Welsh Joint Education Committee

WELSH JOINT EDUCATION COMMITTEE CYD-BWYLLGOR ADDYSG CYMRU

General Certificate of Education Tystysgrif Addysg Gyffredinol Advanced Subsidiary/Advanced Uwch Gyfrannol/Uwch

MARKING SCHEMES

SUMMER 2003

BIOLOGY

INTRODUCTION

The marking schemes which follow were those used by the WJEC for the 2003 examination in GCE BIOLOGY. They were finalised after detailed discussion at examiners' conferences by all the examiners involved in the assessment. The conferences were held shortly after the papers were taken so that reference could be made to the full range of candidates' responses, with photocopied scripts forming the basis of discussion. The aim of the conferences was to ensure that the marking schemes were interpreted and applied in the same way by all examiners.

It is hoped that this information will be of assistance to centres but it is recognised at the same time that, without the benefit of participation in the examiners' conferences, teachers may have different views on certain matters of detail or interpretation.

The WJEC regrets that it cannot enter into any discussion or correspondence about these marking schemes. ASSESSMENT UNIT BI 1

JUNE 2003

Marks Question Answer/Explanatory Notes Available

1 (a) Characteristic Prokaryotic Eukaryotic Plant Cell

Chromosomes  Ribosomes   Membrane organelles  Respiration in mesosomes  4

(b) comparison needed Prokaryotic Eurokaryotic

Size up to 5 m/smaller Size up to 40 m/larger Cell wall not of cellulose/ Cell wall of cellulose 1 of murein ribosomes smaller ribosomes larger (not: plasmids/flagella unless structure described/pili) [5]

2 (a) amino acid 1

(b) COOH/carboxyl/carboxylic 1

(c) NH2/amino/amine 1

(d) 'R' group variable/not fixed 1

(e) (i) C – CO – NH – C H2O 2

(ii) Condensation 1

(iii) Peptide 1 (allow: dipeptide) [8]

3 (a) (i) Approximately 20 amino acids 1 (allow: 20 to 27)

(ii) some are punctuation/start-stop codons some are coded more than once/code is degenerate 64 coded in a three base system (<3/4/16) not enough to code for all amino acids 2

1 Marks Question Answer/Explanatory Notes Available

(b) (i) Methionine, valine, glutamic acid, aspartic acid, valine, aspartic acid (one mark for each two correct amino acids) 3

(ii) TAC CAA CTT CTA CAA CTG (one mark for each two correct triplets) 3

(iii) Transcription 1 [10]

4 (a) 1 and 3 2 and 4 2

(b) Children one and three have one band from father Children one and three have one band from mother Children two and four do not/match completely/are clones 2 (not: half from father and half from mother; allow consequential error). Any 2/3.

(c) Police/forensic/identifying criminals/determining new species/paternity/genetic disease research. 1 [5]

5 (a) (i) Lipase 1

(ii) Breaking of a bond (allow: large to small molecules) Chemical insertion (not: addition) Of water 2

(iii) pH reduced/more acidic 1 Lipid hydrolysed to fatty acids/ (Fatty acids) cause low/acidic pH 1

(b) (i) Start with maximum marks and deduct one at a time for the following errors:

Incorrect plot Poorly drawn curve (allow: ruled lines) Inappropriate scales (insufficient use of graph paper) Axes not labelled/no units 3

(ii) Rate remains constant/can't increase 1 Substrate/lipid occupies active site/at lower concentrations of lipid not all active sites occupied/ at 0.7% lipid concentration all sites occupied Extra lipid can't access sites 1 (not: limiting factor unqualified)

(iii) Steeper curve (up to 0.7%) 1 [11]

6 (a) (i) A = Glycoprotein/carbohydrate/glycocalyx/ polysaccharide (not: sugars/glycolipid) B = Phosphate/polar group/hydrophilic head/ phospholipid head C = Hydrocarbon/non polar tails/hydrophobic tails/fatty acids (not: tails/lipid layer) D = Transmembrane protein/carrier protein/ channel protein/intrinsic protein (not: protein) E = Protein/extrinsic protein 5

(ii) Fluid mosaic/Singer and Nicholson 1 (not: mosaic)

(b) Glucose Polar molecule Phospholipid layer/hydrophobic region impermeable Protein channels provide passage Hydrophilic linings to channels (allow: water filled pores) Ref. Protein carriers/transporter molecules/transmembrane 2 protein Ref. facilitated diffusion

Vitamin A Non polar Passes through directly/no channels required Dissolves in phospholipid layer/hydrophobic regions 2 Diffusion

(c) Active transport Osmosis 2 Endo/exo/phago/pino-cytosis or description (not: ref. to diffusion or facilitated diffusion) [12]

7 (a) Light 1

(b) X = cilia/brush border Y = basement membrane 2 (not: cell/plasma membrane)

(c) Cilia move/beat/wave (allow consequential error for 'villi')

Mucus carried along/moved/removed 2 (not: ref. to goblet cells)

(d) Distance allowed 34-36mm 35 1 1000 35  10-3mm/35m or eq. in nm. 1

(e) Collection/many/(large) number of cells/group (not: layer) Similar structure Carrying out a particular function/working together 2 Any 2/3. [9]

8 (a) A Follows interphase

B During which replication/copying/doubling of DNA/chromosomes occurs

C Prophase, metaphase, anaphase, telophase, (correct order anywhere in answer)

D Chromosomes shorten/thicken/condense

E Appear as two chromatids

F Joined at centromere (not: joined together/pair off/just on diagram)

G Centrioles migrate to opposite poles in animal cells (not: centrioles divide)

H Aster formation/spindle fibres span cell/run from pole to pole/spindle formed

I Nuclear envelope/membrane/nucleolus, disappears

J Chromatids line up at equator/metaphase plate

K Centromeres attached to spindle fibres

L Centromeres split

M Chromatids/chromosomes drawn apart/to (opposite) poles

N By shortening/contraction of spindle fibres

O Chromosomes uncoil/lengthen

P Nuclear envelope/membrane formed [10] (allow: annotated diagrams) (reference to chromosomes instead of chromatids penalised once only then consequential error; action in wrong phase penalised)

(b) A Insulin producing gene/mRNA cut/isolated/ identified

B Ref. restriction enzymes/endonucleases

C Production of cDNA/description

D Ref. reverse transcriptase

E Plasmids/vector extracted/obtained from bacterial cells

F Ref. E. coli

G Contain marker gene/antibiotic resistance gene/ DNA or marker gene inserted

H Plasmid cut by same restriction enzyme

I Insulin gene mixed with (cut) plasmid

J Complementary/antiparallel

K Bonding/base pairing

L Ref. Sticky ends

M Ref. to Ligase (seals/anneals)

N Forms recombinant DNA

O Added to bacterial culture

P Bacteria taking up recombinant DNA identified by use of antibiotic

Q These cells cloned/replicated/cultured/allowed to grow/multiply 10

6 ASSESSMENT UNIT BI 2

JUNE 2003

1 (a) decreases 1

(b) ribs move/inspiration 1

(c) capillaries 1

(d) number of deaths/(1000) of population/year 1

(e) pyramid with broad base and narrow tip; 1 producer, primary consumer, secondary consumer 1

(f) pollution with nitrate ions/increase in water temp/fertilizers 1 (not: eutrophication/nutrient levels)

(g) omnivore - meat and plant eater 1 carnivore - meat eater ONLY 1

2 (a) (i) the volume/amount of air breathed in and out in one 1 breath (not: ref. to oxygen/breathing rate)

(ii) correct label of vital capacity 1

(iii) correct calculation of vital capacity = 5.0 - 1.5 = 3.5; 1 dm3 (not: litres) 1

(iv) to absorb/remove carbon dioxide 1 (not: detect/test levels)

(v) (to prevent) volume changes/expansion due to 1 temperature

(b) diffusion 1

(c) asthma - bronchi constrict/inflamed (not: smaller); alveoli unaffected; rate reduced/slower (not: low/slow) emphysema - bronchi unaffected; aveoli coalesce/accept drawing; rate reduced/lower 6

3 (a) biconcave disc (not: doughnut/disc shaped); increasing in surface area/diffusion rate/can fold to fit through capillaries contains haemoglobin; aids oxygen transport no nucleus/organelles - more (space) for haemoglobin (not: more oxygen) (Any 4) 4 (Function must relate to adaptation)

(b) (i) maintains carrying capacity OR appropriate figures/ 1 no change

(ii) blood can carry (nearly) as much oxygen despite 1 drop in available oxygen.

(iii) exercise/respiration rate 1 (not: ref. to CO2)

(iv) enables more oxygen to be unloaded; 1 for a (small) drop in pO2 or converse 1

(c) (i) curve drawn to left of original (max. 100, through 1 origin, labelled) (ii) because Llamas live at higher altitude; with less available oxygen/oxygen deficient atmosphere (Any 1) 1

(d) In red blood cells; CO2 combines with H2O to give hydrogen carbonate ion/ carbonic acid; which combines with Na in plasma to give sodium hydrogen carbonate; chloride shift allows movement of C1  into red blood cell; 2 therefore maintaining electrochemical neutrality (2 max) (not: balancing charge or pH) [13] 4 (a) (i) root hair 1

(ii) active transport/uptake 1 (not: facilitated diffusion)

(iii) symplast route 1

(iv) stops apoplast pathway/ water containing ions freely diffusing through cell walls; enables active transport/facilitated diffusion through cell membrane; 2 (allow: selective absorption, not: selectively permeable)

(b) (i)&(ii) curled leaf; sunken stomata; hairy stomata; thick cuticle; fewer stomata; more hairs on leaf (Any 2) 2 (c) K ions pumped in (requiring ATP)/starch converted to malate; decrease water potential of cells/increase solute potential; water drawn in by osmosis/follows concentration gradient; guard cells become turgid; uneven thickening of Guard cells; push cells apart 3 (3 max) [10] 5 (a) X - ammonia/ammonium 1

+ Y - nitrate/NO3 1 (b) nitrogen fixed/converted (into ammonium); 1 by (symbiotic)/free living bacteria in soil/root nodules 1 (c) de-nitrification/leaching/crop removal/harvest/deforestation 1 (not: burning/monocrop) (d) build-up of dead organisms/excretory products and faeces/ 1 lack of decomposition qualified 1 leads to a reduction in ammonium/soil nitrate/soil fertility (not: nitrogen/nutrients/ref. to carbon cycle) (e) increased drainage/increased aeration/air in soil/nitrifying bacteria use aerobic respiration/more nitrites/reduction in 1 anaerobes (not: refs. to mixing nutrients) [8] 6 (a) The sequence of alteration of communities in time 1 (EQ)/example/development of climax community (b) Less distance for seeds to travel to Krakatoa; Greater diversity on neighbouring tropical islands; ref. warmer climate. (Any 2) 2 (c) Death of plants; provide (humus in) developing soil; breakdown of plant materials leads to nitrogen compounds/ nutrients; humus retains water 2 (Any 2) (d) increase in number of niches/shelter/habitat; 1 increase in available food/variety of food 1 [7]

9 Marks Question Answer/Explanatory Notes Available 7 Heart Question

Cardiac cycle

A Atria contract forcing blood into ventricles

B through atrio-ventricular valves or correctly named

C Ventricles contract & blood forced out of heart into (aorta &

Pulmonary) artery/arteries

D Through semilunar valves/pulmonary and aortic valves;

E ref. Closing of A-V or semilunar valves correctly related to

pressure; (i.e. comparative pressure)

F Heart/Cardiac muscle is myogenic/ external stimulus not

needed to initiate contraction (allow: heart)

G SA node control contraction rate (or rhythm) of muscle cells;

(NOT initiate)/acts as pacemaker

H Wave of contraction/excitation spreads over atria and atria

contract simultaneously/ together

I AV node transmits impulses to ventricles;

J ref. only route for impulse/delay/ Purkinje fibres/bundle of

K Wave of contraction spreads over ventricles & ventricles

contract simultaneously:

(7 max) 7

X2 circulation

L ref. separation of blood supply to pulmonary/lungs and

systemic/body pathways; (actual terms not needed) or

description/diagram

M Sustains high blood pressure in systemic/RA for pulmonary

N Circulation is faster in systemic/RA for pulmonary

O oxygenated/deoxygenated blood kept separate

P improved oxygen distribution/efficiency

Q sustains higher metabolic rate for organism

(3 max) 3 [10]

11 Marks Question Answer/Explanatory Notes Available 7 Pest Control Question Comparative i.e. ref. to both needed, statements together.

Z Comparative description of two methods/integrated control

A Chemical is cheap and biological expensive

B Chemical kills all insect life, biological is specific/allows pollinators to return

C Organisms can develop resistance to chemical but not to biological

(Any 3) 3

Chemical

D fast in action

E localised effect

F affects food chains/can't eat crop

G pest can reappear

Y environmental damage

Biological

H long term effect

I can spread/escape if not controlled/more suitable for closed environment, e.g. greenhouses

J no residues that affect food chains/less environmental damage

K detailed knowledge of life cycle required

L pest level reduced to economically accepted level/RA

M risk of control becoming "super pest"

Example N Encarsia/control of white fly/ladybirds/cane toads

O Pyrethroids (Any 7) [10]

12 AS/ADVANCED MODULE BI 4

June 2003

1 Causative organism

Disease Bacterium Protoctistan Virus

Cholera  1

Malaria  1

Influenza  1

Salmonellosis  1

Smallpox  1

One mark per correct tick [5]

2 (a) (i) Adenosine triphosphate/ATP 1

(ii) A Phosphate (groups) 1 B Adenine/nitrogenous/(organic) base 1 C Ribose/5C/pentose sugar 1

(b) active transport or example e.g. Na/K pump (not: uptake of glucose unqualified); muscle contraction (not: movement/activity); protein synthesis/synthesis of materials within cells; nerve transmission; cell division (not: growth) 2 (Any 2) (c) oxidative phosphorylation (is the breakdown of glucose/eq) using oxygen/aerobically to release ATP (in 1 respiration)/add phosphate to ADP

photophosphorylation is the synthesis of ATP using light/in the 1 light stage (of photosynthesis). [8]

3 Before

1 Mention of (natural) barrier e.g. prevents entry of pathogens/ sebum prevents skin 'cracking' 2 Natural skin/flora/eq preventing growth of many pathogens 3 Mention of skin pH preventing growth of pathogens (Any 2) 2

1 Phagocytosis/bacteria engulfed (not eaten) by phagocytes/ white blood cells/neutrophils; 2 Inflammation/swelling/increase blood supply bringing WBCs/eq and nutrients; 3 Mast cells production of histamine 4 Blood clotting/scab formation to seal wound 5 Local raised temperature reduces bacterial growth (Any 3) (not: ref. to production of antibodies/blood flow flushes 3 out wound) [5]

4 (a) (i) Rennin/prorennin/ Pepsin/pepsinogen 1

(ii) trypsin/trypsinogen (not: endo/exopeptidase) 1

(iii) Bile/pancreatic juice/intestinal/eq juice passes into duodenum/gut; which contains alkaline (salts)/bicarbonate. 1 1

(b) C is involved in digestion; 1 D is involved in absorption (not: absorption of water). 1

(c) (i) 1000 1

(ii) antibiotic gene may transfer to pathogenic/disease 1 causing /harmful bacteria;

5 (a) 36 colonies from 0.1cm3 of 103 dilution; 360 from 1.0cm3 of 103 dilution; 360x103/3.6x105 bacteria in original culture 3

(b) E; E shows the lowest number of colonies of any of the samples at all dilutions/E is the only concentration showing no bacterial growth at 103 dilution/quoted examples/lowest count at highest dilution. 2

(c) 102; 103; Both of these give a range of countable plates/101 gives too many uncountable plates and 104 gives too few countable plates. 3

6 (a) A clear Y shaped molecule 1

(b) (i) A substance/polysaccharide/recognition site/protein/ foreign/non-self molecule which causes the production 1 of/reacts with antibodies/immune system (not: chemical/chemical marker/molecule)

(ii) it will divide/clone continuously i.e. continue to grow 1 (not: quickly/is a clone)

(iii) hybrid/hybridoma 1

(c) pregnancy testing kits; anticancer drugs/cancer treatment (magic bullets in context)/drug targetting; treatment of infections e.g. rabies/tetanus (allow: disease qualified); disease diagnosis; transplant surgery/blocking T lymphocyte activity separation of chemicals from a mixture. (Any 2) 2

7 (a) (i) A light harvesting unit/complex/centre/antenna complex/accessory pigments (not: antenna/light 1 harvesting/ primary pigment)

B reaction centre/trap/chlorophyll a 1

(ii) chlorophyll (a); chlorophyll (b); carotene; xanthophyll. (Any 2) 2

(iii) thylakoid/granal membranes/intergranal membrane; 1 inside chloroplasts 1

(b) (i) oxygen is a (by-)product of photosynthesis; the rate of oxygen production; will be proportional to the rate of photosynthesis/more photosynthesis more oxygen produced. (Any 2) (not: ref. to amounts) 2

(ii) carbon dioxide levels will fall in the tube-replace after each experiment/add CO2 source; temperature will vary-needs a thermostatic water bath/constant temperature/screen; Filter not accurate for wavelength, need to check. (Any 2) (allow: inaccuracy unqualified if clear from 2 correction) (not: ref. to counting bubbles/pH)

(iii) one large peak in the blue region; 1 one smaller peak in the red region. 1 no size difference - one mark only

(iv) action spectrum 1

8 (a) Athletes have a higher rate of oxygen consumption (at all levels)/converse/athletes have a maximum oxygen consumption which is much higher (25% higher) than non-athletes; 1

There is only an increase of 1 from 1200 to 1400 J min 1 kg 1 / max oxygen consumption is reached at 1400 J min 1 kg 1 /max 1 58, 45. alternatively: Non athletes have a lower overall increase in oxygen

consumption over the range of energy expenditures (or figs)/converse;

Max oxygen consumption is reached at 1200 J min 1 kg 1 ; (i.e. comparison needed)

in athletes higher lung capacity; better circulatory system/heart capacity; greater number of mitochondria; in non-athletes accept converse 1 (Any 1) (not: more (developed) muscles) (b) As exercise increases non-athletes produce more lactate than athletes. Athletes have no lactate until 1200 J min 1 kg 1 max figure of 305 mg min 1 kg 1 non-athletes have lactate appearing at 1000 mg min 1 kg 1 (much higher) figure of 590 mg min 1 kg 1 Any 2 2 in athletes more oxygen available so there is less anaerobic respiration/converse 1

(c) (i) It is deaminated (in the liver); the amino group is converted to urea; and excreted; the residue is converted to acetyl CoA/ pyruvate/Krebs cycle intermediates; and oxidised in the respiratory pathway. (Any 3) 3 (ii) liver 1

(d) reduced NAD/NADH2 oxidised NAD/NAD 1

Carbon dioxide/CO2 Ethanol/alcohol 1 [12]

17 Marks Question Answer/Explanatory Notes Available 9 (a) ATP Synthesis Mark Scheme Similarities

a Both need high energy electrons

b Both need stalked particles/ATP synthetase

c Both need proton pumps

d Both involve a series of carriers/pumps in electron transport

e Both need protons which are pumped into a cavity

f Both are involved in creating an electrochemical/

chemiosmotic/H-ion/H+/proton gradient

g Both involve redox reactions

18 Marks Question Answer/Explanatory Notes Available Differences

h Cristae/(folded) inner membrane carries stalked particles in

mitochondria Or Intermembrane cavity in mitochondria/

diagram

i Thylakoid membrane in chloroplasts carries stalked

particles Or Thylakoid cavity in chloroplasts/diagram

j 3 (types of) proton pumps in mitochondria

k 1 (type of) proton pump in chloroplasts

l Water formed during ATP synthesis in mitochondria/

Protons derived from glucose breakdown

m Water broken down (in non-cyclic photophosphorylation) in

chloroplasts/protons derived from water/photolysis produces

H ions

n High energy electrons are derived from chlorophyll in

chloroplasts

o High energy electrons are derived from glucose/reduced [10] NAD/FAD in mitochondria

9 maximum if no comparison

19 Marks Question Answer/Explanatory Notes Available (b) Vaccination essay Mark Scheme a Involves using non-pathogenic/non disease causing forms or products of the microorganism b To stimulate an immune response c Which confers protection against subsequent infection/build up resistance d Any example from weakened/attenuated virus/bacteria killed virus/bacteria neutralised toxin/separated antigen e One disease example e.g. rubella/German measles/tetanus/ smallpox/flu/MMR/diphtheria/polio/any valid vaccination f B lymphocytes/plasma cells are stimulated to produce Ab/Ag stimulates 1 response g And memory cells (which remain inactive) h If the pathogen/Ag enters the body memory cells recognise the Ag i (Clones of) cells produce the Ab immediately j These destroy the pathogen/Ag before the person is ill/causes a 2º (immune) response k Some stable pathogens/diseases/smallpox have been eliminated worldwide l Influenza virus/malaria organism mutates and cannot be eliminated by vaccination m Travel increases infection spread/droplet infection is difficult to control/viruses have no effective curative treatment/animal reservoirs/unvaccinated boys/people act as a source of infection n Reports of possible side effects reduces take-up of vaccination of children/leads to an increased number of cases o Public information/education and identification of contra indication in individual cases minimises risks

20 ASSESSMENT UNIT BI5

JUNE 2003

Question Answer/Explanatory Notes Marks Available

1 (a) (i) anti-diuretic (hormone) / ADH 1

(ii) human chorionic gonadotrophin / HCG 1

(iii) oxytocin 1

(b) actin and myosin 1

(c) amplifies the vibration of the ear drum /sound (waves) / transmits vibration from the ear drum to the inner ear (Any 1) 1

(d) maintains genetic uniformity / multiplying hybrid plants / multiplying plants that won't breed true / breeding plants that are hard to reproduce naturally / quicker as no need for pollination and seed production / larger numbers produced from a single plant / cost effective / easy to transport and store / recovery of endangered plants / no plant disease as healthy stock selected and sterile conditions used / no seasonal restrictions on germination. Cheaper or quicker must be qualified. (Any 1) 1

(e) bans on trade in ivory / bans on whaling / restrictions on trade in furs / restriction on sale of exotic birds / conservation of whole environment (e.g. 'Operation Tiger') / breeding programmes between zoos / botanic gardens / establishment of seed banks / any suitable example that clearly shows international co-operation. (Any 1) (not: name of organisation unqualified) 1 (allow: national parks qualified/fishing - implies international)

(f) geographical isolation / named geographical feature / habitat change / differences in behavioural mechanisms / differences in breeding mechanisms / changes in morphology. 1 (not: volcano/earthquake) [8]

21 Question Answer/Explanatory Notes Marks Available 2 (a) form / variant / alternative form of a gene 1 (b) (i) Parental genotypes Rr  Rr; 1 Possible gametes R and r (2); 1 rr. 1 (ii) Parental genotypes SG  GG; 1 Possible gametes S and G G(G); 1 F1 genotypes SG (SG) GG (GG); 1 F1 phenotypes silvery grey grey. 1 (allow: superscripts, not: lower case G / other letters unless key) (iii) SSrr 1 (c) (i) XeO / XeY 1 (superscript 'e' must attach to X); O or Y needed) (ii) XeXe 1 (iii) XEXE; 1 XEXe. 1 (d) different base (sequence) in gene / allele (not: DNA) different triplet code; sequence of codons different (sequence) of amino acids; different protein / enzyme / polypeptide (Any 3) 3 [16] 3 (a) hydrolysis digestion / breakdown by enzymes of reserves / endosperm (not: breakdown unqualified) starch converted to sugars / glucose / named respiration / loss of carbon dioxide; sugars used by / sent to growing regions / embryo; (not: embryo uses energy store from endosperm); increase as first leaves produced photosynthesis. (Any 4) 4 (b) (i) amylase / enzyme / carbohydrase from the seed; converts starch to maltose; hydrolysis / digestion; (Any 3) (not: breakdown) 3 (ii) less amylase / enzyme produced in absence of embryo 1 (c) cotyledons 1

22 (allow: seed leaf,not: dicotyledon) [9]

23 Question Answer/Explanatory Notes Marks Available

4 (a) mitosis 1

(b) (i) Fusarium 1

(ii) banana plants genetically identical / clones; same susceptibility / lack of resistance to Panama disease; no / little mutation; close planting. (Any 3) 3

(c) natural selection; fungicide is selective agent / selective pressure; variation between individuals; chance / random mutation; some individuals have selective advantage / better chance of surviving; survival of resistants / death of non-resistants (not: survival of the fittest); mutation / ability to survive pesticide passed on to offspring; increased allele frequency. (Any 5) 5

(d) (i) normally achieved with breeding programmes; (using) reservoir of genes / alleles; bananas are sterile / seedless / reproduce asexually; no easy way to incorporate new genes / alleles. (Any 2) 2

(ii) genetic engineering / induced mutation / gene 1 splicing / inserting a (resistant) gene. [13]

5 (a) A germinal epithelium / germ cells;

B mitosis to produce spermatogonia; (not: multiplication)

C growth to produce primary spermatocyte;

D meiosis I to produce secondary spermatocyte;

E meiosis II to produce spermatid;

F maturation / spermiogenesis / differentiation to produce spermatozoa;

G role of Sertoli cells - nutritive or protection;

H digestion / softening of corona radiata / zona pellucida;

I acrosome reaction or description;

J penetration of head into secondary oocyte;

K fertilisation membrane to prevent polyspermy;

L stimulates meiosis II;

M fusion of nuclei to form zygote; (Any 9) 9

N Accurate spelling not detracting from understanding grammar, logical account. 1 (i.e. ease of reading) [10]

5 (b) A inside about -60 to -70mV (compared with outside);

B maintained by sodium (-potassium) pump;

C [K+] higher inside / [Na+] higher outside;

D membrane more permeable to K+ which diffuse / leak / move out;

E all or nothing / threshold value;

F action potential occurs when membrane becomes more permeable to Na+ and they flood in / sodium gates;

G depolarisation;

H inside about +40mV (compared with outside);

I K+ then diffuse / move out and repolarise the membrane; J refractory period explained;

K local currents stimulate next part of neurilemma / membrane / axon;

L myelin sheath increases distance over which local currents can act to bring about depolarisation or speeds up transmission by jumping from node to node;

M depolarisation only at nodes of Ranvier;

(Any 9) 9

N Accurate spelling not detracting from understanding grammar, logical account. 1 (i.e. ease of reading) [10]

6 (a) somewhere to live / housing; logging / wood products; development / industry / roads; fuel. mining / drilling (Any 2) (allow: construction once only) 2

(b) provides fertile, material / soil / acts as a fertiliser; good crop, growth / yield; no need to buy fertilisers; remove pests. (Any 2) 2

(c) less fertile soil; less material to burn; less (plant) has grown during fallow period; less (fertile) ash; less time for soil to regain fertility; crops remove nutrients. (Any 2) 2

(d) food crop and rubber crop / two crops; cash crop / income; land can be felled in (about) same time; sustainability. (Any 2) 2

(e) (i) assume candidate is referring to plantation, unless otherwise stated

far fewer species / very little diversity; only 2 plant types / trees and herbaceous plants; no (2 of) climbers, epiphytes, shrubs; ref. figures (comparative) / 360 vs 10 species. (Any 2) 2

(ii) assume candidate is referring to agroforest, unless otherwise stated

all types represented in both fewer tree species; fewer epiphyte / shrub species; more herbaceous species; (approx.) same number of species of climbers; fewer species / less diversity; ref. figures (comparative) / 360 vs 260 species (Any 3) 3

(f) depends upon agriculture; plantations seem to be destructive; reduced / do not permit species diversity / monoculture; agroforestry allows forest to regenerate; maintains a (fairly) high level of diversity; (Any 2) 2

7 (a) (i) water; or salt / Na+/Cl-; or urea; osmosis; diffusion; diffusion. 2

(ii) too large to pass through (pores in) membrane 1 (not: tubes)

(iii) concentration gradient maintained; continual replacement / flow of dialysis fluid; continual circulation of blood; waste products / impurities / excess water removed from blood more effectively; (Any 3) 3

(b) (i) large surface area / thin membrane so short diffusion distance; dialysis fluid needs to be in close contact with blood (capillaries); 2 so that substances can pass from blood into dialysis fluid. (ii) dialysis fluid not continually replaced; concentration gradient not maintained; (once some movement of substances from blood has taken place) equilibrium is reached; less efficient removal of substances from blood. (Any 2) 2

(iii) increase solute / glucose / salt concentration / 1 more negative water potential.

(iv) less efficient; further distance for substances to diffuse / slower 2 diffusion.

(c) (i) they are genetically identical / clones 1 (not: similar)

(ii) (brother and sister because . . .) have common genetic ancestry / husband and wife are not related genetically / brother and sister have 1 genes / DNA from same parents.

(iii) (cells of) new kidney recognised as foreign / not identical to those of recipient; (cells of new kidney have) antigens T killer (lymphocytes) cause lysis of target cells / destroy kidney; helper T cells are activated; B lymphocytes / plasma cells; produce antibodies. (Any 4) 4

GCE Biology/MS/(June 2003)/AOB 01 August 2003

29 Welsh Joint Education Committee 245 Western Avenue Cardiff. CF5 2YX Tel. No. 029 2026 5000 Fax. 029 2057 5994 E-mail: [email protected] website: www.wjec.co.uk/exams.html