SNAB Biology - Mark Scheme June 09

Mark Scheme Summer 2009

GCE

GCE SNAB Biology (8048/9048)

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Summer 2009

Publications Code UA021125

All the material in this publication is copyright © Edexcel Ltd 2009

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Contents

General Introduction iv

General Information v

Mark Schemes

Unit SN1 6131 Lifestyle, Transport, Genes and Health 1

Unit SN2 6132 Development, Plants and the Environment 11

Unit SN3 6133 paper 02 Report and Practical Review 26

Unit SN4 6134 Environment and Survival 29

Unit SN5 6135 paper 01 written paper

Energy, Exercise and Coordination; Coursework Investigation

39

Unit SN6 6136 Synoptic paper 46

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GENERAL INTRODUCTION Mark schemes are prepared by the Principal Examiners and revised, together with the relevant questions, by a panel of senior examiners and subject teachers. The schemes are further amended at the Standardisation meetings attended by all examiners. The Standardisation meeting ensures as far as possible that the mark scheme covers the candidates' actual responses to questions and that every examiner understands and applies it in the same way. The schemes in this document are the final mark schemes used by the examiners in this examination and include the amendments made at the meeting. They do not include any details of the discussions that took place in the meeting, nor do they include all of the possible alternative answers or equivalent statements that were considered to be worthy of credit. It is emphasised that these mark schemes are working documents that apply to these papers in this examination. Every effort is made to ensure a consistent approach to marking from one examination to another but each marking point has to be judged in the context of the candidates' responses and in relation to the other questions in the paper. It should not be assumed that future mark schemes will adopt exactly the same marking points as this one. Edexcel cannot under any circumstances discuss or comment informally on the marking of individual scripts. Any enquiries about the marks awarded to individual candidates can be dealt with only through the official Enquiry about Results procedure.

Unit Codes and Unit Titles This Mark Scheme covers the unit offered in this examination for Advanced Subsidiary Biology (Salters-Nuffield) (Pilot) 6131. The units available for the complete qualifications, Advanced Subsidiary and Advanced, are listed in the table below.

Level Unit Code Unit Title

1 6131 Lifestyle, Transport, Genes and Health

2 6132 Development, Plants and the Environment

AS

3 6133 Report and Practical Review

4 6134 Environment and Survival

5 6135 Energy, Exercise and Coordination; Coursework Investigation

A2

6 6136 Synoptic Paper

Please note that, in January 2010, only the A2 written units are available.

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GENERAL INFORMATION The following symbols are used in the mark schemes for all questions:

Symbol Meaning of symbol

; semi colon Indicates the end of a marking point

eq Indicates that credit should be given for other correct alternatives to a word or statement, as discussed in the Standardisation meeting

/ oblique Words or phrases separated by an oblique are alternatives to each other

{} curly brackets Indicate the beginning and end of a list of alternatives (separated by obliques) where necessary to avoid confusion

() round brackets Words inside round brackets are to aid understanding of the marking point but are not required to award the point

[] square brackets Words inside square brackets are instructions or guidance for examiners

Crossed out work If a candidate has crossed out an answer and written new text, the crossed out work can be ignored. If the candidate has crossed out work but written no new text, the crossed out work for that question or part question should be marked, as far as it is possible to do so. Spelling and clarity In general, an error made in an early part of a question is penalised when it occurs but not subsequently. The candidate is penalised once only and can gain credit in later parts of the question by correct reasoning from the earlier incorrect answer. No marks are awarded specifically for quality of language in the written papers, except for the essays in the synoptic paper. Use of English is however taken into account as follows: • the spelling of technical terms must be sufficiently correct for the answer to be unambiguous e.g. for amylase, ‘ammalase’ is acceptable whereas ‘amylose’ is not e.g. for glycogen, ‘glicojen’ is acceptable whereas ‘glucagen’ is not e.g. for ileum, ‘illeum’ is acceptable whereas ‘ilium’ is not e.g. for mitosis, ‘mytosis’ is acceptable whereas ‘meitosis’ is not • candidates must make their meaning clear to the examiner to gain the mark. • a correct statement that is contradicted by an incorrect statement in the same part of an

answer gains no mark – irrelevant material should be ignored.

Unit SN1 (6131/01) - Lifestyle, Transport, Genes and Health Question Answer Mark Number 1(a)

phos base

(2)

phate correctly bonded to sugar ;

correctly bonded to sugar ;

Question Answer Mark Number 1(b)

Any

two correct answers for one mark ;;;;

Feature DNA mRNA

Name of sugar present

deoxyribose

ribose

Name the group that links sugar to sugar

phosphate phosphate

Number of strands in the molecule

two

one

Name of complementary to adenine

thymine uracil

(4)

Question Answer Mark Number 1(c)

(2)

1. first bar reaching 2 au ;

2. third bar reaching 8 au ;

1

Question Answer Mark Number 2(a)

(2)

(i) 1. B / eq ;

2. lack of oxygen / reference to anaerobic respiration ;

Question Number

Answer Mark

2(a)(ii)

1. damaged blood vessel / presence of air / rough

surface / other correct named clotting initiator ;

2. {platelets / red blood cells / eq} stick to damaged wall (forming a platelet plug) ;

3. thromboplastin released ;

4. from {platelets / damaged tissue} ;

5. (converts) prothrombin to thrombin ;

6. (which) {converts / eq} fibrinogen to fibrin ;

7. soluble (fibrinogen) to insoluble (fibrin) ;

8. reference to any other appropriate clotting factor (e.g. Ca2+ / vitamin K / Factor VIII) ;

9. fibrin mesh traps {platelets / red blood cells /

eq}(forming a clot) ;

max (4)


max(2)

(i) 1. {electrical activity / eq} travels through atria ;

2. reference to reaches AVN / eq ;

3. {atria / eq} contract ;

4. volume decreases / correct reference to pressure changes ;

5. blood enters ventricles / eq ;

2


(2)

(ii) 1. working correct (e.g. 60 ÷ 0.75) ;

2. 80 ;

3

Question Number

Answer Mark

3(a)

C COOH H2N

H

CH3

X

X

X X

Question Answer Number 3(b)

1. (linear) {sequence / order / eq} of amin

2. joined by peptide bonds ;

Question Answer Number 3(c)

1. 10 amino acids shown in same sequence

2. shaded amino acids shown above water surrounded by unshaded ;

Question Answer Number 3(d)

(i) {nearly / almost /roughly/ eq} halves the time

Question Answer Number 3(d)

(ii) 1. doubling the number of active sites ;

2. twice as many {starch / substrate} creact (at any one time) / eq ;

4

(1)

Mark

(2)

o acids ;

Mark

(2)

;

/

Mark

; (1) / eq

Mark

(2)

an bind /

Question Answer Mark Number 3(d)

max(2)

(iii) 1. DNA polymerase has a {different / wrong} shaped active site / starch shape different to DNA polymerase active site ;

2. so starch cannot bind ;

3. enzyme-substrate complexes cannot form ;

4. reference to specificity ;

5


Hh /

(1) (i) hH / heterozygous ;


max(3)

(ii) 1. because LDL levels vary ;

2. before / after a meal / diet / eq ;

3. age (differences) ;

4. gender ;

5. genetics ;

6. accuracy of test / measuring equipment / eq ;

7. variation within a population ;


max(3)

(i) 1. (deletion can lead to) change / loss of {amino acid / amino acid sequence / primary structure (of protein)} ;

2. changes {tertiary / eq} structure (of protein) ;

3. shape important in {function / function described / recognition / binding of LDL / eq} (hence non-functional) ;

4. reference to frameshift ;

6


no Lrefere

(1)

(ii) DL receptor protein {produced / active / eq} / nce to no LDL {taken up from blood / eq} ;

Question Number

Answer Mark

4(b)(iii)

1. (sample) 3 ;

2. smaller / lighter (fragment) of DNA ;

3. because it is a deletion / eq ;

4. therefore, moves {further / faster} (towards the positive terminal) ;

5. {line / eq} is {twice as thick / eq} meaning that it

is homozygous / eq ;

max (2)

7


max(3)

1. altering the genotype of the organism with the condition ;

2. addition of a ‘normal’ gene ;

3. reference to vector (e.g. virus / liposome) ;

4. details of vector ;

5. incorporation of gene into {target / eq} cells ;

6. reference to transcription and translation / protein (from imported gene) made ;


(2)

1. somatic – altering genotype of body cells / gene into body cells ;

2. whilst germ line relates to sex cells / gametes / eq ;

8


max(3)

(i) 1. uptake increases for both up to about 3 minutes ;

2. sample P levels off / stops increasing before sample Q ;

3. uptake is always higher for Q ;

4. uptake in Q continues but stops in P after approx 3 minutes ;

5. correct comparative manipulation of the data e.g. 13.5 ÷ 4 = 3.4 times as much in Q at the end of the study compared to P ;


max(2)

(ii) 1. (Q) continues to rise / does not plateau ;

2. goes above equilibrium level of 4 au ;

3. the presence of ATP supplies energy to allow concentration above equilibrium ;


facil

(1) itated requires {channel / transport / eq} proteins ;

Question Number

Answer Mark

6(c)

1. vesicles ;

2. move towards cell surface membrane ;

3. vesicle {fuses / eq} with membrane ;

4. contents (of vesicle) released out

of cell ;

ax

m(2)

9

Question Number

Answer Mark

7(a)

Structural feature Sucrose Amylopectin

Glycosidic bonds present

;

Side chains present ;

Contains more than three glucose monomers

;

(3)

Question Number

Answer Mark

7(b)

1. flax ;

2. least amount of saturated fat ;

(2)

Question Number

Answer Mark

7(c)(i)

1. (person) 3 ;

2. more energy in than out ;

3. excess energy laid down as fat ;

max(2)

Question Number

Answer Mark

7(c)(ii)

1. (person) 2 ;

2. energy taken in less than energy given out ;

3. burning off energy reserves / fat /eq ;

max(2)

10

Unit SN2 (6132/01) - Development, Plants and the Environment

Question Number

Answer Mark

1

hloroplast(s) ;

lasmodesma(ta) ;

noplast ;

myloplast(s) ;

iddle lamella ;

)

c p to a m

(5

11

Question Number

Answer Mark

2(a)

adhesion - water (molecules) sticks / attracted / bonded to (walls of) (xylem) vessels / tubes ; cohesion - water molecules stick together ;

(2)

Question Number

Answer Mark

2(b)

{mineral / inorganic} {salts / ions} / nitrates /phosphates ;

(1)

Question Number

Answer Mark

2(c)

the water columns are pulled (from the top by transpiration stream rather than pushed) / under tension / the water columns contract as they are stretched / reference to reduced pressure (in xylem) / eq ;

(1)

12

Question Number

Answer Mark

3(a)

X = acrosome / lysosome ; Z = mitochondria / mitochondrion ;

(2)

Question Number

Answer Mark

3(b)

Structure X

1. releases (digestive) enzymes / hyaluronidase;

2. dissolves {pathway / hole / way / route / eq} through follicle (cells) / jelly (layer)/ zona pellucida ;

Structure Z

1. provide energy / {provide / create / eq} ATP ; 2. for movement / to enable sperm to reach ovum /

eq ;

(4)

13

Question Number

Answer Mark

4(a)

C ;

(1)

Question Number

Answer Mark

4(b)

1. reliable supply of {water / food / nutrients /

resources} ; 2. plants (deliberately) introduced to encourage

{insect life / prey species} ; 3. artificial control of {temperature / air conditioning

/ humidity} ; 4. reduced competition in {zoo / garden} /

populations (artificially) {controlled / manipulated} / eq ;

5. reference to reduced predation / protection from

predators ; 6. veterinary care / use of antibiotics / medicines /

immunisation (to control disease) ;

max (3)

14

Question Number

Answer Mark

5(a)

more growth of {crown / more leaves / more leafy shoots} / dead (upright) shoot has got smaller / trunk /stem wider / thicker ;

(1)

Question Number

Answer Mark

5(b)(i)

1. it is 7/8 years old ; 2. {it has grown more rapidly / growth conditions

have been favourable} in the recent past than when it was young ;

3. (use of dating) grew most rapidly in 1998, 1999,

{grew faster / there was more growth} in 1998 / 1999 / 2000 than 1995/1996/ 1997/ grew slowly in 1995 / 1996 / 1997 ;

max (2)

Question Number

Answer Mark

5(b)(ii)

rising (atmospheric) concentrations of {carbon dioxide / nitrogen deposition} / increased solar radiation /increased light intensity / increased rainfall ;

(1)

Question Number

Answer Mark

5(b)(iii)

(xylem) {vessels / tracheids} ; sclerenchyma / fibres ;

(2)

15

Question Number

Answer Mark

5(c)

1. absorbed by roots / leaves ; 2. and used to make {amino acids / protein / nucleic

acids / ATP} ;

3. enzymes / chlorophyll / membrane proteins ;

max (1)

Question Number

Answer Mark

5(d)(i)

photosynthesis ;

(1)

Question Number

Answer Mark

5(d)(ii)

1. {when {trees die / leaves fall of trees} they {rot

away / decay / are burnt} and give off carbon dioxide (back to the atmosphere)} / trees give out CO2 through respiration ;

2. and give off carbon dioxide (back to the

atmosphere) /trees (also) give out CO2 through respiration ;

3. (only) newly-planted forests {take in more CO2 than they give out / turn CO2 into wood faster than they give it out} ;

4. mature forests {give out as much CO2 as they take

in / are carbon neutral} ;

5. carbon offsetting only reduces atmospheric CO2 if forests are constantly expanded / there would not be enough land available to plant enough trees to make a difference / eq ;

max (2)

16

Question Number

Answer Mark

6(a)(i)

use a water bath / description of using a water bath ;

(1)

Question Number

Answer Mark

6(a)(ii)

1. maintain a constant pH throughout the

experiment ; 2. to provide a particular pH / control pH ;

3. enzymes are sensitive to pH / work within a

narrow pH range /only work at a certain pH / each one has a specific pH optimum ;

max (2)

Question Number

Answer Mark

6(a)(iii)

1. gene / allele for β galactosidase {switched on /

induced / turned on / expressed / transcribed} ; 2. switched on / induced by lactose ;

3. yellow colour appears when ONPG is broken down

(to a yellow substance) ;

4. β galactosidase only produced when lactose is present ;

max (2)

Question Number

Answer Mark

6(b)(i)

1. (depending on the source) the enzymes / β

galactosidase differ in temperature optima / work best at different temperature / eq ;

2. P.haloplanktis has a temperature optimum of

15/16 oC whereas that of E.coli is over 35 oC or {higher / over} ;

3. P. haloplanktis {is adapted for / has evolved in a cold climate} / the P. haloplanktis (used in the experiment) came from a cold place / had been (recently) exposed to low temperature (and become cold-adapted through environment) ;

(3)

17

Question Number

Answer Mark

6(b)(ii)

1. less energy needed (to warm the milk);

2. the milk is less likely to go off during the process

(due to microbial action) / enzymes {more stable / last longer} at low temperatures ;

max (1)

18

Question Number

Answer Mark

7(a)

1. a cell which can divide ; 2. and can differentiate / change into different

types of cell / has not yet differentiated ;

3. primal cells / reference to having retained the ability to divide / differentiate from an earlier stage ;

max (2)

Question Number

Answer Mark

7(b)

1. adult stem cells are {pluripotent / multipotent} ; 2. whereas embryonic cells are totipotent ;

3. adult stem cells can only develop into certain

cells (whereas) embryonic stem cells can develop into any kind of cell /eq ;

max (2)

Question Number

Answer Mark

7(c)

1. does not involve the ethical issues associated with

embryonic stem cells /eq ; 2. can use patients own stem cells therefore no

immunity problem ;

3. easier to obtain ;

max (1)

Question Number

Answer Mark

7(d)

1. overcomes problem of shortage of donors ; 2. can use patients own stem cells therefore no

immunity problem ;

3. necessary surgery less invasive / drastic / life threatening / recovery time ;

4. (probably) less expensive ;

max (2)

19

Question Number

Answer Mark

7(e)

1. by fertilisation ; 2. of ova by sperm / eq ;

3. in vitro / in a test tube / ova {removed

from/outside} woman’s body ;

4. (usually) surplus /spare fertilised ova from IVF treatment / eq ;

max (2)

20

Question Number

Answer Mark

8(a)

1. (cells) mutate / DNA damaged ; 2. {BRCA1 / BRCA2 / TP53 / oncogenes / tumour

suppress genes} as examples of genes which {mutate / undergo mutation} ;

3. uncontrolled cell division ;

4. damage to DNA not repaired / tumour repressor

substances not produced ;

5. new cells produced faster than cell death ;

max (3)

Question Number

Answer Mark

8(b)(i)

Human Genome Project ;

(1)

Question Number

Answer Mark

8(b)(ii)

to prevent the cancer spreading to other parts of the body / development of secondary carcinomas / to prevent metastasis ;

(1)

Question Number

Answer Mark

8(b)(iii)

1. avoid raising false hope in the patient ; 2. use an alternative drug which might work ;

3. identify the need to carry out research to develop

an alternative for the patients for whom doxcetaxel is ineffective ;

4. avoid unwanted side effects of the drug ;

5. avoid wasting money on ineffective drug / aid to

NHS in planning ;

max (2)

21

Question Number

Answer Mark

8(c)(i)

1. {self examination / frequent medical checks} for

early diagnosis ;

2. (choose to) avoid {alcohol / HRT / smoking} ;

3. (choose to) {take plenty of exercise / control energy intake / avoid getting over weight} ;

4. (take plenty of exercise / control energy

intake/avoid getting over weight) particularly after menopause ;

max (2)

Question Number

Answer Mark

8(c)(ii)

1. data protection issue / afraid {other people /

organisations} might find out ; 2. (if third parties got access to data) higher

insurance premium / fear of discrimination ;

3. would cause anxiety / stress / depression / eq ;

4. (would cause anxiety when) only a risk not a certainty ;

max (2)

22

Question Number

Answer Mark

9(a)

1. improves yield of cotton ; 2. saves the cost of buying / applying insecticides ;

3. increases the farmer’s {income / profit} ;

4. less harmful to {humans / wildlife} than chemical

sprays ;

max (3)

Question Number

Answer Mark

9(b)

Similarities:

1. plants with desired characteristics are selected ; 2. new (desirable combinations) of {characteristics /

genes} are produced / hybridisation /eq ;

3. done deliberately to improve }yield / usefulness / eq} ;

Differences:

4. conventional done by transferring pollen / reference to GM techniques ;

5. (genetic) change achieved more quickly / much

less hit and miss / eq ;

6. can combine genes from a wider range of sources (whereas in conventional method hybridisation only possible between plants of {same / similar} species / transfer of genes from a bacterium to a plant (as in this example) not possible with conventional method /eq ;

max (4)

23

Question Number

Answer Mark

9(c)

To gain full (four) marks candidates must include a rebuttal item i.e. one which recognises an opposing argument but attempts to place it in perspective.

If a candidate says ‘for’ arguments against do not count (and vice versa for ‘against’). An exceptional answer which balances a series of opposing points of view and really argues that it is impossible to come down on either side may gain full marks if they have included 4 points For GM crops Maximum of three points from 1 to 7

1. {little / no} convincing evidence that GM is harmful ;

2. yet widely used in {North America / USA / India} ;

3. great potential in GM to {increase crop yields

/reduce food prices / feed more people (in a starving world / help economy of developing nations} ;

4. potential to reduce dependency on chemical

pesticides ;

5. can reduce damage to environment / make agriculture more sustainable ;

6. better that GM research in places like UK where it

can be properly regulated rather than left to rogue states / whether UK develops GM or not other countries will do it anyway ;

7. same basic idea as conventional crop breeding

and we’ve been doing that for thousands of years ;

Rebuttal arguments

8. some cases where GM has not been a success but this does not prove that there is anything wrong with GM in general (just needs more research) ;

9. there could be (as yet undiscovered) risks with

GM but the potential is so enormous we cannot afford/not ethical to ignore ;

24

Against GM crops Maximum of three points from 1 to 7

1. not all GM crop projects have been a success / reference to specific example which has not been successful ;

2. {genes / pollen} may get transferred to other

organisms (with unforeseeable consequences);

3. (potential for) exploitation of developing world farmers by international biotech countries ;

4. reliance on small number of (GM) strains would

mean loss of {genetic diversity / scope for natural selection / evolution} ;

5. impossible to be sure there may not be serious

consequences in future ;

6. cannot be controlled properly / might get into the wrong hands ;

7. GM different to conventional means (with

example e.g. can transfer genes between bacteria and plants) ;

Rebuttal arguments

8. some examples where GM has been a success but we cannot afford to take the risk ;

9. maybe in future GM may be useful but we should

wait until we know more about it / we don’t need it – can use conventional methods of crop breeding ;

max (4)

25

Unit SN3 (6133/02) – Practical Work Review


max(3)

1. relevant procedure / method ;

2. detail of procedure / method ;

3. reason / explanation ;

4. further detail ;


(3)

1. named dependent variable ;

2. suitable apparatus / technique ;

3. further detail ;

26


max(3)

1. suitable systematic error identified ;

2. why is it systematic ;

3. method to minimise ;

4. further detail of method ;


max(4)

1. suitable, correct variable named ;

2. suitable method to control ;

3. further detail ;

4. how control variable affects dependent variable ;

5. further detail ;

27


Disc

max(4)

ussion of decisions concerning:

1. correct choice of graph type with reason ;

2. axes correctly orientated ;

3. detail of scales ;

4. straight line / curve / best fit / distinguish between bar chart and histogram ;

5. error bars / eq ;

6. some manipulation of line or chart (e.g. gradient / anomaly / identification) ;


(3)

1. suitable conclusion stated ;

2. link to data ;

3. link to one pertinent bit of science ;

28

Unit SN4 (6134/01) - Environment and Survival Question Number

Answer Mark

1(a) 1. formation of new species (from existing species) ;

2. reference to isolating mechanism / (reproductive) isolation / eq ;

3. no longer able to produce fertile offspring (with existing species) ;

max (2)

Question Number

Answer Mark

1(b)

1. engulf / ingest (large) particles / eq ;

2. formation of {vesicle / phagosome} / eq ;

3. reference to lysosome / digestion / enzymes / eq ;

max (2)

Question Number

Answer Mark

1(c)

1. non-living / physical / chemical / eq ;

2. environmental factor affecting {distribution / growth / survival /abundance / species composition} / eq ;

3. e.g. pH / temperature / light / water content / soil

chemistry / topography /edaphic factors ;

max (2)

29

Question Number

Answer Mark

2(a)

1. competition for food supply / eq ; 2. predation of native species / eq ;

3. (harlequin ladybird) has wider range of food

sources / eq ;

max (2)

Question Number

Answer Mark

2(b)

1. biodiversity includes number of species / eq ; 2. will lead to fewer ladybird species ;

3. may reduce number of moth / butterfly species ;

4. population becomes non-viable / less genetic

diversity / eq ;

max (3)

Question Number

Answer Mark

2(c)(i) position in a food chain / eq ;

(1)

Question Number

Answer Mark

2(c)(ii)

1. (2196-42) = 2154 ; 2. =2 154 000 / eq ; (ecf)

3. kJ ;

(3)

30

Question Number

Answer Mark

2(c)(iii)

1. light {reflected / not absorbed} / eq ; 2. losses due to {respiration/ metabolism} in plants /

eq ;

3. inedible parts / not all eaten / eq ;

4. losses of indigestible matter / in faeces ;

max (3)

31

Question Number

Answer Mark

3(a)

1. contraction {slower / eq} at lower temp /

converse ; 2. peaks later at lower temp / converse ;

3. both reach same peak of contraction / peaks

differ slightly ;

4. relaxation slower at lower temperature ;

5. credit comparative figures ;

max (3)

Question Number

Answer Mark

3(b)

1. reference to rigor mortis / eq ;

2. idea of heat loss related to temperature

difference between body and environment ;

3. this (degree of rigor) depends on temperature / eq ;

4. estimate inaccurate (if environmental

temperature is not known) / eq ;

5. comment on degree of contraction gives a range of time i.e. depends on pre- or post- rigor / eq ;

max (2)

Question Number

Answer Mark

3(c)

1. core temperature ;

2. decomposition / colour / putrefaction / bloating

/ gas blisters / eq ;

3. entomology / eq ;

max (2)

32

Question Number

Answer

Mark

4(a)

1. grow in habitats where other plants cannot /

at advantage / eq ; 2. therefore less competition / more

competitive / eq ;

3. and more reproductive success / eq ;

max (2)

Question Number

Answer Mark

4(b)

1. standard sample used e.g. quadrats ; 2. method for determining position of sample

(e.g. random coordinates, transect) ;

3. method for recording abundance or frequency ;

4. record abiotic factor in each quadrat / eq ;

5. {presentation / analysis} of relationship (e.g. scatter graph, correlation) ;

max (4)

Question Number

Answer Mark

4(c)(i)

1. parent genotypes AaBb ;

2. gametes AB, Ab, aB, ab ;

3. 16 combinations shown ;

(3)

Question Number

Answer Mark

4(c)(ii)

AAbb , Aabb ;

(1)

33

Question Number

Answer Mark

4(c)(iii)

1. observed results approximate to 9:3:4 / eq ;

2. expect most to have dominant alleles for

both genes / converse / eq ;

3. predicts most are normal / converse ;

4. one character controlled by two genes ;

5. not 9:3:3:1 ;

max (2)

34

Question Number

Answer Mark

5(a)

1. reduced cell mediated response / T-cells not

activated / fewer T killer cells made / eq ;

2. reduced humoral response / B cells not activated / less antibody production / eq ;

3. opportunistic infection / eq ;

max (2)

Question Number

Answer Mark

5(b)(i)

1. antibody / T killer cell ; 2. (antibody production) by plasma cells ;

3. effect of antibody (e.g. precipitation) / cell

lysis by T killer cells ;

4. phagocytosis / eq ;

5. reference to antigen presentation / eq ;

6. reference to cytokines / interferon ;

max (3)

Question Number

Answer Mark

5(b)(ii)

1. secondary response ; 2. more rapid {antibody / T killer cell} production ;

3. faster / stronger response / eq ;

4. memory cells involved ;

5. prevents symptoms ;

max (3)

35

Question Number

Answer Mark

5(c)

1. changes in humans / eq ; 2. e.g. immune system preventing HIV growth ;

3. selection pressure on HIV ;

4. only adapted organisms replicate / eq ; 5. e.g. strain avoiding immune system / eq ;

6. these become more common / eq ;

7. selection pressure back on people / eq ;

max (4)

36

Question Number

Answer Mark

6(a)

1. species B ; 2. growth faster at lowest light intensity ;

3. correct comparative use of figures from graph ;

4. out competes species A ;

5. {bigger leaf area / more leaves} shade other

plants ;

6. {bigger leaf area / more leaves} absorb more light ;

max (3)

Question Number

Answer Mark

6(b)

1. limited light energy available for biomass

production / light limiting factor / eq ; 2. less light absorbed by chlorophyll / eq ;

3. correct reference to photolysis ;

4. slower light dependent reactions / less ATP /

less reduced NADP / eq ;

5. reduced Calvin cycle / eq ;

6. less carbohydrate for cellulose /eq ;

7. less carbohydrate for respiration / eq ;

8. correct reference to compensation point / eq ;

9. reference to heat radiation / temperature (at low light) ;

10. effect of this on rate of reaction / eq ;

max (5)

37

Question Number

Answer Mark

6(c)

1. reference to NPP higher ;

2. reference to NPP = GPP - R /eq ;

3. less energy is lost to respiration ;

4. more energy available for producing biomass /

eq ;

max (3)

38

Unit SN5 (6135/01) - Energy, Exercise and Coordination Question Number

Answer Mark

1(a)(i)

a (simple) form of learning / organism learns not to respond to {repeated / eq} / stimuli / reference to changes at synapses ;

(1)

Question Number

Answer Mark

1(a)(ii)

sea slug {ignores harmless / eq} repeated stimuli / idea of still obtains oxygen / saves energy / prevents build up of carbon dioxide ;

(1)

Question Number

Answer Mark

1(b)

1. {neurones / synapses /eq} of both similar ; 2. sea slug’s behaviour modified by learning ;

3. simpler nervous system (so easier to study) ;

4. idea that there are fewer ethical issues ;

5. sea slug has large neurones, (easier to study) ;

max (2)

Question Number

Answer Mark

1(c)

1. sensory neurone {stimulated / eq} by {receptor /

sense organ / eq} ; 2. sensory neurones carries {impules / eq} to {relay /

motor / CNS / eq} neurone / {relay / motor / eq} neurones receive impulse from sensory neurone ;

3. relay neurone {synapses / connects / eq} with

sensory and {motor neurones / lots of neurones} / idea of allowing coordination of reflex ;

4. motor neurone {carries impulse / stimulates / eq}

{effector / muscle / gland / eq} ;

max (2)

39

Question Number

Answer Mark

2(a)

1. hormonal coordination is {chemical / via blood}

whereas nervous coordination is electrical / along axons ;

2. hormonal slow whereas nervous fast / eq ;

3. hormonal longer term action whereas nervous

short term / eq ;

4. idea that hormone action is widespread whereas nervous action is localised ;

max (3)

Question Number

Answer Mark

2(b)(i)

polygenic / epistasis / non-allelic interaction / mulitfactorial ;

(1)

Question Number

Answer Mark

2(b)(ii)

1. more mitochondria for {aerobic respiration /

eq} ; 2. (slow twitch) have less sarcoplasmic reticulum

{Ca 2+ release / action potentials / muscle stimulation} / eq ;

3. resistant to {fatigue / lactic acid build-up / eq} /

eq ; 4. extensive capillary network for continuous

oxygen supply / eq ;

5. more myoglobin for oxygen {store / release} / eq ;

6. reference to having beneficial {genes / alleles} ;

max (3)

40

Question Number

Answer Mark

2(c)(i)

1. {unfair / competitive} advantage ;

2. may damage athlete / thrombosis / heart attack / stroke / death ;

3. idea of unacceptable role model ;

max (2)

Question Number

Answer Mark

2(c)(ii)

no point in banning a drug you cannot test for / eq ;

(1)

41

Question Number

Answer Mark

3(a)(i)

pyruvate / pyruvic acid ;

(1)

Question Number

Answer Mark

3(a)(ii)

1. reference to phosphorylation ;

2. ATP is needed / eq ;

3. reference to enzyme ;

max (2)

Question Number

Answer Mark

3(b)

1. reference to involvement of 6C, (5C) and 4C

compounds ;

2. CO2 formed / reference to decarboxylation / eq ;

3. ATP formed / eq ;

4. reference to dehydrogenation ;

5. reduced {NAD / FAD / coenzyme} produced ;

6. reference to substrate level phosphorylation ;

7. idea of 4C compound used to regenerate 6C compound (which allows cycle to continue) ;

max (3)

Question Number

Answer Mark

3(c)

1. production of ATP ; 2. heat / maintain body temperature / {wasted /

lost} / eq ;

(2)

42

Question Number

Answer

Mark

4(a)(i)

1. any appropriate working ;

2. answer in the range 2.1 to 2.4 dm3 ;

(2)

Question Number

Answer Mark

4(a)(ii)

1. {10 / 10.5} breaths in 30 seconds / (10 ÷ 30) x 60 ;

2. {20 / 21} breaths per min ;

(2)

Question Number

Answer Mark

4(a)(iii)

1. {tidal volume / eq} lower at rest / converse ; 2. {breathing rate / eq} slower at rest / converse ;

3. credit correct comparative manipulation of

figures ; Note must be comparative statements

max (2)

43

Question Number

Answer Mark

4(b)

Describe:

1. before exercise, breathing rate constant ; 2. during exercise, breathing rate increases and

becomes {constant / eq} from {4.8 / 5} minutes ;

3. after exercise, breathing rate decreases to {starting rate / eq} ;

Explanation:

4. reference to change in {CO2 / pH / eq} in blood ; 5. detected by chemoreceptors ;

6. in carotid / aorta / medulla / eq ;

7. reference to ventilation centre (in medulla) ;

8. idea of nerve connection to {intercostal muscles /

diaphragm} ;

9. reference to involvement of stretch receptors ;

max (5)

44

Question Number

Answer Mark

5

1. reference to rhodopsin ; 2. (rhodopsin ) {breaks down / bleaching / splits / eq}

retinal and opsin ; 3. (opsin) {attaches to / hydrolyses a molecule on}

{cation / ion / Na+} channels (in outer segment) ; 4. (cation) channels close ; 5. influx of Na+ decreases ; 6. (inside) cell {more negative/ hyperpolarised} ; 7. {neurotransmitter / glutamate} release stops ; 8. reference to synapse no longer inhibited ; 9. idea that (cation) channels in {post-synaptic

membrane / eq} {open / depolarised / action potential generated} ;

max (5)

45

Unit SN6 (6136/01) - Synoptic paper


max(3)

1. (they published) the theory of evolution by natural selection / eq ;

2. theory (appeared to) contradict prevailing {creationist / Genesis / biblical / religious / eq} point of view / eq ;

3. especially idea that humans evolved from {primates / apes / monkeys / simpler organisms / eq} ;

4. (theory required) Earth to be much older than thought by most people at the time / eq ;

5. theory caused heated debate / eq ;

6. lack of knowledge of {genes / inheritance / eq} (at the time) ;


max(4)

1. if a CREB gene does not work then (long-term) memories cannot form / eq ;

2. (this is evidence) for role of nature in ability to form memories / eq ;

3. {the act of learning / environmental factors / stimulus / eq} turns on the genes / if you do not learn anything genes are not activated / eq ;

4. (this is evidence) for the role of {nurture / environment} in ability to form memories / eq ;

5. CREB genes needed to form new synapses ;

6. synapses store memories in the brain / eq ;

46

Question Answer Mark Number 1(c)

Markchang

max(4)

as a pair i.e. change & effect – maximum 2 es

1. habitat destruction by humans / deforestation / eq ;

2. effect on human population e.g. less water available ;

3. climate change / global warming / eq ; 4. effect on human population e.g. flooding ;

5. overfishing / overstocking / overhunting / eq ;

6. effect on human population e.g. loss of food supply ;

7. named pollutant e.g. heavy metal ; 8. effect on human population e.g.

contaminated water ;

9. overcrowding / eq ; 10. e.g. more disease / lack of clean water

supplies / eq ;

47

Question Answer Mark Number 1(d)

Reas reement about If th

If th

max(2)

on must be linked to agreement or disagStephen Mobley’s defence.

ey disagree with his defence:

1. {environment / nurture} also effects {behaviour /personality / genes} /eq ;

2. knowledge of {instinct /criminal tendency /eq} can make it possible to {overcome /avoid /override} that instinct / eq ;

3. we still have choices / free will despite influence of genes / eq ;

ey agree with the defence:

1. his inherited genes from his criminal ancestors caused him to commit murder ;

2. genes determine his personality / nature causes his instinct /eq ;

3. genes prevent ‘free will’ / eq ;

Question Answer Mark Number 1(e)

max(2)

1. if {young rats / pups} are groomed by their mothers, {their DNA is not methylated /a methyl group is not added to their DNA} ;

2. a receptor gene (in the hippocampus) responsible for mediation of stress not affected / eq ;

3. groomed rats produce lower levels of stress hormones ;

48

Question Answer Mark Number 1(f)

max(2)

1. twin studies help to quantify the relative contribution of genes and the environment (in determining a characteristic) /eq ;

2. {identical twins /twins with the same genes} have 80% correlation (in body mass) AND {fraternal twins/non-identical twins} have {43% / less} correlation (in body mass) ;

3. (therefore) both {genes / nature} and {the environment / nurture} have an influence on body mass ;

4. if identical twins show any differences it must be due to the environment / eq ;

Question Answer Mark Number 1(g)

max(3)

1. gene {expression / transcription /induction} is influenced by other {genes / proteins made by other genes} ;

2. transcription factors are products of other genes / eq ;

3. correct reference to {promoters / transcription initiation complexes} ;

4. characteristics can be determined by {several different genes / environmental factors / polygenic /multifactoral} ;

5. correct reference to epistasis ;

49


max(4)

(i) 1. natural selection / survival of the fittest / eq ;

2. different selective pressures in each place / evolved according to local environmental conditions / eq ;

3. (random) mutations (in each place) / founder effect ;

4. reproductive isolation / different species can not inbreed / eq ;

5. geographical isolation / (sea is a) barrier to gene flow / eq ;

6. (sea is a) barrier to exchange of pollen / seeds ;

7. reference to {allopatric/ eq} speciation ;

8. genetic drift / eq ;


succ

(1) (ii) ession / colonisation ;


redu

(1) (iii) ced competition (from other plants) / eq ;

Question Number

Answer Mark

2(a)(iv)

limited genetic diversity / small gene pool / inbreeding / less

(1)

frequent mutations / eq ;

50

Question Number

Answer Mark

2(b)

1. {characteristic of / phenotype of / round / purple

2. because these characters are the same in both

3. {stem length / spacing of leaves} is

inerals}} /

4. because these characters are different in both

5. {stem length / spacing of leaves} is caused by {soil

max(3)

/ hairy} leaves are determined by genes / eq ;

soils / eq ;

{environmental / affected by {soil / meq ;

soils / eq ;

/ edaphic} conditions rather than climate / eq ;

51

Question Number

Answer Mark

2(c)

1. numbers (of Edmondston’s Chickweed) have been

2. the number of growing days has been increasing /

3. growing days data very variable (trend difficult to

4. possible increase in rainfall / pattern {not a very

5. (according to Figure 5) the numbers (of

variable

6. so {difficult / too early} to establish if there is a

7. (according to Figure 6) plant data only comes

of

8. no direct measurement of temperature / eq ;

9. (according to Figure 5) no data was collected

10. no statistical evidence / eq ;

11. reference to other factors may affect growth ;

12. credit specific reference to data illustrating a

max(4)

declining since 1995 / the decline was steep 1996 to 2000 ;

eq ;

recognise) / not a long enough series of data to establish long term trends / might be only short term patterns / eq ;

clear one / inconclusive} ;

Edmondston’s Chickweed) have been very(1978-2006 / over past three decade) ;

long-term trend / eq ;

from one quadrat – may not be representative the whole site ;

between 1996 and 2006 ;

point or trend e.g. maximum growth does not correspond with {maximum rainfall / maximumgrowing days} ;

52

Question Number

Answer Mark

2(d)

1. allows observations on exactly the same area /

2. allows comparisons year on year / eq ;

(2)

eq ;

Question Number

Answer Mark

2(e)

1. GPP = photosynthesis only / eq ;

2. NPP = photosynthesis – respiration / eq ;

3. temperature increases {metabolism / chemical

4. reference to enzymes (being effected by

5. (temperature has) greater effect on respiration /

6. photosynthesis limited by another factor (other

max(4)

reactions / respiration} / reference to kinetic effect ;

temperature) ;

respiration going up faster than photosynthesis / eq ;

than temperature) / eq ;

53

3. While our biological understanding and medical technology may have advanced

ctised

Blood – The fluid of life’: Write an essay about the importance of blood and circulatory

Breadth: maximum of 6 marks

te if e

le. If

ly

to

cript

Depth: maximum of 8 marks andidates

e an idea

m of 4 B marks per

he script as

considerably over the last 200 years, the art of balancing bodily fluids has been prafor centuries. ‘systems.

These marks are to be awarded to the candidathey successfully introduce thgeneral area of Biology relevant to the essay tita relevant B point is awarded then the corresponding A pointshould also be awarded. Key ideas to look for are in bold type – the candidate need onshow evidence that he or she realises that key idea is appropriate in the essay gain a breadth (A) mark. Indicate A1 to A10 on the sas appropriate

These marks are awarded to cfor demonstrating an understanding of relevant A level biological detail expanding on the areas of biologyintroduced in A. This list is not exhaustive but is designed to givof the type of response worthy of credit for a (B) mark. Allow a maximucorresponding A mark. Indicate B1a to B10a on tappropriate

1 iscussion/explanation of

1a

1b

1c

escription of mass transport

iscussion of limitations of diffusion to

escription of what is meant by blood

A Dwhy many animals/humanshave a heart and circulation

B B B

D Dprovide an organisms needs Dpressure and how it is involved in masstransport

2

iscussion of the role of

2a

2b

2c

2d

tructure of arteries and veins compared

tructure of capillaries related to their

iscussion of the advantages of a closed

etailed description provided of the es

A Dblood vessels

B B B B

Sand related to their functions Sfunction in exchange systems Dcirculatory system compared to an open circulatory system Ddifferent layers of tissue in the arteriand veins related to their functions e.g. tunica media, collagen and elastin fibres etc.

54

A3

Discussion of the structure and function of the heart

B3a B3b B3c B3d

Discussion of the double circulatory system and why it is an advantage to pump the blood twice for each complete circuit of the body Good description of the structure of the heart including 4 chambers, valves, etc – may be included in a diagram Good description of the cardiac cycle including diastole, atrial systole, ventricular systole Description of the control of the cardiac cycle including {SAN/eq} and AVN as a minimum

A4

Discussion of the role of the blood in transport around the body

B4a B4b B4c B4d B4e

At least 3 named examples of materials carried around the body via the blood Role of blood in the endocrine system explained with at least one example Good description of at least one exchange network together with the molecules exchanged and why e.g. oxygen and glucose going into tissue fluid for providing cells the things needed for aerobic respiration, while removing carbon dioxide for excretion in the lungs Description of how carbon dioxide is carried in the blood including reference to hydrogen carbonate Correct reference to the Bohr shift and how it helps the release of oxygen from haemoglobin in actively respiring tissues

A5

Description of the cells associated with blood

B5a B5b B5c B5d

Reference to red blood cells, white blood cells and platelets Description of how oxygen is carried in red blood cells involving haemoglobin Description of the role of platelets in blood clotting Discussion of the role of the bone marrow / stem cells in the production of new blood cells

55

B5e

Discussion of the role of erythropoietin in the stimulation of the production of more red blood cells

A6

Description of the role of blood in homeostasis

B6a B6b B6c B6d B6e

Explanation of the role of negative feedback in maintaining systems within narrow limits Description of a control mechanism for CO2 levels Description of the role of blood in the distribution of heat and thermoregulation, especially vasoconstriction / vasodilation Osmoregulation /oedema related to role of blood / blood pressure / damage to blood vessels Reference to receptors in circulatory system e.g. chemoreceptors

A7

Discussion of the role of the blood system in defence and immunity

B7a B7b B7c B7d B7e B7f B7g

Description of the blood clotting process including at least 2 of thromboplastin, prothrombin and fibrinogen Discussion of antibodies and how they can affect antigens Description of how plasma cells are produced and stimulated into producing antibodies – include antigen activation and role of cytokines Description of role of killer / cytotoxic T cells Discussion of how immunity may be acquired including the role of memory cells Description of role of phagocytic blood cells such as macrophages in the non specific immune system / antigen presentation / describe the role of blood cells in the inflammatory response Reference to role of T helper cells and cytokines

56

A8

Discussion about conditions that can affect the health of the blood or circulatory system.

B8a B8b B8c B8d B8e B8f B8g B8h B8i B8j

Clear description of atherosclerosis / blood clots leading to stroke / myocardial infection / eq Discussion of the potentially damaging effects of high blood pressures and conditions that can lead to high blood pressure e.g. obesity / stress Discussion of inheritance of risk such as hypercholesterolemia. Discussion of effect of diet / drugs on balance / risk of atherosclerosis etc with at least one clear named and explained example Discussion about leukaemia and its effects Discuss the importance of balancing LDL and HDLs Haemophilia Auto-immune responses Description of the effect of blood loss e.g. shock Sickle cell anaemia

A9

Discussion about medical intervention and the heart/blood/circulatory system.

B9a B9b B9c B9d B9e B9f

Discussion of at least one named drug and its effect on the blood e.g. warfarin, aspirin, etc. Discussion of surgery e.g. balloon angioplasty, heart transplants, valve replacements etc. Discussion of xenotransplantation as a potential alternative to human donor organs due to shortages of suitable donors Discussion about lifestyle factors that can be changed to reduce risk of CVD (do not credit exercise here) Reference to blood donors saving lives. Blood used to test / research drugs / eq

57

A10

Discussion about exercise and the effects it can have on the circulatory system

B10a

Discuss the benefits of exercise on the cardiovascular system such as strengthening the cardiac muscle, stimulating red blood cell formation, reducing cholesterol levels etc.

Unpacking the question:

C1 Response shows a clear understanding that a circulatory system enables animals to grow bigger and maintain a higher metabolic rate. C2 Good description conveying a clear message that a healthy circulatory system is needed for the health of the entire organism. C3 Descriptions of the effects of the sympathetic and parasympathetic nervous systems on the circulatory system. C4 Clear description of tissue fluid formation and how tissue fluid is returned to the circulatory system. C5 Outline description of the lymphatic system and its roles in association with the circulatory system. C6 Response includes a clear comparison of the systemic and pulmonary circulatory systems together with their roles. C7 Response shows a clear understanding that control of the circulatory system enables the body to respond to different demands placed upon it. E.g. in response to adrenaline increased blood flow to muscles and brain, but decreased flow to digestive system enables improved response to danger. C8 Comparison between blood flow in veins and arteries, including how movement of blood is achieved in veins. C9 Clear description about how cardiac muscle is unique and different to skeletal and smooth muscle, e.g. myogenic and does not fatigue. C10 Importance of the coronary circulatory system to supply the cardiac muscle with what it needs.

58

D: Coherence, clarity and expression of the answer: maximum of 4 marks This strand will award students for style of their answer and is quite distinct from mentioning the big ideas (C). It isn’t what candidates say but how they say it. 4 marks: A truly synoptic essay which links together information from different parts of the specification in a coherent and logical style (introduction, conclusion, good use of paragraphs and well illustrated by examples). Good spelling, punctuation, grammar and sound use of technical terminology. 3 marks: Good logical structure with good spelling, punctuation, grammar and sound use of technical terminology, but tends to be a collection of information which, although relevant, tends to be disjointed and only partly attempts to synthesise information. 2 marks: A reasonably coherent account that includes satisfactory spelling, punctuation and grammar, which tends to be disjointed. A collection of information with little or no attempt to link ideas together. 1 mark: Some relevant information is presented in an intelligible way using correctly formulated simple sentences. 0 marks: The use of English is not adequate to convey scientific information beyond naming a list of examples. A candidate who has scored some marks (particularly in strand A) for mentioning some relevant points may nevertheless fail to score marks in strand D if he or she fails to form simple sentences. Note that the maximum total mark which can be awarded is 20

59

4. In the absence of enzymes, chemical reactions in organisms would be too slow to sustain life. ‘Enzymes – The miracle molecules’: Write an essay about the structure and functions of enzymes.

Breadth: maximum of 6 marks These marks are to be awarded to the candidate if they successfully introduce the general area of Biology relevant to the essay title. If a relevant B point is awarded then the corresponding A point should also be awarded. Key ideas to look for are in bold type – the candidate need only show evidence that he or she realises that key idea is appropriate in the essay to gain a breadth (A) mark. Indicate A1 to A11 on the script as appropriate

Depth: maximum of 8 marks These marks are awarded to candidates for demonstrating an understanding of relevant A level biological detail expanding on the areas of biology introduced in A. This list is not exhaustive but is designed to give an idea of the type of response worthy of credit for a (B) mark. Allow a maximum of 4 B marks per corresponding A mark. Indicate B1a to B11 d on the script as appropriate

A1

Description of enzymes as catalysts

B1a B1b B1c B1d B1e

Lower activation energy Provide alternative reaction pathway (via enzyme/substrate complex) Speed up reactions without being used up themselves The presence of an enzyme does not alter the nature or properties of the end products of the reaction Enzymes are very efficient: a very small amount of enzymes brings about the change of a large amount of substrate.

A2

Enzymes are proteins

B2a B2b B2c B2d

Globular proteins Hydrophilic {R groups/eq} on outside of the protein and inside active site enable enzymes to work in aqueous solutions Most enzymes are far larger than the substrates they act on Good description of levels of protein structure and shape provided

60

A3

Mechanism of enzyme action

B3a B3b B3c B3d

Enzymes are specific to their substrate due to the shape of their active site Correct description of lock and key hypothesis of enzyme action Correct description of induced fit hypothesis of enzyme action Evidence for enzyme action has come from X ray crystallography and/or computer assisted modelling

A4

Factors affecting the rate of enzyme reactions

B4a B4b B4c B4d B4e B4f B4g B4h B4i B4j B4k

pH and temperature Substrate concentration and enzyme concentration Rate of reaction is measured by the amount of substrate changed, or amount or product formed, during a period of time Description of temperature coefficient Q10

Temperature affects kinetic energy of molecules and shape of the protein / can denature the enzyme Explanation that changes in pH alter the ionic charge of acidic and basic groups of amino acids and therefore effect ionic bonding in the enzyme Small changes in pH may produce reversible changes in the shape of the active site, larger changes will produce permanent denaturation Enzyme/substrate concentrations (and kinetic energy) effect number of collisions and therefore number of enzyme/substrate complexes formed Enzyme inhibitors mentioned Good description of competitive or non competitive inhibitors provided Reference to role of coenzymes / cofactors

61

A5

Role of enzymes in respiration/photosynthesis


Role of coenzymes described for photosynthesis or respiration e.g. NAD, NADP, Coenzyme A Most enzymes associated with respiration and photosynthesis are found packaged into a specialised organelle to increase their concentration Matrix of mitochondria / stroma of chloroplast Calvin cycle / glycolysis / Krebs cycle / link reaction enzyme controlled Example of specific action of a named enzyme within photosynthesis or respiration e.g. ribulose bisphosphate carboxylase (Rubisco), alcohol dehydrogenase, glucose isomerase, decarboxylase enzymes, dehydrogenase enzymes Reference to ATPase / chemiosmosis

A6

Role of enzymes in replication/transcription/cell cycle

B6a B6b B6c B6d B6e B6f B6g B6h

Helicase in DNA replication DNA polymerase needed to synthesise new DNA strand in replication DNA ligase used to fill in gaps on one of the newly synthesised DNA strands RNA polymerase needed to make RNA in transcription Enzymes needed to load tRNA molecules with amino acids Enzymatic action of ribosomes forms peptide bonds between amino acids in translation Active CDK stimulates mitosis in the cell cycle Reverse transcriptase / integrase in retrovirus replication

62

A7

Role of enzymes in anabolism/catabolism of other biological molecules e.g. digestion

B7a B7b B7c B7d B7e B7f B7g B7h B7i

Role of enzymes in the digestive system described Specific examples of at least 2 digestive enzymes mentioned Role of enzymes in forming bonds by condensation reactions to build up biological molecules e.g. starch/ cellulose/ glycogen/ proteins, etc. Describe digestion of food as an example of a hydrolysis reaction. Role of enzymes in germinating seeds described Role of enzymes in decomposition Role in autolysis of cells Role of ATPase in hydrolysis of ATP in muscle contraction Role of enzymes in acrosome reaction

A8

Role of enzymes in gene technology


DNA polymerase needed for PCR Restriction enzymes used to cut DNA Ligase used to join strands of DNA together e.g. making recombinant DNA for genetic modification, gene therapy, etc. Cellulases used to make plant protoplasts for genetic modification Reverse transciptase Integrase

A9

Other Industrial applications of enzymes

B9a B9b B9c

Biological washing powders/stain removers Used in brewing e.g. malting/mashing process Predigest baby foods e.g. trypsin

63

B9d B9e B9f B9g B9h B9i B9j B9k B9l B9m B9n

(B galactosidase/lactase) used to digest lactose in milk for lactose intolerance (Cellulases/pectinases) to produce fruit juice (Rennin) to make cheese Meat tenderisers (Amylases) used to make syrups from starch (Glucose isomerase) converts glucose into fructose for high sweetness but low calorific values Used in paper industry Cellulases used to break down cellulose into sugars for the biofuel industry. Proteases used in contact lens cleaners to remove proteins and prevent infections (Proteases) used to reclaim silver from photographic film Reference to immobilisation of enzymes

A10

Role of enzymes in controlling synapses

B10a B10b B10c B10d

Enzymes break down neurotransmitters at synapses (to prevent continuous activation of the synapse) Drugs may affect synapses by blocking/inhibiting the action of the enzymes that breakdown the neurotransmitter Example e.g. acetylcholinesterase Reference to condition caused by an imbalance of neurotransmitter if linked to enzymes activity e.g. Parkinson’s disease

64

A11

Enzymes associated with the immune system

B11a B11b B11c B11d

Lysozyme to digest cell walls in bacteria in tears, etc. Role of enzymes in blood clotting e.g. thromboplastin, thrombin Proteases released by {killer / cytotoxic} T cells to destroy infected cells Hydrolytic enzymes used by phagocytic white blood cells to destroy pathogens etc

Unpacking the question:

C1 Reactions can take place at a high rate at a temperature suitable for living organisms due to action of enzymes.

C2 Enzymes often work together in metabolic pathways, where the reactions proceed in a controlled manner due to the specific nature of the enzymes.

C3 Mutations in genes can alter the structure of the protein made, effecting {the tertiary structre/ 3D shape} and therefore may change the active site and function of an enzyme.

C4 Description of lac operon to convey the control of enzyme production by the substrate it acts on.

C5 Coenzymes act as cofactors but do not remain attached to the enzyme between reactions e.g. NAD, coenzyme A

C6 Some enzyme pathways are regulated by the products they produce – end- product inhibition or negative feedback inhibition.

C7 Homeostasis is vital in the body to maintain optimum conditions for enzyme activity.

C8 Enzymes are adapted to have optimums corresponding to the position of the enzymes activity e.g. pepsin optimum pH ~2.

C9 Bacteria thrive in a wide range of environments and therefore their enzymes may work in environmental extremes as well, making them useful for industrial applications.

65

D: Coherence, clarity and expression of the answer: maximum of 4 marks This strand will award students for style of their answer and is quite distinct from mentioning the big ideas (C). It isn’t what candidates say but how they say it. 4 marks: A truly synoptic essay which links together information from different parts of the specification in a coherent and logical style (introduction. Conclusion, good use of paragraphs and well illustrated by examples). Good spelling, punctuation, grammar and sound use of technical terminology. 3 marks: Good logical structure with good spelling, punctuation, grammar and sound use of technical terminology, but tends to be a collection of information which, although relevant, tends to be disjointed and only partly attempts to synthesise information. 2 marks: A reasonably coherent account that includes satisfactory spelling, punctuation and grammar, which tends to be disjointed. A collection of information with little or no attempt to link ideas together. 1 mark: Some relevant information is presented in an intelligible way using correctly formulated simple sentences. 0 marks: The use of English is not adequate to convey scientific information beyond naming a list of examples. A candidate who has scored some marks (particularly in strand A) for mentioning some relevant points may nevertheless fail to score marks in strand D if he or she fails to form simple sentences. Note that the maximum total mark which can be awarded is 20

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Further copies of this publication are available from Edexcel Publications, Adamsway, Mansfield, Notts, NG18 4FN Telephone 01623 467467 Fax 01623 450481 Email [email protected] Code UA 019993 Summer 2008 For more information on Edexcel qualifications, please visit www.edexcel.org.uk/qualificationsEdexcel Limited. Registered in England and Wales no.4496750 Registered Office: One90 High Holborn, London, WC1V 7BH

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SNAB Biology - Mark Scheme June 09

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