Marking Scheme Edexcel

M

Edex

cel G

CE

GCE Edexcel GCE

Biology (Salters-Nuffield) (Pilot)

8048/9048

S ummer 2006

ark Schemes

Biol

ogy

(Sal

ters

-Nuf

fiel

d) (

Pilo

t)

8048

/904

8

Edexcel is one of the leading examining and awarding bodies in the UK and throughout the world. We provide a wide range of qualifications including academic, vocational, occupational and specific programmes for employers.

Through a network of UK and overseas offices, Edexcel’s centres receive the support they need to help them deliver their education and training programmes to learners.

For further information please call our Customer Services on 0870 240 9800, or visit our website at www.edexcel.org.uk.

Summer 2006

Publications Code UA 017718

All the material in this publication is copyright © Edexcel Ltd 2006

Contents

General Introduction p ii

General Information p iii

Mark Schemes

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

Unit SN2 6132 Development, Plants and the Environment p 9

Unit SN3 6133 paper 02 Practical Work Review p 21

Unit SN4 6134 Environment and Survival p 24

Unit SN5 6135 paper 01 written paper

Energy, Exercise and Coordination p 32

Unit SN6 6136 Synoptic paper p 38

8048/9048 Mark Schemes ii

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

iii 8048/9048 Mark Schemes

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.

8048/9048 Mark Schemes 1

Unit SN1 (6131)

Question 1 Maximum mark (a) (i) condensation ;

1 mark (ii) glycosidic ;

1 mark (iii) water ;

1 mark (b) (i) An explanation to include two from: 1. compact therefore large numbers of molecules can fit in a small space / eq ; 2. insoluble therefore osmotically inactive / eq ; 3. large molecule therefore remains within cells / cannot pass through membranes / contains a lot of energy ; 4. easily hydrolysed when required for energy /eq ;

2 marks

(ii) glycogen has side branches only / more side branches / starch composed of two components / amylose and amylopectin ;

1 mark

Total 6 marks

2 8048/9048 Mark Schemes

Question 2 Maximum mark (a) protein; fatty acid / {hydrophobic / phospholipids} tail ; phosphate / glycerol / {hydrophilic / phospholipids} head ;

3 marks

(b) A suggestion to include two from: 1. small (molecular size) ; 2. recognised by protein receptors /eq ; 3. lipid soluble/non-polar/hydrophobic ; [Accept uncharged]

2 marks (c) (i) both involve (carrier) proteins / both transport hydrophilic molecules / named molecule / selective ;

1 mark

(ii) active transport requires energy / ATP, facilitated transport does not / active transport moves molecules against a concentration gradient, facilitated diffusion allows molecules to move down a concentration gradient / eq ;

1 mark

Total 7 marks


Question 3 Maximum mark

(a) (i) A description to include four from: 1. white blood cells move into wall (of artery) / inflammatory response ; 2. cholesterol deposited / reference to foam cells /eq ; 3. fibrous tissue develops / reference to plaque / atheroma ; 4. artery wall hardens / becomes less elastic / atherosclerosis ; 5. narrowing of lumen / aneurysm ; 6. restricts {blood flow / oxygen} to the brain ; 7. detail of blood clotting process ; 8. correct reference to positive feedback ;

4 marks (ii) A suggestion to include two from:

1. monitor or treat high blood pressure ; 2. avoid smoking ; 3. treat high blood cholesterol ; 4. correct reference to a specific dietary change ; 5. avoid air travel ; 6. use suitable drug treatment ; 7. more exercise ; 8. reduce stress in context ;

2 marks


(b) platelets thromboplastin prothrombin fibrinogen fibrin red blood cells All six correct - 3 marks five or four correct - 2 marks three or two correct - 1 mark one correct - 0 marks [Credit one mark for each two correct answers rounded down]

3 marks

Total 9 marks


Question 4 Maximum mark (a) (i) adenine ;

1 mark (ii) uracil ;

1 mark (iii) phosphate ;

1 mark (b) A description to include two from: 1. double {stranded / helix} ;

2. base pairing / A-T,C-G ; 3. hydrogen bonds (easily broken) ;

2 marks (c) Any two from: 1. DNA replication – both strands copied / transcription only one strand copied ; 2. DNA replication uses T, transcription uses U ; 3. Reference to DNA polymerase / RNA polymerase ; 4. DNA replication copies whole strand / transcription only copies part of the strand / eq ; 5. mRNA synthesised in transcription, not in DNA ;

2 marks

Total 7 marks


Question 5 Maximum mark (a) parents’ genotypes shown (Nn and Nn) ;

parents’ gametes shown (N and n for both); son NN and daughter nn ;

3 marks

(b) A description to include four from: 1. cells obtained by cheek (cell) swab / blood test / eq ;

2. DNA extracted (from cells) ; 3. reference to use of restriction enzymes ; 4/5. any detail of gel electrophoresis method, for example, reference to pipetting into wells / use of agarose gel / electrodes / electric current / use of buffer / correct reference to fragment size and speed ;; 6. reference to use of alkali /eq ; 7. transferred to {nylon / nitrocellulose} membrane / southern blotting / eq ; 8. reference to use of gene probe ;

9. further detail of gene probe, for example, radioactive / complementary / eq ;

10. reference to use of X ray film / eq ;

4 marks (c) (i) amniocentesis / chorionic villus sampling /CVS ;

1 mark

(ii) peace of mind if result is negative / can consider abortion / can prepare for another child with cystic fibrosis ;

1 mark

Total 9 marks

Question 6 Maximum mark (a) (i)

O

C N

H ; 1 mark

(ii) peptide ;

1 mark (b) An explanation to include two from: 1. chain folds into secondary structure / reference to α-helix or β pleated sheets ;

2. then folds into tertiary structure ; 3. {bonds / interactions} between R groups ; 4. reference to named bond ; Reject peptide

2 marks (c) (i) An explanation to include: 1. substrate concentration limiting the rate / eq or converse ; 2. correct reference to not all active sites occupied by substrate / eq ;

2 marks (ii) An outline to include four from: 1. identify independent variable and dependent variable ; 2. select suitable range of concentrations (at least 5) ; 3. fixed volumes of enzyme / substrate ;

4. control of named variable(s) ;

5. description of apparatus used ; 6. correct method of obtaining quantitative results ; 7. reference to replication / calculation of rate / mean values ;

4 marks

Total 10 marks



Question 7 Maximum mark (a) (i) {semilunar / aortic} valve ;

1 mark (ii) ventricular systole ;

1 mark (iii) A description and an explanation to include three from: 1. ventricles contract ; 2. atrioventricular(AV) valves close ; 3. semilunar valves open /eq ; 4. due to higher pressure in ventricles ; 5. compared to {atria / artery} ; 6. blood passes into {aorta / artery} ;

3 marks (b) (i) A suggestion to include three from: 1. reduced flow of blood to heart {muscle / cells} ;

2. lack of oxygen (to cells) / reference to anaerobic respiration / ischaemic / eq ; 3. cells / muscles damaged / die / eq ; 4. reference to lactic acid / angina ;

3 marks (ii) walls of the artery are elastic /eq ;

1 mark (c) An explanation to include: 1. angioplasty operation has less risk / eq ;

2. angioplasty is less invasive / less major operation / may not need general anaesthetic / faster recovery rate ;

2 marks (d) arteries carry blood under higher pressure / eq ;

1 mark

Total 12 marks

TOTAL FOR PAPER: 60 MARKS

Unit SN2 (6132)


O E [

Starch Cellulose Molecule with branches attached by 1-6 linkages Molecules always long and straight

Formed from α glucose molecules

Form microfibrils by hydrogen bonding

Major component of plant cell walls

Stored in amylopasts

ne mark for each correct row ; ; ; ; ;

mpty box = no marks

Reject ticks that might be crosses]

Total 5 marks



Question 2 Maximum mark Meiosis ; Halved / ½ ; Random(ly) / independently ; (Digestive) enzymes / lysozyme / eq ; Acrosome ; Zygote ; Mitosis ;

Total 7 marks


Question 3 Maximum mark (a) ii Mitochondrion / mitochondria ; iii Ribosomes / rough endoplasmic reticulum / RER; iv Golgi body / golgi apparatus / smooth endoplasmic reticulum / SER; v Vacuole ; vi Centriole ;

5 marks (b) A description to include two from:

1. pits contain plasmodesmata / pass through pits ;

2. (plasmodesmata) are strands of cytoplasm (which connect plant cells) ;

3. pits are holes through (cell) walls ; [Accept thinning of wall / eq ] 4. {plasmodesmata / pits} allow {substances / named appropriate substance} to pass between (plant) cells / eq ;

2 marks (c) Any two from: 1. (prokaryotic cell) has no nuclear membrane (whilst a eukaryotic cell does) / DNA not enclosed in a {nuclear membrane / nucleus} ; 2. (prokaryotic cell) has circular chromosome (whereas eukaryotic cell has linear ones) / (prokaryotic cell) has single chromosome whereas eukaryotic cells have {many / several}) ; 3. (prokaryotic cells) do not have {mitochondria / chloroplasts / endoplasmic reticulum / golgi body / centriole / lysosomes / membrane bound organelle / structure within cell} (whereas eukaryotic cells can have) ; 4. (prokaryotic cells) can have {plasmids / pili / slime} capsule (eukaryotic cells do not) ; [Reject flagellum]

5. (prokaryotic cells) are much smaller (than eukaryotic cells) ;

6. (prokaryotic cells) always have a cell wall (only some eukaryotic cells have cell

wall) ;

[To gain a mark there must be no ambiguity about whether the candidate is referring

to a prokaryotic or eukaryotic cell]

2 marks

Total 9 marks



A description to include six from:

1. reference to xylem (vessels) ;

2. which are tube-like ; 3. hollow / no content / dead ; 4. with waterproof walls / lignified ; 5. (adhesion) water molecules stick to side of xylem vessel ; [Accept cellulose / cell wall in correct context] 6. (cohesion) water molecules stick to each other ; 7. transpiration / evaporation from leaves causes water movement ; 8. creates negative / reduced pressure / creates tension ; 9. correct and appropriate reference to root pressure ;

Total 6 marks


Question 5 Maximum mark (a) A suggestion to include three from: 1. reference to seed (not pollen) dispersal by wind / animals ;

2. reference to a specific adaptation (of fruits) that aid dispersal by wind, for example, wings / parachute / eq ; 3. reference to a specific adaptation (of fruits) that aid dispersal by animals, for example, contain food for animals / may have hooks which stick to animals fur; [N.B. candidates are not expected to know about how individual species are dispersed but only about adaptations for dispersal in general therefore examples of methods of dispersal need not refer specifically to pine, hazel or oak]

3 marks

(b) A suggestion to include two from: 1. the idea that the seeds of a single tree are only carried a short distance, for

example, one squirrel is not going to carry an acorn more than a few 100 metres ;

2. therefore it will take many generations to cover the distance (750 km) ; 3. suitable reference to slowness of climate change / temperatures would rise more slowly / the ice would take longer to melt in the {north / Scotland} 4. long time to reach reproductive age / eq ; [Reject long to grow unqualified] 5. oak requires warmer conditions than pine / differential response to pine against oak ; 6. dispersal limited by low number of animals ;

2 marks


(c) (i) An explanation to include: 1. need to find a place nearby with peat / take a peat core / look at layers in the peat / the deeper the layer the older the pollen / eq;

2. pine and oak pollen look different ; [Accept types of pollen are different] 3. reference to method of identifying pollen ;

2 marks (ii) pine (pollen) would be in deeper layers than oak ; correct reference to relative abundance of pine / oak pollen ;

1 mark

(d) An explanation to include three from: 1. they assume that current trends will continue / we cannot be sure current trends will continue ;

2. there is only limited amount of long term data used to produce them /eq / older records may have been made with inadequate equipment ; 3. something unforeseeable may happen / not all the relevant factors may have been included in the model / appropriate reference to chaos theory; 4. many factors involved / inadequate computing power ;

3 marks

Total 11 marks


Question 6 Maximum mark (a) A suggestion an explanation to include: 1. to remove / separate the soft tissues from the fibres ; 2. by microbial / bacterial decomposition / activity ;

2 marks

(b) A description to include four from: 1. measure samples of fibres to standardise(same length / width) ; 2. increasing range of suitable masses / eq ; 3. record mass needed to break fibre or record force (if a newton meter used) ; 4. repeats for reliability ; 5. one good safety precaution ; 6. appropriate reference to calculation of cross sectioned area ;

4 marks (c) A suggestion to include two from: 1. cotton has to be imported / eq ;

2. lower transport costs ; [Accept other good reference to costs] 3. more expensive fertilisation / pesticides used to grow cotton or converse for nettles / grow any where / waste ground ;

2 marks

Total 8 marks



(a) (i) Any unambiguous attempt to label the outermost layer (inside the bark) ;

1 mark

(ii) 1999 ; [Accept 2001 if the candidate has incorrectly labelled the centre as 2003 or 2002 if the previous ring inside has been labelled 2003]

1 mark (b) (i) Three measurements totalled and divided by 3 ; Correct answer with units in the range 3 to 4 mm / 0.3 – 0.4 cm ;

2 marks (ii) A description to include two from:

1. (generally) the more rainfall the greater tree growth / converse ; 2. specific reference to the fact that the correlation is not a perfect one ; 3. reference to a specific anomaly, for example, 2003 value / the differences between the size of the rings is much bigger in proportion to the differences in rainfall ;

2 marks (c) A suggestion and an explanation to include: 1. increased temperature increases growth / leads to wider annual rings ;

2. reference to enzymes / reference to increases growth within a particular temperature range / along as the temperature is not so high that it denatures enzymes / unless high temperature lead to drought ;

2 marks


(d) (i) (coppicing is a) renewable (energy source)/ can be replaced by growing some more / same piece of ground can be used over and over again / reduces reliance on fossil fuels / non renewables / carbon neutral ;

1 mark

(ii) An explanation to include three from:

1. (the CO2 released by burning) is {immediately/rapidly} reabsorbed ; 2. by photosynthesis / turned back into {biomass/wood} ; 3. C neutrality explained ; (no net increase of CO2 or CO2 taken up or by CO2 release) 4. (so) no increase in greenhouse effect / no (extra) {heat / infra red} absorbed / trapped by atmosphere ;

3 marks

Total 12 marks



(a) supercoiling / transcription factors /repressor molecules / hormones ;

1 mark (b) A suggestion to include two from: 1. (due to) uncontrolled mitosis / cell division ; 2. the rate of cell division greater than cell death / apopotosis ; 3. correct reference to mutation ;

2 marks (c) (i) A description to include four from: 1. animals / cell culture tested for humans ; 2. reference to female subjects ; 3. (phase I) preliminary (small scale) tests on healthy volunteers ; 4. {independent / official} body of {scientists / medics} / (UK) Medicines Control Agency decides whether work can progress (to phase 2} ; 5. (phase II) drug tested on small groups of (volunteer) {patients / people} who already have the disease ; 6. (phase III) {larger / 1000 to 3000 group of} {patients / people} who already have the disease ; [Accept if no reference to phase I and II] 7. placed randomly in two groups one to receive treatment the other not / as control ; 8. one group given medical product the other a placebo / dummy treatment / no active ingredient ; 9. (double blind test) neither patients nor doctors know who has the active compound ; 10. statistics used to analyse results / test for significance ; [Credit points 6-9 in context of animal testing]

4 marks


(ii) An explanation to include two from: 1. only sick patients treated ; 2. high risk doses / patients nearly died ; 3. no placebo / control used / not a double blind test ; 4. no control by regulatory body ; 5. small sample size ;

2 marks


(d) In favour: 1. Relief of human suffering ; 2. Cancer a very serious condition / causes death / severe distress / no satisfactory alternative way of treating it ; 3. Debatable whether an embryonic stem cell can be regarded as a potential human life but adult stem cells are not a potential human life ; 4. Developing stem cell technology could lead to cures for other conditions ; 5. Any balanced view on the use of stem cells ; [Level marking award points 1-4 to a max 2 marks and point 5 for the 3rd mark] against: 1. Stem cells can be harvested from human embryos / increases pressure to produce embryos specially for treating people ; 2. Embryos have right to life / use of embryos = murder ; 3. Research using non-embryonic stems could make use of embryonic stem cells unnecessary ; 4. Could be unforeseen side effects for the woman / any children she has / correct reference to gene line / might lead to even more ethically questionable practices ; 5. Any balanced view on the use of stem cells ; [Level marking award points 1-4 to a max 2 marks and point 5 for the 3rd mark] [A candidate who does not express a position can only be awarded a maximum of two marks unless he or she has deliberately chosen and attempted to justify an undecided position supported by an argument that the ethical issues are so finely balanced that he or she would not like to come down on either side]

3 marks

Total 12 marks


Unit SN3 Practical Review (6133/02)

Question 1 Maximum mark (a) Look for two correctly identified dependent variables ; ; And a suggestion in each case as to how it could be measured accurately (e.g. stopwatch for timing / good judgment of end point / use of colorimeter (zeroing, cleaning cuvette etc.) / calipers rather than ruler / counting method for heart rate etc.) ; ;

4 marks (b) A description to include two from: 1. Repeat ;

2. Deal with anomalies ; 3. Control qualified variables ; 4. Standardize procedure ; Reject calculate mean

2 marks

Total 6 marks


Question 2 Maximum mark (a) Any three from: 1. Appropriate measurement (e.g. transmission / absorbance in beetroot practical / time to end point in enzyme concentration / heart rate etc.) ;

2. Suggestion as to how an error was made which was one way (and constant) (e.g. dirty cuvettes giving absorbance where there should be none / stopclock inaccuracy / end point judgment problems / undercounting heart rate because of speed etc.) ; 3. Suggestion for improvement ;

3 marks (b) Appropriate data presentation method clearly stated (line / bar / histogram) ; Reject scatter graph

1 mark Then, for graph/chart,, any three from:

1. ….with reasons ; 2. Errors shown ;

3. Axes described ; 4. Justified ; 5. Scale justified ; 6. Values (eg %, mean etc) ; 7. Justified ; 8. Identify anomalies / trend ; 9. Appropriate choice of line, justified ;

10. Any other valid point ; Accept for one mark valid manipulation of a table

3 marks

Total 7 marks


Question 3 Maximum mark (a) (i) Independent variable (IV) identified correctly in context ;

1 mark (ii) Two factors correct in context ; ;

2 marks (b) Appropriate factor chosen, with suitable control method ; Description of effect on dependent variable ;

2 marks (c) Two appropriate aspects discussed ; ;

2 marks

Total 7 marks



Unit SN4 (6134)

Question 1 Maximum mark (a) A possible / alternative form / eq ; (of a) gene ;

2 marks (b) Any two from: 1. Stable community /ecosystem / community dominated by dominant species ; Reject ‘environment’ 2. Succession stops ; 3. Last {seral / eq} stage ;

2 marks (c) Number of organisms / ref to abundance scale ; In an area / description of area eg quadrat ; Reject ‘amount’

2 marks

Total 6 marks


Question 2 Maximum mark (a) Primary consumer - seed eating birds / grasshopper / field mice ; Secondary consumer - spider ;

2 marks (b) (i) 1980 + 3600 + 62 ; = 5642 ; Allow full marks for correct answer with no working shown

2 marks (ii) Either: subtract respiration / 3600 ; Or: 2042; NPP=(GPP – R)/GPP=NPP + R;

1 mark (c) (i) 44.4 - (12.5 + 25.4) ; 6.5 out of 44.4 ; 14.6% ; Allow full marks for correct answer with no working shown

3 marks (ii) Faeces/ indigestible material ; Reject ‘inedible parts’ Nitrogenous waste / eq ;

2 marks (d) An explanation to include two from: 1. Small proportion reaches next level / converse ; 2. Correct use of figures ; 3. Insufficient energy to support another level ;

2 marks

Total 12 marks


Question 3 Maximum mark (a) An explanation to include six from: 1. Increased use ;

2. More bacteria exposed ;

3. Reference to mutation ;

4. Reference to plasmids ;

5. Reference to conjugation / sexual reproduction ;

6. Reference to genetic variation / existence of different genes ;

7. Reference to selection by the antibiotic ;

8. Description of selection ;

9. Reference to resistance gene passed to offspring ;

10. Selected organisms become more common ;

11/12.Reference to graphs ; ;

6 marks (b) (i) Greater clear area ;

1 mark (ii) An explanation to include two from: 1. Larger molecules / antibiotic C {diffuse / eq} more slowly ;

2. Through agar ;

3. Does not reach as many bacteria as the smaller antibiotic B ;

4. Clear area of C is reduced ;

5. Under estimates the effectiveness of C / converse ;

2 marks (iii) An explanation to include: 1. Viruses no cell wall ; 2. or ribosomes/ viruses use host cell for protein synthesis ;

2 marks

Total 11 marks


Question 4 Maximum mark (a) An explanation to include two from: 1. Engulfed / endocytosis ; 2. Digested / eq ; 3. Reference to enzymes / lysosomes ;

2 marks (b) (i) An explanation to include three from: 1. Reference to APC ; 2. Reference to cytokines ; 3. (T cells) stimulate response ; 4. CD4 depleted cannot respond ; 5. Injected cells restore immune response ; 6. Reference to specific response ; 7. Prevents TB ;

3 marks (ii) An explanation to include two from: 1. HIV destroys / kills T helper cells ; 2. Reduced response ; 3. More likely to show symptoms / develop TB ;

2 marks (c) An explanation to include two from: 1. Chemicals (from infected lung) stimulate HIV production ; 2. In T helper cells ; 3. Reference to control ;

2 marks


(d) A suggestion to include three from: 1. Chemicals / lymphokines from macrophages from infected lung ; 2. HIV infects more T helper cells / number of T helper cells falls ; 3. Less able to destroy M tuberculosis / eq ; 4. More phagocytosis ; 5. More lymphokines / chemicals ; 6. Reference to positive feedback / eq ; 7. Both diseases progress more rapidly ;

3 marks

Total 12 marks


Question 5 Maximum mark (a) Any two from: 1. DNA does not change ; 2. DNA unique to individual ; 3. Test reliable / reference to probability ;

2 marks (b) Tissue / eq ; Intact DNA / contain DNA / nuclei ;

2 marks (c) An explanation to include: 1. Sample from corpse ; 2. Match with family ; 3. Match with sample / previous test ; 4. Example of source of comparison (e.g. hairbrush, toothbrush) ;

3 marks (d) Any two from: 1. Dental records ; 2. Face / recognition / eq ; 3. Normal fingerprints ; 4. Personal artefacts ;

2 marks

Total 9 marks


Question 6 Maximum mark (a) An explanation to include two from: 1. Biodiversity depends on number of species ; Reject ‘amount’ 2. (Extinction) reduces this ; 3. Dependent species affected ;

2 marks (b) (i) Source of protein / source of energy / reference to protein synthesis / growth / few suitable alternative protein sources / reference to economic significance ;

1 mark (ii) A suggestion to include two from: 1. Smaller catch ; 2. For African fishermen ; 3. Eat bush meat instead / eq ; 4. Correct reference to aquatic mammals ;

2 marks (c) A description to include two from: 1. People will not change way of life easily ; 2. Like European fishermen ; 3. So unexpected effects ; 4. Elsewhere; 5. African culture of using bush meat / eq ;

2 marks


(d) An explanation to include three from: 1. Cannot control external factors ; 2. Which might affect local area ; 3. Could send problem elsewhere ; 4. Conflicting needs not considered ; 5. Reference to globalisation of human activities ; 6. Wild populations not confined (to human boundaries) ; 7. Law of the commons / eq ; 8. International agreements carry more weight / eq ;

3 marks

Total 10 marks



Unit SN5 (6135/01) Question 1 Maximum mark (a) (i) X - CO2 ;

1 mark (ii) A - Glycolysis B - Krebs cycle / TCA cycle

1 mark (b) An explanation to include four from: 1. Reference to cristae / inner membrane of mitochondria / intermembrane space ; 2. Correct reference to {reduced coenzymes / NADH2 / FADH2 } / eq ; 3. Hydrogen splits into electrons and {protons/H+} ; 4. Electrons / H (atoms) pass along series of carriers / down ETC ; 5. From higher energy levels to lower energy levels / redox /oxidation ; 6. (Reactions) release energy (for synthesis of ATP) / correct ref. to chemiosmotic theory ; 7. Oxygen acts as terminal electron acceptor / water is formed ;

4 marks (c) {Broken down / hydrolysed} into ADP + Pi / ATP → ADP + Pi (+ energy) ;

1 mark

Total 7 marks


Question 2 Maximum mark (a) (characteristics) controlled by more than one gene / many genes ; Accept ‘alleles’ / ‘loci’ Reject ‘multiple alleles’

1 mark (b) 100% / above 95% suitably qualified reference to mutations;

1 mark (c) An explanation to include two from: 1. Multifactorial ; 2. Environment has an effect/genes and environment (interact) ; 3. Correct use of figures ;

2 marks

Total 4 marks


Question 3 Maximum mark (a) Impaired synthesis / serotonin reabsorbed before it reaches postsynaptic membrane / reference to vesicles ;

1 mark

(b) An explanation to include six from:

1. {Nerve impulses / action potentials} arrive at {synapse / presynaptic membrane} ;

2. Calcium ion channels open / calcium ions enter ;

3. Vesicles fuse with presynaptic membrane ;

4. Correct reference to exocytosis ;

5. Neurotransmitter diffuses across (synaptic cleft);

6. Binds to receptors on postsynaptic membrane ;

7. Leads to opening of sodium ion channels / sodium ions enter ;

8. Depolarisation of postsynaptic membrane ;

9. {Threshold / action potentials / impulses}in postsynaptic neurone ;

10. Neurotransmitter broken down by enzymes / reabsorbed ;

6 marks (c) A suggestion and an explanation to include two from:

1. Increases serotonin synthesis ;

2. Blocks serotonin re-uptake into (presynaptic) neurones / correct ref. to SSRI ;

3. Therefore high levels of serotonin remain in cleft / eq ;

4. Binds with postsynaptic receptor ;

5. {Threshold / more impulses / more action potentials} in postsynaptic neurone ;

2 marks (d) A suggestion to include three from:

1. Similar shape to serotonin / eq ;

2. Binds to molecules on {presynaptic membrane / re-uptake mechanism} ;

3. Therefore high levels of serotonin remain in cleft / eq ;

4. Impulses / action potentials continually generated ;

5. Correct reference to postsynaptic neurone ;

3 marks

Total 12 marks


Question 4 Maximum mark (a) (i) Curve shows a decrease from 0 ; Decrease followed by a rise ; Reject if above 0

2 marks (ii) An explanation to include two from: 1. {Intercostal muscles / diaphragm} contract ;

2. Ribs move up and out / diaphragm flattens / eq ;

3. Volume increases and pressure decreases ;

2 marks (b) A description and an explanation to include three from: 1. Increase in rate of respiration ; 2. Rise in (blood) CO2 / fall in pH / fall in (blood) oxygen ; 3. Reference to chemoreceptors / eq ; 4. Reference to medulla / ventilation centre/ eq ; 5. More impulses to breathing muscles / named muscles ; / eq ; 6. Increase in {breathing rate / depth of breathing / tidal volume} ;

3 marks

Total 7 marks


Question 5 Maximum mark (a) (i) 0.96% ;

1 mark (ii) Any two from: 1. Time of administering drug prior to exercise ; 2. Dose of drug ; 3. Body mass / age / sex ; 4. {Food / fluid} intake / smoking / eq ; 5. Rest period between trials ; 6. Correct reference to swimming conditions ; 7. Same three swimmers ; 8. Ability /experience (of swimming) ;

2 marks (iii) Reference to control / allows the effect of the drug alone to be measured / ref. to

psychological effect of placebo / eq ; 1 mark

(b) (i) {Vasoconstriction / constriction} of arterioles ;

1 mark (ii) Less heat lost by convection / radiation / conduction ;

1 mark


(iii) An explanation to include three from: 1. Hypothalamus detects increase in (core) temperature ;

2. Sweating cools body by evaporation ; 3. Hairs lie flat, therefore less insulation / more heat lost / eq ; 4. Correct reference to negative feedback ; 5. Correct explanation of behavioural mechanism ;

3 marks (c) Against:

Reference to damaging effect on synapses / leads to abnormal behaviour or eq / unfair advantage / correct ref. to long-term effects on body ;

OR

for:

Individual choice / responsibility ;

1 mark

Total 10 marks



Unit SN6 (6136) Question 1 Maximum mark (a) An explanation to include four from: 1. Temperature rise detected by hypothalamus / temperature receptors in skin / thermo receptors ; 2. Adrenaline released ; 3. Increases sweat production / above 37 ◦C sweating is only effective way to cool / eq; 4. Evaporation of sweat, removes heat from {skin / body} ; 5. Cooled blood circulates back to the core / eq ; 6. Behavioural mechanism explained ; 7. Reference to need to replace {water/salts/fluids} ;

4 marks (b) A suggestion to include two from: 1. Natural selection / because they have a selective advantage ; 2. Lower surface area to volume ratio ; 3. Those Inuit with short stocky bodies have more chance of surviving to reproduce and pass on {genes / alleles} to their offspring ;

2 marks

(c) An explanation to include two from: 1. CFTR protein channel does not work / eq ; 2. Less water moves from cells into sweat gland ; 3. Sweat has a higher concentration of salt / sodium chloride (than normal) ;

2 marks


(d) An explanation to include three from: 1. Exercise can increase heat generation - due to increased rate of respiration ; 2. At end of race there is decreased air flow ; 3. Therefore decreased rate of evaporation of sweat / eq ; 4. Core temperature may rise ; 5. Reference to brain being particularly temperature sensitive / Reference to dehydration aggravates the onset of heat stroke ;

3 marks (e) An explanation to include two from: 1. Porcine stress syndrome was noticeably similar to malignant hyperthermia ; 2. Mutant {gene / allele} responsible for porcine stress syndrome was identified / eq ; 3. Human {gene / allele} identified through similarity to the pig {gene / allele} ;

2 marks (f) A suggestion to include three from: 1. Aspirin blocks the synthesis of prostaglandins /eq ; 2. Therefore reduces fever / rise in body temperature ; 3. {Small rise in temperature / fever} thought to help immune response / increase phagocyte activity / eq; 4. Rise in temperature may {damage / kill} bacteria ; 5. Evidence that lizards have an improved survival rate from bacterial infections in a warm environment than a cold environment ; 6. Fever therapy used to be successful against syphilis and gonorrhoea ;

3 marks


(g) A description to include four from: 1. Muscle contraction is initiated by an increase in the {intracellular concentration of Ca2+ (ions) / opening of Ca2+ channels} ; 2. Ca2+ ions released into the sarcoplasm ; 3. From the sarcoplamic reticulum ; 4. In response to nerve impulse arriving at the {neuro muscular junction / synapse} ; 5. Ca2+ ions attach to troponin ; 6. Causing tropomyosin to move exposing myosin binding sites on the actin filaments / eq ; 7. Allows myosin to join to actin / eq ;

4 marks

Total 20 marks


Question 2 Maximum mark (a) (i) {9 / 10} cm / {medium / brisk} walk uphill ;

1 mark (ii) An explanation to include three from: 1. Need for more energy / to supply more energy / more ATP ; 2. More muscular{activity / contraction} / oxygen not being delivered to the muscle (cells) fast enough / prevent anaerobic respiration / get rid of lactic acid ; 3. (Oxygen needed for) breaking down {carbohydrate / sugar / organic}(molecules) ; 4. Correct reference to ATP as (immediate) supply of energy (for biological processes) ; 5. Correct reference to Krebs Cycle / complete oxidation of glucose / sugar to CO2 ; 6. Oxygen as the ultimate {hydrogen / electron acceptor / sink} / correct reference to NAD+ / ATP production linked to electron transport ;

3 marks (iii) A suggestion to include two from: 1. Loss of surface area due to damage to alveoli ;

2. {Narrow airways/bronchioles blocked} (by mucus) {preventing air from entering alveoli / reaching gas exchange surface} /eq ;

3. Mucus {thickens the gas exchange surface / increased diffusion distance} ; 4. Reference to reduced rate of diffusion into blood ;

2 marks (b) (i) A suggestion to include two from: 1. Person breathes out as fully as possible (for one breath) ; 2. {Spirometer / similar suitable apparatus e.g. bell jar with water} to measure volume ; 3. Correct reference to replication of measurements to increase reliability ;

2 marks


(ii) A description to include: 1. decreases ; 2. Qualified reference to decrease (e.g. to 63-73% of FEV by age 75 / decrease gets faster from age 60-70 / eq ;

2 marks (iii) A description to include two from: 1. FEV is lower in smokers compared with non-smokers / reduces much more rapidly (than in the case of non-smokers) ;

2. Use of figures e.g. (disability) by (anything between) 60 and 65 / (death) by (anywhere between) 65 and 70 ;

2 marks

(iv) An explanation to include two from: 1. It does not support this point of view ; 2. Giving up prolongs life / reduces risk from death by COPD / postpones disability ; 3. Use of figures e.g. giving up at 50 may prolong someone’s life by 25-30 years / appropriate use of figure 3 e.g. reduced rates of cancer in passive smoking ;

2 marks

(c) (i) A description to include two from: 1. The more cigarettes smoked per day (by the partners) the fewer women took part (in the first place) / converse; 2. The number of women taking part reduced during the study (high drop-out rate) ; 3. Increased incidence of cancer in women whose partners {were heavy smokers / partners who smoke over 39 cigarettes per day} ; 4. The more (cigarettes per day) the partners smoked and the {lower / little change} in the incidence of {smoking-related diseases / heart disease /stroke (but not cancer)} in the women ;

2 marks


(ii) An explanation to include: 1. The differences between the people exposed to passive smoking and those who were not could be explained by chance / less than 95% confidence ; 2. Any differences could have been explained by other factors / there could have been other (uncontrolled) variables (responsible for the differences) / not enough data (to support hypothesis) / sample size too small / data could be biased / eq;

2 marks (iii) A suggestion to include two from: 1. This experiment does not show what happens when a lot of people are smoking in a confined space where the level of passive smoking could be much higher (than in a smoker's home) ; 2. A lot of people dropped out of this experiment ; 3. How do we know they were not the ones who died of passive smoking / sample size reduced therefore figures less and less reliable (as study progresses) ; 4. The sample size may not have been big enough (adequate to provide enough evidence) ; 5. The increase in cancer in the case of women who lived with heavy smokers / 39 per day might well be significant / invites further investigation ; 6. It was (part) funded by the tobacco industry therefore could be biased / reference to vested interest ; 7. There are many other studies which show the opposite point of view / eq ;

2 marks

Total 20 marks


Synoptic Essay - General Mark Scheme A: Examples selected are relevant to the question asked. Up to 6 marks available The examples identified should be selected from more than one topic of the A level specification,

ideally making reference to most areas that might realistically be covered from both AS and A2 topics.

Examples need to be relevant to the question asked and need to address all parts of the question

asked in order to receive maximum marks. B: The Biological examples are described and discussed Up to 8 marks available accurately. The Biological examples chosen should be factually correct and explained with some depth, which

demonstrates a sound understanding of the relevant principles covered. C: The Biological examples are used successfully to produce a Up to 6 marks available balanced account that illustrates the points in the discussion or argument raised in the question title. This will involve candidates writing a balanced essay that successfully addresses the key issues of the

question asked. This could also include demonstrating an ability to weigh up advantages and disadvantages, risks and

benefits of the biological examples chosen; or an appreciation of the implications of the applications of the biological principles discussed.

D: Coherence, clarity and expression of the answer Up to 4 marks 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 collection of information which, although relevant, is likely to be disjointed and only partially attempts to synthesise information.

2 marks: A reasonably coherent account that includes satisfactory spelling, punctuation and grammar, which tends to be a disjointed 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.

The maximum total mark for each question is 20.

Salters-Nuffield Examination June 2006 Synoptic Paper SN6 Marking Grid for essays Question 3 One of the unique features of living material is the ability to maintain (or even increase) their own energy content, in contrast to the tendency of dead organic matter to lose energy as a result of the biological, chemical and physical processes in their environment. “All life depends on light and chemical energy.” Discuss the processes involved in the flow of energy in ecosystems and their importance in maintaining life.

A: Up to 6 marks available A = Introducing general area of biology relevant to the essay title – if a relevant B point is awarded then the corresponding A point should automatically be awarded.

B: Up to 8 marks available Max of 4 marks per A strand – each to be credited for a clear specific point of A level detail in the context of the topic area. The following list provides examples of the depth and detail required.

A1 Photosynthesis

B1a Plants can only utilise certain wavelengths in the visible spectrum/mainly red and blue light used

B1b In photosynthesis inorganic molecules built up into bigger organic ones / biomass or specific example

B1c Chlorophyll captures light energy B1d further detail of light dependent reactions / light harvesting

complex / Z diagram / electron transport system / chemiosmosis B1e

and B1f some specific biochemical details of the light independent reactions e.g. reference to enzyme controlled reactions / role of reduced NADP as reducing agent / reference to CO2 combining with ribulose bis phosphate / role of RUBISCO

A2 Feeding relationships B2a When an animal eats another animal or a plant it obtains (second hand) energy from the sun

B2b Described in terms of trophic levels / correct use of the term primary producer ; Note only one mark

B2c The amount of energy flowing along the food chain determines


B: Up to 8 marks available Max of 4 marks per A strand – each to be credited for a clear specific point of A level detail in the context of the topic area. The following list provides examples of the depth and detail required. the size of the consumer populations / eq

B2d Correct reference to net primary productivity (as GPP-R) / due to plants metabolic needs not all energy available to next trophic level / eq

B2e Qualified energy loss from food chain e.g. less digestible material for herbivores

B2f Most energy is lost from food chains as heat from respiration A3 Respiration B3a Respiration releases (usable chemical) energy in the form of ATP

from (breaking down) {organic molecules / biomass / eq} B3b Series of enzyme controlled reactions / broken down in a series

of small steps / eq B3c Credit correct detail of Krebs cycle / glycolysis / link reaction B3d Production of ATP as part of (an efficient) energy transfer

mechanism B3e (respiration) is an oxidative process / involves loss of H /

electrons / correct reference to NAD+ as H/e- acceptor / reference to oxygen as ultimate H / e- sink /appropriate reference to alternative H / e- sinks in anaerobic respiration

B3f Credit detail of chemiosmosis i.e. mechanism of how ATP is generated by H+ concentration gradient in mitochondina

A4 Digestion

B4a Large (organic) molecules need to be broken down into smaller molecules for {absorption / transport}

B4b Role of {digestive / hydrolytic} enzymes

A5 DecompositionB5a

Decomposers feed on {dead organic matter / faeces} to obtain chemical energy



B5b

Decomposers recycle minerals / CO2

B5c

Examples of decomposers – bacteria / fungi / saprotrophs

B5d

Example: e.g. in a cave there is no light but organisms may feed on bat droppings produced by bats which have been out of the cave to feed e.g. Robins feed on soil invertebrates which feed on dead organic matter

A6 ChemosynthesisB6a

Food chains starting with chemosynthetic autotrophes do not start with energy from the Sun

B6b

Example of chemosynthetic organism with brief explanation e.g. nitrifying bacteria obtain energy by converting ammonium ions into nitrite / nitrate / sulphur bacteria

B6c

The energy / reducing agents from the chemical reaction is used to convert CO2 into carbohydrate / sugars

A7 Chemical energy stored B7a

(surplus) energy stored in {organic molecules / starch / fat / oil / glycogen} for organism (to use later / in time of need) {available to organism which eats it / next trophic level}

B7b Specific example of storage of surplus energy : e.g. many plants store energy as starch / oils often in seeds / animals store surplus energy as fat / glycogen / stored glycogen part of homeostatic process of animals Note only one mark



B7c Plants respire stored starch at night (when photosynthesis

stops)/ stored starch / oil in seeds provides energy for germination

B7d accumulation of {fossil fuel / peat / coal / methane} {where

decay is prevented / in anaerobic conditions} represents stored energy

B7e

the energy in fossil fuel / peat / coal / oil / methane has come from the sun through food chains

A8 Energy needed to maintain life processes (in cells) B8a

and

B8b

Up to two examples to illustrate this e.g. {growth/protein synthesis} Active transport across membranes / locomotion in animals / temperature regulation in {mammals / birds / humans} Cell division / overcoming energy barrier / activation energy in chemical reactions / muscle contraction

B8c

Reference to hydrolysis of ATP to release energy for cell reactions

Unpacking the question: focusing on the big ideas behind the question: maximum of 6 marks In this case a key issue is why life depends on light and chemical energy – implying that life would be impossible without them. It also requires these issues to be considered in the context of the ecosystem and needs make clear what is meant by chemical energy. Examiners should be careful not to credit again factual information that has already been credited under A (breadth) or B (depth). Candidates get credit for realising that this has something to do with food chains under A and for recalling details under B. In C we are looking for evidence that they really understand the connection between how the knowledge refers to the wording of the question. Responses under C need not be as detailed as given below but credit should be given to outline the synoptic ideas outlined under C1 to C10. Avoid penalising poor use of technical terminology under C – that is taken into account under D.

C1 Key is transfer of light energy into chemical energy

C2 Making it clear what is meant by chemical energy in this context – (potential / biologically available) energy stored in (organic molecules) such as {sugars / carbohydrates / lipids / proteins}

C3 When respiration takes place these molecules are broken down into smaller ones and the stored chemical energy is released

C4 Living {organisms/cells} are regarded as ‘living’ because they display (most or all of) a range of features all of which require energy [note actual examples are credited in B8b]

C5 Reference to thermodynamics / entropy – all systems tend towards the lowest potential energy level – in living systems continual energy input is required to oppose this (but physics always kills you in the end!)

C6 Chemosynthetic autotrophs offer an exception to the principle that all food chains start with light

C7 Reference to energy flow through an ecosystem driving mineral cycles

C8 Reference to photosynthesis generating the oxygen needed for aerobic respiration

C9 Energy cannot be created or destroyed only transferred from one form to the other e.g. light to chemical energy in photosynthesis

C10 Details of how the light dependent and light independent reactions are linked / reference to ATP and reduced NADP from light reaction enabling light independent reaction / photosynthesis is a reductive process

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 is not 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 collection of information which, although relevant, is likely to be disjointed and only partially attempts to synthesise information.

2 marks A reasonably coherent account that includes satisfactory spelling, punctuation and grammar, which tends to be a disjointed 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.

Note that the maximum total mark is 20

Question 4 Cell theory states that “the basic unit of structure and function in living organisms is the cell”. All living cells are surrounded by a cell membrane and eukaryotic cells also depend on internal cell membranes” ”All cellular life depends on membranes.” Describe and discuss the structure and importance of cell membranes.

A: Up to 6 marks available B: Up to 8 marks available A1

(Phospho)lipid bilayer B1a

Phospholipid has (one glycerol) two fatty acids and one phosphate (may be in form of diagram)

B1b Heads hydrophilic tails hydrophobic causes orientation in lipid bilayer

A2 Provides boundary (adhesive cell / organelle)

B2

A3 Role of proteins B3a Reference to shape giving specificity / tertiary structure and

specificity

B3b Reference to carrier in membrane able to select ions /

molecules and transport through membrane / reference to protein channels as selective pathways through membranes

B3c Enzymes can be embedded in the membrane

B3d specific example of enzyme embedded in membrane e.g.

digestive enzymes such as maltase in the cells lining the small intestine / ATPase in the cristae of the mitochondria / thylakoids of the chloroplast.

A4 Internal / compartmentalisation

B4a Internal membranes surround {organelles / example of organelle} / {organelles example} (may have) internal membranes

B4b Two further examples of membrane bound organelles [for one mark]

B4c Enzymes and compartmentalisation / localisation of enzymes: Any example which illustrates importance of membranes in internal membranes for localising enzymes e.g. lysosomes / acrosome / golgi vesicles moving enzymes to membrane (for exocytosis) in isolating enzymes

B4d Explanation (in appropriate context) of the need to isolate (hydrolytic / proteolytic / digestive) enzymes from rest of cytoplasm to prevent autodigestion Having enzymes confined to organelles (e.g. mitochondria or

A: Up to 6 marks available B: Up to 8 marks available chloroplast) means a locally high enzyme concentration can be maintained (for specific processes like Krebs Cycle or Calvin Cycle)

B4e More detailed description of specific example e.g.

how the golgi body packages up material into vesicles / transfer of enzymes to phagosomes following

phagocytosis brief discussion of the significance of lysosomes as

‘suicide bags’ role in apoptosis A5 (membrane) regulates / controls movement of

substances {through it / in and out of {cells / organelles}}

B5a Brief definition of active transport in terms of can be against gradient and selective / use of example which conveys meaning / correct reference to facilitated diffusion

B5b Only small non-polar molecules can pass through the phospholipids bilayer e.g. carbon dioxide

B5c Involvement of ATP / metabolic / respiration derived energy in active transport

B5d Plasmodesmata permit movement of (soluble substances between plant cells)

B5e Membranes have differential permeability / allow some molecules to diffuse through but not others / importance in osmosis – lets water through but not solutes

B5f Reference to ion pumps across membranes B5g Example to illustrate such as reverse polarity in axon

membranes A6 Sensitivity and communication B6a Glycoproteins / glycolipids may be involved in cell adhesion and

cell recognition B6b Act as antigens in immune response//MHC II receptors are used

in antigen presentation by macrophages / B lymphocytes / CD 4 receptors

B6c Receptors in membranes can respond to chemical signals for communication

A: Up to 6 marks available B: Up to 8 marks available B6d A specific example of a chemical signal detected e.g. hormones,

neurotransmitters B6e Discussion of saltatory conduction on axon membranes / eq A7 Membranes can be specialised B7a Membranes may form structural features e.g. cilia, microvilli,

flagella B7b Any example that illustrates the role of membranes as structural

/ functional organisation e.g. reference to rough endoplasmic reticulum (cristae) / cytochromes arranged in inner mitochondrial membrane / chlorophyll molecules arranged in {thylakoid / internal membranes of chloroplasts} / digestive enzymes on cell surface on the cell surface membranes of cells lining the small intestine / ATPase in inner mitocondrial membrane / mesosome

B7c Discussion of the importance of special arrangement and orientation of molecules for effective interaction e.g. pigment molecules on thylakoid membranes

A8 membranes can form vesictes B8a Large particles and large molecules pass through cell membrane by endo / exocytosis / description of invagination / vesicle formation

B8b Illustrates/emphasises fluid nature of membrane / extra details e.g. difference between endo and exocytosis / pino and phagocytosis

B8c Reference to importance of phagocytosis by macrophages / neutrophils in the immune response

B8d Role of cholesterol in membrane {fluidity / stability}

Unpacking the question: focusing on the big ideas behind the question: maximum of 6 marks In this case a key issue is why cellular life depends on membranes – implying that cellular life would be impossible without it. This also sheds light on the significance of the word importance (of membranes). Examiners should be careful not to credit again factual information that has already been credited under A (breadth) or B (depth). Responses under C need not be as detailed as given below but credit should be given to outline the synoptic ideas outlined under C1 to C11 as part of explaining why membranes are essential for maintaining cellular life. Avoid penalising poor use of technical terminology under C – that is taken into account under D.

C1 What makes a cell a cell. A cell is by definition a discrete unit of organisation of living matter. It is the membrane which makes it a separate / semi autonomous compartment of the organism.

C2 Membranes allows cells to be organised on a bigger scale / to be more sophisticated. Internal membranes allow a higher level of organisation of a cell / cells to be organised on a bigger scale since prokaryotic cells are smaller, simpler – and lack internal membranes / membrane bound organelles.

C3 Cell membrane is a {living / interactive boundary} / membrane allows cell to exchange materials with its environment (in a controlled fashion).

C4 Cell membranes maintain the cell as a living cell by continuously pumping substances / ions / molecules in and out.

C5 Maintaining the membrane as an interactive boundary requires continuous ATP / energy expenditure/ respiration.

C6 Aerobic respiration would be impossible without inner mitochondrial membranes and energy is essential for life (anaerobic respiration does not yield enough energy to support the more sophisticated types of cell).

C7 Membranes and compartmentalisation Membranes allow several complex processes to go on in cell at once - yet independently – e.g. respiration and protein synthesis.

C8 Without membranes protein digesting enzymes could not be used inside a cell without the cell digesting itself so important processes like (example) the acrosome allowing a sperm nucleus to enter an ovum – and fertilisation – or (an alternative example) could not happen / digestion in phagosomes in feeding of Amoeba / destruction of phagocytes by phagocytes could not happen.

C9 Viruses do not have a cell membrane and are incapable of independent life

C10 A cell is a level of organisation of organisms / tissues are groups of cells joined together

C11 Some life forms or tissues are multinucleate - coenocytic

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 collection of information which, although relevant, is likely to be disjointed and only partially attempts to synthesise information.

2 marks A reasonably coherent account that includes satisfactory spelling, punctuation and grammar, which tends to be a disjointed 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.

Note that the maximum total mark is 20

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 UA 017718 Summer 2006 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

Documents

Marking Scheme Edexcel