubes changed in the same way? 3 Which molecules have moved across the tubing membrane—the water molecules or the salt particles? Justify your answer. 4 On your diagram, illustrate the movement of molecules. 5 Assess what this tells you about the dialysis tubing. 6 Identify the term for the movement of water molecules across this type of membrane. 7 Was there any difference in the time it took for the water to move into tubes B and C? Explain why.
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Questions 1 If you used other types of nuts, identify the variable that was changed. 2 Predict what would occur if more than one peanut was used to heat the water. You might like to test your prediction by carrying out the experiment. 3 Determine which nut type contained the most chemical energy.
Chapter review [ Summary questions ]
[ Interpreting questions ]
1 Identify an example of each of the following forms of energy: a nuclear energy c chemical energy b heat energy d light energy 2 Organisms tend to live in relatively small, localised areas. Explain why.
15 What do you think is the most important type of energy? Justify your reasoning.
3 State what the arrows in a food chain show.
18 Deduce the meaning of the statement ‘lightning is a necessary danger’.
4 Determine what percentage of energy is passed on to each level of the food chain. 5 Define the Law of Conservation of Energy. 6 Copy the following, modifying any incorrect statements so they are true. a The unit with which we measure energy is the joule. b Energy that is derived from molten rocks beneath the surface of the Earth is called thermal energy. c Endothermic animals use most of their energy to maintain a constant body temperature. d Bacteria and fungi are decomposers that have a major role in returning atoms in the biotic environment back to the abiotic environment of the ecosystem. 7 Define the term ‘semipermeable membrane’. 8 Explain why coal, oil and gas are described as ‘fossil fuels’. 9 a Define the term ‘hydroelectricity’. b Identify a place in Australia where you will find this form of energy production.
16 Energy and matter both flow through the ecosystem. Distinguish between them. 17 Explain how energy is passed on from a plant to a first order consumer.
19 Assess why it is important to replace trees that have been used to provide heat energy. 20 ‘Bacteria may be small, but they have a big impact on our environment.’ Deduce the meaning of this statement. 21 Evaluate whether the form of ‘wood harvesting’ called coppicing would be beneficial to the environment. 22 Evaluate the implications for society of using more sustainable energy sources. 23 Currently there is no nuclear power plant in Australia. (Lucas Heights in southern Sydney produces radioisotopes used in medicine and engineering.) Evaluate whether introducing nuclear energy into Australia would be beneficial for society and the environment. 24 Discuss the advantages and disadvantages of using the method shown in the photo below, for power generation. Fig 7.3.13
[ Thinking questions ] 10 Construct a food chain that you might find in your local area. Label each of the organisms as either producers or consumers, and their ‘order’ in the chain. (Which ones are first order consumers? Second order?) 11 Construct an energy flow chain for your food chain. What is the original energy source? 12 State a word equation to describe the processes of: a photosynthesis b respiration What do you notice about these two processes? 13 List differing viewpoints about the use of fossil fuels and uranium as energy sources. 14 Identify choices that need to be considered when constructing and furnishing a new home or building.
Worksheet 7.4 Energy in ecosystems crossword Worksheet 7.5 Sci-words
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Sense and control Key focus area
5.2, 5.8.4
Outcomes
>>> The nature and practice of science By the end of this chapter you should be able to: identify parts of the eye, ear, skin, nervous and endocrine systems describe how these organs and systems work identify the specialised cells that give us our senses identify some of the problems associated with the eye, ear and skin, and describe ways to avoid or rectify these problems list five different taste sensations give examples of a stimulus and a response list some hormones and describe their functions identify the specific male and female hormones involved in growth and puberty
Pre quiz
describe how technology allows us to enhance our senses.
1 List our five senses. 2 What is the biggest organ of the human body?
3 What is the advantage of having two eyes and two ears?
4 Why do pimples affect kids more when they go through puberty?
5 What is your body doing right now without any thought from you?
6 Why is it dangerous to dive into water of unknown depth?
7 Why do dogs show so much interest in other dogs’ urine?
8
UNIT
8.1 context
Fishy focusing
Our eyes provide what many would regard as the most important of all our senses—sight. Take a look around you now. If your eyes are working normally, they just transmitted automatically focused colour images of several objects located different distances away to your brain with virtually no effort! But how do eyes work?
Fig 8.1.1
Most animals focus by using the ciliary muscles to change the shape of the lens. Fish, however, focus images by moving each lens backwards and forwards, just like a camera.
Parts of the eye
The eye contains several parts that may remind you of the parts of a camera. When you think about it, both the eye and the camera perform similar tasks—focusing on and capturing images. You may recall from earlier studies of light that images produced by convex lenses are upside down.
The eye focuses images in the retina. Although the image is upside down, the brain processes it so that we perceive it the correct way up.
Prac 1 p. 224
iris retina
lens optic nerve
diaphragm
film shutter
convex lens
Fig 8.1.2
The similarities in the operation of a camera and the eye are obvious.
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Sight
The choroid is a black layer that forms part of the inside lining behind the lens, and prevents light from reflecting all around the eye.
The rest of the eye is filled with a jelly called vitreous humour which helps maintain the shape of the eye.
The retina is a layer containing over 100 million light-sensitive cells which transmit messages to the brain.
The sclerotic layer is a tough, white-coloured protective layer that surrounds the eye and helps maintain its shape.
The yellow spot, or fovea, is a section of the retina directly behind the pupil that contains a large number of colour-sensitive cells. This is why you should look directly at an object to see it most clearly.
The conjunctiva is a clear, thin layer covering the front of the eye. You may have heard of an infection of the eye called conjunctivitis that can occur here.
The blind spot is where blood vessels and the optic nerve join the eyeball, and there are no light-sensitive cells to detect image information.
Under the conjunctiva is the cornea, a clear 'window' in the sclerotic layer that allows light to enter the eye. The hole in the centre of the iris is called the pupil. When conditions are dark, the pupil increases in size to let more light in, and is said to be dilated.
The optic nerve joins the eye to the brain, allowing image information to be processed so we see images the right way up.
The space between the cornea and the lens is filled with a watery liquid called aqueous humour which helps maintain the shape of the eye.
Just in front of the lens is the iris, which changes size to control how much light enters the eye. It also gives your eye its colour.
The clear lens helps focus an image on the The lens is held back surface of the eye. in place by suspensory ligaments. Depending on how far away an object is, ciliary muscles change the shape of the lens to bring images into focus.
Worksheet 8.1 The eye
The human eye
Fig 8.1.3
Eye protection pupil
bright light
Fig 8.1.4
dilated (dim light)
The pupil adjusts according to the amount of available light.
Prac 2 p. 225
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There are a number of features that help protect our eyes. Our eyebrows and eyelashes help keep dust out, and tear ducts produce tears to flush out any foreign particles. Our eyes are set back in depressions in our skulls called orbits to give them some protection from being knocked. Warning! Always use protective eyewear in science classes when handling or heating chemicals that could spit or spill from their containers. If a foreign substance does get into your eye, flush it immediately with water while trying to keep your eye open to allow water to contact the affected area. An eyewash bottle should be available for this purpose.
If red light falls on the retina, ‘red’ cones are activated. With purple light, both red and blue cones are activated. Both rods and cones send messages to the brain to help us see. Some people lack one or more types of cone cells and cannot easily tell the difference between some colours, most notably red and green. This condition is known as colour blindness and affects about 1 in 15 males and 1 in 1000 females.
An eyewash bottle can be used to rinse foreign matter from the eye—make sure you know where one is in your science rooms.
UNIT
8.1
Fig 8.1.5
Why two eyes? Two eyes allow us to judge distances more accurately. Each eye sees a slightly different view. The brain combines the two images to create a threedimensional view that gives us more information about how far away an object is. This is called binocular vision.
Colour vision
Fig 8.1.7
The retina contains special cells called rods and cones. Rods are more sensitive than cones, but respond only to light and dark, helping us to detect shapes. Cones need more light to be activated and come in three types, which detect the colours red, blue and green. A scanning electron microscope photograph of rods and cones
Fig 8.1.6
A colour blindness test. What do you see?
Animal eyes The eyes of various animals are specialised to increase The largest their chances of survival by eyes in the detecting predators or food world more easily. A rabbit’s eyes The giant squid can grow up to 14 metres are positioned on the sides of long and has eyes as its head so that it can see large as soccer balls! most of its surroundings without moving its head and attracting attention. The eagle has excellent eyesight and can detect a rabbit from three kilometres away! Like most predators, owls have both eyes at the front to allow better judgement of distance when swooping on prey. Insects may have multiple lenses to provide an all-round view. Spiders have four, six or eight eyes, and scorpions have Prac 3 between six and twelve. p. 225
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Sight A rabbit can see both sides at once.
Fig 8.1.8
Wobbly chook heads Have you ever wondered why chickens wobble their heads so frequently? A chicken’s eyes are on opposite sides of its head, but to judge distance it needs to see an object with both eyes. The only way it can do this is to quickly move its head to view the object with one eye, then the other.
Fig 8.1.10
A chicken must continually move its head to obtain a complete view of its surroundings.
Cats’ eyes Cats’ eyes are unusual for a couple of reasons. They have a slit-shaped pupil which opens and closes much faster than a round one, allowing their eyes to adjust to changes in light intensity more quickly. Have you ever noticed how cats’ eyes shine at night? This is because a mirrored lining at the very back of the eye (called a tapetum) reflects light through the rods and cones a second time, giving the cat more chance of seeing objects even in very dim conditions.
Fig 8.1.9
The forward-facing eyes of the owl give it good binocular vision, allowing it to judge distance as it swoops on prey.
Do animals see in colour? Yes, many animals see in colour, but not the same as we do—it depends on the number and type of cones they have. Some animals, like bees, see colours that we can’t, as they have extra types of cones in their eyes. Birds that are active in daytime are able to see colours, but those that are active at night cannot. Cats, dogs and rabbits are thought to have very poor colour vision, and probably see virtually in black and white.
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An insect’s compound eye contains thousands of lenses.
Fig 8.1.11
Sheep and horses have good colour vision. Insects can see colours, but not red. Some insects can see ultraviolet light, which is normally invisible to humans.
Eye defects The job of the lens is to bend light so that an image is formed on the retina. It does this by using the ciliary muscles to change its shape. When these muscles relax, they pull on the suspensory ligaments and
Eye focused on a distant object
circular fibres relaxed
image on retina
Eye focused on a near object
circular fibres contracted
image on retina
meridional fibres relaxed
meridional fibres relaxed
light from close object
light from distant suspensory object ligaments taut
suspensory ligaments slack light bent more by fatter lens
light bent little by thin lens
Fig 8.1.12
UNIT
8.1
How the eye focuses on close and distant objects
stretch the lens, making it thinner so it bends light less. When the ciliary muscles contract, they pull less and allow the lens to fatten up. Fatter lenses bend light more, which is what’s required when looking at close objects. The ability of our eyes to change lens shape and focus at different distances is called accommodation. In some people, the lens has become less elastic and is unable to become thin enough or fat enough to focus images at exactly the right position in the eye. Short-sighted people can focus on objects a short distance away, but not on distant objects. This condition is known as myopia. Myopia can be corrected by wearing concave lenses that move the focus point of the image back onto the retina, as shown in Figure 8.1.13. Correcting short-sightedness
Long-sighted people can see long distances away, but cannot focus on close-up objects. Another name for long-sightedness is hyperopia. Hyperopia can be corrected by wearing convex lenses which bend light more so the focus point of the image is brought forward onto the retina, as shown in Figure 8.1.14. Presbyopia is a condition in which a person loses the ability to focus at short distances (e.g. when reading) due to ageing. People with presbyopia often use reading glasses. Bifocal contacts Some people have trouble focusing The first bifocal contact lenses were invented by at both short and long distances, and Queensland optical may use bifocal lenses, which have research scientist Stephen two types of lens in one (e.g. convex Newman in 1992. at the bottom for reading, and concave at the top for distance vision).
Fig 8.1.13
close object distant object
convex lens concave lens
close object
distant object
Fig 8.1.14
Correcting long-sightedness
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Sight Fig 8.1.15
Contact lenses can be used to correct impaired eyesight.
As well as spectacles, contact lenses can be used to correct vision. Soft plastic lenses are available which are more comfortable than hard glass lenses, but are not suitable for everyone. Wearers of contact lenses must ensure that their eyes still receive enough oxygen. Modern plastic contact lenses are gas permeable, allowing some oxygen to pass through to the cornea. The eye may react to a lack of oxygen by growing additional blood vessels to supply Artificial eyes more oxygen via the Medical researchers are bloodstream, but the working on an artificial extra vessels eye that they hope may can cause restore sight to blind people. The artificial eye irritation implants directly into the and other optic nerve. Prac 4 problems. p. 225
UNIT
8 .1
The Lasik procedure being used to correct myopia
Conjunctiva
Fig 8.1.16
Description/function Thin, clear layer covering front of eye
Checkpoint Parts of the eye 1 Compare the eye and the camera, listing similarities and differences. 2 Copy and complete the table above right to summarise each part of the eye described in this section. The first entry has been done for you.
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Monovision does not mean having one eye! The term refers to vision correction in which a person who is unable to focus at both short and long distances wears a different strength contact lens in each eye. With time, the brain learns which lens to use depending on the distance of the object being viewed.
A recent development in eyesight correction is laser surgery. Two main methods are PRK (photoreactive keratotomy) and Lasik (laser in situ keratomileusis). PRK involves removing a layer of cells from the surface of the cornea and remodelling the shape of the cornea using a laser. With Lasik treatment, a thin flap of the cornea is lifted up, but not removed, and a laser is used to reshape the cornea before the flap is replaced over the laser-treated area. Patients undergoing Lasik feel less discomfort and healing time is reduced, while with PRK there is more cornea to work with.
Part
[ Questions ]
Monovision
Laser surgery
3 Describe ways in which the eye is naturally protected.
Colour vision 4 Identify the light receptor in the retina that detects: a light or dark b colour 5 Explain what causes colour blindness.
UNIT
8.1 Animal eyes 6 Describe two facts you find interesting about animals’ eyes. angle of vision
7 Define ‘tapetum’.
Eye defects 8 State the common names for hyperopia and myopia. 9 Define ‘presbyopia’. 10 Illustrate what happens to the light path in the eye of a short-sighted person. 11 Describe how defective vision can be corrected. Illustrate your answer.
Think 12 Identify where most of the bending of light occurs in the eye. 13 Propose a reason why the choroid is black and explain what might happen without it. 14 There are no light-sensitive cells in the blind spot. Explain why. 15 When you walk indoors after being outside in bright sunlight, it is very difficult to see well for a short while. Explain why. 16 Explain why we squint when suddenly exposed to bright light. 17 If we had only one eye, state what we would not be able to do as well. 18 Explain why it is important for insects and animals active during daytime to see colours. 19 How good do you think an owl’s colour vision is? Explain your answer. 20 Explain why some racehorses wear blinkers. 21 Identify the parts of the eye involved in focusing. 22 Distinguish between Lasik and PRK surgery. 23 Clarify the purpose of blinking.
Analyse 24 Robert can drive safely without glasses, but has trouble reading the street directory without them. a Identify the condition Robert may have. b Explain why you have selected this condition. 25 If an insect’s eye provides almost all-round vision, images of the Sun must be frequently produced. Propose why the Sun does not appear to damage insects’ eyes. 26 Explain why we virtually only see black and white and very little colour when outside at night. 27 Can you tell for sure whether you see the same colours as other people? Discuss. 28 Justify the need for humans to have two eyes.
Fig 8.1.17 29 The approximate angle of vision for a person is shown above. Draw diagrams to demonstrate the approximate angle of vision for: a an owl
b a rabbit
[ Extension ] Investigate 1 a Use Word or PowerPoint to construct an eye chart. b Use your chart (on screen or a printed version) to test the sight of several people. 2 a Investigate some other eye defects such as glaucoma or cataracts, and their possible treatments. b Produce a brochure for a doctor’s waiting room that outlines the defect, its signs, symptoms, and treatments available. 3 Create a poster to explain how a camera works. Describe how an image is captured on film and developed. Compare this to how our eyes capture and process images. 4 Investigate the Braille system used by blind people to read.
Surf Complete the following activities by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. 5 Examine an online dissection of a cow’s eye. 6 Explore further information about the eye and perform an interactive labelling of the eye’s structure.
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Sight
UNIT
8 .1 [ Practical activities ] Fig 8.1.19
Eye tests Prac 1 Unit 8.1
Aim To construct a mini eye chart and to find your eye’s blind spot Equipment Pen and paper or card
Method PART A: Your yellow spot 1 Use a centimetre grid to draw a larger version of the mini eye chart shown in Figure 8.1.18.
R N F
3 Gradually bring the textbook closer and note when the dot disappears. This happens when light from the dot falls on your right eye’s blind spot. 4 Repeat with your left eye open and right eye closed. PART C: Distance perception 1 Have a partner hold a pen upright at arm’s length as shown. 2 With one eye shut, try to vertically line up another pen to touch your partner’s pen. This may take several attempts.
S K R N F S K • K S F N R K S F N R Fig 8.1.18
Mini eye chart
2 Hold the chart about 20 cm from your right eye while shutting your left eye. 3 Stare at the dot in the middle of the chart.
3 Repeat steps 1 and 2 with the other eye shut.
4 Note which letters you can make out clearly (do not memorise them).
4 Try again with both eyes open.
5 Repeat, this time looking with your left eye while shutting your right. PART B: Your blind spot
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Fig 8.1.20
Questions 1 a State the number of letters you could see in part A. b Calculate a class average.
1 Hold the textbook at arm’s length and look directly at Figure 8.1.19.
2 a At what distance from your eye did the cross disappear (when its light fell on your blind spot)? b Compare this with others in your class.
2 Shut your left eye, and stare at the cross with your right eye.
3 Evaluate your ability to judge distance with one eye only, compared to two eyes.
Prac 2 Unit 8.1
Persistence of vision
Angle of vision
Aim To investigate the persistence of images
Design an experiment to test the ability of humans to see objects at various angles when keeping the head still. Over what angle can people see? How well can they distinguish objects and colours at extreme angles?
formed by the eye
Prac 3 Unit 8.1
Equipment
Wooden rod (e.g. bamboo skewer), stiff white cardboard, pencils, sticky tape, scissors
Method
UNIT
8.1
DYO
1 Construct the apparatus shown in Figure 8.1.21. Fig 8.1.21 rod
Eye dissection Aim To identify the main structures of the eye
card Prac 4 Unit 8.1
tape
Equipment A pig’s eye or cow’s eye, sharp fine scissors, paper towel, dissection board, newspaper
Method 1 Place the eye on a dissection board on some newspaper and carefully trim any fat or muscle away from the outside of the eye. 2 Sketch the eye, labelling any parts you can identify.
drawing of cage
drawing of bird
3 Carefully cut a hole in the back of the eye near the optic nerve. 4 Hold the eye so it ‘looks’ at a window, and look through the hole you cut at the back of the eye. What do you see?
3 Study the effect of various speeds of rotation.
5 Use scissors to remove the lens from the front of the eye. Describe the shape of the lens. Place it above a scrap of newspaper containing small text. Press down on the lens. How does this affect the view of the newspaper?
Questions
Questions
1 Explain what is meant by persistence of vision as it applies to this activity.
1 Describe the appearance and consistency of each part of the eye.
2 Describe the difference caused by varying the speed of rotation.
2 Determine which way up the image appeared when you looked through the rear of the eye.
3 Compare this activity to movies at the cinema (which some people refer to as ‘the flicks’).
3 Explain why the lens is flexible.
2 Look at the card and spin it about the central rod.
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UNIT
context
8.2 detecting sound waves. They also sense the position of our head, helping us to keep balance. The ears are thus really two sense organs in one.
When we cross a road, our ears can warn us of approaching traffic before we see it. In sport, sound helps players decide who to pass a ball to when their eyes are directed elsewhere on the field. Our ears work by
Sound Sound travels though air at about 340 metres per second, in waves of vibrating air particles. When the sound wave reaches our ears the vibrations travel through the auditory canal and in turn cause the eardrum to vibrate. The various parts of the ear then convert the sound energy into electrical impulses, which are sent via nerves to the brain for interpretation. The loudness of sound is measured in decibels (dB).
Parts of the ear The ear consists of three main sections: the outer, middle and inner ear. The outer and middle ear are filled with air, and the inner ear is filled with fluid. Fig 8.2.1
The outer ear consists of the highly visible pinna, which helps to collect sounds and funnel them into the auditory canal. The auditory canal connects the outer ear with the eardrum or tympanic membrane. The eardrum is the beginning of the middle ear and is made of a thin sheet of muscle and skin that vibrates in response to sounds. Vibrations are passed to a set of three tiny bones: the hammer, anvil and stirrup. This group of three bones is known as the ossicles. By the time the sound reaches the stirrup, it has been amplified to about 30 times louder than at the eardrum. The stirrup vibrates against a section called the oval window at the boundary between the middle ear and inner ear, causing vibrations to pass into a coiled, fluid-filled tube called the cochlea. This fluid passes vibrations to a layer of tiny hairs connected to auditory nerves. These send messages to the brain, which are then interpreted as sounds.
The human ear
stirrup anvil hammer
oval window
semi-circular canals to brain
pinna auditory nerve
cochlea
ear canal ear drum outer ear
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eustachian tube round window
middle ear
inner ear
Bang the drum The eardrum is delicate and can easily be broken. Sharp, loud noises such as explosions can rip it, as can things inserted in the auditory canal. Never put anything smaller than your little finger into the auditory canal. Even cotton buds are too small. They can easily reach the eardrum and rip it.
Above the cochlea are the semicircular canals. There are three sections, each perpendicular to the others (like two walls and a floor that meet at the corner of a room). These contain fluid which moves when we do. Nerves send messages to the brain, which in turn signals muscles to help us keep our balance. Worksheet 8.2 The ear
Why two ears? Two ears help us determine the direction of a sound. If a sound reaches both ears at the same time, our brain interprets this to tell us that the source of the sound is directly in front of, behind or above us. If a sound reaches, say, the left ear before the right ear, the brain tells us that the source of the sound is to our left. Fig 8.2.2
Popping ears Sometimes when you climb to a higher altitude, you experience an uncomfortable ‘blocked ear’ sensation. This is caused by a pressure difference between the outer and middle ear. When climbing (e.g. in an aircraft), the outer ear responds quickly to the falling pressure, but the middle ear lags behind and is at a higher pressure. The resulting pressure difference causes the blocked feeling. Eventually the Eustachian tube opens and allows air to rush out of the middle ear so pressure on both sides of the eardrum is again equal. Some people experience a ‘popping’ sensation when this happens. When descending, air rushes into the middle ear to increase pressure to the same as that in the outer ear. If the Eustachian tube gets blocked due to an infection such as a cold, pressure differences will once again give that ‘blocked ear’ sensation.
Prac 1 p. 230
Two ears help us locate the direction of a sound.
the flattened hairs take some time but do recover. This gives partial deafness and ringing in the ears. As these hairs recover so does the hearing, but not completely. Some hairs are flattened permanently and destroyed. Repeated rock concerts will destroy more hairs, leading to more permanent deafness. A blow to the head or a very loud sound (e.g. an explosion) will rip the eardrum. A small tear in the eardrum may heal itself but usually leaves permanent scarring. This interferes with its vibration, so the hearing impairment is also permanent. Damage to the nerves cannot be repaired at all and results in permanent hearing loss. Deafness and partial deafness can be due to a number of things. Wax is produced in the auditory canal to help prevent entry of dust and bacteria. A build-up of wax can stop the eardrum from vibrating correctly, causing temporary deafness. A doctor can easily cure this by flushing out the excess wax with warm water. The ossicles may get jammed together due to exposure to loud sounds or infection, so that vibrations are not passed on to the cochlea. Some people are born with ear defects that reduce the amount of vibration reaching the auditory nerves. Hearing aids work by amplifying sounds and transmitting them to the auditory canal. If the cochlea is damaged, however, hearing aids may not be as effective, since unclear signals to the brain are produced, even if they are amplified. An Australian invention known as the cochlear implant or bionic ear can restore a degree of
UNIT
8.2
Coo-eee
right ear detects sound first
Ear problems Ears in your armpit! A grasshopper’s ears are not on its head, but on each side of its body, below its wings.
Prolonged exposure to loud sounds can flatten the hairs of the cochlea. Hence when leaving a loud rock concert, the hairs have been flattened by the intensity of the noise. Most of
A hearing aid amplifies sound.
Fig 8.2.3
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Hearing
Beethoven’s genius
transmitter coil
most One of the world’s greatest and l sica clas of famous composers wig Lud rn -bo man Ger was music van Beethoven (1770–1827). age Beethoven became deaf at the ed of 30 but, amazingly, continu and ing tand outs e pos to com beautiful music.
mastoid bone
microphone receiver-stimulator cochlea behind-the-ear speech processor
auditory nerve
body worn speech processor
Fig 8.2.4
A bionic ear has several components.
hearing to some people. The bionic ear replaces a nonfunctioning inner ear. It consists of a microphone that sends information to a small speech processor worn behind the ear or attached to a belt. The speech processor sorts out which information is important for understanding speech, transmitting it to a receiver–stimulator implanted in the mastoid bone. The receiver–stimulator then produces electrical signals in probes embedded near the cochlea. These are detected by the nerves and transmitted to the brain.
If you are to operate noisy machinery, mow the lawn or use power tools, your ears may be in for prolonged exposure to loud sounds. The use of small earplugs or earmuffs will electrode array protect your ears and avoid ringing in your ears, which can last for several hours. Any ringing in your ears after exposure to loud sound means that some permanent damage has been done to your hearing. Tinnitus, a condition in which a person hears a permanent ringing in the ears even when there is no sound, can be caused by Prac 2 exposure to loud sounds over a long period p. 230 of time. Use this chart to work out which sounds will harm your hearing.
Fig 8.2.6
Decibels (dB) 160
Worksheet 8.3 Hear hear!
150 140
Dangerous
Harmful
Ear protection
jumbo jet on take off
130 120
threshold of pain
110
loud thunderclap
100 90 80
train motor mower
Loud
70 60
normal conversation
Quiet
Normal
50 40 30 20 10 0
Ears should be protected when exposed to loud sounds.
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Fig 8.2.5
whisper
quietest sound that can be heard
blah blah blah
UNIT
8 .2
UNIT
8.2 [ Questions ]
Checkpoint
Ear protection
Sound 1 State the word that best describes the movement of air, fluid and bones within the ear when a sound passes through it. 2 Identify the unit used to measure the loudness of sound.
Parts of the ear 3 Copy and complete the table below to summarise each part of the ear described in this section.
14 Identify three common situations in which some form of ear protection is advisable. 15 Use Figure 8.2.6 to identify some sounds that can be: a dangerous b harmful c quiet 16 State the sound level in decibels at which sound becomes hazardous to your hearing.
Think Part Pinna
Description/function Fleshy ear flap, collects sound
17 Identify an example of a task that involves mainly hearing. 18 Propose a reason why airlines sometimes offer lollies to travellers during takeoff and landing. 19 Propose a reason why animals like rabbits, deer and zebras have large ears.
4 Identify the part of the ear that is filled with fluid. 5 Identify the three small bones in the middle ear and state the name for them as a group. 6 Identify the part of the ear that the auditory nerves attach to. 7 State where most sound amplification happens in the ear.
Why two ears? 8 A sound arrives at your right ear just before it reaches the left. State which direction the sound came from. 9 Sounds from directly in front arrive at both ears at the same time and so do sounds from directly behind. Propose how we know which direction it is coming from.
Ear problems 10 Propose a reason why there are three semicircular canals instead of just one. 11 Describe how ear wax may be: a useful b a hindrance 12 Describe two ways in which damage can be done to your hearing.
20 Evaluate whether two ears are more valuable than one for survival. 21 Explain why an ear infection may upset your sense of balance. 22 In young children, the Eustachian tube is almost horizontal. In the adult ear shown in Figure 8.2.1, this tube is nearly vertical. Use these facts to explain why young children are more prone to middle-ear infections. 23 Caleb and Sarah both have hearing difficulties. Speaking louder to Caleb makes it easier for him to hear, but it makes no difference to Sarah’s hearing. Propose a reason for this. 24 For each of the following sounds state the approximate decibel level, and whether the sound will damage the ear. Use figure 8.2.6 to help you decide. a Motor mower b Large truck passing by c Helicopter up close d Person shouting at 1 metre away e Formula one racing car from the side of the track f Normal level of music through headphones g Normal classroom chatter.
13 Explain what happens to your hearing after a loud rock concert.
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Hearing
[ Extension ] Investigate
Action
1 Investigate how a stethoscope works.
4 a Design an experiment in which a sound level meter measures the sound levels produced by different walkmans. Record DYO your results in an appropriate table and column graph. b Evaluate your results to determine whether the levels at which you regularly listen are harmful to your hearing.
2 Investigate more about how the bionic ear works. Illustrate the important parts of the bionic ear to show how it functions. Who was the first recipient of a bionic ear?
Create 3 Construct a model ear to demonstrate how the ear works, labelling the important parts. Demonstrate the path of sound energy through the ear and the energy transformations that occur.
UNIT
8.2 Prac 1 Unit 8.2
DYO
Surf 5 Explore information about the ear by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button.
[ Practical activities ] Hearing tests
Reading decibels
Aim To examine the directional ability of our ears in detecting sounds
Aim To measure the sound level of various sounds around the school
Method Seat one of your group and blindfold them. Ensure they are facing straight ahead. Develop a test that will indicate how well they can detect a sound coming from various directions. Test what effect changing distance and blocking one ear have on your results.
Questions 1 Describe how the distance of the sound source affects results. 2 Describe what happens if the person covers one ear. 3 Evaluate the need for two ears.
Prac 2 Unit 8.2
Equipment Sound level meter
Method Each sound level meter operates slightly differently. Acquaint yourself with how to measure and read the sound level. 1 Use the meter to measure at least five different sounds around the school. For example, you might measure the sound levels of two people chatting and then arguing, a noisy classroom, and traffic on the road outside the school. 2 For each measurement, estimate your distance from the subject.
Questions 1 Use a table to record your sound level measurements. 2 Use the table and Figure 8.2.6 to classify each of the sounds as harmful, dangerous, loud, normal or quiet.
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UNIT
context
8. 3 It is said that we have five senses. Sight and hearing are provided by the eye and the ear. Three other important sense organs are the nose, tongue and skin, responsible for the senses of smell, taste and touch respectively. Imagine life without these sensations!
Smell You detect a smell because a few tiny chemical particles enter your nose and dissolve in its moist lining. Considering some of the nasty smells we detect each day this may not be a pleasant thought! The dissolved substance triggers nearby nerve cells in the upper part of the nasal cavity, called olfactory cells. Impulses in the olfractory nerve send messages to the brain so we can smell the substance. The typical human nose can detect around 2000 smells, and may be trained to Prac 1 detect up to 10 000. p. 235
Ahh—choo!
The male fruit fly can Sneezing is a reflex action that detect smells emitted by removes irritating dust or other a female fruit fly using foreign particles from the nasal chemically sensitive hairs on its front legs passages. A sneeze can travel at and its antennae. 160 kilometres per hour right across a room, so duck next time one comes your way! You also close your eyes when you sneeze—some say to stop your eyes from popping out!
Taste The surface of the tongue is covered with thousands of bumps, called papillae. More than 10 000 taste buds are embedded between the papillae. Humans can detect five primary taste sensations: sweet, sour, salty, bitter and umami. Umami is distinctly different from the other basic tastes and is believed to activate a separate set of taste receptors. It is the savoury taste Scanning electron microscope image of a taste bud (centre) surrounded by papillae
tiny particles from pizza
Smelling without a nose
Fig 8.3.2
brain moist lining
mmmmm!
nerve cell (olfactory cell) pizza
Fig 8.3.1
How we detect smells
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Smell, taste and touch of glutamate found in processed meats, cheeses and monosodium glutamate (MSG). Saliva in our mouths must first dissolve samples of food so that the taste buds can detect them and send messages to the brain. A single taste bud contains fifty to one hundred taste cells, which can detect all five taste sensations. Our taste buds also provide information on the intensity and pleasantness or unpleasantness of taste. Although all areas of the tongue are able to detect all taste sensations, some areas Prac 2 Prac 3 Prac 4 p. 235 p. 236 p. 236 may be more sensitive to certain tastes.
Flavour When we eat, our senses of smell and taste work together Artificial to detect flavour. flavouring As much as 80% of Many processed foods what we perceive as rs. have artificial flavou Although made in flavour is actually laboratories, they are smell. Flavour is often identical to those largely the smell of the found in nature. If gases emitted from banana flavouring amyl acetate is distilled from food that has just bananas, it is classified been taken out of as a natural flavouring. your mouth. When Amyl acetate is also made in the laboratory your nose is by mixing vinegar with blocked, your sense amyl alcohol, using of smell is not as sulfuric acid as a good as usual. catalyst. Although exactly the same flavouring, That’s why food it is now classified as seems less tasty artificial flavouring. when you have a cold. Likewise, pinching your nose will make food you don’t like more tolerable. The tongue is most sensitive at temperatures between 20°C and 30°C. Sweet and sour tastes are increased at higher temperatures, and bitter and sour increase at lower temperatures.
Touch Most of us probably don’t think of the skin as an organ, but it is.
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It contains millions of nerve endings that send information about touch, pain, pressure and temperature to the brain. In humans, the touch receptors are more concentrated in the face, tongue, lips, fingertips and toes. Body hair also plays an important role in our ability to sense touch. A large number of receptors are found in the skin at the base of hair follicles.
pain receptor
The biggest organ The average human adult has a 290 g heart, 1090 g of lungs, 1330 g of brain and 1560 g of liver. At nearly 11 kg, however (10 886 g to be exact), the skin is by far the largest organ. Over an average lifetime, a human will shed roughly 18 kg of dead skin!
layer of dead skin
hair
sebaceous gland light contact receptor
pore
epidermis
dermis
sweat gland
fattty layer pressure receptor
cold receptor
hair movement
heat receptor
A cross-section of human skin
Animal tongues The giant anteater’s tongue may reach lengths of over 60 cm. Dogs do not sweat. Instead, they use their tongues to cool down. Rapid panting at rates of up to 200 times per minute allows heat to be removed from the dog’s body as moisture evaporates from the tongue.
Fig 8.3.3
Below the top protective layer of dead skin cells is a ‘living’ layer of skin. It has different nerve receptors located at varying depths. Thermo receptors respond to heat and cold, and there are about four times as many heat receptors as cold receptors. Pain receptors are located throughout the skin and can experience prickling pain (fast pain) or burning and aching pain (slow pain). The sebaceous glands produce oil that helps keep the skin soft and stops it cracking. The sweat glands produce sweat, which, on reaching the surface, removes Prac 5 p. 236 heat from the body when it evaporates.
Skin conditions Many conditions may affect the skin. One of the most common is acne, which causes pimples to appear, often on the face. Pimples often occur more severely during puberty, when the skin secretes more oil than usual from the sebaceous gland into a hair follicle. Dead skin cells or dirt can block the follicle. If it becomes infected with bacteria, it can become swollen with pus. Contrary to popular opinion, diet has little to do with pimples. Apart from puberty, other possible causes include stress, medications and some cosmetics. Pimples may be treated with pharmaceutical creams and lotions, and by gently washing the affected area. Over-washing and harsh soaps should be avoided. Dermatitis is a condition in which the skin becomes itchy and swollen and exhibits a red rash. It may be caused by exposure to certain chemicals. Eczema is a common type of dermatitis. Warts are harmless, rough, raised lumps that grow on the surface of the skin. They are caused by a virus, and can spread to other parts of the body if scratched open. Chemical treatments are available, or warts may be frozen off by a doctor with liquid nitrogen. Freckles are darker spots caused by a pigment called melanin in the skin cells. Darker-skinned people have more melanin in their skin than those who are lighter-skinned. Freckles are normally harmless, but any change in the size or shape of one should be referred to a doctor. Moles are raised, dark spots that are normally harmless, but have the potential to develop into skin cancer. Again, any changes to a mole should be referred to a doctor.
Skin cancers There are three main forms of skin cancer. Basal cell carcinoma (BCC) is the most common form, and the least dangerous, appearing as a red, flaky or waxy bump on the skin. It rarely spreads to other parts of the body, provided it is treated as soon as possible. Squamous cell carcinoma (SCC) is not as common, and is more serious, appearing as red scaly sores, and can spread to other parts of the body. Melanoma is the least common, and most deadly, form of skin cancer. New spots, or old spots that change colour or size, or itch or bleed, may be a sign of a melanoma, and should be checked immediately. The major cause of skin cancer is exposure to ultraviolet or UV radiation. Unfortunately, Australia leads the world in skin cancer rates. Sunbaking is the deliberate exposure to UV radiation to get a ‘suntan’ and is a very dangerous practice. A suntan is a sign that damage has been done to the skin, whose reaction is to produce more melanin and go darker. Sunburn is even worse, since the damage is more severe and more immediate. Nowadays most of us cover up, using hats and protective clothing and swimwear, or stay in the shade and use sunscreens to reduce the damage caused by UV rays. UV levels from the Sun are most dangerous between 11 am and 2 pm during summer. Whatever the time of day, even on cloudy days, UV rays are always present and damaging.
UNIT
8.3
Worksheet 8.4 The skin Worksheet 8.5 Senses and codes Skin cancers a Melanoma b Basal cell carcinoma (BCC) c Squamous cell carcinoma (SCC)
Fig 8.3.4
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Smell, taste and touch
UNIT
8.3
[ Questions ]
Checkpoint
15 Besides taste, describe what else the tongue is used for.
Smell 1 True or false? a When you smell a substance, tiny parts of it have dissolved inside your nose. b Olfactory cells are nerve cells in the nose. 2 Draw a diagram to demonstrate where the olfactory cells and olfactory nerves are in the nose.
Taste 3 Are papillae the same as taste buds? Explain.
16 Evaporation of sweat from the skin helps remove heat from the body. Describe how.
Analyse 17 Smells may be categorised as: burned, foul, fragrant, fruity, resinous (e.g. nail polish) or spicy. State an example of each type of smell. 18 Write a paragraph explaining how to reduce your risk of getting skin cancer.
4 List a food that would give each of the different types of taste. 5 State the senses that combine to help us appreciate flavour. How could you more easily eat a food or vegetable you don’t like?
[ Extension ] Investigate
Touch 6 Starting from the surface, list in order the layers of the skin.
1 Determine what pheromones are and how insecteating plants use them.
7 List five types of skin receptors.
2 Research the history of perfumes. Possible ‘leads’ include: Ma Griffe, Dior, Nina Ricci, Guerlain, Givenchy and Estee Lauder. Summarise your information in a timeline.
8 Explain the purpose of the fatty layer of the skin.
Skin conditions 9 Briefly describe two skin conditions. 10 Propose some reasons why Australia has such a high skin cancer rate compared to other countries. 11 Outline how you can be ‘sunsmart’.
Think 12 Copy and complete the following table. Sense
Sense organ
Sight The ear Smell The tongue
3 Research other skin conditions, and their causes and treatments. Possible conditions to research include tinea, boils, cold sores, thrush, ringworm, scabies, shingles and psoriasis. a In small groups, present your information to the class using a presentation media such as PowerPoint. b Use peer assessment to evaluate the effectiveness of the presentation. 4 a Research skin cancer statistics over the past decade or so. Is it increasing or decreasing? What reasons could you suggest? Comment on your findings. b Analyse whether increased awareness of the dangers (e.g. through the media or doctors) has had an impact on the occurrence of skin cancer. c Examine what it means if a sunscreen is ‘factor 15’ or ‘SPF 15’. Are other factors available? 5 Create a poster promoting ‘sunsmart’ behaviour.
13 A chemical is added to normally odourless liquid petroleum gas (LPG) to make it smell unpleasant. Explain how this makes LPG safer. 14 Identify a profession or situation in which the senses of smell and taste are important.
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Surf 6 Explore information about the nose and skin by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button.
UNIT
8.3 Smell fatigue Prac 1 Unit 8.3
Aim To investigate the phenomenon of smell fatigue Equipment A safe, strong-smelling substance (e.g. aftershave, soap or perfume), a watch, a small container (e.g. a film canister and lid)
3 Re-seal the container and wait 30 seconds before taking a similar whiff. Rate the strength of the smell from 0 (no smell) to 5 (the strength of your first smell). 4 Continue to take a whiff every 30 seconds, giving the strength of the smell a rating each time until you have about six ratings.
Questions
Note: Check with the class for students who may be allergic to any of the substances to be used in the experiment.
1 Describe what happens to the strength of what you smell after several whiffs.
Method
2 Construct a graph to display your ratings.
1 Obtain a sample of a safe, strong-smelling substance in a container that can be sealed. 2 Carefully take a small whiff of the substance. Do not breathe in too deeply. Avoid taking your breath away.
3 Record whether each area is sensitive to the solution (e.g. sweet).
Taste regions Aim To determine whether some areas of the
4 Repeat for the other three solutions.
tongue are more receptive to certain tastes
Questions
Equipment
1 Record your results on a copy of Figure 8.3.5 but without the marked zones.
Clean cotton buds, samples of the following solutions in new plastic cups (do not use beakers or other lab glassware): sugar, salt, vinegar or lemon juice, coffee
2 Compare your results with those of your classmates. Figure 8.3.6 is the tongue map usually proposed in textbooks. 3 Compare your own map to this.
Method 1 Dip a cotton bud in one of the solutions and touch it to each area of your tongue (shown as A, B, C and D below).
4 Using your own and class results evaluate the accuracy of the map below.
Fig 8.3.5
B
A
D
C bitter
sour
sweet
r
Prac 2 Unit 8.3
2 Do not share cotton buds with others in the class. Use a new end for each sample.
sou
UNIT
8 .3 [ Practical activities ]
sweet and salty
E Fig 8.3.6
This taste map has been presented in many textbooks. How accurate do you think it is?
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Smell, taste and touch
Brand name versus no name Prac 3 Unit 8.3
Skin receptors
Aim To compare the taste of various products
Prac 5 Unit 8.3
and investigate the role of smell in the taste process
Equipment
Aim To investigate the sensitivity of your skin in various areas Equipment Toothpicks, tape, ruler, blindfold
Method
Samples (in pairs) of various edible substances, e.g. ‘brand name’ chocolate, ‘no name’ chocolate, brand name lemonade, ‘no name’ lemonade; blindfold; new plastic cups
1 Attach two toothpicks to a ruler as shown.
Note: Check with the class for students who may be allergic to any of the products to be used in the experiment.
toothpick ruler
Method 1 Work with a partner or group and blindfold one person.
0
1
2
3
4
5
6
7
8
2 Give the blindfolded person a taste of a ‘brand name’ and ‘no name’ pair of foods, and record their brief description of the taste of each. 3 Repeat for the other food items. You may wish to share the blindfold and tasting job among your group members. 4 Repeat the tests, but have the tester pinch his or her nose shut while tasting.
Questions 1 Were testers able to distinguish between brands of foods? Give details. 2 Did removing the ability to smell affect the results? Explain. 3 Evaluate any relationship between product brand and quality of taste.
9 10 11 12 13 14 15 16 17 18
20 21 22 23 24 25 26
28 29 30
tape
Fig 8.3.7 2 Make sure your partner cannot see while you touch both toothpick points to a region of skin. Ask your partner how many points they feel. 3 Move the toothpicks closer to each other and test again. Progressively move the toothpicks closer together until only one can be felt. 4 Test other regions of the skin the same way. Some possible areas to try are the back of the hand, palm, inside forearm, back of forearm, leg, foot, back of neck. 5 Swap jobs and have your partner test you.
Questions 1 Give each area of your skin a sensitivity rating.
Prac 4 Unit 8.3
DYO
236
Taste trickery
2 Compare results with your partner.
Design and carry out an experiment to test whether a blindfolded person who is pinching their nose can tell the difference between the taste of apple, potato and pear.
3 Propose reasons why some areas are more sensitive than others.
UNIT
context
8. 4 Through our senses we are constantly receiving information from our surroundings. This information may be of many types: the smell of a classmate’s tuna sandwich, the hot air near a Bunsen burner or the noise of a passing bus. When this information is received it could lead to a variety of responses: holding your nose, moving away from the flame or turning towards the bus. Our responses enable us to react to changes around us, enhancing our chances of survival in a world full of potential threats.
Responding to stimuli One of the fundamental characteristics of living things is that they respond to information received from their surroundings. This ability is needed to feed, escape, move, reproduce and keep warm or cool down. Humans respond to increased temperature by involuntarily sweating and increasing blood flow to the skin (making you look ‘flushed’). Our behaviour changes too: we remove clothes and grab a cold drink. Humans show an amazing ability to respond to changes in their surroundings. For instance, the body temperature of humans stays at approximately 37°C, and blood acidity or pH at around 7.38 regardless of whether they are in the deserts of Africa, the jungles of South America or the icy Arctic zones. This maintenance of a constant internal environment despite changes in the surroundings is called homeostasis. Homeostasis allows cells to keep working efficiently, maintaining temperature, glucose and water levels within strict limits.
Stimulus Heat or cold
Thermoreceptors in the skin
Water levels in blood
Osmoreceptors in the brain and large arteries
Pressure and touch
Mechanoreceptors in the skin
Sound
Cochlear cells in the inner ear
Light
Photoreceptors in the retina of the eye
Chemicals
Chemoreceptors on the tongue and in the nose
Gravity
Semicircular canals in the ears
contains receptors to detect all these stimuli. When a receptor receives a stimulus, a message is Prac 1 Prac 2 sent to an effector. An effector is p. 240 p. 240 an organ, such as a gland or a muscle, which causes a response. A simple example of the stimulus–response model is what happens when you burn your finger
finger cut by knife
stimulus
muscle contracts to withdraw hand from knife
pain receptors
response
receptor arm muscle
Stimulus–response model Homoeostasis requires a sequence of steps known as the stimulus–response model. The sequence begins when a sense receptor is stimulated. A stimulus is something that acts on a receptor, causing a change in the activity of an organism. Stimuli include heat, light, pressure, touch, sound, chemicals and water levels. Your body
Location of receptor
relay by nerves effector
Fig 8.4.1
The stimulus–response model of what happens when you cut your finger
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Responding (the stimulus). Heat and pain receptors in your finger send messages via nerves to an arm muscle (the effector), causing the muscle to contract and pull your hand away from the flame (the response).
Feedback and coordination Often this sequence of events involves some kind of feedback of information. The response generally affects the original stimulus in some way, so the organism is able to adjust its response. The total response of an organism is often complex, involving several parts of the body. For this to occur, some kind of coordination is required. All organisms are coordinated in some way. Even a single-celled amoeba can respond to changes in temperature or pH. The response usually involves moving away from the stimulus. In most larger organisms there are a Thermostat feedback number of structures to detect, transmit, coordinate and respond to stimuli. The control of carbon dioxide levels in your blood is an example of the stimulus–response model that includes both feedback and coordination. Blood carbon dioxide levels may rise (the stimulus) after exercise. Special areas in
UNIT
8.4
A thermostat on a heater uses a stimulus–response model and feedback to keep the temperature stable. When the temperature of the room drops, the thermostat detects the change (stimulus) and turns the heater on (response). The increasing temperature is then detected (feedback). The thermostat responds by turning off the heater. This cycle of feedback continues, keeping the temperature almost constant.
[ Questions ]
Checkpoint Responding to stimuli 1 List six pieces of information you are currently receiving from your surroundings. 2 a Define homeostasis. b Explain why homeostasis is necessary. 3 Identify three substances in the body whose levels are controlled by homeostasis.
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some large arteries (the receptors) detect this rise and transmit messages to the brain (the coordinating centre). Messages are then sent from the brain to various muscles (the effectors) to produce an increase in breathing rate (the response). Rapid breathing causes a decrease in blood carbon dioxide levels. This decrease is detected (the feedback) and the breathing rate subsequently returns to normal. Fig 8.4.2
Control of carbon dioxide levels in blood
increase in carbon dioxide level in blood stimulus
(lower carbon dioxide level) feedback
receptor cells in main arteries
increase in breathing rate response
receptor relay by nerves
diaphragm and chest muscles
effector
the brain
relay by nerves
coordinating centre
Worksheet 8.6 Concussion in football
Stimulus–response model 4 Distinguish between a receptor and an effector, giving examples of each. 5 Match each receptor with the stimulus to which it responds. Receptor Cells of the retina Cells of the inner ear Taste buds Osmoreceptors in the brain Semicircular canals in the ear Thermoreceptors in the skin
Stimulus Gravity Chemicals Heat Light Sound Water levels
UNIT
8.4 Feedback and coordination i increase in body temperature
6 Define the following terms: a feedback b coordination 7 If the carbon dioxide level in your blood was to increase after exercise, identify: a where the receptors that detected this increase would be located b the coordinating centre that would receive messages c the structures that would act as effectors d the response you would notice
viii (decrease in body temperature)
ii thermoreceptors in the skin iii
vii increase in sweating and blood flow to skin
iv hypothalamus in the brain
Think vi blood vessels and sweat glands
8 State the approximate value of the: a body temperature of a healthy human b pH level in the blood of a healthy human
Fig 8.4.3
9 Describe the most usual response to a stimulus for single-celled organisms. 10 Use the terms in the list below to label the diagram in Figure 8.4.3 (marked i to viii) showing control of body temperature: response, relay, feedback, stimulus, effectors, coordinating centre, receptor, relay
v
11 Draw a diagram to illustrate the stimulus–response model that happens when you touch a hot stove. 12 List the different responses you coordinate when stepping barefoot onto hot sand at the beach.
[ Extension ] Investigate 1 The body’s homeostatic control can fail in extreme temperatures. Body temperature may rise (hyperthermia) or fall (hypothermia). a Investigate either hyperthermia or hypothermia, listing its symptoms and likely causes. b Prepare a report explaining how to avoid these two conditions. 2 A fever caused by infection may result in your body temperature rising two or three degrees above normal. Research how this happens and whether the higher temperature is beneficial or damages body cells. 3 Acidity is measured using the pH scale. a Investigate whether blood (pH 7.38) would be described as neutral, acidic or basic (alkaline). b Investigate what might cause a change in blood pH, and how the body responds to this. Fig 8.4.4
We wear less clothes in hot weather to avoid hyperthermia
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Responding
UNIT
8.4 [ Practical activities ] Sweet and salty
3 Compare the class results. Is there a difference in the taste thresholds between males and females?
Aim To identify the threshold of a stimulus Prac 1 Unit 8.4
Equipment
4 Justify the value of receptors in the body having thresholds.
12 new small paper cups, 2–3 mL each of solutions of sugar of varying concentrations (0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%), 2–3 mL each of solutions of salt (0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%), waste jar for rinsings, bottled water for rinsing mouth
5 a You knew what type of solution you were tasting. Evaluate whether this knowledge affected your judgement. b Describe how you could modify the activity to overcome any problems.
Method 1 Draw up a results table as shown here. 2 Sip the most dilute (0.001%) sugar solution. Can you taste the sugar? Record a ‘+’ in the table if you can, or a ‘0’ if you cannot.
Concentration
0.001%
0.005%
0.01%
0.05%
0.1%
0.5%
Result for sugar Result for salt
3 Spit the sample into the waste jar. 4 Repeat the test with 0.005% sugar solution. 5 Continue tasting each solution of next higher concentration until you can taste the sugar. Try the next higher concentration to be sure of your results. 6 Thoroughly rinse your mouth using the bottled water.
Sound threshold Prac 2 Unit 8.4
7 Repeat the procedure using the salt solutions, once again starting with the most dilute.
Questions
DYO
The loud tick of a mechanical clock or watch can be used to test hearing. The distance of the clock from the ear can be used as a measure of the loudness of the sound. Design an experiment to test the sound threshold for members of your class. Compare the thresholds for males and females.
1 The minimum intensity that causes a response is known as the threshold for the stimulus. State your taste threshold for sweetness. 2 State your taste threshold for saltiness.
Fig 8.4.5
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UNIT
Your nervous system controls and coordinates all parts of your body. It is the most complex of all your body systems and, despite many years of research, it is the least understood. Here is some of what we know.
Fig 8.5.1
CNS (brain and spinal cord)
The nervous system The nervous system has two parts: • the central nervous system • the peripheral nervous system. The central nervous system (CNS) is made up of the brain and spinal cord. They act as the control centre, receiving messages from all parts of the body, examining the information received, and then sending out messages to tell parts of the body what to do. The peripheral nervous system (PNS) is made up of sensory receptors and nerves. These continuously inform the CNS of changing conditions, and transmit the decisions made by the CNS back to effector organs. Messages are passed through the system by nerve cells called neurons. These are specialised cells that transmit and receive messages in the form of electrical impulses. s rosi scle iple Mult In the disease called multiple sclerosis, patches of myelin deteriorate at intervals along neurons in the CNS. The affected areas cannot conduct electrical impulses and the neurons cannot be replaced if damaged. Victims of multiple sclerosis have symptoms including loss of coordination, tremors, difficulty in seeing and partial paralysis. The cause is still a mystery, but evidence suggests that a measles-like virus may be responsible in genetically susceptible people.
The human nervous system
special
skin
organs
muscle
mo
to rve r s
ne
effectors (muscles and glands)
sen ne sory rve s
context
8. 5
Neurons
A neuron has the usual features of any cell found in an animal. It has a nucleus, cytoplasm and cell membrane, but it also has a number of other specialised parts. Around the cell body are small threads called dendrites. These make contact with other cells and receive information from them. There is also one long thread, the axon, which carries information away from the cell. Axons are often encased in a white fatty substance, called myelin, which insulates the axon like the plastic
large arteries and other tissues PNS (sensory receptors and nerves)
coating on an electrical wire. Myelin also enables messages to pass more quickly along the axon. The information is carried by electrical impulses that travel at speeds between 1 and 100 metres per second.
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Nervous control A typical neuron
cell body
Fig 8.5.2
dendrite cell membrane nucleus cytoplasm
axon
myelin sheath
nerve ending
Fig 8.5.3
Neurons are grouped together in bundles called nerves, in much the same way as an electrical cable is made up of smaller wires bound together. Some neurons, called sensory neurons, have motor neuron specialised endings sensitive only to stimuli such as heat dendrites and light. These form part of the body’s larger sense organs (eyes, ears etc.), which function by collecting different energy forms. The sensory neuron then converts this energy into an electrical impulse. In this way, cells direction of in the retina convert light impulse energy to electrical energy. Another type of neuron, the connecting neurons or axon interneurons, transfer these electrical messages within the CNS. A third type, motor neurons, transfer messages from the CNS to effector organs such as muscles.
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A scanning electron microscope image of a neuron (light brown) showing the thick axon and several thin dendrites.
Fig 8.5.4
Two types of neurons—motor and sensory sensory neuron
cell body
axon
nucleus
myelin sheath
long distance
muscle fibres
direction of impulse
sensory receptor
The synapse Throughout the nervous system there are small gaps between neurons, called synapses. Messages cross these synapses, but not as electrical impulses. The message is carried chemically by special compounds called neurotransmitters. When an impulse reaches a synapse, neurotransmitters are released and quickly move across the gap. They move to sites on the other side, restarting the electrical impulse. The neurotransmitter is then broken down so that new messages can be received.
end of the axon of one neuron neurotransmitter
Pain relief The pain-relieving processes of acupuncture and hypnosis appear to be related to neurotransmitters called encephalins. These are the body’s own pain-deadening neurotransmitters. Acupuncture is thought to stimulate the production of encephalins. Morphine, codeine and pethidine act in much the same way as these neurotransmitters.
synaptic gap
neurotransmitter crosses the gap
dendrite of another neuron
Fig 8.5.5
Crossing a synapse
Around fifty different neurotransmitters have been identified. Many drugs and poisons affect neurotransmitters. Curare is a poison used by South American Indians on arrow tips. It blocks reception of the neurotransmitter acetylcholine, preventing messages from getting to muscles, stopping breathing and other movements. Some insecticides work by preventing the breakdown of acetylcholine, so messages are constantly received, resulting in continuous muscle spasms. Another neurotransmitter, noradrenalin, is associated with alertness. Another is dopamine, associated with emotions. Drugs such as amphetamines, cocaine and ecstasy increase production of these neurotransmitters. This results in an increased state of alertness and heightened emotions, along with high blood pressure, irritability and, later, depression and insomnia.
Pain relief using acupuncture
UNIT
8.5 Fig 8.5.6
So why do we have synapses? If neurons touched each other it would be something like turning on one switch and having every light in the house come on at once. Synapses are similar to a switchboard, allowing messages to be directed to the correct places. It is also thought that synapses in the brain play an important part in learning and memory.
The brain The brain is soft, wrinkly tissue with a mass of around 1.4 kg. Each of its twenty-five billion neurons are connected to as many as 1000 others, and there are as many as one hundred million million synapses. This huge number of neurons does not exist as a tangled mess. They form neuron networks, with neurons arranged in specific circuits. Not even the largest, most intricate computer comes close to the complexity of the human brain. It is hardly surprising then that scientists know little about what actually happens in processes such as thinking, sadness or when we try to remember what happened yesterday.
Don’t interrupt the flow Although the brain makes up only 2% of the body’s weight, it receives 20% of the body’s blood supply and uses 20% of its oxygen. If blood flow to the brain is interrupted, consciousness is lost rapidly and irreversible damage occurs within minutes. To avoid this, jet fighter pilots wear special pressure suits to maintain blood flow to the brain during rapid turns. The most common form of brain damage is ‘stroke’, where part of the brain is deprived of blood. This can happen if a blood vessel bursts in the brain (a haemorrhage), or more commonly when a blood clot blocks a vessel.
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Nervous control The human brain
cerebellum
ati
vis ion
on a
re a
a
r are
taste ring ci hea a ss o
oto
cerebrum (right and left hemispheres)
n
touch smell
a are
m
associa tio
Fig 8.5.7
cerebellum medulla
medulla spinal cord
The cerebrum controls many functions.
Fig 8.5.8
Protecting the brain The brain has three main structural parts: the cerebrum, cerebellum and Bumpy criminals medulla. The cerebellum In the nineteenth century controls complex muscular many scientists believed that criminals had different movements like cycling, brains to those of walking and running. The law-abiding citizens. Bumps medulla controls vital on the outside of the skull were supposed to give some activities you do not have idea of the brain and to think about, like criminal intent inside. After breathing and heartbeat. executions, death masks The cerebrum makes up were often moulded from the shaved skull as a mould. 90% of the brain’s volume. The bumps could then be It is divided into right and examined at leisure. The left hemispheres. The study of the criminal brain and skull was called surface has many folds, phrenology and is not taken creating a large surface area seriously today. with billions of neurons. These are a grey colour (hence the expression ‘using your grey matter’). The cerebrum is responsible for complex thoughts. The right side is responsible for artistic, musical, intuitive and perceptual abilities. The left takes care of language, learning mathematics and logical thinking. Some regions (the sensory areas) are concerned with receiving and interpreting impulses from sense organs. The motor areas control muscles. The association areas are concerned with memory and thinking.
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Your brain is so important that the body protects it very carefully. It is protected by the bony case of the skull and by layers of connective tissue called meninges. It also has a jacket of fluid around it called cerebrospinal fluid (CSF) to cushion against shock. The base of the brain is connected to the spinal cord. It too is protected by a bony case, the backbone, and cushioned by cerebrospinal fluid. The spinal cord transmits messages between the brain and the PNS, and controls some actions that do not require thinking.
Nervous reactions Actions that need to be carried out automatically and without thinking usually require only a few neurons, and are therefore very fast. A pathway known as a reflex arc carries these reactions (see Figure 8.5.9). For example, if you prick your finger with a pin (the stimulus), pain receptors in the skin send a message via a sensory nerve to the spinal cord. The message crosses synapses to a motor nerve which carries the message to muscles (the effector). Notice that the brain itself is not yet involved. A message may be sent to the brain, but only to keep it informed of what is happening. A secondary response might be a cry of pain. The brain may also store information so that next time you avoid touching the pin. Other reflex actions include blinking, sweating, shivering, coughing and the knee-jerk reaction.
UNIT
8.5 spinal cord sensory nerve impulses to brain vertebra
motor nerve
interneuron cell body of sensory nerve
spinal cord
pain receptors in skin
muscle
sensory nerve motor nerve
pin prick Fig 8.5.9
A reflex arc
More complex actions require messages to be sent to the brain, decisions made and responses sent back to various effectors. Some learned actions may become so automatic as to appear to be reflexes. For a nine-month-old baby, eating, especially with a spoon, requires conscious effort. As the years pass, pathways that control this process become so well established that the action appears to be automatic. Likewise, people who excel in sport or music perform actions with little effort after years of practice. The rest of us stumble with Prac 1 Prac 2 Prac 2 Prac 4 p. 247 p. 247 p. 247 p. 247 the task.
5 Describe the function of neurotransmitters. 6 a Explain why synapses are necessary. b State two disadvantages of synapses.
The brain 7 a Identify the three main structural parts of the brain. b State the major functions of each. 8 Label the diagram shown here, using the following words: cerebellum, medulla, spinal cord, cerebrum.
a
Worksheet 8.7 The nervous system b c
UNIT
8.5
[ Questions ]
Checkpoint The nervous system 1 a Identify the two main parts of the nervous system. b Describe what each part consists of and the main function of each. 2 Compare the neuron with other cells in the body. a How is it like other cells? b How is it different? 3 Distinguish between a neuron and a nerve. 4 Distinguish between sensory, motor and interneurons.
d
Fig 8.5.10 9 Identify which part of the brain: a you use to think b controls breathing c helps you balance while cycling d gives you sensations of touch 10 State three ways in which the brain is protected from injury.
Nervous reactions 11 Identify which of the following would be reflex actions: coughing, sneezing, reading, cycling, writing, blinking.
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Nervous control
Analyse
12 State one reflex action that occurs when: a a bright light is shone in your eyes b food enters your windpipe c you are hungry and you smell food d you spend a long time in the sun on a hot day
16 Identify which side of your cerebrum is most active in helping you answer these questions. 17 List two conscious acts that are so automatic that they may appear to be reflex actions. 18 Propose reasons why it is important that scientists continue to research the brain and nervous system.
Think 13 State the type of energy conversion carried out by each of the receptors listed. a retinal cells in the eye b cochlear cells in the ear c taste buds on the tongue d thermoreceptors in the skin 14 a Identify the type of neuron shown in Figure 8.5.11. b Identify and label parts i to v. 15 Arrange the following list of events in the correct order to describe a reflex action. Write your answer as a flow chart.
iii i
direction of impulse
iv
v
ii
Fig 8.5.11
An impulse is sent along a sensory neuron to the brain. An impulse is sent along a motor neuron to iris muscles. A bright light is shone in the eye. Iris muscles contract, causing the pupil to narrow. Receptors detect a change in light intensity.
[ Extension ] Investigate 1 Investigate the effect of caffeine, marijuana or alcohol on the CNS and perform a role play to teach other students about your findings. 2 Research and report on one of the following disorders of the nervous system: Parkinson’s disease, Alzheimer’s disease, epilepsy. Outline the signs, symptoms and treatments for the disease you have chosen. 3 The blue-ringed octopus is one of the most deadly sea creatures. Investigate how its poison can paralyse the nervous system. 4 Investigate the differences in brain structure of humans, gorillas, dolphins and dogs.
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5 Each year, many young people seriously injure their spinal cord when they dive into water that they did not know the depth of. Many become paraplegic or quadriplegic. a Investigate what ‘quadriplegic’ and ‘paraplegic’ mean, and find the number of diving accidents in Australia last year. b Research one such case and outline factors that led to the injury (e.g. was alcohol involved?). c Report on the person’s life since the accident and their probable life in the future.
Surf Complete the following activities by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. 6 Explore interactive diagrams of the nervous system. 7 Perform a number of activities to test your reflexes.
UNIT
8.5 UNIT
8.5 [ Practical activities ] Prac 1 Unit 8.5
Memory I
Memory II
Aim To investigate how we memorise words
Aim To investigate the effect of distractions on memory
Equipment Three lists of words, each printed on separate cards (A, B and C) (note: your teacher will supply these cards—do not look at them until the activity begins), a person to act as the subject
Method 1 The subject is to read the list of words on card A until they can recall them perfectly (with no mistakes). Record the time taken to develop perfect recall. 2 Repeat the procedure using card B, then card C.
Questions 1 State which list is memorised most quickly. 2 Propose reasons why this was fastest.
Prac 2 Unit 8.5
Equipment Two stanzas of a poem, printed on separate cards, a person to act as the subject
Method 1 The subject is to read the first stanza until they can recall it perfectly (with no mistakes). Record the time taken to develop perfect recall. 2 Repeat the procedure using the second stanza, but this time make distracting noises such as singing, banging occasionally, and so on. Record the time taken to develop perfect recall.
Questions 1 Compare the times taken to learn each stanza.
3 Propose some other factors that might influence the speed at which the subject learns.
2 Account for any difference in the times.
4 Evaluate your results and their implications for how you should memorise material for a test.
3 Identify other factors that might influence the speed of learning. 4 Evaluate the implications of your results for where you should study.
Prac 3 Unit 8.5
Brain dissection
Questions
AIim To investigate the structure of the brain
1 Describe the surface and consistency of the cerebrum.
Equipment Lamb’s brain, dissection board, scalpel, dissecting scissors, newspapers, access to disinfectant, disposable plastic gloves
Method 1 Cover the workbench with a layer of newspaper and place the dissection board on top.
2 Explain how you could tell which was the left and right hemisphere. 3 Describe the colour and consistency of the cerebellum. 4 Describe the medulla.
2 With the edge of the scalpel, try and lift the fine membrane or skin off the brain. If successful, peel it off. 3 When using the scalpel, make many light cuts instead of one deep cut. When cutting, always draw the scalpel away from your hands.
Response time Prac 4 Unit 8.5
4 Separate the right and left hemispheres of the brain and remove the cerebellum and medulla. 5 When completed, wrap all material in the newspaper. Your teacher will tell you what to do with dirty equipment.
DYO
Design an experiment to measure the time taken to respond to either a visual or an auditory stimulus. For example, measure the time taken for your blindfolded partner to press a buzzer in response to the sound of a bell. Alternatively, drop a ball from a given height and measure how far it falls before your partner catches it. Determine whether repetition of the task reduces the time taken. Suggest reasons for any variations observed.
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UNIT
context
8.6 The endocrine system uses chemical messages called hormones to transfer information around the body. These hormones are responsible for controlling many changes that occur in our bodies, most notably those that occur during puberty. Hormones also control many other processes in our bodies such as the storage and release of glucose into the blood. Even plants use hormones to send messages. They are a very important part of our chemistry.
Fig 8.6.1
Major human endocrine glands
pituitary
thyroid
adrenal
ovary (females only)
testis (males only)
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Hormones and how they work Hormones are produced by the endocrine glands, which are scattered throughout your body. Although they may work together, they are not controlled from one central location like the nervous system is. Hormones regulate functions like growth and development, water balance, sexual reproduction and the rate of chemical reactions in cells (see the table on the next page). Although hormones travel to all parts of the body, only particular target cells respond to a particular hormone. Other cells are ‘blind’ to the hormone. How do hormones know which is the target cell? A hormone has a specific shape that fits chemically into a receptor on the target cell’s membrane. This is like placing pieces in a jigsaw puzzle, as shown in Figure 8.6.2. The bonding of the hormone to the receptor starts changes in the cell’s activities. It can be difficult to extract and isolate hormones because they are only secreted in very small quantities. The concentration of hormones in pancreas the blood is very low, about equal to dissolving a sugar cube in a swimming pool. When hormones pass through the liver they are broken down and converted to relatively inactive substances, which are excreted by the kidneys. One test for pregnancy involves measuring the levels of these hormonal breakdown products in urine.
Name of gland or organ where the gland is found
Names of some of the hormones produced
Adrenals
Adrenalin
Ovaries
Oestrogen Progesterone
Pancreas
Insulin and glucagon
Pituitary
Growth hormone (HGH) Antidiuretic hormone (ADH) Stimulating hormones
Thyroid
Thyroxin
Testes
Testosterone
secretes
travels in blood to hormone
endocrine gland
receptor on target cell
target cell change in cell activity hormone-receptor
Fig 8.6.2
The action of hormones
Why hormones? Why does the body use hormones as messengers as well as nervous impulses? Nerve transmissions are very fast. Circulation of hormones takes time. It can
Functions controlled by the hormone Readiness or flight or fight Female sexual development and the menstrual cycle Control of ovary and uterus in pregnancy Blood glucose levels Cell growth and development Water balance Direct other glands to release hormones Rate of chemical reactions in cells Male sexual development and sexual activity
take minutes, hours or even days for the level of a hormone in blood to reach a peak. Concentrations are small, but when the hormone affects a cell, the effect is usually relatively long lasting. This reduces the amount of hormone needed. Hormones provide an ideal mechanism for control of widespread and longterm activities. Often a response to a stimulus will involve both systems. The nervous system sends a rapid response when you are frightened. Messages are transferred swiftly along neurons, reaching an effector to cause an almost immediate and brief reaction. The endocrine system also responds, but more slowly and over a longer period. Adrenalin (known as the fight-or-flight hormone) is released from the adrenal glands and causes various effects. The heart beats faster, breathing rate increases, blood is diverted to the muscles, pupils dilate, hairs on the skin stand on end and the brain becomes more alert. Your heart pounds and you get that sinking feeling Fast and slow control
The nervous system provides rapid messages.
UNIT
8.6
Fig 8.6.3
Hormones provide slower messages.
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Chemical control in your stomach. The overall effect is to boost the speed of your reaction to the fright.
Controlling growth Hormones control longer-term activities like reproduction, growth and development. One gland, the pituitary, plays an important part in controlling growth. It not only releases hormones that directly affect target cells, but also instructs many other glands to release their hormones. The pituitary receives messages directly from the hypothalamus in the brain and thus provides a vital link between the nervous and endocrine systems. One sequence of events involves the hypothalamus, pituitary and thyroid glands. Under instruction from the hypothalamus, the pituitary releases thyroid-stimulating hormone (TSH). This causes the thyroid gland to release thyroxin. Thyroxin controls the speed of cell reactions and therefore influences growth. A deficiency of thyroxin in Fig 8.6.4
The pea-sized pituitary gland is located at the base of the brain.
infancy results in cretinism, or stunted physical and mental growth. This can be cured in its early stages by administering thyroxin.
The pituitary is the ‘master’ gland.
hypothalamus
ting stimula thyroid H) ne (TS hormo
ado gon
kidney
gr
ow (H th h G H orm ) o
ne
other organs e.g. mammary glands
testis
ovary
250
an
rmones
go
trop ic h
r
ot
d na
ch
m
other ho
orm
rm
o
i op
hu
one s
s
thyroid
one
antidiuretic horm (ADH)
pituitary
e on
Fig 8.6.5
bones
Fig 8.6.6
UNIT
8.6 Thyroxin released from the thyroid gland influences growth.
hypothalamus pituitary receives a message from the hypothalamus
thyroid-stimulating hormone (TSH)
stops TSH production (feedback)
thyroid gland thyroxin produced controls chemical reactions in cells
Fig 8.6.8
Gigantism and dwarfism can result from abnormal levels of HGH. Some giants have grown to over 2.7 m tall, while dwarfs may be less than 0.6 m tall.
Controlling glucose levels
Fig 8.6.7
Goitre results from iodine deficiency.
Goitre Iodine is an essential component of thyroxin. A deficiency of iodine can cause enlargement of the thyroid gland (a goitre). Goitres were once common in areas where the soil lacked iodine, but use of iodised salt has largely solved this problem.
Another hormone produced by the pituitary is human growth hormone (HGH), which influences total body growth. Lack of HGH in childhood can lead to dwarfism. Though small, these people have normal intelligence and are well proportioned. If diagnosed early, injections of HGH can be given to children suffering from lack of HGH. Too much HGH in childhood leads to gigantism, producing an abnormally tall person.
Many substances must be kept at a constant level within the body. Cells need a continuous supply of glucose to produce energy, and inadequate levels may result in low energy and possible cell death. Blood glucose levels are usually maintained in a very narrow range Too much or too little? by the action of two hormones, Insulin-dependent diabetics must obtain a regular supply insulin and glucagon, both of insulin. They must also produced by the pancreas (found eat regularly. If a diabetic just below your stomach). injects a dose of insulin (which lowers blood glucose If blood glucose levels increase, levels) but then does not eat for example after eating chocolate, later, their blood glucose insulin is released. This stimulates will fall too far. The brain storage of glucose in the liver, and will be affected, resulting in a hypoglycaemic (low sugar) increases uptake and use of episode or ‘hypo’, and glucose by cells. Blood glucose possible unconsciousness. levels then drop, inhibiting To avoid this problem, many diabetics wear an identifying further release of insulin. label and carry a sugar Glucagon works in a similar way. source (like jelly beans) that In response to low blood glucose can be taken if signs of a levels it directs the liver and cells ‘hypo’ appear. to release glucose.
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Chemical control Fig 8.6.9
• Type II, or non-insulin-dependent diabetics, do not produce enough insulin, or have cells that do not respond correctly to insulin. Treatment involves a special diet, an exercise program, use of drugs and possibly insulin injections.
Control of blood glucose Choc-N
ut Bar
food eaten blood glucose level falls feedback
rising blood glucose stimulus
Worksheet 8.8 Diabetes type I Worksheet 8.9 Hormonal control of the menstrual cycle
glucose removed for storage response
pancreas receptor
Pheromones
insulin released into blood hormonal relay
liver effector
Approximately one million people in Australia suffer from diabetes mellitus, a disease in which blood glucose levels are not maintained within the required range. There are two basic types of diabetics. • Type I, or insulin-dependent diabetics (around 15% of cases), have a defective pancreas. High blood glucose levels result because the pancreas does not produce enough insulin. This may result in glucose in the urine as the body tries to rid itself of its excess. Long-term effects of excess glucose include damage to vital organs such as the kidneys. Treatment involves the use of daily insulin injections.
Hormones are not the only chemicals that influence the behaviour of animals. Chemicals called pheromones may also dramatically affect behaviour. Many insects use pheromones to attract mates. Members of the opposite sex can detect pheromones in the air several kilometres away. These chemicals are effective in very small amounts. The female silk moth carries enough pheromones in her abdomen to stimulate more than one billion males! These sexattractant pheromones act on the CNS, producing immediate behavioural changes. Other types of pheromones act more slowly, affecting growth and development. Termite queens use Aiming high pheromones to stop larvae It has been suggested developing into new queens. that dogs can judge the size and therefore the Ants use pheromones to mark potential danger of food trails. Use of pheromones another dog by the is not restricted to insects. height at which its urine Much information is conveyed has been sprayed up a tree. It has also been by larger animals with the suggested that dogs scent of pheromones. Dogs and wanting to create a more possums use these smells frightening impression try to aim as high when marking out their as possible! territories by spraying urine.
Plant hormones
Type I diabetics require regular insulin injections.
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Fig 8.6.10
Plants also produce hormones. These regulate growth, flowering, fruit production and ripening, and seed germination. A series of experiments by Darwin, Boysen-Jensen and Went in the early 1900s showed that certain plant responses were due to chemicals. A response where a plant grows towards or away from a stimulus is called a tropism. Darwin and others investigated phototropism (growth towards light), and showed that chemicals (hormones) were
responsible for the plant’s response to light. Some of the experiments used are illustrated in Figure 8.6.11.
The action of auxin in phototropism
Prac 1 p. 255
Prac 2 p. 255
tip removed foil light
When covered with foil or with tip removed no bending occurs.
UNIT
8.6 Fig 8.6.12
auxin is made here
auxin diffuses down the shoot concentrating on the shady side cells elongate more due to auxin
tip did not bend light mica (a thin crystal) When diffusion of chemicals is stopped by mica no bending occurs. tip bent light
agar (a type of jelly)
When diffusion of chemicals via agar is allowed bending occurs.
Fig 8.6.11
Experiments examining phototropism
Selective killers Hormones can be used as selective weedkillers. These hormones affect broad-leafed plants (the weeds), but not narrow-leafed plants (the grasses). Herbicides 2,4-D and 2,4,5-T are chemically similar to auxins, but have chlorine added. 2,4,5-T was an active component of the Agent Orange defoliant used during the Vietnam War.
How do hormones bring about phototropism? The tips of growing shoots produce hormones. They then pass backwards from the tip, stimulating cells to elongate. If the shoot is exposed to light from one side, on the exposed side the hormone is destroyed. Hormone concentration on the shady side is therefore greater. The cells here elongate more rapidly, causing bending towards the light. The particular hormone causing this response is one of a group of hormones known as auxins.
Auxins are not the only plant hormones. Other plant hormones include the gibberellins, which control plant growth and have a role in fruit development and seed germination. The dramatic effect of these hormones is seen in the growth of the seeds in Figure 8.6.13. The plant treated with gibberellins grew dramatically compared with the untreated seed.
Rapid responses Some rapid responses shown by plants, like the closing of the Venus flytrap, are not due to hormones. These responses are due to specialised cells, called turgor cells. If these sensitive turgor cells are irritated they collapse, causing the plant to move.
The dramatic effect of one plant hormone
Fig 8.6.13
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Chemical control
UNIT
8.6
[ Questions ]
Checkpoint Hormones and how they work 1 a Describe what hormones are. b State where they are produced. c Describe how they are transported. 2 Outline how hormones recognise their target cells. 3 Match each endocrine gland to the hormone it produces: Gland Adrenal Pancreas Pituitary Thyroid Ovaries Testes
Hormone Oestrogen Adrenalin Testosterone Insulin ADH Thyroxin
15 The diagram shows several endocrine glands labelled using the letters K to P. Identify (using the letters K to P) which gland produces a hormone that controls: a b c d e f
blood glucose levels female reproductive functions rates of chemical reactions in cells water levels within the body readiness of the body for action deepening of the male voice at puberty
K
Why hormones?
L
4 Listed below are several symptoms of stress caused by the release of adrenalin. Explain how each plays a role in preparing the body for action when stressed. increased heart rate, dilation of bronchioles, glucose release from the liver, increased breathing rate 5 Describe a situation in which the response of the body is controlled by both the nervous and endocrine systems.
N
M
Controlling growth 6 Identify which endocrine gland could be called the ‘master’ gland. Explain why. 7 Outline the hormones involved in growth and their effect on the body.
Controlling glucose levels
O P
8 Using Figure 8.6.9 as a guide, draw a flow chart to show the body’s response to a decrease in blood glucose levels. 9 Describe the causes of diabetes.
Pheromones Fig 8.6.14
10 Distinguish between a pheromone and a hormone. 11 Identify two examples of pheromones and describe their effects.
Plant hormones 12 Explain why plants need to detect and respond to: a light b gravity 13 A plant will grow towards a light source. Explain how the hormones known as auxins cause this.
Think 14 Explain what prevents a hormonal response from continuing long after the hormone has been released.
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16 State two reasons why the body would use hormones rather than electrical impulses to send messages.
Analyse 17 Construct a table to compare the nervous and endocrine systems. Your table should include comparisons of the nature of the message produced, how the message is distributed, speed of delivery and length of response produced. 18 State the type of plant response likely to be involved in: a heliotropism b hydrotropism
UNIT
8.6 [ Extension ] Investigate 1 Investigate more about diabetes, including: a how the insulin used by diabetics is obtained b treatments for insulin-dependent diabetics that would eliminate the need for daily insulin injections 2 Explain the role of hormones in controlling the female reproductive cycle. How is this system of control used in the various contraceptive pills? 3 Examine the role of juvenile hormone in the moulting and metamorphosis of insects. How might knowledge of this hormone be used to control insect pests?
5 Investigate one commercial use of plant hormones, such as the use of gibberellins on grapes and in the brewing industry, the use of auxin as a rooting hormone in plant propagation, or the use of hormones to produce flowers at the ‘wrong’ time of year.
Surf 6 Explore interactive diagrams of the endocrine system by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button.
4 Investigate one commercial use of pheromones—for example, the control of oriental fruit moth, a major pest of peach trees in Australia.
UNIT
8.6
[ Practical activities ] Plant tropism Aim To investigate tropism in plants
Prac 1 Unit 8.6
Tradescantia shoot
Equipment 6 shoots of the plant Tradescantia (commonly known as wandering jew), 6 test tubes, melted paraffin wax, water, a darkened area and a well-lit area to place plants
water
Method 1 Place one shoot in each of the six test tubes, add water and seal them with paraffin wax.
test tube sealed with paraffin wax
2 Set up three test tubes as shown in Figure 8.6.15, and place them in a well-lit area. 3 Set up another three test tubes as shown in Figure 8.6.15, and place them in a darkened area. 4 Observe any changes in the plants after two hours.
Questions 1 Sketch the shoots in the six test tubes after two hours. 2 What type of tropism is shown in the experiment? Explain your answer.
Fig 8.6.15
3 Explain why it was necessary to place the tubes in both light and dark.
Investigation of a plant tropism
Plants and gravity Prac 2 Unit 8.6
DYO
Design an experiment to investigate the response of plant roots to gravity.
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Science focus: Remote sensing Prescribed focus area: The nature and practice of science Our limited senses The human senses are amazing things that we use to detect and respond to the environment around us. Imagine trying to survive without them! But humans are limited in the observations and measurements they can make. We can only see so far, and hear sounds to a certain level. There are many things that we cannot detect, and many other things we would detect if we could be in the right place at the right time. But we can only spend limited time in some environments, such as space, before we have to return.
Enhancing our ability to sense Remote sensing allows us to detect many things our own senses cannot. It also allows us to collect data from many places and in many ways that were previously impossible, and to do this with great accuracy over long periods of time. The dramatic increase in the processing power and speed of computers has also enabled us to process information at speeds no human could ever hope to achieve manually. Most scientists now use data logging to collect and analyse their experimental results. This involves using specialised sensors and probes that transmit the information collected to a computer. The data logger may be a simple device such as the types used in schools, or very complex, such as those found on satellites. Data loggers are now common, because of their speed, accuracy, ability to work for long periods, and ability to detect what our senses cannot.
Using electromagnetic waves The electromagnetic spectrum consists of waves of electric and magnetic fields. These waves all travel at the speed of light (300 000 km per second). Humans have specialised sensors—our eyes—to collect the visible wavelengths of electromagnetic radiation. Scientists have used their knowledge of how electromagnetic waves travel through different materials to design a whole range of probes and sensors. These sensors can detect particular
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Data logging is being used here to collect information on locomotion. The patient is wearing infra-red reflective markers and being monitored by infra-red cameras. The data will be used to model how the patient walks, and this information will help to assess leg and foot injuries or implanted joints.
Fig SF8.1
electromagnetic waves that our eyes cannot, and hence explore things that were previously impossible. Sensors can now detect most of the invisible electromagnetic waves. Remote sensing can be either passive or active. Passive remote sensing detects available (background) electromagnetic energy from natural sources (such as sunlight). In active remote sensing, an artificial source of electromagnetic radiation (such as radar) is used to ‘illuminate’ the scene. Remote sensing of different electromagnetic waves coming from space has provided scientists with huge amounts of information about the universe. Many remote sensing probes have also been sent into space to collect data.
Fig SF8.2
The electromagnetic spectrum, showing the different bands of electromagnetic waves
Wavelength in metres (m) 10–12 10–11 10–10 10–9 1 pico1 nanometre (pm) metre (nm) gamma rays
X-rays
1020 1019 1018 Frequency in hertz (Hz)
10–8
10–7
ultraviolet rays
1017
1016
1015
10–6 10–5 1 micrometre (µm)
10–2 10–3 1 millimetre (mm)
infrared rays
visible light
1014
10–4
1013
1012
10–1
microwaves
1011
1010
101 1 metre (m)
102
radio waves
AM radio FM radio short-wave long-wave radio radio 109 108 107 106 105 1 gigahertz 1 megahertz (GHz) (GHz)
MRI uses electromagnetic waves to look inside the body and detect disease such as these brain tumours.
‘The dish’ at Parkes passively collects radio waves from space.
103 105 1 kilometre (km)
Fig SF8.4
Fig SF8.3
Medicine has adapted remote sensing techniques to see inside the body. X-rays have been used for a long time, but more sophisticated techniques like MRI (magnetic resonance imaging) allow us to see even more detail inside the body. With probes and sensors now often mounted on satellites and aeroplanes, remote sensing is proving invaluable in studying and monitoring the Earth’s features, including: • weather patterns • temperature of the Earth and oceans
• shape of the land surface • penetrating the oceans and ice to reveal details of the sea floor • natural phenomena such as bushfires and volcanos • vegetation in agriculture and forestry • the ozone hole • tracking animals
257
• monitoring pollution, algal blooms and oil spills in lakes and oceans • navigation • spying on other countries. This information is used for things such as weather forecasting, scientific research and by the military.
Other remote-sensing applications
This NASA satellite is known as the multi-angle imaging spectroradiometer (MISR). It collects data about the Earth’s climate and atmosphere by measuring reflected sunlight.
Fig SF8.5
Apart from electromagnetic waves, scientists have designed very sensitive probes to measure many important features of the Earth’s surface and to explore what might be found below the surface. As well as satellites, remote sensing can be carried out from aeroplanes to collect information for particular locations. With very sensitive sensors that can detect changes in the Earth’s gravity, a survey of how the Airborne and satellite remote sensing allow us to study many features of the Earth.
258
Fig SF8.6
[ Student activities ] 1 a In small groups discuss reasons why science has begun to rely more on technology to collect data. b List examples of situations where humans would not be able to directly make measurements themselves. c Describe some of the technological tools that are used to assist scientists in their work in each situation you listed for part b. 2 Research the different bands in the electromagnetic spectrum shown in Figure SF8.2 and construct a table to show different types of electromagnetic waves and if/how they are used in remote sensing. 3 Remote sensing is providing enormous amounts of very useful information. This remotely sensed computer-generated image of the Earth is based on satellite data. It shows water (blue), bare land (brown) and vegetation (green). The ocean floor topography is shown by different shades of blue.
Fig SF8.7
gravity in the area changes can reveal important detail on the composition of the underlying rocks. This form of survey has been particularly useful to archaeologists, who can now easily find denser rocky objects indicating tombs and buildings that lie buried below the sands. Geologists can also identify locations where mineral deposits may occur. Another very useful technique is a ‘seismic survey’. In this technique a small explosion, or a series of explosions, is set off in a particular location. A regular array of sensors is placed around the region to collect information on the vibrations of the Earth’s surface, known as seismic waves, produced by the explosion. By combining the information from the sensors using a computer, the nature of the rocks under the surface can be predicted. This is of particular use in mining to locate valuable deposits of minerals including oil and natural gas. Sensing and analysing the seismic waves produced by earthquakes has played an important part in allowing scientists to create a model of the internal structure of the Earth. Sound is also used in remote sensing—examples are ultrasound in medicine (see Chapter 6) and fish finders for commercial and recreational fishing.
a Research remote sensing and choose one example that is proving useful. You may choose one of the examples covered in the text or find another. b Produce a poster to explain how the remote sensing is done and how the information obtained is used. 4 a Evaluate the usefulness of remote sensing to the scientific and general community. b Describe some examples of remote sensing to support your evaluation. 5 a Design and carry out an experiment that uses data logging equipment to collect and analyse information. A simple experiment like measuring DYO the cooling curve of water may be suitable. b Perform the same experiment using traditional techniques. c Compare the different methods to see which was easiest, fastest, most reliable (produces less errors).. 6 Think of a new application for remote sensing. a Outline this new use for remote sensing. b Discuss why this application would be beneficial. c Design a remote sensing probe for your new application.
259
>>> Chapter review [ Summary questions ] 1 Copy and label the diagram of the eye shown here.
2 Describe the function of each of the following parts of the eye: iris, lens, retina, choroid. 3 a Identify the three main regions of the ear. b State what each is filled with. 4 Describe the function of each of the following parts of the ear: eardrum, ossicles, semicircular canals. 5 List as many sense organs as you can. 6 Draw a diagram of a section of skin to demonstrate as many features as you can. 7 Identify the parts of the tongue that detect sour tastes. 8 Explain in a sentence what happens when we smell something. 9 Copy and label the diagram of the ear shown below.
260
10 a State two reasons why organisms need to be responsive to their surroundings. b Explain why response to a stimulus often requires coordination. c Identify the two systems of coordination in humans.
21 Glucose levels in your blood are carefully controlled so they remain within certain limits. a State the name of this careful control. b Explain why it is necessary to control blood glucose levels. c Identify which coordinating system (nervous or endocrine) is most involved in controlling glucose levels. d Identify the name of the condition in which this control is defective.
11 Demonstrate, using examples, what is meant by: a b c d
a stimulus an effector a receptor a response
22 Determine whether the following statements about the endocrine system are true or false: a Chemicals are used to deliver messages. b Messages are passed along neurons. c Messages are delivered more slowly than in the nervous system. d Responses to stimuli are rapid. e Activities are controlled from one central location.
12 a Identify four stimuli to which you respond. b State the type and location of the receptors that detect these stimuli. 13 Draw a labelled diagram to illustrate the structure of a typical neuron. 14 Match the parts of the brain to the functions listed: Part Cerebellum Medulla Meninges Cerebrum
Function Controls involuntary actions such as breathing Centre for sight, hearing and speech Controls muscle movements while you are cycling Protect the brain from injury
23 Match the hormones to the functions they control: Functions Blood glucose levels Female reproductive functions The rate of chemical reactions in cells Water levels within the body Readiness of the body for action Deepening of the male voice at puberty
15 Neurons do not touch each other. They have small gaps between them. a State the name of these small gaps. b Describe how neural messages cross these small gaps.
[ Interpreting questions ]
16 a Clarify what is meant by a reflex action. b Identify three of your own reflex actions. c Explain why reflex actions need to be very fast and how they achieve these speeds.
24 a Identify the type of neuron (sensory, motor or interneuron) shown in the diagram. b Explain your choice.
17 a State three activities in humans that are controlled by hormones. b State three activities in plants that are controlled by hormones.
[ Thinking questions ]
axon
18 A pupil will dilate under certain conditions. Explain why and when this would occur. 19 Describe a condition of the eye (e.g. myopia) and how it can be corrected. 20 Describe how you could reduce the sensation of taking an unpleasant medicine.
Hormones ADH Testosterone Insulin Oestrogen Thyroxin Adrenalin
cell body
direction of impulse
long distance nucleus
>>
261
>>> 25 A simple diagram of the CNS is shown below, labelled A to D.
27 The diagram below shows control of glucose levels in the body. Complete the missing labels a to f.
Use these letters to identify which part: a b c d
is the centre for decision making controls the heartbeat transmits messages from the PNS to the brain receives and interprets messages from the eyes and ears
rise in blood glucose levels stimulus a releases b
blood glucose level falls f
b transported via c
A glucose removed for storage e
d effector
B C D
26 The diagram below shows the reflex arc for what happens when your knee is struck lightly with a hammer. Use the following terms to label the diagram: response, stimulus, sensory, nerve, motor, nerve, receptor, effector.
knee is struck i muscle contracts to move lower leg vi
stretch receptors ii
28 a Define ‘tropism’. b Describe two examples of tropisms. 29 Evaluate the importance of our senses. How would we survive without one or all of them? 30 a Outline 3 uses of remote sensing. b Describe why remote sensing can do things that our senses cannot. c Discuss the applications and importance of remote sensing to society. d Evaluate the importance of satelites to society and the environment. e Describe an example where data logging would be useful. Worksheet 8.10 Sense and control wordfind
relay via iii
Worksheet 8.11 The senses crossword leg muscle v relay via iv
262
Worksheet 8.12 Sci-words spinal cord
>>>
9
Simple machine technology
Key focus area
>>> The applications and uses of science
calculate the mechanical advantage of some simple machines explain some uses and advantages of levers, pulleys, wheels, axles, gears and inclined planes
Outcomes
describe simple technologies and machines that make tasks easier
5.1.2
By the end of this chapter you should be able to:
describe examples of complex machines and their applications describe some Aboriginal technologies and their application to everyday life.
your house that make jobs easier for you.
3 What can humans physically do now that could not be done 100 years ago?
4 What do you think is the most important invention in the history of humankind? Give reasons for your choice.
5 Name an Aboriginal technology and describe what it is used for.
Pre quiz
1 How do aircraft stay in the air? 2 Make a list of machines around
>>>
UNIT
context
9.1 Even before written records began, humans were using the technology of their time to help them hunt for food, build shelters and make life easier. The simple technologies of the ramp, wedge, screw, lever, wheel and pulley were some of the first and most useful devices ever invented. It is these technologies that helped lift the huge pillars and blocks of stone to build the temples and pyramids of the ancient Egyptians, Romans and Greeks. They also helped them to draw water from wells and travel faster than ever before. These simple technologies are useful enough to
Let’s say a certain job takes 12 joules to do. We could do the job in a number of ways:
Energy needed to do the job (J)
Effort force Distance we needed to do need to move to the job (N) do the job (m)
Proof that this will do the job
Work in science
12
12
1
12 x 1 = 12
Simple technologies and the machines that use them are all about force. They generally reduce the amount of effort required, making a job much easier. Sometimes they allow us to move bigger objects than would normally be possible. Effort is the force you need to apply to move an object. The object and its weight are called the load. The word ‘work’ is used in many ways. ‘Hard work’, ‘a lot of work’ and ‘homework’ are expressions we hear every day. Scientists mean something very different by the word ‘work’, however. To understand how simple technologies and machines make a job easier we need to understand the scientific meaning of work. Scientifically, work is the energy needed to move something over a certain distance. Like all energy, work is measured in joules (J).
12
6
2
6 x 2 = 12
12
4
3
4 x 3 = 12
12
3
4
3 x 4 = 12
12
2
6
2 x 6 = 12
12
1
12
1 x 12 = 12
moved in doing the job
work = effort force x distance
needed to get the job done
Some simple mathematics will help us understand what’s happening here.
264
be used on their own. By themselves, each is a simple machine. Complex machines are formed when different technologies are combined. Most machines around us today, from eggbeaters and staplers to a bike gears are complex machines that use multiple technologies.
What this all means is that if the distance we move is greater, the effort we need to put in is less. All simple technologies use this fact to make them effective.
The inclined plane A ramp (sometimes called an inclined plane) is one of the oldest and simplest technologies. It is used when we need to get a heavy object up to a higher level. If you want to lift a load, you need to do a certain amount of work regardless of how you go about it. The work will depend on the weight of the object and the height you lift it, not on how you do it. Imagine you’re helping your family to move house and need to load the refrigerator onto a truck. The shortest path onto the truck is straight up, vertically. This is going to be very difficult (perhaps impossible)
since it requires you to put in an effort force at least equal to the weight of the fridge. Yet if you pull or push the refrigerator up a ramp, you will find the job easier. Although the work is the same, less effort is required because you are moving the fridge a greater distance.
less effort full effort
e
rfac
su ing
slop
Fig 9.1.1
Effort is less when distance is more.
Mechanical advantage Mechanical advantage measures how effective the technology or machine is, and can be calculated by dividing the load you want to move by the effort you need to put in.
Wedges An escalator can be thought of as a moving ramp. So can a wedge. A wedge is simply an inclined plane that moves through another object, forcing apart or splitting the object as it does so. An axe or wood splitter is an obvious wedge. It reduces the effort needed to split a log by forcing the wood to travel up the long edge of the blade. The sharper the blade, the longer the edge and the less effort required to split the timber. Knives and our front teeth (the incisors) also act in this way, making it easier Zip! Coincidence in science to cut and slice through sometimes means that food. two people on opposite The zip fastener is an sides of the world have example of a twentieththe same idea or invent the same contraption at century technology that uses exactly the same time. three wedges. The zipper’s The modern, successful slide contains wedges that zipper was invented in 1911 by Catharina turn a little effort into a Kuhn-Moos and strong force that opens and Henri Foster, neither of closes the fastener. Without whom knew about the other or what they were this assistance, the teeth of working on. the zip are nearly impossible to join or part. A zipper uses three wedges.
UNIT
9 .1
Fig 9.1.2
Mechanical advantage = load/effort
For example, if a simple machine lifted a 60 N weight (this is about 6 kg) but an effort of only 20 N was required, the mechanical advantage would be: mechanical advantage = load/effort = 60/20 = 3
Better machines have larger mechanical advantages, so better machines than this one would be able to either: • lift a bigger load (say, 600 N) with the same effort (20 N). This would give a larger mechanical advantage: load/effort = 600/20 = 30 or • lift the same load as before (60 N) but with a lot less effort than before (say, 2 N): mechanical advantage = 60/2 = 30 The better the machine, the larger the mechanical advantage. Prac 1 p. 267
Prac 2 p. 268
265
>>>
The ramp Screws, nuts and bolts A screw is like a wedge in that it is also a ramp, this time spiralling around a metal cylinder. Screws also penetrate materials such as: • solids—woodscrews are screwed into timber • liquids such as water— a propeller on a boat is The Archimedes a screw screw • gases such as air— Archimedes (287–212 BC) propellers on an aircraft, is usually remembered for his alleged naked dash or an electric fan. from his bath and through Try to hammer a the streets after he solved woodscrew into a piece of the problem of buoyancy. His fame in ancient timber and you won’t get e was, however, as a Greec very far. It would need an scientist, mathematician, extremely large force to do so. philosopher and inventor. Yet if the screw is turned, the One of his inventions still in use today is the timber is moved along the Archimedes screw, a spiral ramp. Because of the device originally used to great distance covered, a much bail out the hulls of warships but now smaller force is required, commonly used to raise although a lot of turning has from dams and rivers
to be done. Once again, distance is increased, so the effort is less. A bolt and its nut work the same way, although in this case the nut is wound down the screw of the bolt.
effort turning screw
wood screw
force on wood
A screw is just a curved ramp.
water in the Middle East.
Fig 9.1.3
Worksheet 9.1 History of ramps
UNIT
9.1
[ Questions ]
Checkpoint Work in science
9 List five examples of where wedges are used to more easily separate or split an object.
1 Define the term ‘work’ when used in the scientific sense.
Screws, nuts and bolts
2 Clarify whether work is energy or a force.
10 Describe how a screw is really just a ramp.
3 Identify the unit normally used for work.
11 Outline three uses of screws.
The inclined plane 4 Copy and complete: A ramp reduces effort by increasing ________. 5 List five examples of ramps being used to make a job easier.
Think 12 Explain why a path zigzagging up a mountain is easier to walk than a track straight up to the top.
7 Define ‘mechanical advantage’.
13 Calculate the mechanical advantage. a load = 12 N, effort = 6 N b load = 18 N, effort = 6 N c effort = 3 N, load = 18 N d load = 5 kg (about 50 N weight force), effort = 10 N
8 Assess whether a machine with a high or low mechanical advantage is better.
14 Determine which of a, b, c or d in Question 13 is the best machine.
6 Construct a rule about how ramps make the job of lifting a load easier.
Mechanical advantage
266
Wedges
15 Construct a table to summarise simple machines that use ramps, such as the screw or wedge. For each machine outline briefly how it makes doing a job easier.
UNIT
9 .1 [ Extension ] Investigate Analyse 16 Twenty-four joules of work was needed to lift an object up to a certain height. Sarah measured its weight with a spring balance and found it to be 24 N. Calculate the load force that Sarah was trying to lift. 17 Sarah then thought about the ramp that would do the job most easily and constructed the following table to help her. Copy and complete her table. Work (J)
Ramp length (m)
Effort needed (N)
Proof that this will do the job
Mechanical advantage
24
1
24
1 x 24 = 24
24/24 = 1
24
2
24 24
2 x 12 = 24 8
24/8 = 3
4
24 24
6 x 4 = 24
24/4 = 6
1 a Record as a series of diary entries all the ramps that you use in one day. b For each ramp used describe how it made your day easier. c Design a ramp that would have made something you did during the day easier. Try to design something unusual, not just replacing stairs with a ramp, for example. 2 a Investigate the design of the Archimedes water screw and draw a diagram to show how it works. b Construct a working model of this technology.
8
24 24
18 Which ramp would make the job easiest for Sarah? Explain.
UNIT
9.1
[ Practical activities ] Ramps
Method
Aim To investigate the relationship between the Prac 1 Unit 9.1
slope of a ramp and effort
1 Make a pile of textbooks on your desk about 10 cm high. 2 Construct a table or spreadsheet as shown below.
Equipment
Spring balance, ramp, dynamics cart and wooden block, small masses, sticky tape, books, protractor
3 Weigh the dynamics cart and the block of wood with a spring balance. Tape masses on them until both are about the same weight. Record their new weights.
>> Angle (°)
Distance along Effort to move ramp (cm) cart (N)
Mechanical advantage
Effort to move block (N)
Mechanical advantage
267
>>>
The ramp
spring balance spring balance block
trolley trolley
books 10 cm 0 12
110
100 90 80 70
60 50
40 30
10 0
180 170 16
20
0 15 0 14 0
0 13
protractor
tape masses to make block about the same weight as trolley
spring balance block 110
50
20
0 15
60
30
10 0
180 170 16
100 90 80 70
40
0 14 0
0 13
0 12
protractor
Fig 9.1.4
Testing a ramp
4 Slowly lift the cart vertically up until it reaches the top of the stack. Record the effort required from the spring balance.
Ramps for the disabled
5 Repeat with the block. 6 Now place the ramp on the books so that its angle with the desk is very small.
Prac 2 Unit 9.1
7 Measure the angle with a protractor and measure the distance along the ramp from the bottom to the top of the books. Record it. 8 Drag the cart up the slope with the spring balance until it reaches the top of the books once more. Record the effort needed, then repeat with the block. 9 Try three different angles. You might need to overhang the books to do so. Take angle and effort measurements each time for both the cart and the block.
Questions 1 The work required to drag the cart and block up was the same in each case. Explain why. 2 Describe what happened to the effort force needed as the ramp got longer. 3 Which was the better ramp? Explain. 4 Which was easier to get up the slope—the block or the cart? Propose reasons for your answer.
268
DYO
Disabled ramps must be constructed with a slope of no more than 1:14 for ramps over 1250 mm long and 1:8 for ramps less than 1250 mm long.
Aim To test commonly used ramps to determine whether they comply with the requirements of the disabled
Method 1 Find ramps around the school, at the shops or at home and take appropriate measurements to find their slope. 2 Carry out appropriate calculations and compare their slopes with those needed by the disabled.
Questions 1 Propose why shorter ramps are allowed to be steeper than longer ramps for the disabled. 2 Did the ramps you checked comply with the regulations?
UNIT
9.2 context
Ancient propaganda?
The lever is an old technology that can be dated back about 5000 years. You use many different forms of levers every day, such as a shovel, a spoon or a tennis racket. A lever can be any solid object that is made to turn round a pivot or fulcrum. A load is placed somewhere along the lever and an effort causes the turning. Generally, levers are force multipliers: we put in a small effort and the lever system multiplies it so that we can lift much heavier loads. As with ramps, levers reduce the effort needed to lift a load. Once again the disadvantage is distance: the more we wish to reduce effort, the further we need to move the lever.
5000-year-old Egyptian The oldest diagrams of levers are seen on Aristotle mentions them er soph philo sculptures. The ancient Greek levers to build huge used y osedl supp s mede Archi gs. writin in his out of the water ships n Roma ing invad cranes that were able to lift rocks. He also built on ships the hing smas ur, harbo use of Syrac ing ships from under other machines that sat on the bottom, grabb ers fell off. It is possible water and shaking them until all the soldi a, however. What is gand propa nt that this was all just ancie and said, ‘With a lever levers ed studi he that is n know itely defin move the world’. long enough and a point to stand on, I could
effort
load
Force multipliers: class 1 and class 2 levers Class 1 levers (or first order levers) have the load at one end, the effort force at the other and the fulcrum somewhere in between (Figures 9.2.1 and 9.2.2).
fulcrum load
Prac 1 p. 274
effort
effort
fulcrum
Fig 9.2.2
Some class 1 levers
load
fulcrum A class 1 lever
Fig 9.2.1
Class 2 levers (or second order levers) are also force multipliers and have the fulcrum at one end, the effort at the other and the load somewhere in between. They can move heavy loads by putting in a little effort a long way from the pivot (Figures 9.2.3 and 9.2.4). Where you apply the effort in these levers is just as important as the effort itself. The effort required
269
>>>
Levers depends on the distance of the load from the fulcrum and where on the lever we put our effort. As with the ramp these levers reduce the effort by increasing the distance the load must be moved.
Class 1 and 2 levers obey a rule called the Principle of Levers: of load from fulcrum
effort x distance = load x distance A class 2 lever
Fig 9.2.3
of effort from fulcrum
This means that a 60 kg student would need to sit 2 metres from the pivot of a seesaw to balance their 40 kg younger sister who is sitting at the very end, 3 metres from the pivot. Proof: 60 x 2 = 40 x 3.
load
Prac 2 p. 275
Mechanical advantage in levers fulcrum effort
You will remember that mechanical advantage gives us an idea about how effective a machine or technology is. For levers, mechanical advantage can be calculated in two ways: mechanical advantage = load/effort =
distance of effort from fulcrum distance of load from fulcrum
For levers, the best mechanical advantage is achieved when the effort is far from the fulcrum and the load is close to it (Figures 9.2.5 and 9.2.6).
ad
lo
fulcrum
The higher the mechanical advantage, the better the machine.
Fig 9.2.5
lo
ad
load effort
effort
effort
low mechanical advantage
high mechanical advantage
load
load
load
effort
Speed multipliers: class 3 levers fulcrum
Fig 9.2.4
270
Some class 2 levers
Class 3 levers (or third order levers) are not used to decrease the required effort. Instead they get the load (often a small one) moving at an increased speed.
oad
fulcrum
UNIT
9 .2 fulcrum
load
load
effort
effort
load fulcrum effort
A class 3 lever
Fig 9.2.6
These levers have the fulcrum at one end, the load at the other end and the effort (usually from our hands) somewhere in between. Bats and racquets are all class 3 levers. We move our hands a short distance at high speed so the ball travels from the bat at an even higher speed: class 3 levers are speed multipliers. Because the distance the ball moves is large, the force on it is small. This requires your hand to move a small distance but with a large effort. Worksheet 9.2 Levers in our body
UNIT
9. 2
Prac 3 p. 276
Prac 4 p. 276
[ Questions ]
Checkpoint Force multipliers: class 1 and class 2 levers 1 What is a force multiplier? Explain using an example. 2 Define the term ‘fulcrum’ and identify alternative names for it. 3 Construct a sketch of a playground seesaw. Draw where you would place a heavy person to balance a light person sitting on the very end of one side. On your diagram, mark the fulcrum, effort and load.
load
fulcrum
Fig 9.2.7
effort
Some class 3 levers
Speed multipliers: class 3 levers 6 Explain how a class 3 lever acts as a ‘speed multiplier’. 7 State the advantage of using a class 3 lever in most ball-sports. 8 A sword is an example of a class 3 lever. Explain why.
Think 9 Describe three examples of a lever in action. 10 Copy the following into your workbook, modifying any incorrect statements so they are true. a All levers are force multipliers. b The fulcrum of a lever is always somewhere in the middle. c A golf club is an example of a force multiplier. d A pivot is the same as a fulcrum. e A speed multiplier is needed in most ball-sports. 11 Define the Principle of Levers.
4 Explain how mechanical advantage is calculated for levers.
12 A heavy rock is to be shifted, and all you have is a long metal bar and another smaller rock. Illustrate how you would shift the rock. Label the load, fulcrum and effort.
5 Describe how a greater mechanical advantage may be obtained when using a lever.
13 Which class of levers is the most effective in lifting a load? Justify your answer.
Mechanical advantage in levers
271
>>>
Levers
Analyse 14 Classify the objects in Figure 9.2.8 as class 1, 2 or 3 levers.
a
c
b
d
Fig 9.2.8 15 Calculate the mechanical advantage of the levers shown below.
a
mass #1
10 N load
5 N effort fulcrum 10 cm
16 A seesaw ruler was set up as shown below. Different masses were added to each side so that the seesaw was just balanced. Copy and complete the results table.
mass #2
pivot
5 cm
distance mass #1
15 N load
b
5 N effort
Fig 9.2.10
fulcrum 3m
6m
c 25 N effort 5 N load
fulcrum
Mass #1 (g)
Distance of mass #1 from pivot (cm)
Mass #2 (g)
6
4
8
6
4
1
20 cm
80 cm
1
3
6
Distance of mass #2 from pivot (cm)
12 12
10
8
Fig 9.2.9
272
distance mass #2
2
5 9 16
UNIT
9 .2 [ Extension ] Surf
Investigate 1 Collect photos of levers from magazines, advertising brochures and newspapers. a Classify each lever as class 1, 2 or 3. b Identify and label the effort, fulcrum and load on each lever. 2 Construct a poster to demonstrate how different levers are used in sport.
Investigate the following information about levers by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button. 4 Revise how levers work by completing an interactive levers activity. 5 Archimedes used simple technologies to invent many different machines. Investigate Archimedes and his work, then write a short biography of his life.
3 Muscles can only contract (get shorter and thicker) or relax (get longer and thinner), pulling the bone up or letting it down. Muscles provide the effort force that controls bone levers. Use a diagram of the muscles of the body to identify the names of the muscles used to flex your arm and to straighten it.
Project Making body parts 1
Make a larger version of the ‘skull’ shown in Figure 9.2.11 out of cardboard. Use a paperclip to hinge the jaw to the skull and a deflated balloon for the muscle that controls it. Explain what happens to the ‘muscle’ as the jaw opens and closes.
2
Use the diagram in Figure 9.2.12 to construct a model of the human arm, its bones and muscles. Describe what happens to your ‘balloon muscles’ as you straighten and flex your model arm. How does this compare with your real arm muscles? An arm lever
Fig 9.2.12
skull first wooden strip
second wooden strip
hinge
balloon lower jaw upper arm
Fig 9.2.11
balloon (muscle) string
Construct a jaw-lever
lower arm balloon (muscle)
273
>>>
Levers
UNIT
9.2
[ Practical activities ] The seesaw Aim To investigate the seesaw as a lever
Prac 1 Unit 9.2
Equipment 7 small masses (such as 5 cent coins), ruler, a fulcrum or pivot (a pencil is ideal), an elastic band
Method 1 Set up a seesaw as shown in Figure 9.2.13.
4 Place four of the small masses on the left side of the ruler and another four on the right and arrange them until the seesaw is balanced. 5 In the table, record the distance of each pile of masses from the pencil fulcrum. Repeat with two masses on the left and three on the right. 6 Repeat for all the other masses shown.
Questions
ruler
pencil
1 What do you notice about your answers in columns 3 and 6? Interpret what you notice. coins
elastic band holds ruler onto pencil
A class 1 lever in action
Fig 9.2.13
2 You have just discovered the Principle of Levers. Use it to predict where you would place a 2 g mass to balance: a another 2 g mass placed 4 cm from the pivot b a 10 g mass, 2 cm from the pivot c a 6 g mass, 6 cm from the pivot d a 1 g mass, 2 cm from the pivot 3 Identify the class of lever used in this activity.
2 Use the elastic band to hold the ruler in place on the pencil. 3 Copy the results table below into your workbook.
Left-hand side Number of masses
274
Distance from pivot
Right-hand side Number of masses x distance from pivot
Number of masses
4
4
3
2
4
3
5
2
6
1
Distance from pivot
Number of masses x distance from pivot
UNIT
9 .2 Lifting books Prac 2 Unit 9.2
Aim To investigate the relationship between fulcrum position and effort on a class 1 lever
6 Now try lifting the book using the class 2 and 3 levers shown in Figure 9.2.15.
Equipment Metre ruler, rubber stopper, textbook
2nd class
Method 1 Set up the lever shown in Figure 9.2.14.
effort load rubber stopper
3rd class
fulcrum effort load
fulcrum effort load
Lifting using class 2 and class 3 levers
Fig 9.2.15
fulcrum
Questions Fig 9.2.14
Lifting a book using a class 1 lever
2 Lift the book by pushing down on the ruler with your finger. 3 Now place the stopper close to the book and repeat the experiment. 4 Repeat once more but with the stopper placed at the far end away from the book. 5 Copy the table below. Complete it using the words ‘high’, ‘medium’ or ‘low’.
Position of stopper
1 Copy the three diagrams (class 1, 2 and 3) into your workbook. Add arrows to show the effort and load forces. Label the fulcrum. 2 The force needed to lift the book using the class 1 lever changed as the stopper moved away from the book and towards your finger. Analyse what happened. 3 Use the Principle of Levers to explain why, in a class 1 lever, it is easier to lift the book if the fulcrum is close to it and far away from your finger. 4 Assess which class of lever made it most difficult to lift the book.
Effort required to lift the book
Far away from book Midway Close to book
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Levers
Class 3 Levers 2 Use the spring balance to measure the effort force needed to raise the load slowly.
Aim To investigate a class 3 lever Prac 3 Unit 9.2
Equipment 1 m ruler, 1 kg mass, spring balance, brick or block to act as the fulcrum
Method 1 Copy the following table into your workbook and then set up the class 3 lever shown in Figure 9.2.16.
Spring balance reading (N)
4 Calculate the mechanical advantage for each measurement.
Load (kg)
Distance of load from fulcrum (cm)
1
100
30
1
100
40
1
100
50
1
100
60
1
100
70
A class 3 lever at work
Spring balance reading (kg)
3 Record your measurements in the table. You might need to convert the newton readings of your spring balance into kilograms by dividing your measurements by 10.
Fig 9.2.16
Distance of spring balance from fulcrum (cm)
Mechanical advantage
Questions 1 Identify which was bigger—the load or the effort required to lift it. 2 Identify which was the most effective lever. Justify your answer.
Levers at work fulcrum
spring scale 100 cm
0 cm
Prac 4 Unit 9.2
Aim To examine various common implements to determine which class of lever is being used Equipment Stapler, nail clippers, scissors, pruning shears, nutcracker or bulldog clips
50 cm
load (1 kg mass)
Method 1 Accurately draw each machine. 2 Label the fulcrum, load and where the effort needs to be applied. 3 Identify the purpose of other parts of each machine.
Questions 1 Classify each lever as class 1, 2 or 3. 2 State whether each one is a force or speed multiplier.
276
UNIT
context
9.3 Most machines do not use the simple up-and-down movement that ramps and levers produce. They use a spinning or rotary motion instead. Wheels, axles and gears apply the principle of levers to our everyday lives. Although they might not look like it, a tap and a doorknob are really wheels. Gears are used in many applications from bicycles to corkscrews. Can you imagine life without the wheel?
The wheel A wheel has a fulcrum, located at the centre, called the axle. The rim, the outside of the wheel, is the other end of the lever. The rim of a rotating wheel moves a larger distance and at a higher speed than the axle, which simply turns on the spot.
movement of wheel movement of axle Fig 9.3.2
A steering wheel, a screwdriver and the key to open a can are all examples of wheels and axles.
The wheel as a force multiplier
wheel
axle centre
As with an inclined plane and levers, you gain in force what you lose in distance moved.
Fig 9.3.1
As with a lever, a wheel can be used to reduce the force needed to carry out a task. The spindle (axle) of a doorknob or tap is nearly impossible to turn with bare fingers. A doorknob or a tap can be either a simple lever or a ‘wheel’. A small force moving the end of the handle or the edge of the knob or tap will turn the spindle easily enough to unlock the
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Levers door or turn on the tap. A small effort applied to the rim has produced a large turning force at its axle: the force has been multiplied. In science, the turning effect of a force on an object is called torque. Torque is calculated by multiplying the applied force by its perpendicular distance from the turning point. Torque is measured in newton metres (Nm). Car magazines frequently report on the torque Prac 1 p. 281 developed by cars.
Fig 9.3.3
A ceiling fan is an example of a speed multiplier.
Fig 9.3.5
high speed
low speed
A tap may use a lever or a wheel.
Changing the motion
Fig 9.3.4
A doorknob may use a lever or a wheel, too.
Once a spinning motion has started, its direction, speed or location often needs to be changed. The simplest way to do this is to connect wheels of different diameters together with belts. A smaller-diameter wheel will spin faster and with greater Prac 2 p. 282 force if it is connected by a belt to a larger wheel.
The wheel as a speed multiplier Wheels can also be used as speed multipliers. A slowly spinning axle turns the rim at a higher speed. The blades of a fan or a propeller must spin very fast to move the quantities of air needed to cool or to move an aircraft along. The motor turns the axle relatively slowly. The bigger the propeller, the faster the blade tips will go and the more air is moved.
278
A fanbelt connects wheels of different sizes.
Fig 9.3.6
Gears
Gear trains
Gears can also be used to change speed, torque or the direction of rotation. A gear is a wheel with identical teeth around its edge. If the axle turns it, it is call the driving gear. If the teeth of another gear (called the driven gear) mesh with the driving gear it too will turn, but in the opposite direction. The speed and torque of the driven gear depends on its size compared to the driving gear. This relationship is shown in Figure 9.3.7. Gearing up, gearing down and parallel gearing
Fig 9.3.7
driven gear
driven gear fast
driving gear
driving gear
slow
slow fast gearing up
gearing down
parallel gears
A gear train is a series of two or more connected gears. If the gears are identical, they Ancient gears both turn at the same speed The first-ever calculator but in different directions. seems to be a machine built by the ancient These are called parallel Greeks in the first gears. century BC. It was built If the driven gear is to predict the timing of eclipses and contained smaller than the driving gear, thirty-two bronze gears. it will rotate faster: the gears When it was discovered act as a speed multiplier. This in 1901 in the wreckage of an ancient ship sunk is called gearing up and is in the Aegean Sea, it useful when high-speed looked like a lump of rotation is needed, say, in a metal covered in barnacles. The gears power drill, kitchen blender, and its function didn’t or coarse focus knob on a become obvious until it microscope. was X-rayed in 1972. Gearing down is when a small driving gear rotates a larger one, which turns at a slower speed. The torque applied is multiplied, making it useful in situations where a strong turning force is required. Gears on bikes use this to make the hard job of climbing hills easier and to allow swift acceleration from traffic lights. Types of gears you will commonly find are rack and pinion, idler, worm and bevel gears. These are shown in Figure 9.3.9; they do different jobs but all work in much the same way. Worksheet 9.3 Gears
Fig 9.3.8
Prac 3 p. 283
UNIT
9.3
Prac 4 p. 283
An eggbeater changes both the speed and direction of rotation.
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Going for a spin: wheels, axles and gears Spur, rack and pinion, worm and bevel gears
Fig 9.3.9
Think spur gear
worm gear
rack and pinion gears bevel gears
14 Copy the following into your workbook, modifying any incorrect statements so they are true. a Rotary motion is up/down motion. b The axle and the rim of a wheel are the same thing. c The driving wheel of a bicycle is an example of a speed multiplier. d Parallel gears turn in the same direction. e The steering wheel of a car is an example of a speed multiplier. f Gearing up is used when high-speed rotation is needed. g Gearing down is used in drills and kitchen blenders. 15 Construct a diagram of a bicycle wheel. Label its axle and rim. Show where the wheel would move the fastest/slowest and where the torque that could be applied would be the greatest/smallest.
UNIT
9. 3
[ Questions ]
Checkpoint The wheel 1 Describe how a wheel is like a lever.
16 a Draw two gears that would act as a speed multiplier and another two acting as a force multiplier. b Identify and label the driving and driven gears in your diagram.
Analyse 17 Predict the direction of rotation and the speed of the gears in Figure 9.3.10.
2 State another name for the fulcrum of a wheel. 3 Define torque. 4 Identify another name for the axle of a doorknob or tap. 5 Draw a labelled diagram to demonstrate how a wheel can act as a speed multiplier.
slow
a
6 List examples of wheels being used as speed multipliers. 7 Explain how the direction of a spinning wheel can be changed.
Gears
b
fast
8 Copy and complete: Gears can be used to change ________, ________ (________ force) or the direction of ________. 9 Distinguish between a driving gear and a driven gear. 10 Explain when gearing up and gearing down are used. 11 Copy and complete: The speed of a driven gear and the torque it can apply depend on ________.
slow c
12 Define a ‘gear train’. 13 Draw or trace diagrams of rack and pinion, idler, worm and bevel gears.
280
Fig 9.3.10
[ Extension ] Investigate
UNIT
9.3 Create 2 Use the diagram in Figure 9.3.11 to construct a mouse-trap racer.
1 Examine a bicycle closely. a What are the gears in a bicycle called? b Draw a diagram to illustrate your answers to the following questions. i How many gears are there front and back in a 10-speed bicycle? ii How many teeth does each gear have on it? iii Do they mesh together? How are they connected?
string
mousetrap
c Construct diagrams to show the arrangements of front and rear gears that a cyclist would use to: i travel at high speed ii climb a steep hill iii ride downhill d Gear ratio is the number of teeth on the front gear divided by the number of teeth of the back gear. i Count the number of teeth on each gear used in part c and calculate the gear ratio for each situation. ii Describe what sort of gear ratios are needed for each situation.
UNIT
9. 3
axle
Fig 9.3.11
Surf 3 Explore further how gears work by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button.
[ Practical activities ] A simple wheel and axle
Prac 1 Unit 9.3
paperclips
Aim To construct a simple wheel and axle Equipment
tape
250 mL beaker or tin can, 100 g mass, 2 paperclips, flexible drinking straw or satay stick, cotton thread, sticky tape
straw or satay stick
Method 1 Set up the apparatus as shown in Figure 9.3.12. 2 Try to lift the 100 g mass by turning the straw or satay stick. 3 Bend the straw or satay stick without breaking it, and try again.
Questions 1 State whether you were able to lift the 100 g mass without bending the straw or stick.
100 g mass
A simple wheel
Fig 9.3.12
2 Propose a way of making the job even easier.
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Going for a spin: wheels, axles and gears
Roping them together Aim To investigate speed changes by connecting Prac 2 Unit 9.3
different-sized wheels
5 Draw an obvious line on each of the lids with the marker.
Equipment
6 Measure the diameter of each lid.
A variety of circular lids of different sizes from jam jars etc (serrated edges are ideal), elastic bands, a piece of wood, a small sheet of thin cardboard, pins, small nails or tacks (they must have a circular cross-section), marking pen, hammer
Method
8 Record your results in a table like this:
1 Put small holes in the exact centre of two lids. 2 Cut several elastic bands and tie them together so that they go right around two lids.
7 Start one wheel spinning. Note which direction the wheels turn and use the line you have drawn to count how many times each lid turns in one minute. You have just measured the rpm (revolutions per minute) of each wheel.
Diameter wheel #1
Clockwise/ anticlockwise?
3 Cut out small circular ‘washers’ from the thin cardboard. 4 Assemble your wheels as shown in Figure 9.3.13. The elastic band should be stretched just a little. Roping wheels together
Fig 9.3.13
rpm wheel #1
Diameter wheel #2
Clockwise/ anticlockwise?
rpm wheel #2
9 How does the size of the wheel affect the force needed to do a job? 10 Try different combinations of lids. 11 Change the elastic band to look like a figure 8, and repeat the experiment.
Questions step 1
1 How did the rpm of a small wheel compare with the rpm of the larger wheel it was connected to? 2 Analyse whether there is a link between wheel diameter and rpm. 3 State whether the wheels spun in the same or different directions.
step 2
figure 8
282
4 Recount what happened when the elastic band was changed to a figure 8.
Model building
Geared machines Prac 3 Unit 9.3
Aim To investigate common implements that use gears Equipment Eggbeater, hand-drill, corkscrew, adjustable spanner
Fig 9.3.14
UNIT
9.3 Aim To build various models using gears, levers Prac 4 Unit 9.3
and wheels
Equipment Model building set such as Lego
Method 1 Use two gears to make a gear train that gears up, and another that gears down. 2 Connect an arrangement to turn the driving gear of each and something that will be spun by the driven gear. 3 Draw your machines. 4 Rotate the driving gear slowly, adding to your diagram the direction the gears move in. 5 Count how many teeth each gear has and the number of times the driving gear must be turned to rotate the driven gear ten times. 6 Put all numbers and ratios on your diagram.
Method 1 Carefully draw the gear arrangements in the machine you have been given, labelling each type of gear (rack and pinion, worm, etc.). 2 Label which gear is driving and which is driven, and the direction each gear moves in.
7 Construct a machine like the one in the previous experiment.
Question 1 Use the numbers of teeth to calculate the gear ratio, and the number of turns to calculate the turn ratio of each.
3 Label any levers or wedges that might also be there. 4 Count how many teeth are on each gear. Put these numbers on your diagram.
Fig 9.3.15
Can you build models of the following geared machines?
5 Make a small mark on the side of the driving gear and another on the driven gear. 6 Turn the driving gear slowly and count the number of times each gear turns. Stop when one of the gears has turned ten times. Write the number of turns on the gears on your diagram.
Questions 1 Identify which gear was the largest—the driving or the driven gear. 2 Explain what the job of your machine is. 3 Does your machine need to be a force multiplier or a speed multiplier? Justify your answer. 4 Calculate the gear ratio by dividing the number of teeth of the biggest gear by the number of teeth of the smallest. 5 Calculate the turning ratio by dividing the biggest number of turns (you chose ten) by the smallest number of turns. 6 What do you notice about the two ratios?
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UNIT
context
9. 4 Humans usually find pulling an object down a lot easier than lifting it up. Our weight already acts downwards and so we can use it to help us pull down. A pulley can be used to convert a lifting force into a pulling-down force. A pulley is simply a wheel with a grooved edge where a string, rope or chain can run.
upper pulley wheel lower pulley wheel
effort
Introducing pulleys A single pulley makes the job of lifting an object easier but only because it changes the direction of the effort force. You still need to put in the same effort that you would if you were lifting the object: the mechanical advantage should be equal to one. In fact you probably need to put in more effort, since you need to overcome the load and some friction in the pulley. Friction always makes us work harder, by reducing the effectiveness or efficiency of machines. Bigger loads can be lifted with little effort if a system of two or more pulleys is strung together.
pulley
Fig 9.4.2
A double pulley system halves the effort required. Double the load can be lifted, but the distance we need to pull the rope is also doubled.
The pulleys now become a force multiplier: we put in an effort and the pulley multiplies it, so we can lift heavier loads. A multiple pulley system, such as that shown in Figure 9.4.2, is often called a block and tackle or sometimes a Prac 1 p. 286 chain hoist.
How do pulleys reduce effort? effort
load A single pulley makes the job easier by changing the direction of the effort.
284
load
Fig 9.4.1
Imagine we need to lift a refrigerator two metres onto a truck. With a single pulley we need to pull the rope down the same distance, two metres. If we use a double pulley, however, the distance that the rope needs to be pulled is doubled, making it four metres.
Whoops! Thomas Midgley (born 1889) discovered in 1921 that tetra ethyl lead could be added to petrol to stop ‘knocking’ in car engines. In 1928 he realised that chlorofluorocarbons, or CFCs, would be perfect as a refrigerant. They couldn’t catch fire, were nontoxic and odourless if they leaked, and they wouldn’t rust the fridge. When stricken by polio in 1940, he became partially paralysed and he invented a system of pulleys and ropes that could lift him from bed to wheelchair. Unfortunately, all his discoveries and inventions proved to be harmful: lead from car exhausts slowly polluted the air in busy cities, poisoning their inhabitants; CFCs caused depletion of the ozone layer; and Thomas himself was strangled to death when he became tangled in his own pulley and rope contraption in 1944.
The advantage is that we need to use only half the effort. You will remember from the section on ramps that work is the energy needed to move something: work = effort force x distance moved
Archimedes again! Archimedes also used pulleys to make machines. Using levers and a primitive pulley system, he enabled his king to drag a fully loaded warship out of the water.
If the distance we move is greater, the effort we need to put in is less. This is how multiple pulleys work: we need to pull further but we put in less effort.
UNIT
9. 4
The effort needed gets less if more pulleys are added to the system: the mechanical advantage equals the number of pulleys used. Unfortunately, friction once again makes us work harder, by reducing the efficiency of a pulley Prac 2 Prac 3 Prac 4 system. p. 287 p. 287 p. 287
UNIT
9.4
Worksheet 9.4 Pulleys
[ Questions ]
Checkpoint Introducing pulleys 1 Explain why humans naturally find pulling an object down easier than lifting it up. 2 State the main advantage of using a single pulley to lift a load.
13 Identify how many pulleys are in each arrangement in Figure 9.4.3. 14 Determine what force multiplication each pulley arrangement in Question 13 would give.
3 Describe the mechanical advantage of a single pulley. 4 Define a ‘block and tackle’.
How do pulleys reduce effort?
a
b
5 Using the work formula, describe how a pulley reduces effort. 6 If we use two pulleys instead of one, describe what happens to the effort and distance we must pull.
Think 7 Distinguish between a pulley and a gear. 8 Friction is a nuisance in a pulley. Explain. 9 Identify the advantage of using a clamp together with a pulley. 10 A hoist does not use rope over a pulley. Identify what it does use. 11 Are pulleys force or speed multipliers? Explain.
Analyse 12 Outline the advantages and disadvantages of using multiple pulleys.
Fig 9.4.3
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Pulleys
[ Extension ] Create 1 Research the pulley arrangements used in car repair shops, yachts and simple cranes. Construct models of each pulley arrangement using weights to mimic the real thing. 2 Construct a model to demonstrate how ramps, wedges, wheels, pulleys (and any other machines) were used in constructing the pyramids.
Action 3 Use Figure 9.4.4 to design a tug-of-war competition that you cannot lose. Add more opponents until you find the maximum number of people you can defeat.
UNIT
9. 4
Fig 9.4.4
[ Practical activities ] Fixed and moveable pulleys Pulley arrangements to try
Aim To investigate the Prac 1 Unit 9.4
mechanical advantage of various pulley configurations
Fig 9.4.5
retort stand
Equipment
a no pulley
100 g mass, spring balance, retort stand, strong cotton thread
spring balance
b fixed pulley
100 g
Method
100 g
1 Use a spring balance to measure the effort force needed to hold a 100 g mass in each of the situations shown in Figure 9.4.5. 2 Record your readings in a table similar to the one shown below.
c moveable pulley
3 Now use the fixed pulley (b) and moveable pulley (c) in Figure 9.4.5 to gently lift the 100 g mass. What are the spring balance readings now?
100 g
‘Pulley’
Questions 1 Did the fixed or moveable pulley require less effort to hold and lift a mass? Propose a reason why.
286
a
No pulley
b
Fixed pulley
c
Moveable pulley
Effort need to hold the mass (N)
Effort needed to lift the mass (N)
Mechanical advantage
UNIT
9.4 Paperclip pulleys Prac 2 Unit 9.4
Aim To compare single and double pulleys made from paperclips
retort stand d double pulley
Equipment 100 g mass, spring balance, retort stand, strong cotton thread, paperclips
paperclip
Method
thread
1 Use a spring balance to measure the effort needed to hold a 100 g mass as shown in Figure 9.4.5 part a. Record its reading.
paperclip
2 Twist the two paperclips apart as shown in Figure 9.4.6 and construct the double-paperclip pulley as shown.
100 g
3 Now use the paperclip pulley to gently lift the 100 g mass. Record the new spring balance reading. 4 Measure the effort required to hold the 100 g and then the effort required to gently lift it.
Questions 1 Did the double pulley make the jobs of holding and lifting easier or harder?
Fig 9.4.6
A double pulley system
2 These paperclip pulleys are not as good as pulleys with moving wheels. Assess why. 3 Calculate the mechanical advantage of the single and double paperclip pulleys.
Using pulleys Prac 3 Unit 9.4
Aim To construct pulley systems to lift various masses Equipment
4 Place the 500 g mass (the load) on the desk next to the books and lift it slowly to the top with the spring balance.
2 single pulleys, 2 double pulleys, 1 m string, a set of 50 g masses, spring balance, ruler
5 Read the effort force required and record it in your table.
Method 1 Construct a table or spreadsheet as shown below. 2 Use the spring balance to measure the effort needed to hold a 500 g mass. This is its weight force. 3 Pile some textbooks on your desk to about 5 cm to 10 cm high, then measure the exact height.
Arrangement
Mass used (g)
a
No pulley
500
b
Spring balance upside down
500
c
One pulley
500
d
Two single pulleys
500
e
Two double pulleys
500
Weight force (N)
6 Also measure the distance your hand had to move to lift the load to the top of the books. 7 Repeat, but with the spring balance upside down. 8 Pass a string over a single pulley and use it to lift the 500 g to the top of the books. Once again measure the effort required and the distance your hand had to move.
>> Effort force required (N)
Distance mass Distance hand lifted (cm) moved (cm)
Mechanical advantage
287
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Pulleys
a
9 Repeat with the other combinations shown in Figure 9.4.7 or some of your own designs.
b spring balance
upside down
10 Calculate the mechanical advantage for each arrangement.
Questions
books 500 g
5–10 cm
c
500 g
d
5–10 cm
1 Was there any difference in the reading of the spring balance when it was upside down? If so, propose why.
e
2 Identify any advantage in using a single pulley. 3 Describe what happened to the effort force as more pulleys were added.
load effort
effort effort
5 Write a conclusion for your findings. load
Fig 9.4.7
4 Describe what happened to the distance your hand moved when lifting the mass.
load
Test these pulley systems.
4 Use the ‘pulley’ to lift the 100 g mass 5 cm. Measure how far you needed to move your hand to do so. 5 Repeat, but with four, then six, then eight sections of thread.
Rope sections Prac 4 Unit 9.4
Aim To construct a pulley system using common materials Equipment fixed pulley
Strong wire that can be bent (coat hangers are ideal), retort stand and clamp with ring, strong cotton thread or string, 100 g mass
Method
thread
1 Construct a table like the one shown here.
moveable pulley
100 g
Number of sections of thread
Distance mass moved (cm)
How far hand moved (cm)
2
5
4
5
Questions
6
5
8
5
1 Describe what happened to the distance your hand moved to lift the mass when the number of sections of thread increased.
Making a multiple pulley
Fig 9.4.8
2 Evaluate what this suggests about the effort required. 2 Build the ‘pulley’ arrangement as shown. 3 Pass the cotton thread or string over the ‘pulley’ so that there are two sections of string supporting the mass.
288
3 Use your knowledge of the formula work = effort x distance to explain your answer.
UNIT
context
9.5 Simple machines and the technology behind them make jobs easier. A complex machine is one made by connecting a number of simple machines so that their technologies become even more useful, allowing us to do things that were previously impossible.
Doing the impossible: flying Humans have always wished they could fly and have the freedom of movement that birds have. The great Renaissance artist and scientist Leonardo da Vinci drew some of the earliest sketches of flying machines, producing two different designs using the simple technologies of the time. One drawing was of a flying machine that used flapping wings to imitate the flight of birds. Another was an aerial screw, a drag primitive ancestor of the helicopter, and is shown on the chapter opening page. Without help we can’t fly or even travel very fast. The successful and unsuccessful flying machines of history have all used the simple technologies that we looked at in the previous units: gears and pulleys to turn the propellers (which are really a screw or inclined plane), and levers to move the flaps on the wings. King Bladud, Two other technologies were the first pilot The first recorded ‘flight’ required, however, before flight was made by Bladud, the was possible. A flying machine ninth King of Britain, in needs to be light, and so in the 843 BC. Unfortunately, King Bladud had simply early days the materials used strapped wings made were often light wood, bamboo, out of feathers onto his paper and oiled canvas. arms, so his flight was Nowadays, scientists working in very short, very vertical and had a very the technology of materials are messy landing. producing lighter and stronger
materials such as titanium, carbon fibre and special alloys for use in aircraft. Wings also need a special curved wedge shape to help give the aircraft the ‘lift’ required to take off. Although modern aircraft use a series of technologies to allow them to operate, the science behind them is quite simple. An aircraft has four important forces acting on it: weight, lift, thrust and drag, as shown in Figure 9.5.1.
lift
thrust
weight
The forces on an aircraft
Fig 9.5.1
You will remember that a force is a push, pull or twist that accelerates (speeds up) or decelerates (slows down) an object or changes its direction or shape. Force is measured in newtons (N). An aircraft stays in the air because of an Prac 1 upward force called lift produced by the p. 292 wings. The special shape of the wings is called the air foil or aerofoil. The top surface of the wing is longer than the bottom surface, making the air move faster over the top so that it can catch up with the air moving the shorter distance underneath the wing.
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The technology of complex machines No air? No aircraft!
High-speed air has lower pressure than air that is slow or not moving. This causes the wing to be ‘sucked’ upwards, taking the aircraft with it. Lift depends on air moving over the wings. As an aircraft picks up speed on the runway, the lift builds until it is greater than the aircraft’s weight. This is when the aircraft takes off. The forces are now unbalanced: there is an overall push upwards lifting the aircraft into the air.
Aircraft would not be able to take off on the Moon. The lack of atmosphere means no lift force is possible, so aircraft would always stay on the ground regardless of how fast they travelled. Helicopters would also be grounded. Rockets are the only craft that can take off when there is no air.
Fig 9.5.2
An air foil at work
wing
cross section
air moves faster and has less pressure
air is slower and has higher pressure
UNIT
weight
airflow direction of travel
[ Questions ]
Checkpoint Doing the impossible: flying 1 Define a ‘force’ and describe what it can do to an object. 2 Explain what is meant by balanced and unbalanced forces, giving examples of each. 3 Copy the following into your workbook, modifying any incorrect statements so they are true: a Air moving over an air foil causes thrust. b The top part of a wing is longer than the bottom.
290
Thorpedo A biomechanist is a scientist who studies the motion of the human body, particularly in sport. Biomechanists have studied champion swimmer Ian Thorpe and suggest that his 22 cm long hands act something like an air foil and provide him with ‘lift’ in the water in addition to his normal buoyancy. His size 18 feet are 35 cm long and provide exceptional thrust. His drag in the water is drastically reduced by wearing an Adidas swimsuit made of Tefloncoated lycra. Teflon is also used in non-stick fry pans. Swimsuits by Speedo are made from a fabric called ‘Fastskin’ that has a texture modelled on sharkskin.
lift
air must travel further over the top
9. 5
At cruising altitude the lift is the same as the weight: the aircraft stays at the same height because the forces are balanced. As the aeroplane approaches the airport it slows down and the lift decreases, making the forces unbalanced once more. The aeroplane’s weight is greater than the lift, and so it starts to descend. Lift needs speed, and an aircraft gets this from jet engines or propellers that push it forward; this force is called thrust. Friction caused by air sliding around the aircraft slows it down, and is called drag. Aeroplanes have streamlined shapes designed to minimise drag. Worksheet 9.5 Whirly bird
c Fast-moving air has higher pressure than slowmoving air. d An aircraft will take off only if the lift is greater than the weight. e There is no overall force on an aircraft when it is at cruising altitude. 4 Outline the four forces that are important in the flight of an aircraft.
Think 5 Identify what is special about the shape of an air foil. 6 Explain how an air foil creates lift. 7 Justify why an aircraft needs to pick up speed on a runway before it can take off. 8 Propose reasons for the following: a Aircraft always try to take off by heading into the wind. b Heavy aircraft need longer runways to take off. c There is no lift and no drag on an aircraft that is stationary. d Aircraft need longer and faster run-ups on hot days than on cold days.
Analyse 9 Construct simple diagrams to show aircraft in the following situations. Include arrows to demonstrate the forces involved. State whether the aircraft is taking off, landing, cruising, at the departure gates or in trouble. a Lift is zero, thrust is zero and drag is zero. b Lift equals weight and thrust equals drag. c Lift is greater than weight and thrust is greater than drag. d Lift is less than weight and thrust is less than drag. e Lift is less than weight, thrust is zero and drag is high.
10 A helicopter also creates lift, but with its rotor blades. Assess what shape a rotor blade would need to be for it to provide lift to the helicopter.
UNIT
9.5 11 Illustrate the likely cross-section of a helicopter rotor blade. On your diagram indicate: a where you would expect the air to be moving fastest b where the pressure would be least c the lift force produced 12 When a helicopter is stationary, the blades on both sides of the rotor give the same lift. When the helicopter is moving, however, the blades provide more lift on one half of their spin than on the other half. Use your knowledge of air movement and lift to explain why
[ Extension ] Investigate 1 Research and construct a timeline of the major developments in human flight.
Project
2 Investigate how a pilot controls the flight of an aircraft.
Making a complex machine
3 Imagine you are a pilot. Write a travel log with details of your flight control, including an incident when you encounter turbulence.
You are to design and build a machine that can lift a small quantity of sand (the load) to a height of 10 cm. Your machine must use two or more simple machines such as ramps, levers, wheels, gears or pulleys. The machine must use less effort than would be required to lift the load directly. Only simple materials such as wood, cardboard, nails, pins, straws, elastic bands, string and cotton reels can be used. Commercial equipment like Meccano or Lego cannot be used. Write a one-page report that includes: • a labelled diagram of your machine • a list of the simple machines that you used • a description of how each machine reduced the effort required to lift the sand.
4 Research more about helicopters. Find out: a why they have a small rotor on their tail b how they get their thrust to move forward c why they don’t tip over because of unequal lift from the two sides of the rotor. Present your findings to the class in group presentations. Use a form of presentation media, such as PowerPoint.
Surf 5 Explore detailed diagrams and information about forces on an aircraft by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button.
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>>>
The technology of complex machines
Project Making an air foil Use the diagrams in Figure 9.5.3 to construct and test an air foil.
Find how many paperclips it can lift. Make and test an air foil.
Fig 9.5.3
paper
card
paper
strings to adjust the angle wing shape paperclips
UNIT
9. 5
[ Practical activity ]
Creating ‘lift’
Fig 9.5.4
Creating lift Prac 1 Unit 9.5
Aim To investigate the action of moving air to create lift Equipment 1 sheet of paper, 2 ping-pong balls, fine cotton thread or fishing line, retort stand, boss heads and clamps, sticky tape, drinking straw
Method 1 Set up the two experiments shown in Figure 9.5.4.
fine line
straw
balls ping-pong
straw
2 Blow air strongly through the straw, in the directions shown. 3 Record your observations.
blow air through straw
Questions 1 In this experiment you have created movement by passing air quickly over a surface. Construct a diagram of each situation, and identify where the air is moving the fastest, where the air has the lowest pressure, and the direction of any movement.
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2 Copy and complete this sentence: An air foil is pulled into an area of ________-speed air or ________. pressure. 3 Have you created lift in this experiment? Explain.
Science focus: Indigenous technology Prescribed focus area: The applications and uses of science A typical spear thrower on top of a pile of hunting boomerangs.
Fig SF9.2
Many ancient civilisations used simple machines to their advantage. Although indigenous Australians moved about to exploit the seasons, and rarely built substantial dwellings, they did use simple machines. Their skill in making observations and their understanding of the environment they lived in allowed them to develop many clever innovations. Most notably the early Australians used their knowledge of forces and simple machines very effectively to aid them in hunting.
The spear thrower The basic design of the spear thrower was similar in many indigenous groups, but the name for this tool varied in different areas. Known as the woomera (wommera/wamarr) in New South Wales or mirr in Western Australia, the spear thrower was a very effective device to increase the time that a force was applied to propel the spear. The spear thrower usually consisted of a piece of wood that
Fig SF9.1
was carefully shaped to be held at one end, and had a hook-like peg, sometimes made from a bone or stone, at the other end. The hook-like peg at the end of the spear thrower fits into a hole at the end of the spear. The shape of the spear thrower varies depending on where it was developed. Modifying the shape allows the spear
An Aboriginal using a spear thrower when hunting
293
Fig SF9.3
The spear thrower is a lever that acts as an extension of the arm, and is a speed multiplier.
1
2
4
thrower to also be used for other purposes, such as a water scoop, a digging stick or a simple axe. As you can see in Figure SF9.3, the spear thrower acts as an extension of the thrower’s arm. The spear thrower uses two levers to launch the spear. Both levers act as speed multipliers, producing an increase in the speed of the spear compared to the speed of the thrower’s arm and hand. The first lever has its fulcrum at the shoulder and its load at the hand, as shown in diagrams 1 to 3. This is the natural throwing lever of the arm, and would be the normal lever if a spear thrower was not used. Diagram 3 shows the second lever coming into action. This lever has a complex fulcrum involving the shoulder, the hand and the hook-like point where the spear attaches to the spear thrower. To use the spear thrower effectively, as the arm reaches the normal release point (like throwing a ball), it is then swept forward and down very quickly (a bit like the follow-through of a fast bowler in cricket). This causes the top of the spear thrower to travel rapidly forward, acting like an extension of the arm. This second motion, where the end of the spear thrower effectively increases the speed of the hand, allows the force to be applied to the spear for longer than would be the case without the spear thrower. This results in the spear being launched with considerably more
294
3
5
6
speed than could have been achieved if it had simply been thrown by hand. An added bonus of the spear thrower is that the force on the spear is applied directly along the shaft, allowing a skilled thrower to be extremely accurate.
The boomerang—throwing sticks The returning boomerang that we commonly think of as being for recreation rather than hunting originated from specially shaped sticks used
Fig SF9.4
Hunting boomerangs with different shapes
A
different flight paths they follow when thrown. One surface is usually flat, while the other is curved into the shape of an air foil (just like a wing). This is why there are right-handed and left-handed boomerangs, and why boomerangs can ‘hover’ for some time in the air. The flight of a returning boomerang involves some complex physics created by the combination of lift created by the wing-like surfaces moving through the air, and the ‘gyroscopic’ forces created by the rapidly rotating boomerang (just like a spinning top).
C
B
Different returning boomerangs: A Novice/‘rotor’, B Intermediate/‘crow’, C Advanced/‘lobed’
for hunting. Several forms of boomerang-like throwing sticks were used by different indigenous tribes. These throwing sticks were carefully shaped according to the purpose they were going to serve and the prey they were to be used to hunt. It is the different curvature of the surfaces, and the shape of the boomerang, that give rise to the
Fig SF9.7
The boomerang acts as a wing with two leading edges. The forces shown here are those acting just after the boomerang is launched.
Fig SF9.5
Direction of rotation
Fig SF9.6
Cross section of wing at point shown Leading edge
Direction thrown Drag
Lift
Weight
Leading edge
A typical flight path for a returning boomerang
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The skill of making a boomerang is passed on through observation and practice.
Fig SF9.8
[ Student activities ] 1 The spear thrower relies on two levers to act as speed multipliers in order to increase the speed of the spear when it is thrown. Describe some important things that would have to be considered when designing spears to be thrown. (Hint: Remember how simple machines work and the Law of Conservation of Energy.) 2 a Construct and test a spear and spear thrower of your own. b Compare throwing the spear with and without the spear thrower. Which is more effective? 3 a The figure opposite shows how a returning boomerang should be released when thrown. In the sketch the boomerang is being thrown straight into the page by a right-handed person. The curved surface is to the left and the top of the boomerang is pointed in the direction it will be thrown. Describe the forces on the boomerang when it is first released. b Explain what would be likely to happen if a lefthanded person threw the boomerang in the same way as described for the right-handed person.
296
4 Examine the different hunting boomerangs shown in Figure SF9.3. a Based on their surfaces and shape, discuss their features with others and produce an outline of how each might behave when thrown. b Predict what each boomerang might be used to hunt. c Research boomerang shapes and uses to see if your predictions are correct. d Find a pattern for making boomerangs and construct your own. 5 As well as the spear thrower and the boomerang, indigenous Australians used many other technologies to make life easier. These include fire, drugs, stone tools, glues, baskets, fish traps and string. a Explore information about these technologies through the internet by connecting to the Science Focus 3 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button. b From your research, construct a poster that could be used to demonstrate some of the clever innovations developed by the earliest Australians.
Chapter review [ Summary questions ] 1 True or false? a Machines make less work. b Machines reduce the effort required to do a job. c Lift is the force provided by the wings of an aircraft. d Thrust is the force that slows an aircraft as it moves through the air. e The shape of the wing of an aircraft is called an air foil. f A ramp is the same as an inclined plane. g Ramps reduce effort because the distance travelled is less. h A screw is an example of a ramp. i A machine that gives a high mechanical advantage is a good one. j A pivot and a fulcrum are different things. k Ramps and levers use rotary motion. l Wheels can never act as speed multipliers. m Two connected gears always turn in opposite directions. n Gearing up is when the driven gear turns faster than the driving gear. o Single pulleys reduce the effort needed to lift something.
[ Thinking questions ] 9 Aircraft wings flex upwards on take-off. Propose a reason why. 10 Explain how ramps reduce effort. 11 Construct diagrams of class 1, 2 and 3 levers and give three examples of each. 12 Identify what idler, worm and bevel are examples of. 13 Identify what parallel gears are. 14 Discuss the advantages and disadvantages of a single pulley. 15 A double pulley can lift twice the load of a single pulley. Determine what distance the rope must be pulled in order to do so. 16 Copy and complete: The more pulleys in a system, ________.
[ Interpreting questions ] 17 Use the principle of levers to predict where a 20 g mass should be located to exactly balance each of the see-saws in the diagram.
2 Explain what a simple machine does. 3 List six simple machines. 4 Describe what a complex machine is.
a
load
5 Copy and complete: Work = effort force x ________ 6 Distinguish between the effort and the load on a machine. 7 Construct a diagram of an aircraft, showing all important forces that act on it. 8 a Define mechanical advantage. b State whether mechanical advantage should be high or low in a machine.
10 g
10 cm b
100 g load
2 cm
18 Describe how mechanical advantage is calculated for levers. 19 Calculate the mechanical advantage for the levers in Question 17.
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297
>>> 20 Predict the direction and speed of the wheels and gears shown in the figure.
a
22 Construct diagrams to show how gears could be connected to: a gear down b gear up c rotate in the same direction d increase the speed of rotation e decrease the speed of rotation f change the direction of rotation by 90°
fast
23 Examine the pictures of common kitchen appliances shown below. a Identify the simple machines that are used in each appliance. b Describe how each one uses simple technologies to make life easier.
slow b
Worksheet 9.6 Simple machine technology crossword
fast c
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21 Use examples to demonstrate a wheel acting as: a a force multiplier b a speed multiplier
Worksheet 9.7 Sci-words
a pizza cutter
b whisk
c waffle iron
d tongs
e garlic crusher
f corkscrew
consumers, 189 contraception, 177–178 convection current, 123, 125 convex (lenses), 100–101 copulation, 177 covalent compounds, 47–48 critical angle, 93–94
bases, 58–59, 61 big bang, the, 70–71, 73–75 binoculars, 102 bioaccumulation, 194–196 bioenergy, 210 biogas, 211 biomass, 210–211 biotic environment, 197 black hole, 79 body waves, 135–137 boundaries (plate), 127 brain, 243 budding, 166
ears bionic, 227–228 parts of, 226–227 problems, 227 protection, 228 earthquake, 134–139 aftershock, 138 epicentre of, 134 shadow zone, 136 ecosystem, 189 electromagnetic (radiation), 256–257 electrons, 3, 17–19, 24 electronegativity of, 24 electronic configuration of, 17–18 energy levels of, 17–18 electroplating, 54 electrostatic attraction, 45 elements, 4, 29–32 artificial, 15–16 chemical properties of, 9 physical properties of, 9 embryo, 179 endocrine system, 248 endoscopes, 94–95 endothermic reactions, 40 energy, conservation of, 190 from water, 209–210 in ecosystems, 189–190 non-renewable sources of, 205 renewable sources of, 206–211 evaporation, 198 exothermic reactions, 40 extraterrestrials, 80–82 eyes animal, 219–220 defects, 220–222 parts of the, 217–218 protection, 218
carbon, 197 cycle, 199–200 Carey, S. Warren, 123 carnivores, 181 cellulose, 149, 168 central nervous system (CNS), 241–242 chemical, bonds, 41 properties, 9 reactions, 38–42 cinder cones, 150 clones, 165 colour, 110–113 absorption of, 112 addition, 111 blindness, 219 complimentary, 112 dispersion, 110 pigments of, 112 printing of, 113 primary, 111 secondary, 111 combination reactions, 51 combustion reactions, 53 composite cones, 150 compounds, 4–5 covalent, 47–48 ionic, 45–47 compression waves,135 concave (lenses), 100–101 connecting neurons, 242 conservation, 190–191
INDEX
abiotic environment, 197 acids, 57–62 and carbonates, 60 and hydroxides, 60 and metals, 58–59 and oxides, 60 and neutralisation of, 59–60 activity series of metals, 53 adrenalin, 249 aerofoil, 289–290 alkali metals, 30 alkaline earth metals, 31 allotropes, 31 amniotic fluid, 179, 181 anticline, 149 antimatter, 83 asexual reproduction, 165–166 asthenosphere, 122 atomic number, 3, 7 atoms, 3 auxins, 165–166 axon, 241
Dalton, John, 4, 14 dark energy, 74 decomposers, 200 decomposition reactions, 51 depth illusion, 93 diabetes, 252 diatomic (gases), diffusion, dilute solutions, dispersion, 104, 110 displacement reactions, 40–41 DNA, 165 dopamine, 243 doppler effect, 69 drugs (pregnancy), 181
faults, 127, normal, 148 reverse, 148 transcurrent, 149 fault scarp, 148 fertilisation, 168
299
Index fission, 143, 166 focal length, 99–100 finding the, 101 foetus, 179 folds, 149–150 anticline, 149 overfold, 149 syncline, 149 food chain, 189, 195 food pyramid, 191, 195 fossils, 156–157 fossil fuels, 152 fragmentation, 167 gametes, 167 gases, noble, 29 gears, 279–280 geological time, 157–158 geothermal energy, 207–208 gestation, 179 glucose, 251 glycogen, 251 halogens, 29–30 hearing, 226–228 herbicides, 194 herbivores, 191 homeostasis, 237 hormones, 248–253 and plants, 253 Hubble, Edwin, 70 human growth hormone (HGH), 251 hydroelectricity, 209 hydrolysis, 41 hyperopia, 221 hypothalamus, 250–251 image real, 100–101 virtual, 100–101 implantation, 178 indicators, 61–62 infertility, 184 inorganic matter, 197 insulin, 202 international space station, 87–89 interneurons, 242 in-vitro fertilisation (IVF), 184 ionic compounds, 45–48 ions, 46–48 metal, 46 non-metal, 46 polyatomic, 47 IVF, 184 lattice, 5 lava, 145 Lavoisier, Antoine, 14–15, 23, 45 laser, 222 law of conservation of energy, 190 law of conservation of mass, 191 lenses, 99–104 concave, 100–101 convex, 100–101 levers, 269–271 lift, 289 light year, 83 lithosphere, 122
300
>>> longitudinal waves, 135 love waves, 136–137 magma, 144 mantle, 122 mass number, 3 matter, conservation of, 191 menarche, 175 Mendeleev, Dmitri Ivanovich, 9 menstruation, 174 mercalli scale, 137–138 metalloids, 11, 24 metals, 11, 23 activity table of, 53 and acids, 58–59 Meyer, Lothar, 9 microgravity, 88 microscope, 102 milky way, the, 80 mirages, 94 mirrors, concave, 102–103 convex, 103–104 mixtures, 5 molecules, 5, Moseley, Henry, 11 motor neurons, 242 mountain building, 129–130 mutation, 165 myelin, 241 myopia, 221 nebula, 77 nervous system, 241–245 neurons, 241–245 neurotransmitters, 243 neutralisation reactions, 53, 59–60 neutrons, 3 Newlands, John, 9 nitrogen, cycle, 200–201 fixation, 200 noble gases, 29 non-metals, 11, 23 non-spontaneous reactions, 41 nuclear fission, 166 nucleus, 3 ocean trenches, 129 oestrogen, 175 optical fibres, 94–95 optical instruments, 101–102 ore deposits, 152 organic matter, 197 ovulation, 167 Penzias, Arno, 74 periodic table, 9–11 peripheral nervous system (PNS), 241 pH scale, 61–62 pheromones, 252 photon, 73 photosynthesis, 199 photovoltaic cell, 206 physical properties, 9 pituitary gland, 250 placenta, 179 plate boundaries, 127–130
plate tectonics, 120–122 polyatomic ions, 47 precipitation reactions, 40, 51–52 pregnancy, 180–181 and drugs, 181 and nutrition, 180 primary colours, 111 printing, 113 producers, 189 protons, 3, protostar, 77 puberty, 174–175 pulleys, 284–285 quark, 73 radioactive waste, 205 radicals, 47 rainbows, 111 ramps, 264–266 rayleigh waves, 136–137 reactants, 38 reactions, combination, 51 combustion, 53 decomposition, 51 displacement, 53 neutralisation, 53 precipitation, 40, 51–52 receptor, 237 red giant, 77 reflection, 93 critical angle, 93–94 total internal, 93–94 reflex arc, 135, 245–246 refraction, 92–93 regeneration, 166, 167 remote sensing, 256–259 reproduction asexual, 165–166 sexual, 167–168 vegetative, 167 reproductive system, female, 173–174 male, 172–173 respiration, 200 responding, 237–238 richter scale, 137–138 rift valleys, 127–128, 148 rocks (folding), 149–150 scattering, 110 screws, 266 secondary colours, 111 seismic waves, 134–135 semi-metals, 11, 24 sensory neurons, 192 SETI, 81 sexual reproduction, 167–168 sexually transmitted diseases, 183 shield cones, 150 sight, 217–222 skin, cancers, 233 conditions, 233 slide projector, 103 solar cell, 206 solar ponds, 206 solutions, insoluble, 40, 51–52
soluble, 40, 51–52 sound, 226 levels, 228 sneezing, 231 spectrometer, 70 spectrum, 69, 256–257 sperm, 167 spinal cord, 244 spontaneous reactions, 41 spores, 166 stars, life of a, 77–79 neutron star, 78 protostar, 77 pulsar, 78 red giant, 77 red supergiant, 78 white dwarf, 78 STDs, 183 stimulus, 237 subduction zones, 128–130 sun, the, 77 surface waves, 136–137 synapse, 243 syncline, 149
UNIT
9 .1
taste, 231–232 tectonic plates, 120–122 telescope, 101 testosterone, 174 thyroxin, 250 tiuch, 232–233 transcurrent faults, 149 transition metals, 32 transverse waves, 135 tropism, 252–253 tsunami, 138–139 twins, 177 ultrasound, 180 unconformity, 150 uranium, 205 vegetative reproduction, 167 vision, binocular, 219 colour, 219 Volta, Alessandro, 15 volcanic landscapes, 150–151 volcanoes, 143–145 water cycle, 198–199 water table, 199 waves, compression, 135 longitudinal, 135 transverse, 135 wedges, 265 Wegener, Alfred, 120 wheels, 277–278 white dwarf, 78 Wilson, Robert, 74 wind, 208 wind turbine generators, 208 work, 285 worm holes, 85 zygote, 167, 178
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