Mark Scheme January 2008

GCE

GCE SNAB Biology (8048/9048)

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January 2008

Publications Code UA 019766

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Contents

General Introduction p i

Unit Codes and Unit Titles p ii

General Information p iii

Mark Schemes

Unit SN1 6131 Lifestyle, Transport, Genes and Health p 1

Unit SN4 6134 Environment and Survival p 9

i

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.

ii

Unit Codes and Unit Titles This Mark Scheme covers the units offered in this examination for Advanced Subsidiary Biology (Salters-Nuffield), 6131 and for Advanced GCE Biology (Salters-Nuffield), 6134. 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 Visit / Issue 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 Units 6132, 6133, 6135 and 6136 are only available in the Summer examination series.

iii

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

[CE] or [TE] Consecutive error / transferred error 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.

1

Unit 6131/01

Question Number

Answer Mark

1(a)

Statement about Daphnia Tick or cross

(i) The movement of fluid through the heart is an example of mass transport

;

(ii) Daphnia uses diffusion to transport oxygen into muscle cells

;

(iii) Daphnia tends to lose water from its body to the freshwater by osmosis

;

(iv) Daphnia can use active transport to move ions from the freshwater into its body

;

4

Question Number

Answer Mark

1 (b)(i)

A = 50, B = 75 & C = 100 ;

1

Question Number

Answer Mark

1 (b)(ii)

200 ;

1

Question Number

Answer Mark

1 (b)(iii)

1. only three Daphnia used / not enough {samples / repeats}

to be representative / only one Daphnia used per concentration ;

2. different Daphnia used (for each caffeine concentration) /

different Daphnia used for 35 au ; 3. range not large enough to make prediction / eq ; 4. Daphnia may respond differently at higher concentrations

/ eq OR they may die ; 5. taking readings for 10 seconds not sufficient ; 6. describe one environmental variable to be controlled /

allow time for Daphnia to acclimatise ; 7. need for a control ;

max 3

2

Question Number

Answer Mark

2 (a)(i)

1. (waxy layer) is waterproof ; 2. {enzyme / pectinase} in (aqueous) solution ;

3. (therefore) {enzyme / pectinase} unable to pass through

(waxy layer) / unable to get to {pectin / polysaccharide / carbohydrate} / eq ;

4. pectinase is specific and will not digest lipid / waxy

surface ;

max 2

Question Number

Answer Mark

2 (a)(ii)

1. shape of (enzyme / pectinase) active site ;

2. fits pectin / does not fit cellulose / reference to specificity of enzymes ;

2

Question Number

Answer Mark

2 (b)(i)

1. increases the surface area ;

2. more {substrate /pectin} available / increases the number

of {enzyme-substrate complexes / collisions between enzyme / eq and substrate / eq} ;

2

Question Number

Answer Mark

2(b)(ii)

1. hydrolysis uses up water ; 2. evaporation of water /eq ;

3. idea of same number of the {enzyme / pectinase}

molecules but in less {solvent/water} ;

4. pectinase released from orange tissues/eq ;

5. correct reference to osmosis (into orange) ;

max 2

3

Question Number

Answer Mark

3 (a)(i)

P = protein ;

Q = fat ; R = carbohydrate ;

3

Question Number

Answer Mark

3 (a)(ii)

calculation (e.g. 3.3-1.0 or 2.3) x 8 (g) ;

answer (18.4) ;

2

Question Number

Answer Mark

3 (b)

1. more protein (in formula milk) ; 2. protein needed for growth / muscle deposition ;

3. {protein / muscle} {heavier / more dense} than same

amount of carbohydrate / fat /eq ;

max 2

Question Number

Answer Mark

3 (c)

1. description of equation / body mass divided by height2 ; 2. look up on a chart to make judgement / over 30 (on BMI

scale) ;

2

4

Question Number

Answer Mark

4 (a)

(nitrogenous / organic) base / named base ;

1

Question Number

Answer Mark

4 (b)

1. 8 double strands drawn ; 2. 2 hybrid and rest all light DNA ;

2

Question Number

Answer Mark

4 (c)

DNA polymerase / helicase / DNA ligase / primase / eq ;

1

Question Number

Answer Mark

4 (d)

TCG AAT GGT ;

1

Question Number

Answer Mark

4 (e)

1. correct reference to description of gene mutation ;

2. change {mRNA / codon / eq} ; 3. {different / wrong / no} amino acid included /

stop codon ; 4. different / eq {sequence of amino acids / primary

structure of protein} ; 5. different R groups ; 6. change bonding in protein / correctly named bond(s) ; 7. protein forms different {secondary / tertiary / quaternary}

structure ; 8. different (3D) shape ;

max 5

5

Question Number

Answer Mark

5 (a)(i)

X = aorta/ aortic arch ;

Y = (left) ventricle / cardiac muscle ;

Z = coronary artery /eq ;

3

Question Number

Answer Mark

5 (a)(ii)

second box down on the left ;

1

Question Number

Answer Mark

5 (a)(iii)

SAN / sino atrial node / pacemaker / eq ;

1

Question Number

Answer Mark

5 (b)(i)

1. sequence of events from one beat to the next beat / eq ; 2. reference to {contraction / systole} and {relaxation /

diastole} ; 3. correct detail of sequence e.g. atrial systole → ventricular

systole → diastole / approx 30% of time spent in systole and 70% in diastole ;

4. correct detail of electrical regulation of cardiac cycle/eq;

max 2

Question Number

Answer Mark

5(b)(ii)

1. left ventricle has {more / thicker} muscle / eq ; 2. blood from (left ventricle) has to divide between more

capillaries / eq ; 3. left ventricle has to pump blood further / eq ;

max 2

6

Question Number

Answer Mark

5(b)(iii)

1. pressure increases as blood forced into ventricle during

atrial systole ; 2. pressure increases during (initial) ventricular systole/eq ; 3. (due to) reducing volume of ventricle (causing pressure

increase) ; 4. pressure starts to decrease due to blood into artery / loss

of blood from ventricle ; 5. decreases during diastole / eq ; 6. (due to) increasing volume (of chamber) ;

max 2

Question Number

Answer Mark

5 (c)

1. gender 2. smoking 3. genes / inheritance / eq 4. stress 5. high LDL level / LDL to HDL ratio / high blood cholesterol 6. reference to inappropriate diet such as high {salt / fat /

cholesterol / calorie} intake / eq 7. high alcohol intake 8. obesity 9. lack of exercise / eq

Notes: two correct answers needed for one mark

max 1

7

Question Number

Answer Mark

6 (a)

1. fluid – (phospholipid) molecules can move within

phospholipid {layer / monolayer} ;

2. mosaic – {proteins / glycoproteins / eq} dotted throughout the {membrane / bilayer / eq} ;

2

Question Number

Answer Mark

6 (b)(i)

(act as) receptors / antigens ;

1

Question Number

Answer Mark

6 (b)(ii)

1. two {fatty acid / eq} ‘tails’ ; 2. glycerol ; 3. phosphate ;

3

Question Number

Answer Mark

6 (c)

1. charged region (of cholesterol) only in line with

hydrophilic phospholipid head /non-charged region only in line with hydrophobic phospholipid tails ;

2. all within 1 monolayer ;

2

8

Question Number

Answer Mark

6 (d)

1. LDLs carry most cholesterol / HDLs more protein / eq ; 2. LDLs bind to receptors on cell membranes ; 3. if in high concentration, they overload receptors ; 4. results in high blood cholesterol ; 5. high risk of atheroma / atherosclerosis / eq ; 6. HDLs transport cholesterol to liver ; 7. cholesterol broken down therefore less risk of

atherosclerosis /eq ;

max 4

PAPER TOTAL: 60 MARKS

9

Unit 6134/01 Question Number

Answer Mark

1 (a)

1. detection by (thermo) receptors ; 2. hypothalamus ;

3. sweating ;

4. vasodilation ;

5. reduced activity / reduced metabolic rate ;

6. effectors stopped when return to normal ;

max 3

Question Number

Answer Mark

1 (b)

1. set point normal / higher ; 2. effectors not activated until higher temperature /eq ;

3. switched off sooner / at higher temperature ;

4. reference to chemicals / lymphokines ;

max 2

Question Number

Answer Mark

1 (c)

1. higher core temperature at death ;

2. cooling takes longer / raises cooling curve ;

3. higher measured temperature ;

4. estimated time since death shorter / eq ;

max 2

10

Question Number

Answer Mark

2 (a)

1. cross over recombines existing alleles ;

2. mutation produces new alleles / changes DNA ;

3. mutations happen in any cell division / cross over only

occurs in meiosis ;

4. mutations more likely to be non-viable ;

max 2

Question Number

Answer Mark

2 (b)(i)

2 marks all correct, lose one mark per error

Genotype Tick RLT rlT RlT RLt Rlt rLt

2

Question Number

Answer Mark

2 (b)(ii)

1. (Parents) RRTT x rrtt ; 2. (Gametes) RT rt ;

3. (F1) RrTt ;

4. (Gametes) RT, Rt, rT, rt ;

5. (F2 genotypes) R_T_, R_tt, rrT_, rrtt ;

6. 9:3:3:1 ;

7. Correct phenotypes (purple present, purple absent, red

present, red absent) ;

max 5

11

Question Number

Answer Mark

2 (c)

1. conserve genetic variety / prevent inbreeding / increase

gene pool ; 2. breeding programmes ;

3. research / eq ;

4. education ;

5. reference to attracting visitors / increasing revenue /

increasing publicity ;

6. ethics of killing healthy animals / would die if released into wild ;

max 3

12

Question Number

Answer Mark

3 (a)

1. fixed / constant area ; 2. reference to sampling ;

3. valid comparisons possible ;

4. easy so can be repeated ;

max 2

Question Number

Answer Mark

3 (b)

1. sampling along changing conditions / environmental

gradient ; 2. systematic sampling /random sampling does not show

distribution / eq ;

2

Question Number

Answer Mark

3 (c)

1. more coverage by plants in 5 / converse ; 2. more organic matter in 5 / converse ;

3. more species in 5 / converse ;

4. different species present ;

5. credit figures (e.g. 3 times more plants, 2.4g more

matter, 17 more species) ;

max 3

13

Question Number

Answer Mark

3 (d)

1. different communities at different distances ; 2. few species near beach ; 3. reference to pioneer species ; 4. organic matter (increase with distance from beach) ;

5. consequence of increased organic matter (e.g. increased

water holding, mineral content) ; 6. suited to more species further from beach ; 7. reference to competition ; 8. few dominant species ; 9. (might be) climax community / mature community ;

max 5

14

Question Number

Answer Mark

4 (a)

photolysis (of water) ;

1

Question Number

Answer Mark

4 (b)

light / enzyme / chlorophyll /eq ;

1

Question Number

Answer Mark

4 (c)

1. passed to chlorophyll / photosystem / replace electrons

lost by chlorophyll / eq ; 2. light energy {promotes electrons to higher energy level /

excites electrons } / electrons emitted ; 3. ATP production ; 4. reduction of NADP / production of NADPH / eq ; 5. reference to electron carriers / electron transport chain ; 6. reference to redox / eq ;

max 4

Question Number

Answer Mark

4 (d)

1. GP ; 2. reduced ; 3. using H from reduced NADP ; 4. and ATP as source of energy ;

4

Question Number

Answer Mark

4 (e)

1. 10/12 GALP /eq ;

2. (regeneration of) RuBP /eq ; 3. (rest used to form) glucose ; 4. and starch / other organic chemicals /eq ;

max 2

15

Question Number

Answer Mark

5 (a)

1. response of immune system / body’s immune cells /eq ; 2. to antigen /eq ; 3. producing antibodies ; 4. T killer cells ;

max 2

Question Number

Answer Mark

5 (b)

1. memory cells produced ; 2. response more rapid (on reinfection) / faster antibody

production ; 3. prevents symptoms /eq ; 4. higher concentrations of antibodies produced ; 5. antibodies produced for longer ; 6. reference to secondary response ;

max 2

Question Number

Answer Mark

5 (c)

1. population can be protected more quickly /eq ; 2. possible to keep high levels of immunity / herd immunity; 3. distribution more reliable / possible to remote areas /eq; 4. ref. to example of distribution benefit ; 5. allows rapid response to change in pathogens /eq ;

max 3

16

Question Number

Answer Mark

5 (d)

1. also T memory cells ; 2. more lymphocytes to combat infection / eq ; 3. virus infects body cells ; 4. antibodies only destroy virus in blood / eq ; 5. T killer cells destroy virally infected cells ; 6. virus cannot spread / hide inside cells;

max 4

17

Question Number

Answer Mark

6(a)

same genus / reflects close relationship /eq ;

1

Question Number

Answer Mark

6(b)

1. isolation of populations; / reproductive isolation /eq ; 2. mutations cannot pass between populations ; 3. genetic drift / founder effect ;

4. different selection pressures / eq ; 5. (reference to effects of local conditions on) allele

frequencies ;

max 3

Question Number

Answer Mark

6(c)

1. requires co-ordination between governments / eq ; 2. (government might have) different approaches to

conservation / e.g. tourism / eq ; 3. (government might have) different needs for local

populations / different wealth of countries / eq ; 4. leopards know no boundaries ;

max 2

PAPER TOTAL: 60 MARKS

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