SN June 2007 MS.pdf - HG Biology

Mark Scheme Summer 2007

GCE Mark Schemes

GCE SNAB Biology (8048/9048)

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Summer 2007 Publications Code UA018960 All the material in this publication is copyright © Edexcel Ltd 2007

Contents General Introduction

p ii

General Information

p iii

Mark Schemes

Unit SN1

6131

Lifestyle, Transport, Genes and Health

p1

Unit SN2

6132

Development, Plants and the Environment

p8

Unit SN3

6133 paper 02

Practical Work Review

p 19

Unit SN4

6134

Environment and Survival

p 21

Unit SN5

6135 paper 01 written paper

Energy, Exercise and Coordination

p 28

Unit SN6

6136

Synoptic paper

p 34

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 AS

A2

Unit

Code

Unit Title

1

6131

Lifestyle, Transport, Genes and Health

2

6132

Development, Plants and the Environment

3

6133

Report and Practical Review

4

6134

Environment and Survival

5

6135

Energy, Exercise and Coordination; Coursework Investigation

6

6136

Synoptic Paper

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GENERAL INFORMATION The following symbols are used in the mark schemes for all questions: Symbol ; semi colon eq / oblique {} curly brackets () round brackets [] square brackets

Meaning of symbol Indicates the end of a marking point Indicates that credit should be given for other correct alternatives to a word or statement, as discussed in the Standardisation meeting Words or phrases separated by an oblique are alternatives to each other Indicate the beginning and end of a list of alternatives (separated by obliques) where necessary to avoid confusion Words inside round brackets are to aid understanding of the marking point but are not required to award the point 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.

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June 2007

GCE Biology SNAB Unit 1 – 6131/01

Unit SN1 (6131) Question 1

Maximum mark

(a)

{fatty deposits / plaques / cholesterol / atheroma / eq} {narrows / blocks} arteries; less blood flow {to cardiac muscle (cells/tissues) / through coronary artery}; less oxygen; anaerobic respiration; build up of {lactic acid / lactate} (causes pain); 3 marks

(b)

(i)

(ii)

1873, 1614, 1790 kJ; [all three required for (1) mark]

1 mark

A; 1 mark

(iii)

A less saturated fatty acids / FA; less {cholesterol/LDLs} (made by liver); less / no cholesterol in diet; less chance of atherosclerosis/eq / {atheroma / fats} building up / depositing / being laid down on arteries; 3 marks Total 8 marks

June 2007

1

GCE Biology (Salters-Nuffield)

June 2007


Question 2

(a)

(i)

Maximum mark

arrows moving from direction of veins through the atria towards ventricles on both sides; 1 mark

(ii)

sinoatrial node / SAN / pacemaker; 1 mark

(b)

(i)

some backflow of blood {(from ventricle) to atrium / through A-V valve}; during ventricular systole / eq; less blood (pressure) into the {aorta / artery}; less (efficient supply of) oxygen to the body / muscles / less aerobic respiration; 2 marks

(ii)

ECG / electrocardiogram / MRI / magnetic resonance imaging / CT scan / CAT scan / blood pressure monitor / sphygmomanometer; 1 mark Total 5 marks

June 2007

2


June 2007


Question 3 (a)

Maximum mark

mother’s and father’s genotypes correctly stated e.g. mother Aa and father aa; gametes shown clearly and correctly; F1 genotypes clearly linked to phenotypes; probability 50% / 0.5 / 1in 2 / ½ / eq; 3 marks

(b)

(i)

amniocentesis / chorionic villus sampling / CVS / pre-implantation genetic diagnosis / PIGD; 1 mark

(ii)

1. extract DNA from cells; 2. cut DNA using a restriction enzyme; 3. gel electrophoresis; 4. credit one further correct detail of gel electrophoresis; 5. treat with alkali / make DNA single stranded; 6. southern blotting / transfer to a {nylon/nitrocelluose} membrane; 7. use of a gene probe; 8. further detail of a gene probe (complementary sequence / radioactively labelled / fluorescent marker / eq); 9. disclosure {x-ray film / UV light / laser}; 10. comparison with marker gene; 5 marks Total 9 marks

June 2007

3


June 2007


Question 4 (a)

(i)

Maximum mark X: phospholipid; Y: (channel) protein; Z: glycoprotein / carbohydrate; 3 marks

(ii)

(b)

P: (passive) diffusion; Q: active transport; R: facilitated diffusion;

3 marks

1. CFTR protein defective / eq; 2. chloride ions remain in cells / eq; 3. mucus lacks water/is very sticky / eq; 4. mucus blocks pancreatic (duct); 5. {fewer enzymes / correctly named enzyme} released into the small intestine; 6. lower concentration of enzymes / fewer active sites; 7. fewer collisions between substrate and the active site of the enzymes / named substrate and enzyme; 4 marks Total 10 marks

June 2007

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June 2007


Question 5 (a)

Maximum mark

(i)

ester;

(ii)

hydrolysis;

1 mark 1 mark

(iii)

fatty acids; glycerol; 2 marks

(iv)

unsaturated / eq are {liquid at room temperature / lower melting point} whilst saturated / eq solid at room temperature; MUST be a comparative point 1 mark

(b)

(i)

phosphate;

(ii)

ref. to {hydrophilic / charged / polar / water attracting} {head/group} and {hydrophobic /not charged / non-polar / water repelling} {tail /group } / eq; ref. to forming a bilayer; ref. to orientation in membrane; 2 marks

1 mark

Total 8 marks

June 2007

5


June 2007


Question 6

(a)

(i)

Maximum mark

E: phosphate; F: ribose; G: uracil; 3 marks

(ii)

nucleus; 1 mark

(b)

(i)

Tyr, Val, Glu, Arg;; 2 marks

(ii)

translation; 1 mark

(iii)

1. change in amino acid sequence / primary structure of the protein; 2. Tyr replaced by a stop codon / UAG; 3. {polypeptide chain/protein} would be shorter / eq; 4. protein would have a different shape/structure / fold differently / eq; 5. protein would not function (normally); 6. RNA polymerase not functioning would mean that {no/less} transcription could take place; 7. {no/less} RNA could be synthesised by this cell; 8. {no/less} proteins could be made by this cell; 5 marks Total 12 marks

June 2007

6


June 2007


Question 7

(a)

Maximum mark

energy / glucose storage; 1 mark

(b)

(i)

diagram showing 1 glucose molecule / monosaccharide; diagram shows H and OH groups on each of carbon 1 and carbon 4; 2 marks

(ii)

(c)

ref to specificity / shape; correct ref to active site on enzyme; correct ref to enzyme-substrate complex / eq; lock and key concept / induced fit; ref to amino acids in proteins versus glucose in glycogen / peptide versus glycosidic bonds;

3 marks

reduces activation energy / provides an alternative reaction pathway; (biological) catalyst / speeds up reaction without being used up; allows reactions to occur rapidly at body/lower temperature; 2 marks Total 8 marks

PAPER TOTAL 60 MARKS

June 2007

7


June 2007


Unit SN2 (6132/01) Question 1

Maximum mark

Feature

Sperm

Egg

Tail

9

X

(i)

Haploid nucleus

9

9

(ii)

Acrosome present

9

X

(iii)

Mitochondria present

9

9

(iv)

Cytoplasm containing many lipid granules

X

9

(v)

Use ATP for movement

9

X

(1) per line NB an empty box = (0) for that line a tick/cross hybrid = (0) for that line Total 5 marks

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June 2007


Question 2

(a)

(i) (ii)

Maximum mark

onion / garlic / other suitable species; root tip; 2 marks

(b)

(acidic/acidified/acetic/ethanoic/propanoic) orcein / feulgen / toluidene blue; 1 mark

(c)

to macerate them/to separate the cells;

(d)

A = centromere; B = chromatids;

1 mark

1 mark Total 6 marks

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June 2007


Question 3

(a)

Maximum mark

by wind; large surface area / spins as it falls / falls more slowly / eq; increases chances of being blown further; 2 marks

(b)

(i)

(ii)

{thick / tough / strong / impermeable / {enzyme/decay} resistant} {(seed) coat / testa} / reference to dormancy;

identify appropriate food store e.g. starch / carbohydrate / lipid / triglycerides / protein; starch / carbohydrate / lipid / fatty acids and glycerol provide energy; protein / amino acids for growth;

1 mark

2 marks Total 5 marks

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June 2007


Question 4 (a)

(i)

Maximum mark height (partly) determined by genes; half of child’s genes (for height) from each parent / children of tall parents more likely to inherit genes for tallness (than children in general); {taller children / children of tall parents}stronger / more likely to survive (in the past); tall {women/men} might be {more fertile / more able to survive child birth}; tall people tend to marry tall people; 3 marks

(ii)

protein/amino acids {important/needed/essential} for growth / making new cells; in the past growth of (many) children was limited by lack of protein (compared with today)/ adequate protein intake needed to reach genetic potential/eq / reference to dietary protein a source of amino acids to make human protein; improved quality of protein / all necessary amino acids; 2 marks

(iii)

children who are (frequently) unwell do not grow (as well as healthy ones); sick children use resources to fight disease instead of for growing; sick children have reduced appetite/vomit a lot/have poor digestion; 1 mark

(b)

mutation / reference to tumour repression substance; triggered off by carcinogenic substances / tar in tobacco smoke; leading to uncontrolled cell division; leading to formation a mass of cells / tumour; cycle/rate of cell formation exceeds rate of cell death/apotosis; NOT ‘more cell division’, ‘damages DNA’ 3 marks Total 9 marks

11


June 2007


Question 5

(a)

Maximum mark

reduced enzyme activity / metabolic activity / metabolism / eq; 1 mark

(b)

global warming / climate change / getting warmer on average {year on year/eq} / they have evolved / natural selection; 1 mark

(c)

hibernate before it gets cold / might be too late to hibernate once it gets cold / day length better indicator of season than temperature; 1 mark

(d)

genes / genetic factors / mutation; not triggered by temperature change / it is genes (controlling response to day length) which trigger hibernation; 2 marks Total 5 marks

12


June 2007


Question 6

(a)

Maximum mark

signal protein {binds to / joins to / interacts with / activates} receptor on surface membrane; messenger molecule crosses cytoplasm and enters nucleus; {produces / activates} transcription factor; reference to gene switching / gene promotion; so transcription occurs / description of transcription e.g. in terms of base pairing; 3 marks

(b)

DNA retained as master copy / eq; DNA molecules are {much larger (than RNA)/{unable/too big} to pass through nuclear pores}; DNA double helix while RNA single strand / eq; proteins cannot be made in nucleus /made in cytoplasm on ribosomes; amino acids must be assembled in the sequence specified by genetic / DNA code; 2 marks

(c)

pass through RER; vesicles made; vesicles fuse with Golgi apparatus; proteins modified to active form; vesicles budded off Golgi apparatus; ref to exocytosis / description e.g. fusing with membrane;


13


June 2007


Question 7 (a)

(i) (ii) (iii) (iv)

Maximum mark photosynthesis; decomposition; respiration; combustion; 4 marks

(b)

(i)

(coal contains) carbon that has been taken from the atmosphere (in the past) / carbon that has been taken out of circulation (in the carbon cycle); 1 mark

(ii)

burning wood does not add to the amount of CO2 in the atmosphere / does not cause a net increase; carbon dioxide in (roughly) equals carbon dioxide out; burning wood releases carbon recently absorbed (by photosynthesis) / burning fossil fuels releases CO2 trapped a long time ago / eq;

2 marks

(c)

not enough room to keep planting enough forest to use up all the surplus CO2; a {mature/fully grown} forest is carbon neutral / only {young / growing} forest is a net absorber / eq; in the end the forest will die and decay / be burnt by humans; 2 marks Total 9 marks

14


June 2007


Question 8 (a)

Maximum mark

One mark (an honest attempt to make the contrast): Global warming is a (general) increase in the temperature of the atmosphere / environment whereas greenhouse effect (is a way of explaining) explain why it is happening/the trapping of heat (in the atmosphere) / greenhouse effect is how the sun keeps the Earth warm whereas global warming is an increased greenhouse effect / greenhouse effect causes global warming; Two marks – As for one mark plus further detail: Global warming is {an increase in global mean surface temperature/average of measurements made in many different places throughout the world} / current global warming may be due to (anthropogenic) burning of fossil fuel / global warming is a fact whilst greenhouse effect is a theory / two greenhouse gases named;; Three marks (makes the contrast with some detail and which clarifies fact and conjecture and clearly disentangles global warming, greenhouse effect and the possible role of burning fossil fuels): As for two marks but also: widely believed that (some clear implication that it may not be the only explanation) current global warming is due to {enhanced/increased} greenhouse effect due to raised CO2 concentration (of the atmosphere) / global warming may be caused by something other than greenhouse gases e.g. changes in solar radiation;;; 3 marks

(b)

(i)

any reasonable attempt at a J shaped curved best fit line;

(ii)

credible attempt at extrapolating the line as a curve; for correctly reading both points off the candidates own extrapolated graph; (would expect 0.50C for 2000 and around 1.2oC for 2020 if extrapolated as a curve or 1.0oC extrapolated as a straight line) for subtracting to get increase using own figures (e.g. 1.1-0.5 = 0.6oC) including units; 3 marks

(iii)

assumes present trend continues; line not based on long enough series of data / older data may be less accurate / reliable; (graph shows) that temperature has fluctuated (over period 1880 – 2000); numerical evidence taken from graph to illustrate an occasion when the temperature fell approx 1900 to 1908 or approx 1945 to 1970 ; ALLOW any reasonable attempt to use figures to make a valid point about predicting future climate from these data; some unpredictable event may affect trend e.g volcanic eruption / sharper than expected change in fossil fuel consumption / changes in solar radiation;

1 mark

3 marks

15


June 2007


Question 8 continued (c)

Maximum mark

enzymes temperature sensitive / damaged by high temperature; damage to enzymes may affect respiration / metabolic activity / photosynthesis / supply of energy; may give competitor an advantage; may affect water availability; may affect supply of food plants / prey species / predators; change of sex ratio in reptiles / crocodiles; 2 marks Total 12 marks

16


June 2007


Question 9 (a)

Maximum mark

(i)

(superovulation) from IVF treatment;

(ii)

totipotent cells can give rise to a complete human/all cell types; pluripotent can only give some cell types;

1 mark

2 marks (b)

(i)

cells allowed to multiply / produce more cells; in petri dish/test tube / any reasonable attempt to refer to suitable culture vessel; reference to culture medium/incubator/sterile conditions; to produce more (identical) cells; 2 marks

(ii)

cell becomes specialised (in function)/stem cells develop into different types of cells; cells stop dividing; one type of cell can be used to produce a specific type of tissue / named example; one cell type can be sued to produce tissue / use of named example; 2 marks

(c)

This question is intended to test the candidate’s ability to deal thoughtfully with a moral dilemma and to balance scientific knowledge and ethical considerations. These are the kinds of skills developed through well-informed class discussion. Candidates must decide for or against - a candidate who does not make his or her choice clear is limited to a maximum of 3 marks. A candidate who presents points for and against without expressing an opinion is limited to a maximum of 3 marks for valid points either for or against (which ever is the greater) unless he or she presents a good case why the matter is too finely balanced to come down one way or the other. To gain 4 marks a candidate must include one of the points marked with an asterisk in the mark scheme which attempts to counter the opposing view.

Against: • Embryonic stem cells are (potential) people/babies; • From the moment of conception; • Objectional on religious/ethical grounds; [do NOT credit unqualified statements such as ‘unnatural', against nature' 'playing God’] • Pressure on women to produce surplus embryos; • Cloning/stem cell techniques may get into the wrong hands/regulation might be difficult to police* / might be the thin edge of a wedge like designer babies; • It will soon be possible to use non-embryonic stem cells so research into the use of embryonic stein cells is unnecessary / eq; * • Although there are some advantages there could be unexpected dangerous consequences therefore not worth the risk / eq;*

17


June 2007


Question 9 continued For: • • • • • • •

Maximum mark

Potential for alleviating human suffering / eq*; Specific example e.g. culturing patient's own cells to provide replacement tissues/organs; Stem cells from IVF would otherwise be discarded; Embryos should not be considered as human at an early stage (awareness that only cells at a very early stage are used)*. Use of non-embryonlc cells will need a development phase using embryonic cells / more can be done with embryonic stem cells; Ethically questionable to use embryonic stem cells but these objections are outweighed by the greater evil of not using embryonic stein cells to alleviate human suffering*, Could be excesses but these can be regulated*; 4 marks Total 11 marks

PAPER TOTAL 70 MARKS

18


June 2007

GCE Biology SNAB Unit 3 6133/02

Unit SN3 Practical Review (6133/02) Question 1

Maximum mark

(a) line graph (if appropriate); because continuous data (or eq.); scattergraph, if plotting derived values but (A) if plot all data; justify why (e.g no IV/DV, relationship not causal; bar chart (if appropriate); because discontinuous/discrete/categoric (accept only 2 values as with/without); pie chart; proportionate data (justified); any other suitable type of graph/chart; with data type (and justification of data type) ; 4 marks (b)

(i)

specific pattern(s) described; 1 mark

(b)

(ii)

see degree of error in some suitable way (error/range (plotting all data might demonstrate this) /SD/etc, bars)/display of anomalies 1 mark

Question 2 (a)

invertebrate / vertebrate issues, chose invert because less sophisticated nervous system; therefore less suffering/pain ;

OR (as specific example) Daphnia transparent; thus can monitor HR without needing invasive procedure; OR OR

plant/microbe rather than animal source, because no nervous system; therefore less chance of suffering ; organism to be used for food etc. anyway; will suffer no more in experiment ;

OR human would need consent; not needed from Daphnia ; OR Daphnia not endangered; so no important/worrying/significant population decline as a result of its use; 2 marks

19


June 2007


Question 2 continued (b)

Maximum mark

values lying (equally) above or below the true value; explanation of example can be of error in set-up (e.g. measuring out an IV or monitoring/controlling a CV) OR in measurement of DV); 2 marks

(c)

repeats; identify anomalies; deal with anomaly (e.g. ignore/redo etc); variables controlled (with specifics)/ standardized methods/conditions;; any 3 marks

Question 3 (a)

(i)

vague or verbose (e.g. reasons given, 'because' etc.) for (1); precise and concise for (2); (must be testable so couched in words that allow something to be measured for 2). 2 marks

(ii)

as seen;; correct statement about trend which (usually ) matches hypothesis; supporting data/derived data quoted; 2 marks

(b)

precaution; with precise reason; consequence of not taking measure; 3 marks TOTAL 20 MARKS

20


June 2007


Unit SN4 (6134) Question 1 (a)

(i)

Maximum marks prokaryotae/eq ;

1 mark

(ii) Kingdom

Feature

protoctista / protista

single celled;

fungi plantae animalia

mycelium / hyphae / chitin cell wall / heterotrophic nutrition ; cellulose cell wall/{large/ permanent} vacuole /photosynthesis / autotrophic/ chloroplasts; no cell wall or large vacuoles / heterotrophic;

(1 mark per correct 2 boxes) (rows must match) (b)

(i)

B D E

4 marks

Formica aquilonia Formica exsecta Formica sanguinea

(2) marks for all three, lose one mark per error (ii)

Formica ; 1 mark Total 8 marks

21


June 2007


Question 2 (a)

(i)

Maximum mark BBhh – black, long hair ; bbHH – white, short hair ; 1 mark

(ii)

BbHh ; 1 mark

(b)

(i)

BbHh x bbhh; bh BH BbHh Bh Bbhh bH bbHh bh bbhh 1 for gametes correct ; 1 for offspring correct ; 1 for phenotypes: black short, black long, white short, white long ; 4 marks

(ii)

new combinations of characteristics/alleles ; in offspring but not parents ; example ; 2 marks

(c)

mutation produces new alleles/changes DNA /eq ; independent assortment mixes alleles/ new combinations of alleles ; 2 marks

(d)

provides new alleles / new combinations of alleles / keeps large gene pool ; allows adaptations / allows natural selection /allows response to changes in environment / reduces inbreeding / avoids homozygosity and consequent problems ; 2 marks Total 12 marks

22


June 2007


Question 3 (a)

(i)

Maximum mark A stroma B starch (grain) / lipid droplet C thylakoid (membrane) / chlorophyll D granum (2) for all correct (1) for 2 or 3 correct 2 marks

(ii)

C / thylakoid / granum / D ; 1 mark

(iii)

photolysis/splitting water using light energy ; release of electrons to chlorophyll ; releases hydrogen ions ; oxygen released ; OH source of oxygen ; 3 marks

(b)

reduced production (of carbohydrate) ; less carbon dioxide fixed ; ref RuBP ; ref Calvin cycle / eq ; less carbon available for reduction to carbohydrate ; ref to enzyme / RuBPcarboxylase ; 3 marks

(c)

high light intensity ; ref. to change in wavelength ; high temperature ; high humidity ; high carbon dioxide concentration ; 2 marks Total 11 marks

23


June 2007


Question 4

(a)

(i)

Maximum mark

GPP and NPP similar to start with ; both increase ; (After 2 days) GPP and NPP diverge/eq ; figures in support ; 2 marks

(ii)

more energy is used in metabolism/eq in {older / bigger} plants ; figures in support ; suitable explanation e.g. protein synthesis/flower initiation/differentiation / ref. to herbivores ; more photosynthesis tissue ; (as grows) / eq ; 2 marks

(b)

GPP-NPP=R /eq ; biomass production reduced by respiration / eq ; 2 marks Total 6 marks

24


June 2007


Question 5 (a)

Maximum mark

present inside {cells/ macrophages} ; 1 mark

(b)

B-cells : antibody production ; ref memory cells ; ref plasma cells ; T-cells : antigenic presentation ; stimulation of B-cell proliferation / eq ; 3 marks

(c)

(i)

HIV destroys T (helper) cells ; Bacterial cells not destroyed by the immune system / eq ; Bacteria proliferate/eq ; 2 marks

(ii)

tubercles ; fever ; excessive coughing / coughing blood ; weight loss ; 2 marks Total 8 marks

25


June 2007


Question 6 (a)

Maximum mark

changed body temperature ; (detected by) thermo-regulatory centre/hypothalamus ; ref. to thermoreceptors /eq ; causes changed heat production/changed heat loss ; example heat loss mechanism ; example heat gain mechanism ; return to normal temp ; regulatory mechanisms switched off/eq ; 5 marks

(b)

raised set point ; ref. chemical secretions ; in hypothalamus ; increased body temp/fever ; loss of control if too high/positive feedback ; 2 marks Total 7 marks

26


June 2007


Question 7 (a)

Maximum mark

proportion of total alleles ; for one gene (in a population)/eq ; 2 marks

(b)

different alleles exist / ref mutation ; advantage in specific environment ; ref selection pressure ; more likely to reproduce ; allele passed to offspring more often ; ref at disadvantage in other environment ; Allow converse argument 4 marks

(c)

faster life cycle of bacteria/converse/ eq ; greater selection pressures on bacteria (eg antibiotic use) ; ref plasmid transfer in bacteria/eq ; larger numbers of bacteria hence larger gene pool/eq ; ref. mutation ; 2 marks Total 8 marks PAPER TOTAL 60 MARKS

27


June 2007


Unit SN5 (6135/01) Question 1

Maximum mark

(a)

medulla (oblongata);

(b)

1. ref. to increase in rate of (anaerobic / aerobic) respiration ;

1 mark

2. {increase in carbon dioxide levels / increase in {lactic acid / lactate} levels / decrease of pH / increase in {hydrogen ions / H+} / increase in carbonic acid} in the blood; 3. ref. to chemoreceptors; 4. {aortic / carotid} bodies or ref. to carotid {artery / aorta}; 5. {cardiac / cardiovascular} centre (in medulla); 6. {more / increase in frequency} of impulses along sympathetic nerve; 7. ref. to SAN / sinoatrial node; 4 marks Total 5 marks

28


June 2007


Question 2 (a)

Maximum mark

1. food (alone) leads to salivation, bell and food leads to salivation (bell alone leads to salivation) ; 2. food – unconditioned stimulus ; 3. bell – neutral stimulus ; 4. salivation is the conditioned response ; 3 marks

(b)

1. (peck key / colour) by {accident / chance / trial and error / random} ; 2. (correct key) obtain {food / reward} / (wrong key) receive punishment ; 3. repeats behaviour in order to get reward ; 2 marks

(c)

1. all animals have common evolutionary origin / share genes / eq / OR human and mammal brains are similar ; 2. {nervous system / neurones / synapses / neurotransmitters / eq} work in a similar way in all animals ; 3. ref. to studies of {Aplysia / sea slug / chimpanzees (Kohler)} ; 4. details of {Aplysia / sea slug / chimpanzees (Kohler)} studies; 5. ref to limitations of animals in explaining learning in humans/eq ; 2 marks

(d)

1. (fMRI) shows which parts of the brain are active / eq ; 2. oxyhaemoglobin does not absorb radio signals / deoxyhaemoglobin absorbs radio signals ; 3. active parts of brain absorb fewer radio signals; 4. rapid image production / 3D image ; 5. non-invasive / brain of living person ; 2 marks Total 9 marks

29


June 2007


Question 3 (a)

Maximum mark 1. {calcium ions / Ca2+} released from sarcoplasmic reticulum ; 2. calcium (ions) binds to troponin ; 3. (troponin) causes tropomyosin to move ; 4. exposing (myosin) binding sites (on actin); 5. myosin head attaches to binding site / cross bridge formation ; 6. myosin head {moves / nods forward / eq} ; 7. release of ADP and inorganic phosphate ; 8. actin slides over the myosin ; 9. (ATP causes) myosin head to detach ; 10. {ATP hydrolysis / ATPase} ; 5 marks

(b)

1. ref to prevention of release of neurotransmitter from presynaptic membrane ; 2. similar shape (to neurotransmitter) ; 3. {binds / blocks / fits into} receptor on postsynaptic membrane ; 4. ref to {sodium ion / Na+ / cation} channels / hyperpolarisation / permanent depolarisation} of postsynaptic membrane ; 5. no nerve impulses / action potentials / continuous action potential / eq ; 6. inhibits acetylcholinesterase / breakdown enzyme / (bungarotoxin) not affected by breakdown enzyme ; 3 marks Total 8 marks

30


June 2007


Question 4

Maximum mark

Immune suppression: 1. fewer infections / immune system most effective with moderate exercise OR {too little / too much} exercise {suppresses immune system / more infections} ; 2. fewer natural killer cells ; 3. details of changes (to cells) of the immune system after vigorous exercise ; 4. inflammatory response in muscles reduces (non-specific) immune response elsewhere ; Joint damage: 5. (articular) cartilage / patella / bursae / ligaments / muscle (fibre) ; 6. further details of damage ; 7. detail of how damage occurs ; Benefits to cardiovascular system: NB max of 4 marks from this section 8. moderate exercise lowers (resting) blood pressure ; 9. due to increased arterial vasodilation ; 10. improves ratio of HDL to LDL / increases levels of HDL / reduces levels of LDL ; 11. beneficial effects of exercise on obesity / BMI ; 12. ref. to prevention (type II) diabetes; Total 6 marks

31


June 2007


Question 5 (a)

(i)

Maximum mark 1. (light hits) photoreceptors (on the retina); 2. impulses pass to the brain ; 3. ref. to sensory neurone ; 4. ref. to innate / inborn / autonomic response ; 5. impulses along parasympathetic nerve ; 6. ref to motor neurone ; 7. circular muscles contract / radial muscles relax ; 8. pupil {contracts /constricts / becomes smaller} ; 4 marks

(ii)

1. {faster / eq} impulses due to ; 2. myelin acting as an {electrical/ eq} insulator ; 3. ref to Schwann cells producing myelin ; 4. depolarisation only occurs at the nodes of Ranvier ; 5. ref. to saltatory conduction ; 6. need rapid response to protect retina ; 3 marks

(b)

1. visual stimulation is essential for visual development ; 2. ref. to critical window / critical period / sensitive period ; 3. ref. to visual cortex ; 4. growth of axons / formation of synapses / inactive synapses eliminated ; 5. kittens less than 4 weeks old have not developed (visual cortex) {connectionssynapses} OR kittens over 5weeks old have already developed (visual cortex) {connections / synapses} 3 marks

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June 2007


Question 5 continued (c)

Maximum mark

1. ref. to animal experiments helping to test {medicines / treatments} / give greater understanding of the {human / animal} body ; 2. ref. to utilitarian philosophy ; 3. expected benefits greater than expected harms / eq ; 4. reduces chances of harm when testing on people ; 2 marks Total 12 marks PAPER TOTAL 40 MARKS

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June 2007


Unit SN6 (6136) Question 1 a)

Maximum mark

has gene(s) which increase chance of developing CVD / eq; named example of gene (e.g. SRY, APOE4, AZE, MTHFR); genes do not necessarily mean you will develop the disease /eq; {other risk factor / named risk factor}also contributes to chance of developing CHD; 3 marks

b)

more than one gene can (cause the condition) / the condition is caused by different genes in different people; 1 mark

c)

one copy of APOEε4 increases risk (3 fold / 2 copies increases risk 8 fold) in French people; Alzheimer’s tends to affect the elderly / eq; high rate of death among pygmies (due to {disease / accidents}) means that few survive to an age where Alzheimer’s will be seen / eq; APOE ε4 may be less dangerous to {pygmies / Africans} than Europeans / environmental differences / eq; APOE ε4 has negligible effect on reproductive success so may not be selected against / invisible to natural selection / eq; 3 marks

d)

Falling childhood mortality rates / {elimination / reduction} of most fatal childhood infectious diseases / eq; 1 mark

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June 2007


Question 1 continued e)

Maximum mark

reproduction is less common when food is in short supply; less energy / resources given over to reproduction (when energy / food is in short supply); {energy / calorie} deprived flies reduce gene expression for genes involved in reproduction; {energy / calorie} deprived flies increase gene expression for genes involved in the immune system; enhanced immune system; immune system protects against {disease / other causes of ageing / cancer / diabetes / autoimmune disease}; restricted growth aids survival; ref. IGF; marsupial mice spend most of their adult life copulating and die young; restricted diet may result in fewer free radicals being released; 3 marks

f)

superoxide dismutase protects against free radicals / few free radicals means less damage to DNA / eq; {SOD(1)/overactive superoxide dismutase} may cause {amytrophic lateral sclerosis (ALS)/neurological disease/Lou Gehrig disease/early death}; SOD may kill neurones / eq; SOD linked to Down’s syndrome; free radical theory of aging may be wrong / eq; gene may {have other roles / moonlight} (that may be harmful); SOD results in production of {hydrogen peroxide / H2O2}; need balance between SOD and catalase to avoid damage / eq; 3 marks

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June 2007


Question 1 continued g)

i)

Maximum mark

MARKS IN THIS SECTION NEED TO BE IN CONTEXT identify the gene responsible for the disease; {use of / design} a gene probe for the disease gene; further detail of probe (e.g. complementary to gene / radioactively labelled / fluorescently labelled); extract DNA from patient / cheek cell swab / eq; {cut / digest} DNA using restriction {enzymes / endonuclease}; separate DNA using gel electrophoresis; further detail of gel electrophoresis; [e.g. use of {agarose/polyacrylate} gel / apply {current through/pd across} / DNA moves towards anode / smallest fragments move {fastest / furthest}] treat with alkali to make DNA single stranded; southern blotting / transfer onto a {nylon/nitrocellulose} membrane; disclosure using x-ray film / UV light / laser; provide counselling (with results); ask for family history of the disease/eq; 4 marks

ii)

advantage: can avoid passing disease onto children if negative / if positive can use Preimplantation Genetic Diagnosis / eq / change diet to delay {onset/symptoms} of disorder / peace of mind with negative result / suitable ref. to existing children / choose not to have children (if positive) to avoid passing on / eq; disadvantage: no known cure available so increased stress with positive result / worry that subsequent children may inherit the disease / eq / insurance discrimination / high insurance premiums / ref to abortions / may choose not to have children due to risk / eq / increased risk of miscarriage (due to antenatal screening); 2 marks Total 20 marks

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June 2007


Question 2 a)

i)

Maximum mark lack of oxygen / eq; anaerobic respiration (produces lactate); (respiration) produces reduced NAD / NADH H+ / NAD H2 /reduced co-factors; pyruvate produced by glycolysis; pyruvate converted to lactate (in anaerobic conditions); lactate production oxidises NADH so glycolysis can continue/eq; in anaerobic respiration {glucose / lactate} cannot be fully oxidised / correct reference to Krebs cycle / oxidative phosphorylation / suitable ref. to mitochondria /eq; allows continued production of ATP;

ii)

4 marks

the difference {cannot be explained by chance/is really caused by diving / not some other factor}; the {probability/chance} that the difference could be due to chance/accident is less than 5% / 0.05 / 1 in 20 / 95% confident that difference is not due to change alone; 2 marks

iii)

correct description of change of lactate in dives of different duration e.g. little change in blood lactate concentration up to six minutes, faster increase in blood lactate concentration after {five / six} minutes / eq / ref. to greater variability of blood lactate in longer dives; in dives of up to {five / six} minutes there is enough oxygen (in the lungs / blood / body) to maintain (largely) aerobic respiration /in a dive of six to twelve minutes (all / most) oxygen gets used up therefore respiration (more / or less) entirely anaerobic / eq; 2 marks

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June 2007


Question 2 continued b)

Maximum mark

heart rate decreases when the seal dives / rises when the seal surfaces; use of figures to emphasise that the HR falls very low from e.g from 130 - 150 beats per minute to 10 - 30; at the surface increases supply of oxygen to remove lactate / to repay oxygen debt; ref. to moving the lactate away from the muscles / to the liver; when submerged little oxygen carried to muscles in blood / eq; correct ref. to cardiovascular centre / correct ref. to nerve action on the SAN / reflex action; ref. to myoglobin; 4 marks

c)

(i)

QRS (complex); resulting in contraction of ventricles / ventricular systole; 2 marks

(ii)

90 – 120 bpm; 20 – 40 bpm; 2 marks

d)

(i)

{shock / disruption of control mechanisms / eq} at the sudden change in temperature at the {lower temperature / 25oC}; 35oC is close to normal body temperature (therefore less of a shock than 25oC); reduced (blood) circulation to conserve heat / a thermoregulatory mechanism / vasoconstriction (to surface) ; ref. to diving reflex / bradycardia; 2 marks

(ii)

she hyperventilated / filled her body / lungs / blood with as much oxygen as possible before diving; she {had prepared herself mentally / was afraid / stressed} and this caused the increase in heart beat; ref. to adrenaline / hormone; ref. to autonomic nervous system / sympathetic nervous system;


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June 2007


3. Some people claim that many medical problems, such as the shortage of suitable organs needed for transplant surgery, may become a thing of the past simply by extracting some stem cells from a patient and inserting a specific gene or genes. ‘Manipulating stem cells - a miracle cure or a dangerous diversion?’

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.

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. A1

Description of Stem Cells:

B1a B1b

B1c B1d

B1e B1f/g

A2

Source of embryonic stem cells:

B2a B2b

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Cells that are able to differentiate into more than one cell type/eq; Correct descriptions making use of the words totipotent, pluripotent and/or multipotent; Reference to cell/ nuclear division as source of new cells; Good description of mitosis and/or cell cycle including details such as the names of the phases; Introduction of concept that cells specialise during their development; Good description of gene switching/induction/inactivation such as the use of transcription factors/methylation [2 marks available for excellent description including 2 methods of specialisation] IVF as a source of spare embryos; Details of how IVF tends to produce excess embryos and that those embryos may be stored for long periods in liquid nitrogen.


June 2007


B2c B2d

A3

Other sources of stem cells:

B3a B3b

Cloning to produce embryonic stem cells; Details of a suitable cloning technique; e.g. description of how Dolly was cloned Coral blood (from placenta/umbilical cord); Explanation that placenta/umbilical cord contains stem cells that will be identical to the new born child and they may be harvested and stored or used.

B3c B3d

Adult stem cells; Example of tissue that contains stem cells e.g. bone marrow, testes, etc

A4

Therapeutic uses of Stem cells

B4a/b

Credit two specific examples of a tissue/organ that could be replaced/healed through the use of stem cells e.g. repairing spinal cord injuries

A5

Cloned/Adult stem cells are less likely to be rejected by the patient

B5a

Details of the specific immune system and reasons why traditional transplants may be rejected

B5b

Details of why cloned cells are not going to be rejected by the immune system e.g. ref to antigens/MHCs etc.

B5c

No need to use immune suppressant drugs with stem cells/converse.

A6

Adult stem cells will need to be reprogrammed

B6

Use of chemical signals to enable stem cells to differentiate to produce the desired cell types.

A7

Stem cells can be manipulated by gene therapy

B7a

Details of how to insert a gene into a stem cell

B7b

Description of a suitable vector e.g. liposome, retrovirus, etc

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June 2007

A8

A9

A10


Alternatives to the use of stem cells

Ethical Issues

Dangers/Disadvantages

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B7c

Example of specific disorder/disease that could be treated through gene therapy e.g. cystic fibrosis, diabetes, SCID etc

B7d

Further detailed explanation of the case study named in B7c e.g. replace gene for insulin production into pancreatic stem cells and stimulate them into becoming Islet cells

B8a B8b

Xenotransplantation. Details and examples e.g. heart valves from pigs

B8c

Dangers of xenotransplantation e.g. new viruses become active/ or need for genetic modification of the animal so that it is not rejected by the immune system

B8d B8e

Prosthetic replacements Specific example e.g. artificial heart valves or hearts, limbs

B9a B9b

eugenics Issues described related to selection of embryos, designer babies etc through genetic modification

B9c B9d

Pro-life issues Discussion about embryos having the potential for independent life in the future – should we be allowed to manipulate/destroy

B9e B9f

Technology may be misused Once therapeutic cloning is possible others will use the technology for reproductive cloning or similar.

B10a B10b

Developmental deformities/Cancers Explanation linked to cells not being fully reprogrammed/ new mutations/

B10c B10d

Premature aging of cells/organism Chromosomes come from an older donor nucleus – shorter telomeres etc.


June 2007


Unpacking the question:

The C points might be made as discrete points in the introduction and/or conclusion or indirectly as part of the way the factual material has been presented in the body of the essay. But it should be possible to identify precisely where each C mark has been awarded by, for example, writing C1 or C2 on the script.

C1 Recognition that embryonic stem cells have more potential than adult stem cells but they raise more ethical issues regarding their use. C2

An issue of balancing risks and benefits for any new therapies.

C3 Adult stem cells will not need to be cloned, but will need to be reprogrammed and may be harder to extract. C4 Issue of whether it is better to make use of spare embryos resulting from IVF rather than disposing of them. C5 Essay provides a balanced argument that includes at least 2 good examples of the use of stem cells and 1 danger/ethical problem associated with the use of stem cells. C6 Discussion of how the human genome project has helped identify candidate genes for gene therapy.

C7 Evidence that candidate is aware of the key issues of needing to understand the precise series of chemical signals required for cells to specialise successfully and form the correct tissues/organs required. C8 reference to the role of clear legislation/supervision of work in these key areas e.g. outline of the role of the Human Fertilisation and Embryology Authority (HFEA). C9 Recognition that stem cells may be cultured and manipulated in tissue culture before use/storage C10

Need for greater research/understanding careful testing before proceeding with new therapies

C11 Key question is about the status of the embryo – a ball of undifferentiated cells or a potential human being.

C12

Tissue typing may reduce need for cloning as we may only need a few stem cell lines to avoid tissue rejection in most people.

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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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June 2007


4. The effect of global climate change on the World ecosystems is often seen as a potential catastrophe. Yet agriculture, wild species and ecosystems are able to adapt to climate change and have done so many times in the past. The biological effects, including the consequences for agriculture, that may result from global warming in the 21st Century: catastrophic or just different? Depth: max 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.

Breadth: max 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. A1

Global warming is happening at present/the surface air temperature/sea temperature is getting warmer:

B1a B1b

B1c B1d

A2

Climate change may cause sea levels to rise

Explain the possible link between greenhouse gases and global warming;

B2a

Loss of agricultural land due to sea level rise Increased sea flooding may result in salt contamination of agricultural land Only plants with halophytic adaptations / modifications may be able to survive in many areas

B2c

Global warming has happened in the past

Discussion of the natural carbon cycle and how human activity may be changing the natural balance. Might be the result of humans burning fossil fuels but could be due to other nonanthropogenic causes/the contribution of CO2 emissions due combustion of fossil fuel to global warming is difficult to evaluate;

B1e

B2b

A3

Plenty of data from direct records going back over >100 years/pollen analysis/dendrochronology/ice cores; Climate change related to global warming includes changes/increased temperature and {changes in rainfall pattern}/some places become drier/wetter;

B3b

There was global warming at the end of Ice Age: Ice Age ended (in UK) about 10 000 BC/12 000 BP/12 thousand years ago [accept +/2000y];

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B3a

June 2007

A4

Some species survive by change in distribution /{growing / living} elsewhere


B3c

Examples to illustrate the scale of the effect e.g. (In UK) from tundra to forest/species entered UK across land bridge;

B3d

Reference to time scale e.g. (tundra to forest in UK) in a few thousand/anything in the range 2000 to 5000 years;

B4a

Some species may grow further north/at higher altitude;

B4b

Species lost (from a particular place/example) will be replaced by ones from further South;

B4c

How habitat fragmentation may make species dispersal/migration/succession harder than in the past;

B4d

Appropriate reference to seed dispersal in enabling plant species to grow somewhere else; Example to illustrate B4d;

B4e B4f

Ref to animal migration compared to plant dispersal;

A5

Reference to succession as a way ecosystem/vegetation may change;

B5

Example to illustrate how succession works e.g. new species arrives and out-competes indigenous species/{new species/loss of old species} may change/modify the (ecological) conditions/specific example;

A6

Some species will face extinction/ population decline;

B6a

Species on mountain tops/northern coast may have nowhere to migrate to; Species may lose niche/habitat etc and may not be able to adapt/compete well enough to survive/ effects of disrupted food chains; Extinction rate currently extremely high.

B6b

B6c A7

Effects on Agriculture

B7a B7b

Farmers in a particular place will grow different crops /keep different (domestic) animals; Example to illustrate e.g. maize will grow/already growing further north;

B7c

(Agricultural) Winners and losers: Some places will no longer be as good for agriculture as they are now/will become deserts/ some places will be better for agriculture/desertification may take place;

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June 2007


B7d

Example to illustrate candidates response to B7c e.g. sub-Saharan Africa/Spain/Mediterranean area Grow more maize/sunflowers in Scotland Overgrazing/effects of (human) overpopulation in {marginal areas/eq/the Sahel} made even worse/more severe;

A8

Pests/animal vectors/weeds may become more numerous/spread north/become more widespread;

B8

Examples of species which might benefit e.g. Witch weed (in Africa)/mosquitoes carrying malaria (further north) / other suitable examples of specific plants or animals;

A9

Behaviour of plants and/or animals may change

B9

Disruption of breeding cycles/animals may hatch at a different time to their prey species/{seeds may not germinate/ plants may not flower} without cold stimulus

B10a

Correct reference to mutations/random change in genes/DNA change;

B10b

‘new’ genes might provide new adaptations that will enable the species to survive /compete better with pre-existing species;

B10c

(Struggle for survival and survival of the fittest) – the individuals which survive will provide genes for future generations/will reproduce faster than the original variants;

B11a

Species will become extinct faster than new ones evolve so there will be fewer species in the world

B11b

(Why loss of biodiversity matters) means loss of genes/genetic variation limiting {evolutionary change/ability to adapt in the future/source of genes for use in plant breeding/GM in the future

B12a

Outline description of how plants may be modified through genetic modification and/or details of selective breeding. Example: produce drought resistant/temperature resistant varieties with heat resistant enzymes/salt tolerance (in context of rising of sea level/similar examples;

A10 (Wild species) may change by evolution/natural selection;

A11 There will be loss of biodiversity

A12 Plant breeding/GM will produce new varieties able to cope with new conditions

B12b

A13 Reference to computer models to predict climate change

B13

Qualification e.g. only make predictions not provide certainty/predictions continually improving/derived from a lot of data/based on extrapolation of current trends/specific example e.g. (some models predict) drier in SE England wetter in Scotland;

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June 2007


Unpacking the question:

the focus of this of this question is on the biological effects including agricultural consequences of global warming. It is not primarily about the greenhouse effect nor issues surrounding combustion of fossil fuels although these may gain a mention when discussing uncertainties and difficulties of making predictions. Nor is it primarily about whether global warming is taking place or not although observing that it is clearly taking place and mentioning some of the evidence for this could be a good place to start. Some of the points below might have already have been awarded a mark under B but the C mark is for making connections. To be awarded a mark for each of the points below a candidate must have made the point in bold type and to have qualified it sufficiently to show they know what they mean – the material that is not in emboldened is intended to illustrate how the idea might be qualified rather than a prescriptive mark scheme. The C points might be made as discrete points in the introduction and/or conclusion or indirectly as part of the way the factual material has been presented in the body of the essay. But it should be possible to identify precisely where each C mark has been awarded by, for example, writing C1 or C2 on the script.

C1 Might not be as bad as all that – e.g the extent of global warming is difficult to predict; C2

Linked to C1: because of several possible scenarios e.g {if Atlantic conveyor/Gulf Stream breaks down UK will be much colder otherwise UK will be warmer}/{future levels of anthropogenic CO2 production from fossil fuel are difficult to predict/if humans reduced CO2 production from fossil fuels may take time to make a difference}/ Ref. to education about global warming;

C3 The global warming which ended the last Ice Age was much greater than the current global warming predictions C4 Linked to C3: Yet successional processes, dispersal and natural selection took care of it bringing change not catastrophe; C5 The rate of change may happen too fast for biological processes like dispersal, succession and evolution to keep pace and this may disrupt ecosystems/make it more difficult to feed the world’s human population/lead to greater loss of biodiversity than previous climatic change/Ice Age; C6 Humans have fragmented natural habitats making it more difficult for living organisms to disperse as the climate changes; C7

Might be a catastrophe for the human race but not for the global ecosystem:

C8

Linked to C7: the world is already over-populated/ climate change could result in mass human starvation/war over dwindling resources and dry land/collapse of world economy/much of world’s population lives in places likely to be flooded by rising sea level. But the ecosystem, unhindered by the negative effects of humans could become more stable/have more biodiversity.

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June 2007


C9

In the past what appears to be catastrophic has led to major evolutionary change/ has been ecologically/biologically creative.

C10

Linked to C9: For example, the meteor/asteroid which is said to have caused the demise of most of the Dinosaurs when it collided with the earth might well have accelerated the evolution of mammals – including humans. There might be fewer humans but they might be an evolutionary improvement!

C11

Science and Technology will cope – it always does;

C12 Linked to C11: A lot of scientists are studying global warming and climate change so we know what needs to be done/GM technology will be used to produce crops able to survive in a warmer climate/we shall adapt our {homes/cities/energy sources/ways of producing food}... 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.

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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] Order Code UA018960 Summer 2007 For more information on Edexcel qualifications, please visit www.edexcel.org.uk/qualifications Alternatively, you can contact Customer Services at www.edexcel.org.uk/ask or on 0870 240 9800 Edexcel Limited. Registered in England and Wales no.4496750 Registered Office: One90 High Holborn, London, WC1V 7BH