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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
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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
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Revision techniques
4
How to use this Revision Guide
5
Biology
6
Question types in GCE
Unit 4: The Natural Environment and Species Survival Topic 5: On the wild side
Photosynthesis
1
10
Energy transfer, abundance and distribution
12
Investigating numbers and distribution
14
l I
l
l l
so
Homeostasis
52
Health, exercise and sport
54
Topic 7 checklist
56
ResultsPlus: Build Better Answers
57
Practice questions
58 60
Topic 8: Grey matter
Responding to the environment
60
Neurones and nerve impulses
62
Vision
65
The structure of the human brain
66
Speciation and evolution
16
Brain development
67
Greenhouse gases and the carbon cycle
18
Learning and habituation
69
Impacts of global warming
20
Effects of imbalances in brain chemicals
70
Topic 5 checklist
22
Uses of genetic modification
72
ResultsPlus: Build Better Answers
23
Topic 8 checklist
74
Practice questions
24
ResultsPlus: Build Better Answers
75
26
Practice questions
76
Decay and decomposition
26
Unit 5 specimen paper
78
DNA profi ling
28
Unit 5 comprehension practice
82
DNA and protein synthesis
30
Infectious diseases and the immune response
32
Getting started with your investigation
84
Infection, prevention and control
34
Planning
85
Topic 6 checklist
36
Planning- trial investigations
86
ResultsPlus: Build Better Answers
37
Observing and recording
87
Practice questions
38
Dealing with data
88
Unit 4 specimen paper
40
Interpreting and evaluating
Unit 6:
Practical Biology and
Investigative Sk ills 84
89
Unit 5: Exercise and Coordination
Answers to in-text questions
90
Topic 7: Run for your life
44
Answers to practice questions
95
44
Answers to specimen paper questions
99
Energy and the role o= ATP in respiration
46
Index
Krebs cycle and the electron transport chain
48
Muscles and movement
L
8
Photosynthesis 2
Topic 6: Infection, immunity and forensics
l
8
The heart. energy and exercise
102
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.
Active
I
�
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.
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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.
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The final unit consists of advice and support on research skills, giving guidance on
I
specimen papers, can be found at the back of the book.
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... _
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
(1)
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:
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Control
-Are you investigating simply with I without a particular factor?
Organism
-Are you using organisms of the same sex I age 1 size I species?
Repeat
-Take readings more than once and average
What range of values are you looking atl
Measure
-What are you measuring? How will you measure this? What units? -Which variable(s) are you keeping constant?
Same
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.
(3)
soo �
400
� § :.0 -� � g_ 300 Cl! 0 .Co_
Key
D D
(5o Cl!
g zoo
�� Cl!
female male
� Cl!
"0 ·u a.. c
100
18-44
4S-64
6S-74
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,
t.-
ZH20 from the soil
1\
4H
;
02
co, f
4000
:e "'
'OJ 3000 N
·v; c 0
";il
:;
0.. 0 0..
2000
----·- --- "-- �-
Antibiotic B
1000
0
15
10
5
antibiotic added Time/hours
{a)
Use examples from the graph to explain the differences between bactericidal and bacteriostatic antibiot i cs (3) .
{b)
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.
{a)
Explain why HCV infection is common in HIV posit ive people.
(2)
(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
I
�--\ �
inactive
--•, �
()
-----+
PKR
active PKR
I
1
l
�
•
interferon
ce!l surface protein
protein synthesis prevented
L
__
_ _
(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
J
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.
Total
(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.
(4)
(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-
...
··,.i.
-
-
·�
�
inflammation engulf and digest bacteria lysosyme action
-prevents viruses from multiplying
(4)
Total
8
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.
(2)
(b) Suggest one reason why collecting data about several species of insect would make the estimate of time of death more reliable.
(1)
(c) Suggest a reason why the scientist could not be more precise as to the time of death. (2)
Total
5
marks 2006)
(Biology (Salters-Nuffield) Advanced, June
...
Unit 4: The Natural Environment and Species Survival
1
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
I
fluorescence
light
(a)
......... ......�
...
�DO :
I I AI I I I ....
...
...
�(
'4
red u ced Y
�
--
X
00'----,./
Name the molecules
X
and
Y
(2)
shown on the diagram.
(b) Explain the importance of reduced
Y
in the process of photosynthesis.
(3)
(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.
0
Time since light switched on/seconds
2
(i)
Suggest an explanation for the increase in fluorescence.
(2)
(ii)
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]�_,;] � �
nmrm
0.5
2850
0
1.0
3770
1.5 2.0
I
, ·�
I I
0
53
0
0
55
5600
0
0
31
47
6390
0
12
15
53
4
48
6
35
3
32
2
4rl
2.5
8170
5
36
3.0
8700
38
36
3.5
8780
27
40
10
22
10000
4.0
��
I II '
I
I
43 40
I
i
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
zone
Arctic
Boreal
Temperate
n
larch
n
spruce
/\ pine
beech
-
Sub-tropical
(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)
(2)
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).
(2)
(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.
(2)
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 '
i
�I
r--1
�-j
capsid
n
LJ -----.
nucleic acid
'I
_I
_j
cytoplasm
I
ribosome
=:J
D []
(5)
(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 -
L
I
1994 2004 (i)
148 281
98 59
629 535
Describe the trends shown by the data.
(2)
(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. -
Total
(2)
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
5
marks
(A2 6734 Biology Salters-Nuffield January 2009)
5
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.
F··
I
�
��·-;-
0
80
170
250
500
1
1
5
11
0.4
0.3
0.3
0.9
Bare sa n d
80
30
30
8
Sea couch
20 70
50
20
5
5
5
40
55
40
Distance from
650
980
1600
1980
18
7
5
6
7
2.8
6.4
25.1
23.4
32.8
top of beach/ metres Number of species found Mass of organic material/grams
!
t
}_ij� ��
I
-
Marram grass Red Fescue Sea buckthorn
80
Common heather
90
Corsica pine
100
(a) Explain why it is necessary to use a quadrat to estimate percentage cover.
(2)
(b) Explain why a transect is more appropriate than random sampl.ng in this study.
(2)
(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) .
Total
12 marks
(A2 6134 Biology Salters-Nuffield Jan 2008)
I
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
------1-i-4+1
ligament •
joins bone to bone
•
strong and flexible
absorbs synovial
fluid
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
A
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
myosin
actrn
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
tropomyosin
"'-
_'),.
...., • .
I V
Ca2' attaches to
(
.r •
•
Myosin binding sites
'- - ,, . �
__/"C,
blocked by
p
========:;=====:!
actin) causing it
_____
to move together
with the threads of tropomyosin.
��:�;; ' �;
··�;:
Myosin binding
.
'" •
.
i
tropomyosin. Myosin head
cannot bind
. .....
fJ �
- AtdP
A'ffiP
��---c-L
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 ?
�
ADP+P
£
)
p "'""'
�
The myosin heads release the ADP shape as a result
m
•
, •,
•
actin
troponin (on the
tropon
•
{c.;.
�
ATP binds
to the myosin
head causing it to detach
from the actin.
;:
The slidmg filament theory of muscle contraction
·
as
cs
o
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
I
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
Q1
Give one reason why fast-twitch muscles are more likely to get t i red faster than slow-twitch muscles.
Q2
D escribe the role of ATP in m uscle contraction.
Q3
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.
6C02
�
+ 6H20 + -30 ATP
Anaerobic respiration glucose� lactic acid+energy
C6 H1206 � 2C3 H603
+
2 ATP
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
ATP
is an example of a condensation reaction, the reverse of which i s hydrolysis:
ATP
t
H20-:=: ADP
t
P i + e nergy
cell.
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)
(6C)
hexose phosphate
Glycolysis means sugar splitting. Glyco =sugar, lysis= splitting. Hydrolysis means splitting using
(6C)
hexose bisphosphate
water. Hydro=water.
!
2 molecules of triose
glycolysis
(6C)
phosphate (3C)
1-----� 2ATP
1-----
2H c2NAD 2
reduced
intermediates
1
2 mo le cules of pyruvate
>
2ATP
(3C)
NAD
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
glucose
n
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.
NAD
y
2ATP
2H
pyrJvate
_,_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
l.r
g l ucose molecule respired.
l
IS
(6C021 as per
absorbed by the org a n i sm (602)
II'1
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
fluid
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-·
Q1
Suggest four examp l es of biological processes that require the use of ATP.
Q2
Compare the role of ATP with glycogen.
Q3
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
7.1
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
o
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
��w�;�
C;·C_ �
reacdon)
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
FAD
"""
1
�'-
�/ _,.. --,
NA:rp
•
co, {
controlled and catalysed by a specific intra c e l l u l a r enzyme.
I
� � ./
�'-� - CO
,
�/
reduced NAO
produce ATP.
l
Krebs cycle
·:,_�j
respiratory chain to
compound
compound
com��und
,.,./\� ,_ \,
"'-...
2
NAO
reduced NAD
The reactions involved in the breakdown of pyruvate in aerobic respiration.
�� ��
Green Book 7.1
Orange Book 7 2
reduced
hydrogen through the
6C
4C
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
intermembrane
the electrochemical gradient
space
5 W diffusion allows AT Pa se to
inner mitochondrial
catalyse ATP synthesis.
membrane ATPase on
mitochondrial
stalked particle
matrix
6 Electrons and W ions recombine to form hydrogen atoms wh ich then combine
2W
ATP
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. ,
__ _ _____ _ ....__
Q1
Describe what happens to the carbon and hydrogen atoms trom a glucose molecule in aerobic respiration.
Q2
Explain what oxidative phosphorylation means.
Q3
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
ae·c:
Unit 5: Exercise and Coordination
1 Elect r ical impulses from the
3
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 .
4
2 Impulses pass to the
ventricles via the AVN after
a short delay to allow time for the atria to finish
contracting.
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-
�____,_ ! ---_ --l 1 s I P wave
•
1 0� �·
5� segment
�e�a��--��--�--+--+ �
r
I
•
•
, 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
x
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.
Q1
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
Q2
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
Q3
Outl ine the role of transcription factors in the control of gene expression.
athletes?
Green Book 7.4
have a level playing field for
Orange Book 7 5, 7.6
Unit 5 : Exercise and Coordination
By
the e n d
of
this
topic you should be able to:
___.___..
-�-
--
Muscles a n d
Describe t h e structure o f a muscle fibre a n d explain
movement
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.
L02
L03 L04 LOS
Describe a practical to investigate rate of respiration.
L06
Recall what ATP is a n d how it supplies energy for cells.
L07
Describe the roles of glycolysis in both aerobic and
LOS
anaerobic respiration. You do not need to know a l l
�
h
�
D
" "
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
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
L014
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.
(a)
(i)
Outline the differences between fast- and slow-twitch mLscle fibres.
(ii)
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.
(2)
(1)
(2)
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.
(b)
During fast movement, lactate builds up in the muscles of a predator. such as a cheetah. Explain what happens to this
(3)
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
a
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.
(c)
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.
(3)
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.)
1
(a) Name the region of the hum an brain involved in control of heart rate.
(1)
(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
-
glycolysis
matrix of mitochondrion
Krebs cycl e electron transport chain
I
II
I ATP and water
-
(4)
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
X
�__,_,...,.___7 pathways for the conduction of �------
electrical impulses
(a) Name the structure labelled
X.
(1)
(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
radial
muscles relax
radial
circular
m usc les
muscles contract
contract
circular muscles
relax
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
Light
//.�l"."t
¥"
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 '
·."( .
Light
Light
Zone of
from one side, auxins
move down from the shoot tip towards the
elongation
Take care not to mu d d l e tropic and trophic. Tropic responses
shaded side of the
i
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.
�
I
-
Electrochemical changes
giving an electrical i mpulse. Chemical neurotransm itters used at most synapses.
I
I
-
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 .
I
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.
cells.
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
I J
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
All
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 � ""-
,1;
Schwann cell
'\,_�"'
axon
dendrites
)
=( ====)�:;, ;:f�). ; E
"'i u �
c
£
-o
,_c
2:: .,§: c
-70
I
resting potential + + + + + + + +
=ao=u=t t:: - - - - - - - -
outside
3 The membrane is hyperpolarised. Voltage-dependent K• channels
inside
close, K• diffuse back into the axon to recreate the resting potentiaL
Key
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
Time
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
Na·
++++++++++ high K'
axon
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
++
stimulation
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
3
r= ---
action
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
ion
channels open. Potassium ions leave the axon, repolarising the membrane. The membrane becomes hyperpolarised.
K'
third action potential
4
4� -:�t� K'
refractory period
Na'
+
+
+
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
.,.i.
Unit 5 : Exer ci s e a n d Coordination
5
Synapses
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
axon
potential arrives.
If two or more excitatory 1
synaptic
2 The membrane depolarises.
vesicle
Calcium ion channels open.
i m pu lses arrive at a synapse
Calcium ions enter the
at the same time their effect
neurone.
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
3
�J,. "QJ
04
t o :: 0
II
7
.
.
fl 0
mem orane
cleft
�
6
5
�
pres napt1c
synaptic
N� + CPS� Q
·
will have the same effect
�
� ® W � IL�
3 Calcium ions cause synaptic vesicles containing
the postsynaptic membrane
neurotransmitter
\j
.
postsynaptic mem brane
5 Neurotransmitter binds with receptors on the
6 The membrane depolarises and
postsynaptic membrane. Cation channels open.
initiates an action potentiaL
I
I
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
��l§!�i��----
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.
B--�
Green Book 8 . 2
down ) , or it can diffuse away and be broken down.
Q3
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
I
-
.
- '-+
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
light
,--
� Na
'=
Na
outer
-
+
di ffuse in
g
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.
v
inner
rhodopsi n to retinal
-�____.- an d opsin
h nl
Na+ m o e down
segment
light breaks down
(I'
concentration gradient
v-
I
·->
'\ -
I \J li \_
(C[ (��
O oO
Na + act ivel
y
�+ - Na + actively
N
pumped out
pumped out
membrane slightly
membrane hyperpolarised
depolarised -40mV
No neurotransmitter is Neurotransmitter is released
released.
and binds to bipolar cell,
Cation channels in
v
p re enting it depolarising.
bipolar cell open and
membrane becomes --a
s
g
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
stored.
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
cerebrum
corpus callosum
The hypothalamus controls thermoregulation. pituitary gland
------,f---------,-:-st
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
01
D i stinguish between the cerebrum and the cere b e l l u m .
02
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
strengthened.
Eye has
no working connection to
cortex and is effectively
blind,
the visual
even though
of th e retina and optic nerve work normally when exposed to light the cells
Synapses
only present for axons coming from
the light-stimulated eye. So the v is u a l
cortex
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
an
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 "' � � ,., �..:; "
•
-�J
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.
Q1
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
Q2
research? F o r example, how
m a n y a fruit flies, b mice,
c
cats,
Q3
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
80%
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.
neurone.
water jet
-abituation in a sea slug.
gill
sensory neurone
motor neurone
from the siphon
to the gill
01
Write out the reflex arc involved in the sea slug's response to water being sprayed onto its siphon.
02
Suggest why sea slugs used in this habituation experiment need to have been reared in captivity rather than in the sea.
03
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��- �$
O!fil
synapses
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
0
postsynaptic m���
0�
oo
0
0
� �� .
.··.
·
� -- -
3
•
�--
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.
I
I
I
I
I
I
I
I
I
I
I
Topic 8: G'ey matter
4
5
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.
Q2
Expl a i n how L-dopa m ay reduce the symptom s of P arkinso n's disease.
Q3
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•
lri.1S��J:J"e
•
•
•
•
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
·
.
�'iL
.:- = ,.
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
A.
The plant is infected with
bacterial DNA fromTi
the modified bacterium and part of the Ti
plasmid
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
chromosomes.
new plant contain ing
tumefaciens causes a tumour
crown gall (tumour) --
caused
chromosome
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
Q1
Descri be what is meant by the term ' genetic po l l utio n of the environment'.
Q2
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
a
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 -
you
should
r-.'!"::o: �-� ��
.@"�C!"ili!l)
be able .
to:
'
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.
Vision
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
systems
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
(CT)
scans.
Discuss how the Human Genome ProJect is helping to
·=· L07 L02 L08 L03 L04 LOS L06 L09
I
Describe how drugs can be produced using genet1cally mi croor ganisms) .
Discuss the risks a nd benefits of genetically modified
or ganis ms .
I
L019 L020 L021
'l
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ur�;;w: ·�, x:.'•ti �tt�� D D
�·
D 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
�·
I
D D
I
D
D
D
D
D
D
D
D
D
D
D
D
D
I D D
D D
D
D
D D
D D
D
D
D
D
D
D
D
D
D
D
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.
(a)
(3)
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.
-
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.
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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.
(b)
(4)
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
,
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.
.
:
.
. Examiner com
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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.)
·
111
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!
2
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)
I
(b) Describe the detection of light in flowering p la nts.
(3)
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
E,
state which region o f the brain:
D
I,
I·
, II
Ill
(a) coordinates movement
(1)
(b) controls heart rate
(1)
(c) receives sensory input fro m the eyes.
(1)
Total 3 marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 58 June 2005)
-
Topic 8: Grey matter
4
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.
(1)
(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' .
(1)
(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.
(2)
(2)
(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)
�
'
�
1
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.
I
(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
I
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
-�
c
�� �:0 § ro
u� I
6 .· �·� c
;.,_.=! X 0 0 V\
� ---------------------
(a) (i)
Time/milliseconds
Describe and explain the trends shown on the graph above.
(3)
(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.
(4)
(b) ATP is used to provide an immediate supply of energy for biological processes. Describe the role of ATP in the following processes . (i)
(2)
nerve impulse transmission
(ii) hyperpolarisation of rod cells i n the retina.
(2) marks (Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 58 June 2008)
Total
3
(a) Explain what is meant by the Human Genome ProJect.
13
(2)
(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)
I
I
4
(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.
t,eiU1iij
�t?illltil
����-37.0
0
Started investigation
5
Got into bath
36.9
10 15
Lying in bath
36.7
Got out of bath
36.5
20
Sitting on a chair
368
I
25 (i)
j
37.0
Sitting on a chair
Describe the c ha nges i n body temperature that o c c urred during this investigation.
(3)
(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)
12
18
14
15
17
20
20
25
27
(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)
(2) Total 4 marks
(Edexcel GCE Biology Advanced -paper 6112/01 June 2008)
6
(a) The diagram shows some of the stages of anaerobic respiration in a muscle cel l . Glucose
.I,I
Stage 1
phosphorylated GC sugar
'
Glycolysis
Stage 2
I
phosphorylated 3C sugars
l
Stage 3
I
Substance A
l
Stage 4
I
Lactic Acid
I
i
(i)
( 1)
Name substance A.
(ii) State which of the stages shown in the diagram
1. uses ATP
2. produces ATP.
(2)
I
I
(b) The Krebs cycle occurs during aerobic respiration and is an example of a metabolic pathway. (i)
.I
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
fourth
1 x
reduced
NAD
�FI
third
�
4C acid
\
(2C)
6C
8
4C acid
>econd
� �co ·
i:c
1 x
first
4C acid
� 1 x
reduced
reduced
NAD
2
SC acid
4C acid
(1)
1 x
reduced
NAD
COz
FAD
(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 c
-e ,2
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unshaded area
WI
500--599 600--699 700-799
100
0
unshaded area
shaded area
Unit 6: Practical B i o l ogy and Investigative Skills
I Imagine you are taking random samples from two areas and you wish to decide whether they are different To make this decision scientifically you need to follow these rules:
I
1
I
Begin by assuming that the averages of the two samples are the same. This is a null hypothesis.
2
Take samples from each area.
3
It is very unlikely the averages will be identical so you can calculate the chance (probability) of obtaining results like yours, even if the two samples were not really different, using a statistical test
I
4 If the chance (probability) calculated is higher than the significance level then you must accept that your first assumption is correct and there is no difference. If the chance of getting these results is lower than the sig n ifica n ce level then you would reject the null hypothesis.
I
�:u:�mp�es o'! !11 U � � �ypotheses •
There is no significant difference in the numbers of mayfly nymphs found in slow flowing streams and fast-flowing streams.
• There is no significant correlation between the abundance of creeping buttercup a n d soil moisture content.
�; � g n ificance ��ve�s In most i nvestigations you should use a significance level of 5% . This means there are 5 chances in 1 00 that the results you obtain could occur even if there was no difference between the two sets of data. This can be written as a probability of p=0.05. To find this value for your data you normally have to calculate a test statistic and then look up the probability in a published table.
You are not expected to know the formulae or fine details of each test. You should concentrate on selecting the correct type of test and demonstrating your understanding of how to interpret the results. The three types of test you are most likely to consider are:
I 1
� �- -,
-
: I
'
•
te sts for s i gnifi can t difference e.g. t-test or Mann Whitney U test
e
test for significant correlations e.g. Spearman's Rank C orrelation test
•
tests for significant association or 'goodness of fit' e.g. C hi Squared test
'
Other statistical �erms You cannot achieve more than 4/5 marks if you do not explain the
re s ults of your stati sti cal t e st in
You are also expected to understand the following terms where applicable: •
number of measurements
your own words. You can use a
compute r programme to calculate
•
the test statisti c but not to explain
its meaning.
arithmetical mean (average) - the sum of a l l the measurements divided by the
•
median - the middle value of your data where half the sample measurements are above this value and half are below mode - the measurement which occurs the greatest number of times in your sample.
I
It is vital that you begin by describing accurately the trends and patterns shown by your data. At this stage do not be influenced by theoretical expectations. The next stage is to try to interpret your results using biological pnnciples. This does not mean simply adding a lot of biological theory. You must use your biolog1cal knowledge and link it very clearly to your data.
or 'shows that'. Use more cautious
lim itations
terms s u c h a s 's u p p orts the
I t i s expected that you will take a n object1ve, critical look at the method you have used and assess how it might affect the reliability of your conclusions. The important question to ask yourself is 'no matter how carefully I carry out this investigation what factors could still cause variations in my repeat readings/'
Poo r limitations : • •
admiss1ons of practical mcompetence when describing li m i ta tion s
suggestions of l im ita :i ons that should have been eliminated by sensible planning
or
a
tri a l experi m ent Good l imitations: •
'I
set up a series of co l o u r standards to make my judg em ent of the end-point as accurate as
possible but this was still very subjective.
It wo u l d be more accurate to
filter my samples
and use a coiori mete· to give a precise measurement.'
This section should follow from your analysis of limitations. If you have identified factors which could cause variations then what modifications could be made to your method to minimise their effect/ Don't: •
•
Avoid terms s u c h as 'proves that'
simply suggest taki:1g more samples - you should have thought about this in planning and JUSt doing more of the same will not normally improve your method modify your investio;Jation so that it begins to test a completely different hypothesis
Corru m u L"ll n �ati ng High-scoring reports always make it clear where each of the criteria has been addressed by using sub-headings. This will prevent you omitting importa nt details or repeating yourself. Use the advice given in other parts of this section of Unit 6 to tabulate your results accurately and choose the right form of graph. Keep your sentences short but accurate and use a spelling check, especially for scientific terms. You will be given credit for selecting information from sources in 'research & rationale' but for higher marks you must use at least one professional journal and list all your sources in a bibliography, identifying where in your report each has been used. For the highest marks you will need to evaluate your chosen sources, describing their credibility to scientists as a whole.
hypothesis that' o r 'agrees with the
s u g g e st i o n th a t' .
I
Urni t ! : lopRc 5 -
QQ 1 R GPP- NPP 2 The place where an organism lives and the role it
QQ 1 reduced NADP; ATP 2 a gain of electrons; b loss of electrons
=
plays (job it does) there.
TT 1 The alga produces oxygen from the water it uses
TT 1 First need to work out the energy that is actually
in photosynthesis, but only in the light. At all other
transferred to consumers. It is the total fixed minus
times both types of oxygen, which are chemically
respiration loss, i.e.
indistinguishable, are being used in respiration
1 .9
therefore levels are falling due to this, both in the 160 light and the dark. The fall in 2 in the light is
so efficiency=
QQ 1 In recreating RuBP and in the formation of GALP. used in the 'first' step, carbon fixation. 2 Catalyses reaction of carbon dioxide with RuBP.
�i(i.( • tlt f(k.
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wudl(�I
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light -dep
thylakoid
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reactions
membrane
I
cooto;m
i
:
I I I
an organism is its
the pH is, etc)
stages including
Quadrat is a fixed area sampling device. It is sometimes, but not always, gridded to make work out. 3
e.g. Rocky shore: abiotic- salinity, temperature, light intensity/solar input; biotic- any three of: competitors, predators, parasites, herbivores. Sand
many open protein
dunes: abiotic- soil factors (as in
channels
01 - any three);
biotic- any three of: competitors, predators,
I I I I
parasites, herbivores. Woodland: abiotic- soil
gated and active
01 - any three); biotic- any three of:
substances which
transport channels,
factors (as in
need to enter or
together with open
competitors, predators, parasites, herbivores.
leave the chloroplast
channels
I I
�-------·�
f
12 gtycerate
6 carbon dioxide
f------->-1
3-phosphate
� (GP} NAOP
J; who decides who deserves very expensive treatment on the NHS?; 6. data protection issues- who will have access to genetic information about individuals; [this marking point could be a development of 3 marking point 2] Total 7 marks
4 ('>' 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
7
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)
(a)
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)
(b)
6
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
(ii)
(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
e
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)
f
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
abiotics
correlation
absolutist view
cortex
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
cytoplasm
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
data
12.22 28,78 9-11, 22,24, 40-1, 45-6, 48-9,56-7,59,78,
ecosystems
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
copper
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
graphs
79,81,85,87
greenhouse effect
18-19
greenhouse gas gross primary productivity growth rates
motor neurones
60,66,74,78
MRI scans
71,74,92-3
18
mRNA
30-1
12,25
muscles
27,44-5,47,51, 54,56-61,66,70,75,78-9
21
mmation
16-17,22-3,31,35
mutations
17,35, 91-2
habitat
13-16,22
myelin sheath
62
habituation
69,74,94
myofibrils
44
myogenic
SO, 56
health
42,54,58,71 50-2,54-6,58,66,77-8
heart
38
hepatitis C
myoglobin
45 44-5,58-9
myosm
12,90-1
herbivores
natural selection
histogram 87 32,35-9,42
HIV
68
homeostasis
52-3,56-7,61,93
nerve impulse
hormones
51-2,54-6,61,74
nervous system
16
hybrid sterility
8-9,10,22,48-9
hydrogen
45-7
hydrolysis
53,82
hyperthermia
52-3,57,66,74,93
hypothalamus
84-5,87-9
hypothesis
44,60,62-6,68-71,75-6
neurotransmitter
61,64-5,69-71,74-5,94
nitrate
11,15
nitrogen
13,26
27,30-1,34-6,39,92
nucleic acids
27,30-9,42,54,59, 71,82
nucleus
72
nurture
62 10-11,22,42,92 30-1,55,62 68 15, 26
nutrients
28
introns
21,69
invertebrates investigation
21,28-9,38-9,43,69,78-9,84-5,
54
obesity optic nerve
60,65,67
organelles
87,89
isolation
16,22,91
isotopes
9
organisms
11, 62 10,14-17,20,22-3,26-8,32,34-6,46-7,
72-4,90
osteoporosis joints journals Krebs cycle
44,51,53-4,59 17,84 47-9,56,59,80,93
laboratory
39,42,69,85-6
lactic acid
46-7
larvae
26,39
ligaments
44,54
light-dependent reactions
9-11,22,24
light-independent reactions
8-11. 22,47
limpets lipids
14,23 10-11,22
lipoproteins
93
liposomes
72
locus
28
lymphocytes
33
lysozyme macrophages magnetic resonance medulla mesosomes
44-5,78
neurone
immunity
32,36,38-9
12,22,25 44-5,78
neuromuscular junction
nodes of Ranvier
interferon
32,52,60,67,69-71,74,76
neuromuscular
32-3,35,37,39,54-5
infection
45,62-4,74,78
net primary productiYity
immune system
insulin
16
nature
32,34,36 32-3,35-6 71,74 51-2,58,66,74 32,42
54
oxidation oxygen
9,48-9 8-9,15,22,46-9,55-7,71,78-9,81,90
parasites
90-1
Parkinson's disease
70-1, 74-5 34-6, 54,92
pathogens
17,22
peer review
30
peptide
32, 36
phagocytosis phenology
21
phosphate
9-10,15,46-7,78,80,90
phosphorylation
10,47-9,56,90,93
photolysis
8, 11
photoperiodism
60
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
13
plasmids
32
politics pollen
21 18,22,40-1,84,91
46
polymerase
28-9,36,55
methane
18-19,22
polypeptide
30-1,92
microbes
34,73,92
polysaccharides
20,34,74
population
metabolism
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
promoter
55
troponin
prosthesis
53
tuberculosis
proteins 11-12,17,28,30-3,35-6,38-9,44-5,55,62, 71,73, 92, 94
pupae
39
pupil
60-1,74,76
pyruvate
46-9,55,57
\'agus nerYe variation ·
1sodilation
ventilation
\'entricles
quadrat
14-15, 23, 43, 91
vir us es
\·ision receptors
64
reduction
8-10,48,67,70
reforestation
19,22,91
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
54,67
reproduction
16,35, 92
research
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
respirometer
47,63
retina
60,64,67,74,76,78
ribosome
30-32,42,92
rigor mortis
27
risk assessment
35,85
saltatory conduction
62
sarcolemma
44
sarcoplasm
44
sarcoplasmic reticulum schizophrenia
44-5 68,77,94
Schwann cells
62. 74
science
21,28-9
scientists
17,21,26,29, 77,89
sensory neurones
60
seres
13
serotonin
70-1
skeletal muscle solar energy
15
speciation species
44,56
16-17,22,9' 13-17,20.23,27,35,39-41,43,73,86,91
spirometer
51,56,81 11-12
starch stimuli
64,67,69
stroma
11
succession
13,22,27,43
Sun
18
survival
16-17
symptoms
32,35-7,54,68,70-1
synapse
44,61,64-7,69-71,74-5,78
technology temperature
29, 53,56 15, 18.20-2,27, 29,36-7,39,47,51-3,
56-7,78-9,85,90-1
tendons testosterone thermoreceptors thylakoid membranes
w
11 15
toxins
34
transect
I
55 52,57
topography transcription
I l
44
translation trees tropomyosin
30-1,36,55-6
I
14-15,23,43
I
30 13,17-18,29,40-1,91 45
I
J I
PEARSON T 0800 579579 F 0870 8505255
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ISBN 978-1-84690-599-5
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