6131_01_rms_20090312

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Mark Scheme (RESULTS)January 2009

GCE

GCE SNAB Biology (6131/01)

Edexcel Limited. Registered in England and Wales No. 4496750Registered Office: One90 High Holborn, London WC1V 7BH

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General Marking Guidance

• All candidates must receive the same treatment. Examiners must markthe first candidate in exactly the same way as they mark the last.

• Mark schemes should be applied positively. Candidates must be rewardedfor what they have shown they can do rather than penalised for omissions.

• Examiners should mark according to the mark scheme not according totheir perception of where the grade boundaries may lie.

• There is no ceiling on achievement. All marks on the mark scheme shouldbe used appropriately.

• All the marks on the mark scheme are designed to be awarded. Examinersshould always award full marks if deserved, i.e. if the answer matches the

mark scheme. Examiners should also be prepared to award zero marks if the candidate’s response is not worthy of credit according to the markscheme.

• Where some judgement is required, mark schemes will provide theprinciples by which marks will be awarded and exemplification may belimited.

• When examiners are in doubt regarding the application of the markscheme to a candidate’s response, the team leader must be consulted.

• Crossed out work should be marked UNLESS the candidate has replaced itwith an alternative response.

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Unit 6131/01

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1(a) circle to include 1 phosphate + 1 sugar + 1 base ; (1)

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1(b)(i) hydrogen / H (bond) ; (1)

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1(b)(ii) A ; (1)

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1(c) 1. phosphate / phosphoric acid ;

2. deoxyribose / pentose (sugar) / 5C sugar ; (2)

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2(a) {alveolus / alveoli / eq} (membranes) ; (1)

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2(b)(i)

(1)

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2(b)(ii) carbohydrate / glycocalyx /glycoprotein ; (1)

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2(b)(iii) V ; (1)

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2(c)(i) 1. {concentration increases / more pigment leaksout} as temperature rises (up to 80°C) ;

2. credit correct manipulation of the data ;

3. reference to increase in kinetic energy / eq ;

4. due to {channel / eq} proteins denaturing ;

5. (all) proteins denatured by 80ºC / eq ;

6. reference to diffusion of pigment through bilayer/ eq ;

7. reference to damage to both {tonoplast / eq} andcell surface membrane ;

8. only a little pigment leaks out up to 50ºC ;

9. because most membrane proteins closed / eq ;max(5)

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Answer Mark

2(c)(ii) 1. (dynamic) equilibrium has been achieved ;

2. equal concentrations of pigment in water andbeetroot / no concentration gradient ;

3. reference to volume of water used ;

4. correct reference to experimental error /reliability of data ;

max(2)

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3(a) 1. 3 fatty acids ;

2. 1 glycerol ;

3. fatty acids correctly joined via ester bonds ; (3)

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3(b) Statement Tick ()

or cross

()

Triglycerides are building blocks of

polysaccharides

;

Triglycerides can contain a small

amount of nitrogen

;

Triglycerides can be modified into

phospholipids

;

Triglycerides release water during

hydrolysis

;

(4)

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3(c) {no C =C / no double bonds / only single bonds} in {fattyacid chain / hydrocarbon chain} /{fully filled up / eq}with hydrogens ; (1)

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4(a)(i)

(1)

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4(a)(ii) 1. time from one peak to the next (approx 0.82 ±0.02) ;

2. 60 ÷ time / 71-75 beats per minute ; (2)

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4(a)(iii) {more peaks / eq} (in the same time) / irregularheart beat ; (1)

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4(b) 1. stops {oxygenated blood / oxygen /eq} reachingtumour (tissue) / eq ;

2. anaerobic respiration (to tumour tissue) ;

3. build-up of lactic acid ;max(2)

0.0 0.4 0.8 1.2 1.6Time / s

0.5

0.0

1.0

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5(a) 1. has one {β-thalassaemia / eq} allele (and onenormal allele) / heterozygous ;

2. does not show the {condition / symptoms / eq} /phenotype unaffected ;

3. but can pass the allele on to the next generation; max(2)

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5(b)(i) 3 ; (1)

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5(b)(ii) 1. parental genotypes correct (both heterozygous) ;

2. gametes obviously shown ;

3. cross showing 4 correct offspring ;

4. reference to one being double recessive / showingthe trait ;

max(3)

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5(b)(iii) 1. H has the condition so has {2 β-thalassaemia / eq}alleles ;

2. receives one thalassaemia allele from G ;

3. G does not show the condition, therefore must beheterozygous / must also have allele for ‘normal’haemoglobin ;

max(2)

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5(c)(i) 0.25 / 25% / ¼ / 1 in 4 ; (1)

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5(c)(ii) 1. some couples would prefer not to know (so woulddecline CVS offer) ;

2. risk of miscarriage (due to CVS) ;

3. correctly stated level of risk / 1 to 2 % (increasedrisk of miscarriage) ;

4. decision to continue with pregnancy or not (if thalassaemia present) ;

5. to give couple time to become better informedabout condition and its implications ;

max(2)

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6(a) 1. {impairs / eq} (functioning of male reproductive

system) ;

2. commonly causes a lack of vas deferens / sperm

ducts ;

3. therefore no sperm released / eq ;

4. if vas deferens present, {lumen / eq} {narrowed /

eq} ;

5. so fewer (than normal) sperm {released /

ejaculated / eq} ;

max(3)

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6(b)(i) reference to {substitution / eq} / at ref number 6 /named swap

and

reference to {substitution / eq} / at ref number 11 /named swap ; (1)

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6(b)(ii) T A G T A A C A A C A A ; (ignore gap) (1)

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7(a) glucose ;

galactose ; (2)

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7(b) For lactose:1. low fat yoghurt has {more / eq} therefore greater

risk of obesity ;

For cholesterol:2. more cholesterol in high fat yoghurt / eq,

therefore {greater / eq} deposition in arteries /atherosclerosis / eq ;

For fats:3. high fat yoghurt has {more / eq} therefore

{greater / eq} deposition in arteries /atherosclerosis / eq ;

4. total fat would include saturated fats whichincreases risk ;

5. total fat would include unsaturated fats which do

not increase risk / eq ;

6. saturated fats can be made into {cholesterol /LDLs}(in the liver) ;

General – award each one once in correct context:7. obesity linked to CVD ;

8. atherosclerosis can lead to heart disease / eq ;

9. credit correct manipulation of the data once e.g.

2.1 times as much cholesterol in high fatyoghurt ; max(5)

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7(c)(i) Stage 2 – mRNA ;DNA ;

Stage 3 – mRNA ;tRNA ;rRNA ;

max(4)

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7(c)(ii) ribosome / rough endoplasmic reticulum / RER /cytoplasm ; (1)

PAPER TOTAL: 60 MARKS

6131_01_rms_20090312

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