Edexcel A2 Biology Revision Guide Edexcel a Level Sciences

August 14, 2017 | Author: Ghanim Al-Khaledi | Category: Chloroplast, Photosynthesis, Adenosine Triphosphate, Greenhouse Effect, Adenosine Diphosphate
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Published by Pearson Education Limited, a company incorporated in England and Wales, having its registered office at Edi; f.JurghGate, Harlow, Essex, CM20 2JE.

Reg si tere d company number: 872828 Edexcel is a registered trade mark of Edexcel Limited Text© Pearson Education Limited 2009 All past exam questions© Edexcel



The rights of Gary Skin ner Robin Harbourd (Essex Coun ty Council) and Ed Lees to be ,

iden tified as the authors of this work have been asserted by them in accordance with the C opyright, Designs and Patents Ac t of 1988. First published 2009 12 11 10 10 9 8765432 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 978 1 846905 99 5 Copyright notice All rights reserved. No part of t hi s publication may be reproduced i n any form or by

any means (including photocopying or storing it in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright owner, except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a l ice nce issued by the Copyright LicensingAgency, Saffron House, 6-10KirbyStreet, London EC1N 8T S (www.cla.co. uk). Applications for the copyright owner's written permission should be addressed tothe publisher. External project management by Sue Kearsey Edited by Lz i Jones Typeset by 320 Design Ltd Illustrated by Oxford Designers & Illustrators Cover photo© Jupiter Unlimi ted Printed in Malaysia (CTP-VVP) Acknowledgements Edexcel review by Martin Furness-S mith, UYS EG review by Anne Scott We would liketo thank Damian Riddle, Anne Scott and ElizabethSwinbank for their

contributions Disclaimer

This material has been published on behalf of Edexcel and offers high-quality support for the delivery of Edexcel qualifications. T his does not mean that the m ate rial is essential to achieve any Edexcel quali fi ca tio n, nor does it mean that it is the only suitable material available to support any Edexcel qualification. Edexcel material will not be used verbatim in se tti ng any Edexcel examination or assessment. Any resource lists produced by Edexcel shall in clude this and other a ppro pr iate resources. Copies of official specifications for all Edexcel qualifications may be found on the Edexcel we bsi te : www.edexcel.com


Revision techniques


How to use this Revision Guide




Question types in GCE

Unit 4: The Natural Environment and Species Survival Topic 5: On the wild side




Energy transfer, abundance and distribution


Investigating numbers and distribution


l I


l l




Health, exercise and sport


Topic 7 checklist


ResultsPlus: Build Better Answers


Practice questions

58 60

Topic 8: Grey matter

Responding to the environment


Neurones and nerve impulses




The structure of the human brain


Speciation and evolution


Brain development


Greenhouse gases and the carbon cycle


Learning and habituation


Impacts of global warming


Effects of imbalances in brain chemicals


Topic 5 checklist


Uses of genetic modification


ResultsPlus: Build Better Answers


Topic 8 checklist


Practice questions


ResultsPlus: Build Better Answers



Practice questions


Decay and decomposition


Unit 5 specimen paper


DNA profi ling


Unit 5 comprehension practice


DNA and protein synthesis


Infectious diseases and the immune response


Getting started with your investigation


Infection, prevention and control




Topic 6 checklist


Planning- trial investigations


ResultsPlus: Build Better Answers


Observing and recording


Practice questions


Dealing with data


Unit 4 specimen paper


Interpreting and evaluating

Unit 6:

Practical Biology and

Investigative Sk ills 84


Unit 5: Exercise and Coordination

Answers to in-text questions


Topic 7: Run for your life


Answers to practice questions



Answers to specimen paper questions


Energy and the role o= ATP in respiration



Krebs cycle and the electron transport chain


Muscles and movement



Photosynthesis 2

Topic 6: Infection, immunity and forensics



The heart. energy and exercise


Getting started can be the hardest part of revision, but don't leave it too late. Revise little and often I Don't spend too long on any one section, but revisit it several times, and if there is something you don't understand, ask your teacher for help. Just reading through your notes is not enough. Take an active approach using some of the revision techniques suggested below.



works best when

Test yourself

Make sure you don't end up just copying out your notes in full. Use some of these techniques to produce condensed notes. •

Tables and lists to present information concisely

Index cards to record the most important points for each section

Flow charts to identify steps in a process

Diag1 ams to present information visually Spider diagrams, mind maps and concept maps to show the links between ideas

Mnemonics to heir you remember lists

Glossaries to make sure you know clear definitions of key terms

Include page references to your notes or textbook. Use colour and hig hlighting to pick out key terms.

Check the spec. If you use resources from elsewhere, make sure they cover the right content at the right level.

Using a variety of approaches will prevent your revision beco-ning boring and will make more of the ideas stick. Here are some methods to try. •

E xp la i n ideas to a pa rtner and ask each other questions.

Make a podcast and play it back to yourself.

Use PowerPoint to make interactive notes and tests.

Search the internet for animations, tests and tutorials that you can use

Work in a group to create and use games and quizzes.

Once you have revised a topic, you n eed to check that you can remember and apply what you have learnt. •

Use the questions from your textbook and this revision guide. Get someone to test you on key points. Try some past exam questions.





Welcome to your Edexcel A2 Biology Revision Guide, perfect whether you're studying Salters Nuffield Advanced Biology (the orange book), or the 'concept-led' approach to Edexcel Biology (the green book). This unique guide provides you with tailored support, written by senior examiners. They draw on real 'ResultsPius' exam data from past A-level exams, and have used this to identify common pitfalls that have caught out other students, and areas on which to focus your revision. As you work your way through the topics, look out for the following features throughout the text. ResultsPlus Examiner's Tip These sections help you perform to your best in the exam by highlighting key terms and information, analysing the questions you may be asked, and showing how to approach answering them. All of this is based on data from real-life A-level students!

Resul"i:sPius Watch Out The examiners have looked back at data from previous exams to find the common pitfalls and mistakes made by students- and guide you on how to avoid repeating them in your exam. Quick Questions Use these questions as a quick recap to test your knowledge as you progress. Thinking Task These sections provide further research or analysis tasks to develop your understanding and help you revise. Worked Example The examiners guide you through complex equations and concepts, providing step­ by-step guidance on how to tackle exam questions. Each topic also ends with: -;-opic Checklist This summarises what you should know for this topic, which specification point each checkpoint covers and where in the guide you can revise it. Use it to record your progress as you revise. ResultsPius Build Better Answers Here you will find sample exam questions with exemplar answers, examiner tips and a commentary comparing both a basic and an excellent response; so you can see how to get the highest marks. :,�actice Questions Exam-style questions, including multiple-choice, offer plenty of practice ahead of the exam. Both Unit 4 and Unit 5 conclude with a Specimen Paper to test your learning. These are not intended as timed, full-length papers, but provide a range of exam-style practice questions covering the range of content likely to be encountered within the exam.


The final unit consists of advice and support on research skills, giving guidance on


specimen papers, can be found at the back of the book.



... _

Practical Assessment to help you write better individual investigations. Answers to all the in-text questions, as wel l as detailed, mark-by-mark answers to the We hope you find this guide invaluable. Best of luck I

Multiple cho�ce A good multiple choice question gives you the correct answer and other possible

answers which seem plausible. Triglycerides are composed of: 3 glycerol molecules and 3 fatty acid molecules

D 1 glycerol molecule and 3 fatty acid molecules D 1 glycerol molecule and 1 fatty acid molecule D 3 glycerol molecules and 1 fatty acid molecule D


The best way to answer a multiple choice question is to read the question and try to answer it before look ingc: t the possible answers. I f the answer you thought o f is amongst the possible answers- job done! Just have a look at the other possibilities to convince yourself that you were right. If the answer you thought of isn't there, look at the possible answers and try to eliminate wrong answers until you are left with the correct one. You don't lose any marks byhaving a guess (if you can't work out the answer)­ remember you won't score anything by leaving the answer blank! If you narrow down the number of possible answers, the chances of having a luck y guess at the right answer will increase. To indicate the correct answer, put a cross in the box following the correct statement. If you change your mind, put a line through the cross andfill in your new answer with a cross.

How Sccence Works The idea behind How S cience Works is to give you insight into the ways in which scientists work: how an experiment is designed, how theories and models are put together, how data are analysed, how scientists respond to factors such as ethics, and so on, and the way society is involved in making decisions about science. Many of the HS W criteria are practical and will be tested as part of your practical work. However, there will bequestions on the written unit papers that cover some HS W criteria. S ome of thesequestions will involve data or graph interpretation (HS W 5)- see the next section. The other common type of HSW question will be based on the core practicals. Questions will concentrate not so much on what you did, but why various steps in the core practical were important. It's important, therefore, that you k now what the various steps in each core practical were designed to do; and that you revise the core practicals. For example, think about the questions that could be asked in a Unit 2 paper on the core practical in Topic 3: 'Describe the stages of mitosis and how to prepare and stain a root tip squash in order to ::lbserve them practically.' Here, suitable questions could include: -why do we use only the tip of the root? -which stain do we use? -why do we place the cut tip in acid before staining? -what safety precautions wculd be relevant here, and why? You'll also commonly get asked questions involving designing an investigation: these are likely to involve pieces of familiar practical work. The CORMS prompt may be useful here:





-Are you investigating simply with I without a particular factor?


-Are you using organisms of the same sex I age 1 size I species?


-Take readings more than once and average

What range of values are you looking atl


-What are you measuring? How will you measure this? What units? -Which variable(s) are you keeping constant?


Other HSW questions may concentrate on ethical issues surrounding topics such as gene therapy or GM foods.

enterpretatoon of graphs The graph below shows the results of a survey in America, on the incidence of heart disease in adults aged 1 8 and older. Using the information in the graph, describe how the 1ncidence of heart disease is affected by age and gender.


soo �


� § :.0 -� � g_ 300 Cl! 0 .Co_



(5o Cl!

g zoo

�� Cl!

female male

� Cl!

"0 ·u a.. c





7S and over

You almost always get one mark for stating the general trend-in this case that the incidence of heart rate increases, with increasing age, for both genders. You can then concentrate on individual aspects of the data. In this case, what stands out most is that females have a lower incidence of heart disease than males, except in the

18-44 age

group. You may also comment that the difference between the incidence in males and females is largest in the

65-74 age group.

Finally, there is always one mark for manipulation of data. Note that this must be manipulation -you don't get marks for reading off the graph and stating the numbers, you have to do something with them!

fE�tend�d questions In the A2 units (Topic 4 and Topic

5) you will come across questions with larger 7 marks in the question.

numbers of marks, perhaps up to 6 or

Questions in these units are designed to be synoptic-in other words, they are designed for you to show knowledge gained in earlier units. Bear this in mind when you answer the question: try to include relevant knowledge from your AS course when answering these questions. Remember, too, that if the question is worth

6 marks,

you need to make six

creditworthy points. Think about the points that you will make and put them together in a logical sequence when you write your answer. On longer quest1ons, the examiners will be looking at your QWC (Quality of Written Communication) as well as the answer you g1ve.

Unit 4: The Natural Environment and Sp ecies Survival

Photosynthesis involves the r,..e.duction of carbon dioxid� These carbohydrates can be used to provide

hydrogen for this process comes from the s pli ttin g of water by light, the waste oxygen

_5t�.c;, .o"'� P s.r

being released into the atmos p here.


€)-c ewe"' c"- I .tn

(C02l to carbohydrate_

energy in respiration (see Toprc 7). T he

This can be su m marised like this: r,


ZH20 from the soil





co, f


:e "'

'OJ 3000 N

·v; c 0



0.. 0 0..


----·- --- "-- �-

Antibiotic B






antibiotic added Time/hours


Use examples from the graph to explain the differences between bactericidal and bacteriostatic antibiot i cs (3) .


A previous investigation on the same bacterium using antibiotic A had p roduced a curve similar to that for antibiotic B. Suggest an explanation for the change in the response to antibiotic A. (4)

(c) OtJtline a technique that could demonstrate the effectiveness of antibiotics on bacteria. (4)

Total 1 1 marks (Biology (Salters-Nuffield) Advanced, June 2008) 2

The hepatitis C virus (HCV) is transmitted in body fluids and infects t he liver. HCV is very common in people who also have HIV infection. One treatment for HCV infection is injections of interferon.


Explain why HCV infection is common in HIV posit ive people.


(b) Name the type of cell involved in the normal immune response to virus-infected (1) liver cells. Binding of interferon to infected cells causes an enzyme called PKR to become activat ed and this prevents protein synthesis from occurring. The diagram below shows how interferon might be involved in the body's response to HCV infection. ,

interferon binds to


protein on cell surface


HCV infects cell

1 I


�--\ �


--•, �




active PKR





ce!l surface protein

protein synthesis prevented



_ _

(c) Wit h reference to the diagram above, explain the likely effects of interferon binding to the infected liver cell. (3)

Topi c 6: Infection, immunity and forensics Wj ± ='AA


Unfortuna�ely, •b·; treatment is only effective in 20% of cases because many strains of HCV are resistant to the effect of interferon. It has been found that these resistant 'Jiru.>e::> have a protein on their coats which inhibits the enzyme PKR. (d) Suggest a reason why these virus strains are resistant to tnterferon.


(2) 8

marks 2006)

(Biology (Salters-Nuffield) Advanced, June

3 HIV can damage the human immune system.

(a) Describe

two active immune responses that are affected by HIV infection.


(b) Non-specific immune responses are not affected by HIV and can continue to prevent infection. Copy and complete the table below which shows some non­ specific immune responses and descriptions of their functions. i-






inflammation engulf and digest bacteria lysosyme action

-prevents viruses from multiplying




marks 2006)

(Biology (Salters-Nuffield) Advanced, June

4 On 26th September, a forensic scientist was called to a room where a man was found dead. She was asked to determine the time of death.

She recorded the temperature in the room and she collected the larvae and pupae of several species of insect from the body. She took the pupae and larvae to her laboratory, where th2y were placed in a constant temperature of 23 oc On the 4th October, adults from four species of insect appeared, and another species appeared on the 6th October. One of the first species to be seen was the blowfly, which can lay eggs on a corpse within minutes of death, but which is rarely active at night. Records of weather conditions for the area were consulted and the time of death was determined to be 14th or 15th September.

(a) Explain the importance of the temperature data in this investigation.


(b) Suggest one reason why collecting data about several species of insect would make the estimate of time of death more reliable.


(c) Suggest a reason why the scientist could not be more precise as to the time of death. (2)



marks 2006)

(Biology (Salters-Nuffield) Advanced, June


Unit 4: The Natural Environment and Species Survival


The diagram below shows what happens to electrons d uring part of the light­ dependent reactions of photosynthesis Any excited electrons that are not taken up by electron carriers follow pathway A and release energy as light in a process called fluorescence. The excited electrons that are taken up by electron carriers follow pathway B. Key

ooc..==::> ------ �

energy alternative electron pathways electron pathways

electron carriers





......... ......�


�DO :

I I AI I I I ....





red u ced Y




Name the molecules





shown on the diagram.

(b) Explain the importance of reduced


in the process of photosynthesis.


(c) A light was shone on a leaf and left switched on.

Thf' grr�ph below shows changes in the amount of light given off as fluorescence by the leaf.


Time since light switched on/seconds



Suggest an explanation for the increase in fluorescence.



Suggest a reason for the fall in fluorescence.

( 1)

(d) Explain why an inhibitor of carbon dioxide fixation would lead to an increase i n (4) fluorescence. Total 12 marks (A2 6134

Biology Salters-Nuffield January 2009)

2 A study of tree pollen grains in a peat bog in Finland was carried ou�. Th·� ·,umber of pollen grains of different tree species was recorded at d ifferent depths in the peat. The data for four of these trees are given as a percentage of the total tree pollen sample, in the table bel ow. An estimate of the age of the sample at each depth was also made.

' ! '-'�

f · �J llf ...�tf"r:.:t. '=:-:::;;;:.


�J11j]�_,;] � �







1.5 2.0


, ·�










































I II '



43 40



The diagram below shows the present-day distribution of the four tree species found in the main climatic zones of the northern hemisphere. Climatic

Distribution of trees









/\ pine




(a) Suggest how pollen grains can provide evidence about which species of tree were g rowing successfully i n Finland as the peat bog was forming.

(b) (i)


Which species of tree l isted below does not provide evidence about the changes in climate in Finland dunng the last 1 0 000 years? (1) A larch B spruce C pine D beech

(ii) Explain your a nswer to (b) (i).


(c) With reference to the present-day distribution of the four tree species and the results of the pollen grain study, suggest in what way the climate in Finland has changed during the last 10 000 years. Give reasons for your answer. (5)

(d) Describe how dendrochronology can be used to provide evidence for climate change.


Total 12 marks (A2 68104 Edexce/ Specimen Paper)

Unit 4: The Natural Environment and Species Survival

3 Tuberculosis (TB) is caused by the bacterium, Mycobacterium tuberculosis.

(a) The table be low lists five structural features that may be found i n bacteria and viruses. Copy and complete the table by putting a cross in the box if the structural feature is present Bacteria

Structural· feature mesosome

Viruses I '







LJ -----.

nucleic acid








D []


(b) The table below shows the number of new TB cases recorded in 1994 and in 2004 from four different geographical regions. These data exclude people who are HIV positive.

f®l -



1994 2004 (i)

148 281

98 59

629 535

Describe the trends shown by the data.


(ii) HIV positive people were excluded from the data. If they had been included suggest how the data would differ. G ive an explanation for your answer. (3)

(c) TB is increasing in some countries which have well funded health services. Suggest two reasons tor this. -



12 marks

(A2 68104 Edexcel Specimen Paper) 4

MRSA is a strain of the bacterium Staphylococcus aureus. MRSA can survive treatment with several antibiotics. An i nfection with MRSA is difficult to treat It is i mportant to use an a n ti biotic that is effective against specific bacteria. Describe in outline how you could test the effectiveness of an antibiotic on a specific bacterium in the laboratory Include aspects of the method that ensure safe working. (5) Total



(A2 6734 Biology Salters-Nuffield January 2009)


An investigation was carried out to find the distribution of pla n t species on sand dunes. A transect was used which extended i nland from a beach. Quadrats were used at nine positions along the transect. The percentage cover of selected species was recorded in each quadrat as well as the n u m ber of r:; lant species in each quadrat A sample of soil was taken from the area within each quadrat a n d used to measure the mass of organic material present. .

The results are shown in the two tables below.

















Bare sa n d





Sea couch

20 70









Distance from















top of beach/ metres Number of species found Mass of organic material/grams



}_ij� ��



Marram grass Red Fescue Sea buckthorn


Common heather


Corsica pine


(a) Explain why it is necessary to use a quadrat to estimate percentage cover.


(b) Explain why a transect is more appropriate than random sampl.ng in this study.


(c) Use the information in both tables to compare the data collected from quad rat 1 and quadrat 5. (3) (d) Differences in the variety and number of plant spec,es found in th e different ·�quadrats can be explained by succession. Use the Information in the table to suggest how the resu lts of the study could be explained by succession (5) .


12 marks

(A2 6134 Biology Salters-Nuffield Jan 2008)


Bones can move in relat i on to one another at joints. Different types of joint a l low d iffere nt degrees of movement. Ligaments are made of elastic connective tissue.

They hold bones together and restrict the amount of movement possible at a joint.

Tendons are cords of non-elastic fibrous tissue that anchor muscles to bones. bone tendon •

joins muscle to bone

cartilage •

• acts as shock


ligament •

joins bone to bone

strong and flexible

absorbs synovial


absorber pad of cartilage •

gives additional protection

synovial membrane secretes synovial fluid

fibrous capsule •

encloses joints

synovial fluid •

acts as lubricant

A typ1cal synovial joint

Skeletal muscles are those attached to bones a n d are normally a r ranged i n antagonistic p a ir s T h i s means that there are pairs o f m uscles which p u l l i n opposite direct ions Flexors contract to flex, or bend a joint, e . g . b iceps in the arm; extensors .

contract to extend, or straighten a joint, e . g . triceps in the arm. Remember that m u s c l e s c a n't stretch themselves. It is the pull

Each skeletal muscle i s a bundle of millions of muscle cells called fibres. Each muscle

created by the contraction of the

cell may be several centimetres long and contains several nuclei. It conta ins m a n y

antagonistic muscle that stretches a m u s c l e when it is in a relaxed state.

myofibrils which are made up of the fibrous proteins actin (thin fi l a ments) and myosin (thick fila ments) The cell surface membrane of a muscle cell is known as the sarcolemma The sarcoplasmic reticulum is a specia l i sed endoplasmic retic u l u m which c a n store and release ca l c i u m ions. The cytoplasm inside a m u scle cell i s called the sarcoplasm. The specialised synapse (see page 63, Topic 8) between neurones and muscle cells is called the neuromuscular junction.

The p refi x myo- refe rs to 'muscle'

and sarco- to 'flesh' (i.e. muscle) so

spec ialist terms sta rting with myo­ or

sarco- will refer to structu res

within muscle s.

The functional unit of a mu s cle


one sarcomere

fibre is called a sarcomere.

When the muscle contracts the thin actin filaments move between t h e thick myosin f i l a m ent s shorte n i n g the length ,

of the sarcomere and therefore shortening the length of the muscle.

The arrangement of actm and myosin filaments in a sarcomere when relaxed (A) and contracted (B)

Green Book 7.2

Orange Book 7.1



Topic 7: RJn for your life

Myosin filaments have flexible 'heads' that can change their orientation, bind to actin and hydrolyse ATP (using ATPase). Actin filaments are associated with two other proteins, troponin and tropomyosi n , that control the binding of the myosin heads to the actin filaments. When a nerve impulse a rrives at a neuromuscular junction, calcium ions are released from the sarcoplasmic reticulum and the following events take place that lead to the contraction of the rruscle.

. .

k. .

Ca'• binding site




...., • .


Ca2' attaches to


.r •

Myosin binding sites

'- - ,, . �


blocked by



actin) causing it


to move together

with the threads of tropomyosin.

��:�;; ' �;


Myosin binding


'" •



tropomyosin. Myosin head

cannot bind

. .....

fJ � ­

- AtdP



sites on the actin are exposed so myosin forms

cross-bridges with the actin filament.

�. L_ E===� ====Z2:::=:Jo

�. -. .2'"'

and Pi and change =


the power stroke.

"1yosin head returns to upright position.

ATPase causes ATP hydrolysis


·c ?




p "'""'

The myosin heads release the ADP shape as a result


, •,


troponin (on the



ATP binds

to the myosin

head causing it to detach

from the actin.


The slidmg filament theory of muscle contraction





ast-tw· · c·

'Btch muscle ibres specialised for slower, sustained contraction and can cope with long periods of exercise many mitochondria- ATP comes from aerobic


specialised to

prod��e r �pi d, intense

contractions in short bursts few mitochondria- ATP comes from

respiration (electron transport chain)

anaerobic respiration (glycolysis)

lots of myoglobin (dark red pigment) to store

little myoglobin and few capillaries The

02 and lots of ca pilla r es to supply 02. This

gives the muscle a dark colour

muscle has a light colour

fatigue resistant

fatigue quickly

low glycogen conten t

high glycogen content

low levels of creatine phosphate

high levels of creatine phosphate


Give one reason why fast-twitch muscles are more likely to get t i red faster than slow-twitch muscles.


D escribe the role of ATP in m uscle contraction.


Explain why muscles are arranged in antagonistic pairs.

Green Book 7.2

Ora"'ge 3c:

All living organisms have to r espire . There are two different ways in which they do this -aerobic respiration (using oxygen) and anaerobic respiration (without oxyge .. ) Both of these processes make the energy stored in gl ucose available i n the form of ATP, to power metabolic reactions. lemember that energy c a n not

>e created or destroyed, but can

Aerobic respiration

:hange from o ne form into another

glucose + oxygen� carbon dioxide+water+ energy

-so never refer to ene r gy being

C6H1 206 + 602

>roduced or used.


+ 6H20 + -30 ATP

Anaerobic respiration glucose� lactic acid+energy

C6 H1206 � 2C3 H603



ATP (adenosine triphosphate) is the cell's energy currency. Energy is req uire d to add a th i rd phosphate bond to ADP to create ATP When this bond is broken by hydrolysis, the energy released can be used in energy-requi ring processes tak ing pl a ce within the Remember that the formation of


is an example of a condensation reaction, the reverse of which i s hydrolysis:



H20-:=: ADP


P i + e nergy


The brea�< �o�v 1 .-f gh.u:ose 8n glycolysis Starting with one glucose molecule, glyco lys is produces two molecules of pyruvate, two molecules of reduced NAD and a net gain of two molecu es of ATP. Glycolysis takes place within the cytoplasm of cells.

ATP t ATP----��!

glucose (hexose)


hexose phosphate

Glycolysis means sugar splitting. Glyco =sugar, lysis= splitting. Hydrolysis means splitting using


hexose bisphosphate

water. Hydro=water.


2 molecules of triose



phosphate (3C)

1-----� 2ATP


2H c2NAD 2




2 mo le cules of pyruvate





The main stages of glycolysis.

A5ilaerobh: r�spHw�·�ion Glycolysis does not need molecular oxygen (OJ However, for glycolysis to continue, a constant supply of NAD is required . In aerobic respi r at i on the NAD is produced by the electron transport chai n . The reduced NAD must be oxidised to NAD. During anaerobic respiration, NAD m u st come from elsewhere. In animals, p yruvate from glycolysis is reduced to give lactate, NAD is formed and can keep glycolys s going. Green Book 7.1

O range Book 7.2

Topic 7: Run for your life

Anaerobic respiration allows ani:r1al< ' ..; make a small amount of ATP. It is an i neffi cient process but it is ra pi d and can supply muscles with ATP when oxygen is not b eing delivered quickly enough to ce l l s.

lactate pathway



2ADP +2Pi

2H-+ reduced NAD

Lactate forms lactic acid in solution which lowers the pH. This

can i nhi bit enzymes and, if allowed to build up, it can c a use m u scle cramp. Once aerobic respi ration resumes most lactate is converted back to py ruvate. It is oxidised via the Krebs cycle into carbon d i ox i de and water. The extra oxygen required for this process is called tre oxygen debt.






_,_1 __ lactate

_ __ _ _ ___

Anaerobic respiration in animals.

Brnvestigating the rate o(· rr�spiratio"- us�·-.g a respirometer

Don't forget the i m portan ce of including something to absorb the

C02 or the respirometer reading wid

not change during aerobic respiration

1 cm3 syringe

screw clip

of carbohydrates beca use the same

experimental tube

volume of gas is produced


g l ucose molecule respired.



(6C021 as per

absorbed by the org a n i sm (602)


small organisms

Remember that in the A2 Biology exa" you may be asked to: •

bring t o g ether scientific knowledg and understanding from differen; areas

KOH solution absorbs carbon dioxide

apply knowledge and un derstar:


of more than one area to a particular situation or context •

use kn ow l ed ge and understand'rg of pri nciples and concepts in

manometer tube

planning experimental and

containing coloured

investigative work and in the


analysi s and evaluation of da:a

A respirometer

The resp irat ion topic i s a commor

choice for such synoptic quest1ons

because the process Iinks to man·, o�"

The rate of aerobic respiration can be determined using a respirometer by measuring the rate of oxygen abso rbed by small organisms. Any C02 p ro d uc ed is absorbed by the potassium hydroxide (KOH) so l ution, so that a ny oxygen absorbed by the organisms results in the fluid in the manometer tube moving towards the organism (see arrow on diagram). The tube on the right- hand side compensates for any changes in pressure or temperawre within the apparatus.

areas such as photosynt hesis . 'ood chains and muscle contraction

Q1 Draw the main stages of glycolysis al o n g si de the !Tc­

stages of the light-indepe-ce-·


Suggest four examp l es of biological processes that require the use of ATP.


Compare the role of ATP with glycogen.


Describe the role of NAD in anaerobic respi rati on.

re a c t ions of photosynthes s

Use these diagrams to de--­

the similarities and d=e-e-::'5

between the r.-.G p·ocesse::

Green Book


In aerobic respiration, the pyruvate (from glycolysis) is completely oxidised into carbon dioxide and water using oxygen.

Aerobic respiration takes place in two stages Many of the rea ctions involved in


respiration are redox reactions where one substrate i s oxidised and another is reduced. When a molecule is oxidised, it either loses hydrogen or one or more

electrons are lost. A molecule that

gains ele ctrons or h y d rogen is reduced. One way of remembering

this is to think of OILRIG (oxidation is loss, reduction is g a in). When a molecule gains hydrogen it is reduced, and the molecule that

loses the hydrogen i s oxidised. For

example: pyruvate_, a c etyl+ 2H lis oxid ation); NAD + 2H


reduced NAD lis

redu ction).

F1rst pyruvate IS oxidised into carbon dioxide and hydrogen (accepted by the coenzymes NAD and FAD). This takes place in the matrix of the mitochondria and involves the Krebs cycle. In the second stage, most of the ATP generated in aerobic respiration is synthesised by oxidative phosphorylation associated with the electron transport cha i n . This involves chemiosmosis and the enzyme ATPase. I t takes place o n the cristae (inner membranes) of the mitochondria.

P··ep'".:��.;:�on ·.:o§'· ·a:he l{rebs

�:·._. �e


C;·C_ �


In aerobic resp1ration each pyruvate molecule coming from glycolysis in the cell's cytoplasm enters the matrix of the mitochondrion. It is converted from pyruvate (3C) to an acetyl (2C) group. Th1s involves the loss of C02 (decarboxylation) and hydrogen (dehydrogenation) generating reduced NAD. The acetyl group is carried by coenzyme A as acetyl coenzyme A

The Krebs cycle occurs in the matrix of the mitochondria. The main purpose of the cycle is to supply a continuous flow of hydrogen (and therefore electrons) to the e l ect ron transport chain fo r use in the synthesis of ATP by oxidative phosphorylation.

acety!coenzyme A (ZC) Note

You d o not need to know the names of the intermediate compounds of the Krebs cycle for the exam, but

reduced NAD NAD .e

reduced FAD

you are expected to appreciate that a e robic respiration is a many­ stepped process with each step





�/ _,.. --,


co, {

controlled and catalysed by a specific intra c e l l u l a r enzyme.


� � ./

�'-� - CO



reduced NAO

produce ATP.


Krebs cycle


respiratory chain to




,.,./\� ,_ \,




reduced NAD

The reactions involved in the breakdown of pyruvate in aerobic respiration.

�� ��

Green Book 7.1

Orange Book 7 2


hydrogen through the



that all the

hydrogen acceptors channel

Topic 7: Run for your life

Each molecule of th' �-carbon acetyl coenzyme A from the link reaction is used to generate: three molecules of reduced NAD one molecule m reduced FAD • • two molecules of C02 • one molecule of ATP by su bstrate-level phosphorylation (synthe..,ised directly from the energy released by reorganising chemical bonds) • one molecule of a 4-carbon compound, which is regenerated to accept an acetyl group and start the cycle again. •

Note that for each glucose molecule entering g lycolysis two acetyl groups are formed, so the Krebs cycle will turn twice (i.e. p roducing two ATP and six reduced NAD, etc.)

Most of the ATP generated in aerobic respiration is synthesised by the electron transport chain. 1 Reduced coenzyme

carries W and electron

2 Electrons pass from one electron carrier to

the next in a series of redox reactions; the

3 Protons (W) move across the

to electron transport

carrier is reduced when it receives the electrons

chain on inner

and oxidised when it passes them on.

inner mitochondrial membrane creating high W concentrations in the intermembrane s pa ce.

mitochondrial membrane.

4 W diffuse back into the mitochondrial matrix down


the electrochemical gradient


5 W diffusion allows AT Pa se to

inner mitochondrial

catalyse ATP synthesis.

membrane ATPase on


stalked particle


6 Electrons and W ions recombine to form hydrogen atoms wh ich then combine



with oxygen to create water.

If the supply of oxygen stops, the electron transport chain

and ATP synthesis also stop. The electron transport chain and chemiosmosis result in ATP synthesis by oxidative phosphorylation.

The majority of ATP generated by aerobic respiration comes from the activity of the electron transport chain in the inner membrane of the mitoch ondria (cristae). The overall reaction of aerobic respiration can be summarised as the spli tting and oxidation of a respiratory substrate (e.g. glucose) to release carbon dioxide as a waste product followed by the reuniting of hydrogen with oxygen to release a large amount of energy in the form of ATP. ,

__ _ _____ _ ....__


Describe what happens to the carbon and hydrogen atoms trom a glucose molecule in aerobic respiration.


Explain what oxidative phosphorylation means.


Explain why the electron transport chain and the Krebs cycle would stop if there was no oxygen.

(0:,_ . -�


\ �

Q1 Sketch a simple diagram o' a.:: and mitochondria and ouu·�e

Green Book 7. 1

where the main steps in respiration take place.

Orange Book 7.2


Unit 5: Exercise and Coordination

1 Elect r ical impulses from the


SAN spread across the atria

The impulse to contract originates wit hi n the heart itself from the s i noatrial node - the heart is said to be myogenic.

walls. causing contraction.

This is called atrial sys tole .


2 Impulses pass to the

ventricles via the AVN after

a short delay to allow time for the atria to finish


3 Impulses pass down the Purkyne fibres to the heart apex.

4 The i mpulses spread up through the ventricle walls causing

contraction from the apex upwards.

Blood is squeezed i n to the arteries. This is ventricular sys tole.

The route taken by electrical impulses across

Purkyne fibres

the heart during the cardiac cycle.

After contracting (systole), the cardiac muscle then relaxes for a period called diastoie when the blood returning from the ve i ns fills the at ria .

!\J!easuring e!e'.:tr�ca! changes in the hei:H"t Electrical currents caused by the spread of the electrical impulse (wave of depol arisat i o n) during the cardiac cycle can be detected with an electrocardiogram (ECG). If disease disrupts the heart's normal conduction pathways changes will occur in the

ECG pattern which can

be used for diagno sis of cardiovascular disease.


�____,_ ! ---_ --l 1 s I P wave

1 0� �·

5� segment

�e�a��--��--�--+--+ �



, I

The P wave is the time of atrial systol e . The QRS complex is the time of ventricular systole. The T wave is caused by repolarisation of the ventricles during d ia sto le .

A normal ECG pattern in a healthy heart.

You can calculate the heart rate

�-e� �:,::,--�

interval b etween one P wave and

Blood is pumped aro un d the body to supply 02 and remove C02 from respiring

using an ECG by measuring the time the next one (a complete cardiac cycle) and then working out how

many occur in 1 minute.

Green Book 7.3

tissues. How much is pumped in a minute (cardiac output) depends on two factors: how quickly the heart is beating (heart rate) and the volume of blood leaving the left ventricle with each beat (stroke volume)

cardiac output (dm3min-1) =stroke volume (dm3) Orange Book 7.3


heart rate (min-1)

Topic 7: Run for your life

The heart rate can be affected by hormones (e.g. adrenaline) and nervous -::ont• transcription

RNA synthesis

initiation complex

DNA transcription is controlled by transcription factors.


Describe why a lack of exercise may lead to an increased risk of coronary heart d i sease.

01 Even

if all performance­

enhancing substances were


Explain why a lack of T helper cells may increase the risk of an athlete suffering from a sore throat.

formally banned, would we eve1


Outl ine the role of transcription factors in the control of gene expression.


Green Book 7.4

have a level playing field for

Orange Book 7 5, 7.6

Unit 5 : Exercise and Coordination


the e n d



topic you should be able to:




Muscles a n d

Describe t h e structure o f a muscle fibre a n d explain


the differences between fast and slow twitch muscle fibres. -

Explain how skeletal muscle contracts using the sliding

filament theory. Recall the way in which muscles, tendons, the skeleton and ligaments interact to allow movement. Energy and the

Describe aerobic respiration as splitting of glucose to

role of ATP

release carbon dioxide, water and energy.


L03 L04 LOS

Describe a practical to investigate rate of respiration.


Recall what ATP is a n d how it supplies energy for cells.


Describe the roles of glycolysis in both aerobic and


anaerobic respiration. You do not need to know a l l



" "






































the stages b u t you d o need t o know tha: g l u cose i s phosphorylated a n d ATP. reduced NAD a n d pyruvate are produced. Explain what happens to lactate after you stop exercising. The Krebs cycle

Describe how the Krebs cycle produces carbon

and the electron

dioxide, ATP, reduced NAD and reduced FAD You

transport chain

should also understand that respiration has lots of enzyme-controlled steps. Describe how ATP is made by oxidative

LO l l L09

L0 1 0

phosphorylation in the electron transport chain including the roles of chemiosmosis a n d ATPase. The heart, energy

Understa nd that cardiac muscle is myogenic and

a n d exercise

describe how electrical activity in the heart allows it to beat. You should also know how ECGs can be used . Explam that tissues need rapid delivery of oxygen and

L0 1 2

L0 1 3

removal of carbon dioxide during exercise a n d that changes i n ventilation and cardiac output allow this to happen. You should understand how heart rate and ventilat1on rate are controlled. Describe how to use data from spirometer traces to


investigate the effects of exercise. Homeostasis

Explain the principle of negative feedback.

L01 5

Discuss the concept of homeostasis and how it

L0 1 6

maintains the body during exercise, including controlling body temperature. Health, exercise

Explain how genes can be switched on and off by

a n d sport

DNA transcription factors including hormones. Analyse and interpret data on the possible dangers of exercising too little and too much. You should also be

a b l e to talk about correlation a n d cause. Explain how medical technology helps people with injuries or disabilities to take part in sport. Outline the ethics of using performance-enhancing substances.

L0 1 7 L0 1 8

L0 1 9 L020

Topic 7 : Run for your life

Animals that are predators often show bursts of very fast movement. Their prey tend to be able to carry out sustained movement over longer periods of time. Close examination shows that the muscles of predator and prey show a different composition of fast- and sl ow­ twitch fibres.



Outline the differences between fast- and slow-twitch mLscle fibres.


State whether predator or prey would show a higher propJrtion of slow-twitch fibres.

(iii) Discuss why predators show different proportions of fast- and slow-twitch muscle fibres from their prey.




If you are asked for the differences. make sure you refer to both or use a comparative word. e.g. 'more'. I


(a) (i) Slow-twitch muscle fibres have more mitochondria and

This is a good response because not only does it provide a likely

more capillaries supplying oxygen than fast twitch fibres.

comparison, it also provides a clear and plausible explanation

(ii) Prey

(iii) Predators are likely to have more fast-twitch than slow­ twitch fibres, in comparison to their prey. This is because predators tend to be fast and powerful over short distances to catch and kill their prey and therefore use anaerobic respiration to release ATP quickly.


During fast movement, lactate builds up in the muscles of a predator. such as a cheetah. Explain what happens to this


lactate after the chase has ended. I •

I nr.tntP. rliffuses from the muscle into the blood wh e re it is carried

This response is

away from the muscle to prevent cramp.

how the lactate is moved away from the muscle. but not how it is


correct but on ly partial �xpl anati on . I t explains

removed from the body. Lactate is oxidised back into pyruvate using NAD that has been

This response will gain maximum marks because it provides

oxidised in the electron transport chain using oxygen. The extra

a chemical explanation of the fate of the lactate. clearly

oxygen needed is the oxygen debt.

demonstrating an understanding of both aerobic and anaerobic respiration. as well as recognition of the need for extra oxygen.


During the chase, the core body temperature of both predator and prey rises. Describe how changes in blood circulation help to return their core body temperatures to normal.


In longer questions like this try to be clear on writing cause and effect. Where possible use key terms and concepts from your course as part of your description as you will often receive credit for these. However. the terms need to be in the correct context - you will not gain marks

for lists of random terms that do not demonstrate your understanding of what they mean.

. Student answer





. -

This response would only score 1 mark for the recognition that more

An increase in core temperature causes vasodilation so that more

heat would be lost from the skin. The reference to vasod ilation is

heat is lost from the skin.

not enough as it does not describe what change occurs to the blood circulation. This response is better because it includes key terms and structures

This is an example of homeostasis using a negative feedback mechanism. Changes to the core temperature are detected by

in the correct context of how the change is caused (homeostasis.

thermoreceptors in the hypothalamus which send nerve impulses to

negative feedback. hypothalamus). It also clearly describes the

arterioles in the skin. This causes vasodilation resulting in increased

effect of vasodilation on the blood circulation.

blood fiow to the skin. (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 5 June 2008.)


(a) Name the region of the hum an brain involved in control of heart rate.


(b) Heart rate increases during exercise. Explain the mechanisms involved in control ling this increase in heart rate. (4) Total 5 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 5 June 2007) 2 Doing too little exercise can lead to health problems, but too much exercise can also be harmful. D iscuss tre benefits and potential dangers of exercise i n humans. (6) Total 6 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 5 June 2007) 3 The table below refers to three major stages of aerobic respiration and the products of each stage. Copy and complete the table by inserting the part of the cell in which the stage occurs an::l two products in the blank spaces. I



matrix of mitochondrion

Krebs cycl e electron transport chain



I ATP and water



Total 4 marks (Edexcel GCE Biology Advanced Unit 4 - paper 3 June 2007) 4

The diagrams show one sarcomere in its fully relaxed state and when il i� partially contracted. actin myosin

Fully relaxed sarcomere

Partially contracted sarcomere

(a) Calculate the percentage change i n width of the H zone when the sarcomere is partially contracted Show your working. (3) (b) During the contracticn of this sarcomere, the myosin filaments pull the actin filaments towards the centre of the sarcomere. Explain how this is brought about. (4) Total 7 marks (Edexcel GCE Biology Advanced Unit 4 - paper 3 June 2007) 5

The diagram shows the ways i n which the respiratory system and different parts of the brain i nteract with each other to regulate breathing .

stretch receptors

Topic 7 : Run for your life

(a) Breathing can be controlled voluntarily and involuntarily. Name the part of the brain that controls involu ntary breathing

(1 )

(b) Suggest one occasion when the depth of breathing is increased voluntarily.

(1 )

(c) Using the information in the diagram, explain the roles of muscle spindles (3) and nerves in the control of breathing during exercise. (d) The ventilation of the lungs during breathing is essential i n mainta i ning the concentratior gradients of the respiratory gases. This ensures that gas exchange is efficient. Explain why the chemoreceptors are particularly im portant during exercise. (2) Total 7 marks (Edexcel GCE Biology Advanced Unit 4 - paper 3 June 2007) 6

The diagram shows some of the muscles in a human leg. (a) Using the letters A, B, C or D, identify the muscle on the diagram above which (i) contracts to bend the leg backwards at the knee AND (ii) is antagonistic to the muscle identified in (i). (1) (b) Joint injuries often shorten the career of ath letes . Explain the advantages of keyhole surgery on damaged joints, such as the knee, compared with (2) traditional surgery. (c) Two weeks after taking part in a 56 km race, 3 3 % of the runners developed respiratory tract infections. Those who completed the race were three times more likely to develop an infection after the race compared with a control group which did not run. Explain one factor which could contribute to this higher infection rate. (3)

Total 6 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 5 June 2005) 7

The diagram shows the pathways for the conduction of electrical impulses during the cardiac cycle. -::.-- I


�__,_,...,.___7 pathways for the conduction of �------

electrical impulses

(a) Name the structure labelled



(b) Describe how the structures shown i n the diagram control the complete cardiac cycle. (4 ) Total 5 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 7 January 2005)

Animal nervous systems are fast-acting communication systems containing nerve cells (neurones) which carry information in the form of n erve impulses (see page 62). In mammals sensory neurones carry impulses from receptOis to a central nervous system (CNS) consisting of the brain and spinal cord. The CN S (containing relay neurones) processes information from many sources and then sends out impulses via motor neurones to effector organs (mainly muscles and glands).

The pupil reflex The iris contains pairs of antagonistic muscles (radial and circular muscles) that control the size of the iris under the influence of the autonomic nervous system (involuntary). pupil constricted

pupil dilated


muscles relax



m usc les

muscles contract


circular muscles


How the muscles of the iris act to control the amount of light entering the eye.

I n high light intensities photoreceptors such as rods in the retina cause nerve i m pu lses to pass along the optic nerve to a group of nerve cells in the brain. These then send impulses along parasympathetic motor neurones to the circular muscles of the iris. The muscles contract, reducing the diameter of the pupil so :hat less light can enter the eye, thus preventing damage to the retina. In low l ight conditions fewer impulses reach the coordinating centre in the brain impulses are sent down sympathetic motor neurones to tne radial muscles of the iris instead. This causes the radial muscles to contract and the pupil becomes dilated, allowing more light to reach the retina.

S�rrl�����!itv n u1 pi�nts " Photoperiodism: Plants flower and seeds germinate in response to changes in day length. Thephotoreceptor involved is a bl u e-green pigment called phytochrome. Qn absorbing natural (or red) light phytochrome converts from the inactive form e,g to the active formPFR In the dark PFR slowly reverts ba::: k to P� because i t is relatively unstable (or it can change back rapidly_j.n.toJ'R- if exposed to far r�d lig� t). It isthotJght that the active PFR may trigger a rang_e_gf diffe[.ent...Qbot.QPeriodic responses. • Phototropism: T�opisms are growth responses in plants where the direction of the gwwth response is determined bythedi�:e�ternal stimulus. If a plant grows towards a stimulus it is said to be a�:._tropic respo�e .

Green Book 8 . 1, 8.2

Orange Book 8 . 1




With illumination :.-::.:·.:=:..: ·

from all sides, an

even , :;tribution

of auxins moves down from the shoot tip, and causes elongation of cells across the zone of el on gatio n '

·."( .



Zone of

from one side, auxins

move down from the shoot tip towards the


Take care not to mu d d l e tropic and trophic. Tropic responses

shaded side of the


are growth responses in plants.

shoot. Only those

Tro p h i c is connected with how

cells on the shaded


side elongate, a nd the shoot bends towards the light

l i vi ng things

feed and th e i r positi01

within food chains. Fo r example

plant shoots have a pos itive tropic response to l i ght and they are

It is not c lea r what the receptor for phototro pis m is in shoots, but a good candidate in ce re als is riboflavin. The effector for the g rowth response

autotrophic because th ey m a k e

th e i r o w n food a n d therefore

is cell elongation. This ha ppens just below the tip of the shoot a n d is co ntrolled by the plant growth substance IAA (the first auxin discovered).

o c c u p y th e first trophic level on a

food c h a i n .

Mechanism of phototropism in shoots.



Electrochemical changes

giving an electrical i mpulse. Chemical neurotransm itters used at most synapses.




Chemical hormones from

Chemical growth substances

endocrine glands earned 1 n

(e.g. auxins) diffusing from

the blood plasma around the ci rc u l atory system .


Remember, auxins like IAA cause cell e l o n g a ti o n and not cell

cell to cell - some may go i n

d i v i s i on.

the p l ant transport system - the phloem.

ra p id acting

slower acting

slower acting

Usually associated with

Can control long-term

C o ntrols long-term

short-term changes, e . g .

responses, e . g . growth and

growth responses, e.g. cell

muscle contraction.

sexual development. Some

e l ongation .

are involved in homeostasis, e.g. control of blood sugar.

Some can be relatively fast, e.g. effects of adrenaline in . response to stress. Response is very local and

Response may be widespread,

or restricted to specific target

Response may be widespread,

specific such as a muscle cell or gland.


within a short d1stance of

but normally restricted to cells the growth substance being released.

Table to compare commun ication and coordination methods in plants and a nimals.

Q1 Q2 Q3


Explain what is meant by the term p h otoreceptor. Explain why it is an advantage that shoots have positive phototropism and roots have negative phototropism. What effect does IAA have on cells?


, !1 1 1 1 .

·�!. i

Ql Why i s it an ad va nta g e for

animals to have a nervous

system and an endocrine system?

Green Book 8.1, 8. 2

. .

Orange Book 8. 1

neurones (nerve cells) have a cel l body (containing the nucleus and most of the cell's organelles within the cytoplasm), dendrites (that conduct impulses towards the cell body) and an axon (that conducts impulses away from the cell body), The main difference between the structures of sensory, motor and re l ay neurones is the relative position of the cell body


Neurones are able to carry waves of electrical activity called action potentials (nerve impulses) over a long distance because the axons can be very long and the membranes are polarised (different charges on the inside and outside of the membrane), Sensory neurone


cell body

A��======� �, ==F=� ' ======��(� -�1' I � ""-


Schwann cell





=( ====)�:;, ;:f�). ; E

"'i u �





2:: .,§: c



resting potential + + + + + + + +

=ao=u=t t:: - - - - - - - -


3 The membrane is hyperpolarised. Voltage-dependent K• channels


close, K• diffuse back into the axon to recreate the resting potentiaL


CJD Voltage-dependent Na• channel U Voltage-dependent K• channel Movement of ions in and out of the membrane during an action potentia!_

Green Book 8,2


Orange Book 8 , 1

� K•

I I K• channel

Topic 8: Grey matt er *5

If a neurone cell rr,eml- �ne is stim ulated, voltage-dependent sodi u m ion channels open and sodium ions diffuse in. Th1s increases the positive charge inside the cell, so the charge across the rrembrane is reversed. The membrane now carries a potential difference of about +4C mV This is the action potential and the m e m b rane is sa1d to be depolarised. As the charge reverses, the sodium ion channels shut a r , J voltage­

dependent potassium ion channels open so that more potassium ions leave the axon, repolarising the m e m b rane.



++++++++++ high K'


on the

At resting potential there is positive charge

outside of

the membrane and negative charge on the inside, with high sodium ion concentration outside and high potassium ion concentration inside.

++++++++++ first action potential 2



When stimulated, voltagedependent sodium ion channels open. and sodium ions flow into the axon, depolarising the membrane. Localised electric currents are generated in the membrane. Sodium ions move to the adjacent polarised (resting) region causing


N t!_�- �-- +��-��+� + -+ -+ -+ + + +�a �+ + + + + + N � +++ t � + :�2

a change in the electrical charge (potential difference) across this part of the membrane

second action potential


r= ---


The change in potential difference in the membrane adjacent to the first

potential initiates a second action potential. At the site of the first action potential the

and voltage-dependent potassium

voltage-dependent sodium ion channels close


channels open. Potassium ions leave the axon, repolarising the membrane. The membrane becomes hyperpolarised.


third action potential


4� -:�t� K'

refractory period





action potential is

second. In this way local electric currents

A third

initiated by the

cause the nerve impulse to move along the axon. At the site of the first action potential. potassium ions diffuse back into the axon, restoring the resting potential.

======i> progress ot the impulse

Propagation of a nerve impulse along an axon.

Action potentials have an ali-or-nothin g nature (the values of the resti n g and action potentials are always the same for a specific n e u rone) A bigger sti m u l us increases the

frequency of the action potentials (not the strength). A threshold stimulus m ust be applied to produce an action potentia l . Straight after a n action potential there i s a short refractory period when a new action potential can't be g enerated because the sodium ion channels can't reopen. This ensu res that action potentials pass along as separate signals and are

unidirectional (only acle to pass in one direction).

Green Book 8 . 2

Orange Book 8. 1


Unit 5 : Exer ci s e a n d Coordination



The point where one neurone meets another is called a synapse. At thr? tip of the axon a n impulse opens calcium ion channels then triggers the release of a chemical neurotransmitter (for example acetylcholine) from synaptic vesicles. The neurotransmitter can diffuse across the gap between the n e u rones (the synaptic cleft) and b i n d to receptors on the· postsynaptic membrane. If the neurotransmitter comes from an excitatory neurone it may open sod 1 u m ion channels on the postsynaptic membrane, triggering a new action potential in the postsynaptic neurone. However, some neurotransmitters are i n h i bitory and they may open chloride ion channels on the postsynaptic membrane, causing it to become hyperpolarised and therefore harder to get an a bove-thresho l d response needed to trigger the new action potential. An enzyme is often present in the synaptic cleft to hydrolyse the neurotransmitter, so the response does not keep happe n i n g . The neurotransmitter may also be taken back up into the presynaptic membrane ready to be used a g a m . Because the receptors a r e only o n one side o f the synapse (the postsynaptic Pre - before; post- after; uni - one;

membrane) the signal can o n l y pass in one d i rection (unid irectional). Synapses also

summation - a d d i n g .

act as junctions and a l low nerve i m p u lses to converge o r diverge because one neurone can meet many others at a single synapse. 1 An action


potential arrives.

If two or more excitatory 1


2 The membrane depolarises.


Calcium ion channels open.

i m pu lses arrive at a synapse

Calcium ions enter the

at the same time their effect


w i l l be combined a n d you


are more l i kely to depola rise


neurotransmitter to fuse with

(this is spatial summation) If

the presynaptic membrane.

you have a strong sti m u l u s

4 Neurotransmitter is released

along o n e neurone many action potentials will arrive

into the synaptic cleft.

one after the other (due to the high frequency) and this (this is temporal summation). �-------__j


�J,. "QJ


t o :: 0





fl 0

mem orane




pres napt1c


N� + CPS� Q


will have the same effect

� ® W � IL�

3 Calcium ions cause synaptic vesicles containing

the postsynaptic membrane




postsynaptic mem brane

5 Neurotransmitter binds with receptors on the

6 The membrane depolarises and

postsynaptic membrane. Cation channels open.

initiates an action potentiaL



Sodium ions flow through the channels.

7 When released the neurotransmitter will be taken up across the presynaptic membrane

( whole or after being broken

The sequence of events occurring when an action potential arrives at a synapse

01 Look b a c k at your AS Biology


notes for the structure of m e m b r a n e s a n d transport a c ross membranes. Sketch a d i a g r a m of a m e m b r a n e to show how sodium and potassium ions

Q1 Q2

move d u ri n g a nerve impulse. Then a d d to your diagram any other ways that substances c a n m o v e across membranes.


Green Book 8 . 2

down ) , or it can diffuse away and be broken down.


Explain the d i fference between depolarisation and hyperpolarisation. How do the structure of the synapse a n d axon membrane ensure that nerve i m p u l ses are only able to travel in one d i rection/ Describe what happens to sodium ions when a neurone membrane is stimulated.

Orange Book 8 . 1




- '-+

5 �··_ ;

Receptors are specialised cells able to detect stimuli. Receptors are often grouped together into sense organs.

Human eyes have two types of photoreceptor cells found in the retina on the back of the eye. Cones allow colour vision in bri ght l ight and are clustered in the centre of the retina. Rods only provide black and white vision, but are much more sensitive than cones and can work in dim light conditions. dark



� Na






di ffuse in


t hrou h open

s egment


cation channels

Opsin binds to the me mbrane causing a series

of reactions which result i n the Na • c an e s being closed.



rhodopsi n to retinal

-�____.- an d opsin

h nl

Na+ m o e down


light breaks down


concentration gradient




'\ -

I \J li \_

(C[ (��

O oO

Na + act ivel


�+ - Na + actively


pumped out

pumped out

membrane slightly

membrane hyperpolarised

depolarised -40mV

No neurotransmitter is Neurotransmitter is released


and binds to bipolar cell,

Cation channels in


p re enting it depolarising.

bipolar cell open and

membrane becomes --a



depola ri e d , enerating

bipolar neurone

an action potential in a

A rod cell in the dark and in the light.

the neurone of the

optic nerve.

Light energy is absorbed by rhodopsin which splits into retinal and opsin. The opsin binds to the membrane of the outer segment of the cell and this causes sodium ion channels to close. The inner segment continues to pum p sodium ions out of the cell and the membrane becomes hyp e rp o l arise d (more negative). This means that gl utamate is not released across the synapse. Gl utamate usually inhibits the neurones which connect the rod cells to the neurones in the optic nerve. When there is less inhibition an action potential forms and is transmitted to the brain. The information from the optic nerve is processed by the brain in the visual cortex.

connect to a single bipolar cell

------- ----

Q1 Q2 Q3

01 Groups of three rod cells

Explain why rods release a neurotransmitter in the dark, but not in the light.

whereas j u st one cone cell connects to a bipolar cell. Use this information to explain why

Describe what happens to rhodopsin when it is exposed to light.

you can't s e e colour well in d i m

Compare p h ot o recepto rs in mammals and plants.

light conditions.

G reen Book 8 . 2

Orange Book 8 . 2

The cerebrum (cerebral cortex) is the largest part of the brain. It is divided into two

cerebral hemispheres connected by a band of wh i t e matter called the corpus

cal losum . The cerebrum is associated with advanced mental activity like language,

White matter is so c a l l e d b e c a u s e it mainly consists of lots of myelinated axons. Grey matter is where the

memory, calculation, processing i n formation from the eyes and ears, emotion and controlling all of the voluntary activities of t h e body. Frontal lobe (also referred to as the higher centres of the brain) - concerned with the higher brain

synapses o c c u r and therefore

functions such as decision making, reasoning, planning and consciousness of emotions. It is also concerned

where a l l the processing takes

with forming associations (by combining information from the rest of the cortex) and with ideas. It

p l a c e and your memories are

includes the primary motor cortex which has neurones that connect d i rectly to the spinal cord and brain


stem and from there to the muscles. It sends information to the body via the motor neurones to carry out movements. The motor cortex also stores information about how t o carry out different movements. Parietal lobe - concerned with orientation, movement, sensation, calculation, some types of recognition and memory. Occipital lobe (visual cortex) - concerned with processing information from the eyes, including vision, colour, shape recognition and perspective. Temporal l o b e - concerned with processing auditory information, i.e. hearing, sound

The regions of the cerebral

Ce re b e ll u m

(\pft tPmpor�l \oht>). memory.

recognition �nri sreerh

hemispheres and their functions.

Also involved i n


corpus callosum

The hypothalamus controls thermoregulation. pituitary gland


The cerebellum is important for balance and coordinating muscle movements.

midbrain The medulla oblongata controls many body processes such as heart rate, breathing and blood pressure.

The main regions of the human orain.

Green Book 8 . 3


D i stinguish between the cerebrum and the cere b e l l u m .


Which region of the brain is most associated wit h thin king a n d decision making/

Orange Book 8.3

Topic 8 : Grey matter

W"' are born with a range of innate behaviours (behavioural responses that do not need to be learnt) such as crying, grasping and sucking. However, the brain still needs much growth and development after birth through the formation of synapses and the growth of axons.

:-�� Critical windows (or critical periods) for development are those periods of time where it is thought that the nervous system needs specific stimuli in order to develop properly. Evidence for critical windows for development has come from medical observations (e.g. children who develop cataracts before the age of 1 0 days may suffer from permanent visual impairment even if the cataracts are repaired at a later date) and from animal models Hubel and Wiesel used kittens and monkeys as models to investigate the critical window in visual development because of the similarity of their visual systems to that of humans. The iJnimals were deprived of the stimulus of light into one eye (monocular deprivation) at different stages of development and for different lengths of time. They found that kittens deprived of light in one eye at 4 weeks after birth were effectively permanently blind in that eye. Monocular deprivation before 3 weeks and after 3 months had no effect. It was thought that during the critical period (about 4 weeks after birth) connections to cells in the visual cortex from the light-deprived eye had been lost This meant that the eye that remained open during development became the only route for visual stimuli to reach the visual cortex.

Axons pass nerve impu lses to cells

in the

visual cortex.

Inactive synapses are eliminated.

Synapses used by active

axons are


Eye has

no working connection to

cortex and is effectively


the visual

even though

of th e retina and optic nerve work normally when exposed to light the cells


only present for axons coming from

the light-stimulated eye. So the v is u a l


can only respond to this eye.

The use of animals as models for understanding how humans develop, or how new drugs may affect us, is a very controversial area. There are those who hold an absolutist view of animal rights and think we should never keep animals or use them in medical research. From the point of view of medical research, a much more widespread position is the relativist view that humans should treat animals well and minimise harm and suffering so far as is possible. Here the emphasis is on animal welfare, respecting their rights to such things as food, water, veterinary treatment and the ability to express normal behaviours. This is pretty much the position in European law This all assumes that animals can suffer and experience pleasure. A utilitarian ethical framework allows certain animals to be used in medical experiments provided the overall expected benefits are greater than the overall expected harms based on the belief that the right course of action is the one that maximises the amount of overall happiness or pleasure in the world.

Green Book 8.3

Visual development i s


e xamp l e of how the effects of nature a n d nurture can combine i n development The genes control the development of the responsive cells in the visual cortex (nature)

but a stimulus frorr

the environment is needed during the criti c a l window for the correc1 connections to b e made {nurture).

Orange Book 8.4

Unit 5: Exercise and Coordination

�he 1role of natui"e and nurture � n braun ....... yt. .� .-�"'.e'> -. -.,.;; r{' . J. , �-�. n; w "' � � ,., �..:; "


Nature: Many of o u r characteristics develop solely u n d e r the influence of o u r genes with little influence from o u r environmem o r learning, e . g . blood group.

!\!though it is not generally

N u rture: Many cha racteristics are learnt or are heavily i n f l u e n ced by the environment, e . g . how long your hair is.

possible to experiment o n people,

Most of our cha racteristics are actually determined by nature a n d nurture o r nature via

t is possible to select a s a m p l e

n urture. We are the result of a mixture of genetic a n d environmental factors. H u m a n

�arefully so a s t o e n s u r e t h a t non­

behaviours, attitudes a n d skills m a y have a n underlying genetic b a s 1 s b u t a r e mod1fied

�xperimental variables, s u c h a s

by experience o r the environment i n a way which IS very complex. For example, the

3 g e a n d sex, are matched s o it i s

chance of devel o p i n g some diseases, such as some cancers, has a genetic basis,

nore like a traditional controlled

where a gene o r several genes interact to confer susceptib i l ity to the disease with

�xperiment in the l a b oratory.

environmental factors contributing to the risk of devel o p i n g the disease. Evidence for the relative roles of nature and n u rture i n brain development come from a variety of sources: •

The abilities of newborn babies: Newborn babies have some i n nate capacities. These suggest that genes help to form the bra i n and some behaviours before the baby is born.

Studies of i n d ividuals with damaged brain areas: Some patients who have suffered from brain d a m a g e show the a b i l ity to recover some of their bra i n funct1on. This demonstrates that some neurones have t h e a b i l ity t o change.

Animal experiments: e . g . H u bel and Weisel's experiments on critical windows for sight, suggest that external stimulation is important i n brain development

Twin studies: Identical twins share a l l the same genes. Fraternal (non-identical) twins share the same n umber as any other s i b l i n g would. Twi n studies con help to estimate the relative contribution of genes a n d the environment Any differences between identical twins must be due to the effects of the environment Identical twins raised apart i n comparison to those raised together are particularly useful for study. For example if there is a greater difference between those twins raised a p a rt than twins raised together it suggests some environmental influence. However, twins raised a p a rt may not have completely different environments a n d twins raised together may develop different personal ities d u e t o a desire t o be different. In general if genes have a strong influence on the development of a cha racteristic, then the closer the genetic relationship, the stro n g e r the correlation w i l l be between i ndividuals for that trait.

Cross-cultural studies: I n vestigations into the visual perception o f groups from different cultural backgrounds support the idea that visual cues for depth perception are at least partially learnt.


01 What is your personal view on the use of a n i m a l s in m e d i c a l


research? F o r example, how

m a n y a fruit flies, b mice,




d monkeys do you think you c o u l d use to test new drugs to

help treat i breast c a n cer, ii


' .

Green Book 8 . 3

If one identical twin has schizophrenia there is


chance that their twin

w i l l a l s o have symptoms of schizophrenia. However, if one fraternal twin symptoms of schizophre n i a . What do these f i g u res suggest a b o u t the

How d o you justify your position?


Explain why kittens a n d mon keys have been used i n experiments looking a t human brain development.

has schizophrenia there is o n l y a 1 5% chance that their twin will also have

m a l a ria, iii wrinkles in the skin?


Describe why it may be dangerous to leave a patch over the damaged eye of a c h i l d for a prolonged period of t i m e .

contribution of nature and n u rture on the development of schizophrenia?

Orange Book 8 . 6

Topic 8: Grey matter

- S>J

Learning is a process that results in a change in behaviour (or knowledge) as a result of experience. For learning to be effective you must remember what you have learnt. Memories (conscious and sub-conscious) are formed by changing or making new synapses in the nervous system .

Habituation is a very s mple type of learning that involves the loss of a response to a repeated stimulus which fails to provide any form of reinforcement (reward or punishment). It a llows animals to ignore unimportant stimuli so that they can concentrate on more rewa rding or threatening stim u l i .

The core practical i s an example o f a simple investigation into habituation. I t measures the time a snail spends withdrawn into its shell when you tap the surface it is moving on at regular time intervals or gently touch the snail's head. Initially the snail tends to retreat into its shell for a significant period of time after each tap. As the tapping ccmtinues the snail stays in its shell for a shorter duration as it becomes habituated to the tapping. Many invertebrates have been useful animal models for investigating the workings of the nervous system . For example sea slugs (Aplysia) have been used to investigate habituation.

Describing how to inv estig ate h a b ituation to a stimulus is a req u i red practical so you may

well be asked q u estions about

this during the exam. As this is a n exper i m e nt involving animals ( p o ss i b ly humans, depending on

A Gill withdraws when siphon stimulated.

your method) yo u should consider any ethical and safety issues that

may arise in your methodology. It is also worth considering how C How habituation is achieved.

to evaluate your results a s it is

1 With repeated stimulation. Ca2•

often difficult to control many variables when using live animals

channels become less responsive so

less Ca2• crosses the p resyna ptic membrane. (aZ•

in experiments.

2 Less neurotransmitter

is released.

wate r jet

g ill withdrawa l 3 There is less depolarisation of the postsynaptic membrane

B After several minutes of repeated

so no action potential is

stimulation of the siphon the

triggered i n the motor

gill no longer withdraws.


water jet

-abituation in a sea slug.


sensory neurone

motor neurone

from the siphon

to the gill


Write out the reflex arc involved in the sea slug's response to water being sprayed onto its siphon.


Suggest why sea slugs used in this habituation experiment need to have been reared in captivity rather than in the sea.


Suggest whether nature or nurt u re is likely to be responsible for the development of an innate reflex.

Green Book 83

Orange Book 8J

Oopa�1ine arr-1d Pc���drtilsonJs disease Parkinson's disease is associated with the death of a group of dopaminesecreting neurones i n the brain (an a rea of the midbrain known as the substantia nigra). This results in the reduction of dopamine levels in the bra i n . Dopamine is a neurotransmitter which is active in neurones in the frontal cortex, brain stem and spinal cord. It i s associated with the control of movement and emotional responses. The symptoms of Parkinson's a re: • muscle tremors (shakes) stiffness of m uscles and slowness of movement • • poor balance and walking problems • difficulties with speech and breathing • depression. A variety of treatments a re available for Parkinson's disease, most of which aim to increase the concentration of dopam1ne i n the b ram. Dopamine cannot move into the brain from the bloodstream, but the molecule which is used to make dopamine c a n . This molecule is called L-dopa (levodopa) a n d c a n b e turned into dopamine t o help control the symptoms. Some other treatments for Parkinson's are outlined later in this section

Seroton�ru and de�oression Serotonin is a neurotransmitter linked to feelings of reward and pleasure. A lack of serotonin is l inked to clinical depression (prolonged feelings of sadness, anxiety, hopelessness, loss of i nterest, restlessness, insomnia, etc.) Treatments for depression often involve drugs that can help i ncrease the concentration of serotonin in the synapses. For example, Prozac is a selective serotonin reuptake i n h ibitor (SSRI) that blocks the process which removes serotonin from the synapse. See below for discussion on how SSRis might work .

The effe(t of dir��- �$



Many d rugs affect the nervous system by interfering with the normal functioning of a synapse. The d1agram and following text show some of the ways synapses can be affected by drugs . 1 Some drugs affect the synthesis or storage of the neurotransmitter. For example L-dopa used in the treatment of Parkinson's dtsease is converted into dopamine, increasing the concentration of dopamine to reduce the symptoms of the disease. 2

·,:,�· s


postsynaptic m���





� �� .



� -- -



Different stages i n synaptic transmission that can be affected by drugs.

Green Book 8.4

Orange Book 8. 7

Some drugs may affect the release of the neurotransmitter from the presynaptic membrane.

3 Some drugs may affect the interaction between the neurotransmitter and the receptors on the postsynaptic membrane a) Some may be stimulatory by binding to the receptors and opening the sodium ion channels- for example dopamine agonists (which mimic dopamine because they have a similar shape and are used in the treatment of Parkinson's disease) bind to dopamine receptors and trigger action potentials. b) Some may be inhibitory, blocking the receptors on the postsynaptic membranes and preventing the neurotransmitters binding.












Topic 8: G'ey matter



So m e drugs prev ent the reuptake of the neurotransm itter back into th2 prr:- . c�·n a ptic m embr ane. Fo r examole ecstasy (MDMA) works by prevent i ng the r e uptake of serotonin. The effect is the maintenance of a high concentr atio n o f s en.Jcu nin i n the synapse w h ic h b rings about t h e mood changes in the users of the drug. O ne of the many poss ible s ide effects of ecstasy use is depress ion as a result of the loss of s erotonin from the neuro nes b ecause o f the lack o f r eu pta ke. Proz ac is a common example of a s elective seroto n i n reupt ake i n hib itor (SS RI) that b locks t h e reuptake of seroton in in the treatm ent of depression.

Look back at your notes on synapses and nerve impulses to help get your head around this section about how drugs can affec your nervous system.

Som e drugs may inhioit the enzy m es involved in break i ng down the neurotransmitter in the synaptic c l eft, resulting i n t h e maintenance of a high concentrat ion of the neurotr ansm itter in the synapse and therefo re repeated actio n potentials (or in hibition) o f t h e postsy naptic neuron e.

The development of new drugs A s w e have seen in this s ection, chemicals t hat affect m embrane-bo und proteins o r m i m ic t h e effect of naturally occurr i ng neurotrans m itters can have a s i g nificant effect on defective or normal neural pathways. T h e more we k now about the specific proteins ( and t heir shapes) active in cells the more li kely w e are to f i nd complementary chemicals that can have the desired effect. Tr aditionally most m edicines are developed from exist ing ch emicals (often extracted from p lants), but the i nform atio n com ing from the human genome project (see next page for further details) co uld help develop drugs that are highly specific so that t h ey can b e eff ective in lower doses w it h fewer side effects. P h a rmacogenomics links pharmaceutical expertise (drug dev elo pment and m a nufacture) with the knowledge o f t h e hum a n genome. New drugs have to go through a r igorous process of t esting, including an imal trials and clinical trials, lo ng before t h ey can reach t h e market.

lrruagn�1g technBques for t e btraira S everal imaging techniques are useful for m edical diagnosis and invest igati n g brain structure and fu nctio n . For exam p l e, the effects of drugs and diseases such as Park i nson's on the activity of the br a i n can now be seen using imaging techniques such as fMRI. Magnetic resonance imaging (MRI) scans use a m ag netic field and radio waves to m ake images of soft tissues like the br a i n . MRI scans can be used i n t h e di agnosis of tumou rs, strokes, brain injuries and infections. They can a lso be used to track degener ative diseases like A lzheimer's by co mparing scans over a period of t i m e . Functional magnetic resonance imaging (fMRI) i s a modified M RI techniq ue that can allow yo u to see the brain in actio n during live tasks , b ecause it detects activ ity in the brain by following ;:he uptake of oxygen in active br ain areas. Computerised axial tomography (CT or CAT) scans use tho usands of narrow beam X-rays rotated aro und the pat ient. Like M RI they o nly c a pture o n e mo m e nt in t i m e and s o o n ly look at struct ures and damage rather than functions. T h e resolution is worse than M RI so small structures i n the b rain can't b e distinguished; t h ey also use pot entia l ly harmful X- rays. Q1 Explain why treating mental health problems with drugs

is such Q1

Explain why people suffering from Parkinson's may suffer fro m depression.


Expl a i n how L-dopa m ay reduce the symptom s of P arkinso n's disease.


S u ggest how a new drug developed to be a s i m i lar shape to s e roto ni n may help treat clinical depression .

G reen Book 8.4

a difficult process

to get right. (Remember that neurotransmitters are effectivE in extremely low concentratior a n d are active in very specific synapses within the brain.)

Orange Book 8. 7

A genome is all of the DNA (or genes) of an organism. The Human Genome Project was a multinational project that determined the base sequence of the human genome. Many new genes have been identified, including some of those genes responsible for inherited diseases. In addition new drug targets (specific molecules that drugs interact with to have their effects, e.g. enzymes) have been identified Information about a patient's genome may help doctors to prescribe the correct drug at the correct dose. The Human Genome Project may also allow some diseases to be prevented. If you understand what genes you carry you may understand what disease you are likely to be at risk from. The Human Genome Project also helps to provide information about evolution and increases our knowledge of physiology and cell biology. t•


Who owns the information? Some groups have applied for patents on genetic sequences so that they have ownership, or have to be paid for any treatments developed using the knowledge of that sequence. Who is entitled to know the information about your genome if it is sequenced/ Should insurance companies have access to the information? Will genetic screening lead to eugenics (the genetic selection of humans) and designer babies? Who will pay for the development of the new therapies and drugs/ Many possible highly specialised treatments may be very expensive and will only be suitable for a few people.


r� .,. � �'"0•




pro�t u :e




.:- = ,.

GM plants may be useful for producing edible drugs such as vaccines that can be stored and transported easily in plant products such as bananas or potatoes. Useful genes can be transferred into crop plants using a vector such as Agrobacterium tumefaciens, gene guns (pellets coated with DNA) or a virus Restriction enzymes are used to cut DNA at specific sequences and DNA ligase is an enzyme that can be used to stick pieces of DNA together. These make it possible to insert specific DNA sequences into the GM organism. Large numbers of identical GM plants can easily be produced.

Transgenic animals (animals with a human gene added to them) can be used to produce useful drugs that can be harvested from their milk (or even semen) Liposomes and viruses are vectors used to insert genes into animal cells. Drugs produced from transgenic animals include the blood clotting factors used to treat haemophilia.

Micro-organisms such as bacteria are the most common target for genetic modification as they are relatively easy targets for gene transfer and can be grown rapidly in large quantities in fermenters. The drugs produced can be extracted and purified using downstream processing Insulin, to treat type II diabetes, is an example of a drug produced from genetically modified micro-organisms.

Green Book 8.4

Orange Book 8.7


Topic 8: G re y

m atter

Ti plasmid Stage 1

Stage 2

The Ti plasmid is

The gene to be carried to

extracted from

the plant is inserted in to

A. tum.,'aciens.

the Ti plasmid which is then returned to the bacterium. Ti plas mi d

bacterial chromosome

Stage 3

new gene


The plant is infected with

bacterial DNA fromTi

the modified bacterium and part of the Ti


plasmid with the

Stage 4

whole new plants can be grown from them, c ontainin g the new

genes. These are genetically

engineered or transgenic plants.

� newgene , I plant

from gall cells

tumour cells are taken and cultured,

becomes part of the plant

new gene grown

to develop on the plant. These plant cells contain the new gene. If

engineered gene


new plant contain ing

tumefaciens causes a tumour

crown gall (tumour) --­



by A. tumefaciens

The genetic modification of plants.

So .

.,oncerns over tlh!e


de\fe�o metr:lt ar�d t.ise of genet8caUy :"_ •

When pr epar ing for your A2

:at1�s�ms (GIVnOs)

Biology exams try to think why things are the way they are and

genetic po l l utio n (transfer of the genes to natural, wild s pec ies) t h ro ug h c ro ss­ po l li nation

look for links between different

areas of the course. This can after

antibiotic resistance genes are used to identify GM bacteria which co uld lead to antibiotic re sistance develo ping in other m icrobes

help you understand, remember and apply your knowledge even in areas of the course which may

GM crops could become super-weeds that out-compete ot her plants and may be resistant to herbicides. They could damage natural food c hains , resulting i n damage

appear tough.

to the environment because they wo uld e ncourage f armers to use more selective herbicides to kill everything but the cro p.

GM c ro ps may not produce fertile seeds. This preve nts f a rmers collecting seed and replanti ng, so they need to return to the biotech nology com pany to buy new seeds fo r each plant ing. This could make them too expensive for some fa rmers .

--·� l�:llili£

Q1 Outline some of the benefits an disadvantages of settin g up


Descri be what is meant by the term ' genetic po l l utio n of the environment'.


Describe t h e benefits of using bacteria to produce a human protein (like i nsul i n) to treat a disease.

Green Book 8.4


nationa l screening programme for a newly identified gene responsible for an inherited genetic disease.

Orange Book 8. 7

By the end of this topic

�� 'tt{�Jl -



r-.'!"::o: �-� ��


be able .



Respo nding to

"": ·'Explain how the nervous system allows us to r espond to

th e e nviro nme nt

the world around us, usi ng the pupil reflex as an example. Describe how pla nts detect light and res pon d. Compare plant hormones, animal hormonEs and the nervous system all as methods of coordination.

The nervous

Describe the structure and function of sensJry, relay a nd

system and

motor neurones including the role of Schwann cells and

nerve impulses

myelin atio n.

Describe how a nerve impulse passes al ong an axon. Describe what synapses do and how they work, including the role of acetylcholine.


Describe how the rod cells in the retina work to create

action potentials i n the opti c nerves .

Structure of the

Recall where the different regions of th e h u man br ain are

human brain

and what each one does. This should include the cerebral hemispheres, hypothalamus, c erebell um a nd medulla

B ra in de velopm ent

o b l ongat a .

Discuss the concept of a 'critical window' in the development of vision. Describe Hubel and Wiesel's work with monkeys and

kittens and how it ex plored the development of the brain. Consider the different methods used to study the devel opmen t of the brain. Discuss two ethical standpoints on the moral and ethical issues rel ati ng to the use of animals in medical research. Learning and

Describe how animals, including humans, can learn by

habituatio n

habituation. Describe how to in vest iga te h abit ua tion.

Effects of

Explain how chemical levels in the brain m ay ch ange ,

drugs on

resulting in illnesses such as Parkinson's and depress1on

neu rotransm itter


and how this area is a source of research for new drugs. Explain the ways that drugs a ffec t synapses in the brain, inc ludi ng ecstasy and those used to treat Parkinson's.

Describe how differen t imaging techniques are used to study the brain, including magnetic resonance ima gin g

(MRI), func tion al magnetic resonance imaging (fMRI) and computed to mo gr aphy

Uses of genetic modifica tio n



Discuss how the Human Genome ProJect is helping to

·=· L07 L02 L08 L03 L04 LOS L06 L09


Describe how drugs can be produced using genet1cally mi croor ganisms) .

Discuss the risks a nd benefits of genetically modified

or ganis ms .


L019 L020 L021


ur�;;w: ·�, x:.'•ti �tt�� D D



LOll I LO12 L013 L016 L014 L015 L017 L018 ll010

develop new drugs and some of the issues that arise.

modified organisms (plants and animals a n:i


































Topic 8: Grey matter

F �Jple with Parkinson's disease have poor control over their skeletal muscles. caused by a lack of the neurotransmitter dopamine. L2rge numbers of neurones secreting dopamine are found in the basal ganglia region of the brain.


Parkinson's disease can be diagnosed and monitored using brain scans. The fMFI scans on the

off drug

right show the results of a study

on drug

where subjects did a standard fingertapping activity to investigate the effectiveness of a new drug treatment The results above right are from a healthy brain, a patient with Parkinson's disease without drug treatment and a patient with Parkinson's diseose taking drug t1eatment The scan shows a horizontal section with the front of the head at the top. The most active areas are white.



Using the fMRI scans above. discuss the effects of this new drug on brain activity.

When provided with plenty of information to read and diagrams to look at, make sure you study it thoroughly to help you understand the context of the question and what the examiner is actually asking you about For example. this question is comparing activity in different regions of the brain and not the size of the different areas.




�-- ' _-.·



_:·· studeitanswer i ·2�, -







.. :..--':

.·:· .,· . __:-:.� -







There is more activity in the basal ganglia and less activity in


Make sure you make a comparative statement. The student here

the motor cortex for the person treated with the drug than the

includes 'more' and 'less' to make the comparison clear. It is also

person with Parkinson's without the drug. The drug may work by

made clear what is being measured by the fMRI- the activity of the

stimulating the release of more dopamine from the basal ganglia.

brain. Many candidates lost marks for this cuestion by referring to an increase or decrease in the area rather than the activity of the area. This response gains full marks by going on to provide a possible explanation for the differences.



Explain how neurotransmitters. such as dopamine, st1mulate neurones.

Don't get thrown by the context of the example. You may not know much about exactly how dopamine works, but you should be able to recall

what happens at synapses and how a neurotransmitter can stimulate an action potential in the next neurone .

. Student �nswe_r





_-- _

-: .' :






. Examiner com

m�nts .. ; "'.

-: ' '.' · . - -"


· .

This response describes what dopamine do:Js. but doesn't explain

Dopamine can bind to receptors on the postsynaptic membrane.

how it stimulates neurones. Dopamine can be released from vesicles in the presynaptic

This response provides lots of specific detail about how a

membrane in response to calcium ions moving in through the

neurotransmitter stimulates a new action potential in response to the

membrane when an action potential arrives.

arrival of an action potential at the synapse.

The dopamine can diffuse across the synapse and bind to receptors and open sodium ion channels. Sodium ions can enter the postsynaptic membrane and cause the membrane to depolarise. resulting in an action potential in the postsynaptic neurone. (Edexcel GCE Biology (Sa/ters-Nuffield) Advanced Unit 5 June 2008.)



1 (a) (i)

Describe how the nervous system controls the pupil reflex in a mamma l i n response to l:: right light. (4) (ii) Describe and explain how myelination of ne urones is a n advantage in t his reflex pathway. (3)

(b) Hubel and Weisel covered one eye of kittens of different ages to investigate the timing of vis ua l develo pment in mammals. Kittens which had one eye cove red from the fo urt h to the fifth week subsequently ha d ve ry poor visio n in t hat eye. Kittens which ha d one eye covered at ea rlier or later times had normal visio n. Suggest a n expla nation for (3) t hese obse rvations. (c) Some p eople have ethical objections to animal experiments. S uggest how a biologist might j ustify the use of animals in experiments. (2) Total 12 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 58 June 2007}

.I I!


Detection o f light occLrs i n both mammals and flowering plants . (a) In humans, the c entral region of the retina has very few rod cells. Howeve r, in a dog about 80-90% o f the photo receptors in the central region o f the retina are rod cells. S uggest one a dvantage to a dog of having more ro d ce l ls in t his regio n of the retina. (3)


(b) Describe the detection of light in flowering p la nts.


Total 6 marks (Edexcel GCE Biology Adva n ced Unit 4 June 2008 Q3) 3

The diagram below shows a vertical section t h ro u gh a human brain. Using the letters A, B, C, D or

i I


state which region o f the brain:



, II


(a) coordinates movement


(b) controls heart rate


(c) receives sensory input fro m the eyes.


Total 3 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 58 June 2005)


Topic 8: Grey matter


Twin stuc;es c:=;r be used to investigate t he role o f genes in behavio ur . The frequency o; schizophrenia in identica l (monozygotic) twins was investigated. Conditions �:.;ch as schizophrenia are thought to b e polygenic. (a) Define the term polygenic.

( 1)

(b) If one monozygotic twin has schizophrenia then the probabiliTy of the second twin having the condition is 46%.

Predict what you would expect the percentage probability to be if schizophrenia was entirely caused by genes.


(c) The probability of two unrelated people both having schizophrenia is 0.5%. Explain what the results o f t his study show about the roles of genes and the environment in schizophrenia. (2) Total 4 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 58 June 2006) 5

The Human Genome P roject ha s discovered the location of 30 000 genes. Only a small number of human genes have a known function, so the next step is to fi nd out what the rest of the genes do. (a) Explain what is meant by the word 'genome' .


(b) Some scientists want to use knowledge gained from the Human Genome Project to screen peop l e to find out if they have a genetic predisposition to certain diseases, such as heart disea se or lung cancer. They think that screening can help people to lead a heal thie r life.

Other scientists t hink that genetic screening should not be carried out because it w i l l create extra problems for society. (i)

Suggest how knowing that you were more likely than other people to develop heart disease or lung ca ncer could help you to lead a longer, healthier life

(ii) Suggest how compulsory genetic screening of everyone might be o f benefit to society.



(iii) Suggest why people might vote against compulsory g ene ti c screening in a referend um. (3) Total 8 marks (Edexcel GCE Biology (Salters-Nuffield) A dvanc ed Unit 1 June 2004)



Muscle paralysis is common in many cases of poisoning, often as a result of interference with chemical transmission from the motor neurones to the muscles at the neuromuscular junctions. Studies of venomous snakes, such as the Prugasti krait (Bungarus fasciatus) have played a part in the investigation of this chemical transmission.


(a) Describe the normal sequence of events that occurs within a muscle fibre after stimulation of a neuromuscular junction. (5) (b) Bungaratoxin can be isolated from the venom of the Prugasti krait In minute amounts, it can cause paralysis of the diaph ragm and intercostal muscles by its effects at synapses . Suggest how bungaratoxin causes these effects. (3) Total 8 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 58 June 2007) 2


Isolated mitochondria in a solution containing inorganic p hosphate and an electron donor can be used to study respiration. An electrode is used to record changes in oxygen concentration while mitochond ria respire. The graph shows changes in oxygen concentration for some isolated mitochondria.

ot) c ·c :J




�� �:0 § ro

u� I

6 .· �·� c

;.,_.=! X 0 0 V\

� ---------------------

(a) (i)


Describe and explain the trends shown on the graph above.


(ii) Name an electron donor used in the electron transport chain in mitochondria .

( 1)

(iii) State the location of the electron transport chain in mitochondria.

( 1)

(iv) Describe how ATP is synthesised in the electron transport chain.


(b) ATP is used to provide an immediate supply of energy for biological processes. Describe the role of ATP in the following processes . (i)


nerve impulse transmission

(ii) hyperpolarisation of rod cells i n the retina.

(2) marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 58 June 2008)



(a) Explain what is meant by the Human Genome ProJect.



(b) The Human Genome Project is making it possible to identify people who may be at risk of developing medical conditions such as heart disease, cancer and diabetes (i)

Suggest two reasons why identifying people at risk might be of benefit to (2) the people who are tested

(ii) Suggest three disadvantages or ethical objections posed by the Human Genome Project. (3) Total 7 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 2 June 2005)




(a) At high environmental temperatures, the rate of sweating i n humans i n crease;;. Explain how sweating is i nvolved in the regulation of body temperature. (2)

(b) In a n i nvestigation, a healthy vo lunteer meas ured his body temperature. After 5 minutes, he got i nto a bath of water at a temperature o f 18 oc. He stayed in the bath for 10 minutes, then got out and sat o n a c hair. D uring the investigation. he recorded his body temperatu re at regular time i ntervals. The results of this investigation are shown in the table below.





Started investigation


Got into bath


10 15

Lying in bath


Got out of bath



Sitting on a chair



25 (i)



Sitting on a chair

Describe the c ha nges i n body temperature that o c c urred during this investigation.


(ii) S uggest expla nations for the changes in body te mperature that occurred between the fo llowing time intervals: 5 to 10 minutes 1 5 to 25 minutes (3) Total 8 marks (Edexcel GCE Biology Advanced -paper 6 7 7 2101 June 2008) 5

An investigation was car ried out into the effect of cycling s peed on the breathing rate of a healthy student In this investigation, a n exercise bicycle was used.

The breat hing ra:e of the student was meas ured at rest. He then cycled at 10 km per hour fo r 2 minutes and, i mmediately after, his breathing rate was recorded . He rested for 5 minutes, before cycling at 15 k m per ho ur for 2 minutes, afte r which his breathing rate was again measured. T his i nvestigation was repeated at cycling s peeds o f 20 a nd 25 km per hour. T he student rested for 5 minutes betwee n each period of cycling. T he results are s hown in the table below.

0 (rest)










(a) Ca lculate the percentage increase in breathing rate, as the cycling s peed i ncreased from 10 km per hour to 25 km per hour. Show yo u r working.

(b) Suggest a n explanation for these results .


(2) Total 4 marks

(Edexcel GCE Biology Advanced -paper 6112/01 June 2008)


(a) The diagram shows some of the stages of anaerobic respiration in a muscle cel l . Glucose


Stage 1

phosphorylated GC sugar



Stage 2


phosphorylated 3C sugars


Stage 3


Substance A


Stage 4


Lactic Acid




( 1)

Name substance A.

(ii) State which of the stages shown in the diagram

1. uses ATP

2. produces ATP.




(b) The Krebs cycle occurs during aerobic respiration and is an example of a metabolic pathway. (i)



Explain why the Krebs cycle is described as a metabolic pathway.

( 1)

(ii) State precisely where in the cell the Krebs cycle occurs. acetyl coenzyme A


1 x





4C acid





4C acid


� �co ·


1 x


4C acid

� 1 x





SC acid

4C acid


1 x





(c) The diagram shows some of the stages that occur in the Krebs cycle. Oxidoreductase enzymes are involved in some of the reactions in the Krebs cycle. Usin' 1. evaporation of water(in sweat); 2. (evaporation) has a cooling effect I eq; 3. appropriate {reference to I description of} latent heat; (2) (b) (i) 1. temperature dropped {from 0 to 15 minutes I when in the bath}; 2. increased {from 15 to 25 minutes I when sitting on the chair}; 3. lowest {at 15 minutes I when 'he got out of bath'}; 4. credit a m2nipulated change in temperature; (3) (b) (ii) 5 to 10 minutes: 1. temperature of water lower than body temperature i eq; 2. heat lost by onduction (to water); 15 to 25 minutes: 3. increased me:abolism I shivering I eq; 4. generates heat I eq; (3) Total 8 marks 5


practice t"nodel answers a Temperature receptors in the skin and hypothalamus detect the rise in temperature (1) and cause an increase in the volume of sweat produced (1) The sweat evaporates from the surface of the skin taking heat energy away from the body (1 ). This cooling can contin ue as long as the person is able to replace the water and salt lost due to the increased sweating (1) (Max. 4 marks) .

b Inuit with short stocky bodies are at a selective advantage (1) because they have a lower surface area to volume ratio (1) and will therefore lose less heat to their surroundings. (Max. 2 marks)

(a) 1. 1.

c Sufferers of cystic fibrosis have a CFTR protein channel does not work (1) As a result less water moves from cells into sweat glands (1) so the sweat ends up with a higher concentration of salt than normal that can be detected in the sweat test (1) (Max. 2 marks)


d Marathon runners will generate a lot of heat during the race because of the high rate of respiration ( 1) However, at the end of the race there will be less air flow over the body( 1) so less 5weat may evaporate (1). This may cause the core te11perature to rise (1) resulting in a heat stroke. (Max. 3 marks)



Unit 5: Comprehension

calculation; 2. answer(= 92.9%); (2) (as cycling speed increases) more carbon dioxideproduced; 2. {carbon dioxide I low pH} stimulates breathing I eq; 3. increased need for oxygen I eq; (2) Total 4 marks

(i) pyruvate/pyruvic acid; 1. (stage) 1; 2 2. (stage) 3; (b) (i) a {series/seqLence/eq} of(chemical) reactions/ each step is controlled by an enzyme/product of one reaction is the substrate for the next/eq; (ii) matrix of a mitochondrion; (c) (stages) B, C, D(and) F; Total 6 marks


(a) (i) values between 0.4 to 0.55 x 12; =values 2 between 4.8 and 6.6 dm3 min -1; (ii) values between 1.1 and 1.3 x 36 =values between 3 9.6 and 46.8dm3 min-1; increased by about 6 times/increase of between 33.0 and 42.0; 2 (b) (i) heart rate x stroke volume or volume of blood pumped out of the heart in 1 minute. 1 (ii) As the minute volume increases the tidal volume(volume of oxygen breathed in) increases; increased diffusion of oxygen into blood(or muscle); increase in cardiac output increases volume of oxygenated blood reaching muscles; 2 Total 7 marks


Porcine stress syndrome was noticeably similar to malignant hyperthermia (1). They were therefore able to identify the human gene for malignant hyperthermia through compar son to the identified gene for porcine stress syndrome (2). (Max. 2 marks)


Aspirin blocks the synthesis of prostaglandins (1) and

therefore reduces fever in the body (1). This could be a problem because a rise in body temperature may help to kill bacteria (1) and increase the activity of macrophages (1) in the non-sr.:ecific immune system, reducing the effectiveness of the body's response to the infection. (Max. 3 marks)

g Ca2+ ions are released into the sarcoplasm (1) from the sarcoplamic reticulum (1) i1 response to a nerve impulse arriving at the neuromuscular junction (1). Ca2+ ions attach to troponin (1) causing tropomyosin to move, exposing myosin binding sites on the actin filaments (1). This allows myosin to join to actin (1) starting the contraction of the muscle. (Max. 4 marks.)

13,15,22,85,90 54,67 12-15,22-4,88,90 abundance 10 adenosine t riphosp hate (ATP) 93 adrenaline 45-9,56,58,80 aerobic respiration 32,35 AIDS 16-17, 22-3,25,91 allele 16,22 allele frequency 10-11, 17,22,30-1,92 amino acids 46-7,56,80 anaerobic respiration 44-5 antagonistic pairs antibiotics 23,34-6,38,42,73,92 32-4,36 antibodies 33-4 antigen a n tigen presenting cell 33 8,18- 19,22,26,91 atmosphere atrazine 24 atria 50 axon 62-5, 74



absolutist view


23,26,32-9,42,72-3,84,92 34,36,38 34,36,38 19,22,91 12-13,26 13,15,22,90 32,37,50-2,54-5,57,61,66,72 44,53 66,70

bacteria bactericidal

bacteriostatic biofuels biomass biotics blood bones brain stem

Calvin cycle cancer

capillaries capsid carbohydrates carbon

carbon cycle carbon dioxide


18,54,56,68,84,88 5 1,65-7,70,75 11,30,42,44,46,48,62,93

17 9,14-15,17-19,21-2,28,39,41-3,47,56,76, 84-9,91 21,54 debate decay 26-7 12,26-7,36 decomposition deforestation 91 31,36 degenerate code dendrites 62 dendrochronology 18,22,41 94 depolarisation 70-1, 74 depression 54,72,78 diabetes diastole 50-1 49,62,94 diffusion 32-7,50,54-5,68,70-3,75,77-8,92 disease distribution 12- 15,20,22-3,40-1,43,62,84,87,90 DNA 11,16-17,28-32,36,55-6,72-3,92 70,75 dopamine drugs 55,67-8,70-2,74,92 Darwin, Charles


12.22 28,78 9-11, 22,24, 40-1, 45-6, 48-9,56-7,59,78,


electrode electron

90,93 36 27 12-13,16,52,60,67-8,73-4,77 environment enzyme 10,20-1,23,26-8,32-5,38-9,47-8,56,64, 71-2,80 11 eukaryotic cells 17-19,22,36,41,54,85,86 evidence 15- 17,22,36,72,91 evolution 45,50-6,58-9,79,81,86 exercise 9,21,69,85-6,89 experiment

electrophoresis entomology

10- 11 32-3,54,68,77-8 32,45,57 42 8-10,24,47 11,19,26,90 18-19,22,26-7,91 8-11,18-19,21-2,26,40,46-9,56,

8 1,90-1 cardiac cycle cardio\·ascular disease cellulose cerebellum cerebral hemispheres cerebrum chcm iosm o sis

chemoreceptors chlorophyll chloroplast chromatography circulation climax community coenzyme concl usio ns condensation conferences consumers


50-1,58-9 50-1 11-12 66,74,94 66 66 48-9, 56 51,59 8-9,22,24,100 9, 11,22.24 28 57

13,22 48-9,81 17,21,87,89 46 17,22 12-13,90 24-5

fats ferm enters fibres flexors forensics fossil fuels

12 72 44-5,56-7 44 27,30-1,34-6,39 19,91

16 34 16 gene mutations genetics 17,23,25,3 1-2,36,68,72-4,77,82,94 34 genital tract genomics 17 18-22,91 global warming 8,10- 13,46-7,49,56 glucose 45, 47,93 glycogen 45-9,56,59,80,93 glycolysis 32 glycoproteins 11 granum gametes

gastrointestinal tract



greenhouse effect


greenhouse gas gross primary productivity growth rates

motor neurones


MRI scans







27,44-5,47,51, 54,56-61,66,70,75,78-9





17,35, 91-2



myelin sheath







SO, 56


42,54,58,71 50-2,54-6,58,66,77-8



hepatitis C


45 44-5,58-9




natural selection

histogram 87 32,35-9,42





nerve impulse



nervous system


hybrid sterility



















nucleic acids

27,30-9,42,54,59, 71,82




62 10-11,22,42,92 30-1,55,62 68 15, 26





invertebrates investigation



obesity optic nerve









11, 62 10,14-17,20,22-3,26-8,32,34-6,46-7,


osteoporosis joints journals Krebs cycle

44,51,53-4,59 17,84 47-9,56,59,80,93



lactic acid






light-dependent reactions


light-independent reactions

8-11. 22,47

limpets lipids

14,23 10-11,22









lysozyme macrophages magnetic resonance medulla mesosomes





12,22,25 44-5,78

neuromuscular junction

nodes of Ranvier







net primary productiYity

immune system




32,34,36 32-3,35-6 71,74 51-2,58,66,74 32,42


oxidation oxygen

9,48-9 8-9,15,22,46-9,55-7,71,78-9,81,90



Parkinson's disease

70-1, 74-5 34-6, 54,92



peer review



32, 36

phagocytosis phenology







8, 11



photophosphorylation photoreceptor photosynthesis phototropism

9,22 60-1,64,76

8-13,19,21-2,24,26,40,47,90-1 60-1.93

pioneer species




politics pollen

21 18,22,40-1,84,91














microorganisms mitochondria

45,48-9,57, 59,78,93

potassium predators

10,22 16,23,25,27,38,43 15,26,47,62-4,94 57,90-1







proteins 11-12,17,28,30-3,35-6,38-9,44-5,55,62, 71,73, 92, 94







\'agus nerYe variation ·





14-15, 23, 43, 91

vir us es

\·ision receptors






relativist vievv

Wilberforce, William woodland

45 32,42 51 16-17 57 51-2,56,59 50-1 32-3,36,39,42, 72 94 17 13,15,90



16,35, 92


17,20-1,67-8,74,82, 84,89

respiration 8,10-13,22,25-7,45-9,52,56-8,78,80, 90,92







rigor mortis


risk assessment


saltatory conduction






sarcoplasmic reticulum schizophrenia

44-5 68,77,94

Schwann cells

62. 74




17,21,26,29, 77,89

sensory neurones






skeletal muscle solar energy


speciation species


16-17,22,9' 13-17,20.23,27,35,39-41,43,73,86,91


51,56,81 11-12

starch stimuli














technology temperature

29, 53,56 15, 18.20-2,27, 29,36-7,39,47,51-3,


tendons testosterone thermoreceptors thylakoid membranes


11 15





55 52,57

topography transcription

I l


translation trees tropomyosin





30 13,17-18,29,40-1,91 45



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