MS3 £3.00 WELSH JOINT EDUCATION COMMITTEE CYD-BWYLLGOR ADDYSG CYMRU General Certificate of Education Tystysgrif Addysg Gyffredinol Advanced Subsidiary/Advanced Uwch Gyfrannol/Uwch MARKING SCHEMES SUMMER 2005 BIOLOGY INTRODUCTION The marking schemes which follow were those used by the WJEC for the Summer 2005 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. BIOLOGY ASSESSMENT UNIT BI1 Question 1. Answer/Explanatory Notes Marks Available Ribosome mark scheme (i) 1 mark for decent diagram showing 2 clear subunits 1 mark for any label large subunit small subunit groove which mRNA fits into tRNA binding site 2 (ii) RNA/Ribosomal RNA Protein (not: amino acids/nucleic acid) 1 1 (iii) (rough) endoplasmic reticulum 1 (iv) protein/polypeptide synthesis 1 (v) nucleolus/nucleolus and cytoplasm (not: nucleus/cytoplasm) 1 Total 7 marks 1 Question 2. Answer/Explanatory Notes Marks Available Lipid mark scheme (i) Triglyceride Phospholipid Structural difference 1 3 fatty acids 2 fatty acids Structural difference 2 (Glycerol head only) Glycerol + phosphate head (not: phosphorus) Where compound is found in organisms Under skin/subcutaneous/ blubber Around body organs Fur/feathers Nerve cells Smooth ER/golgi/vesicles seeds chloroplasts Cell/plasma membranes (not: hydrophilic/hydrophobic/polar/non-polar/fat unqualified) One mark per row = 3 (ii) Stearic/Saturated has more H or converse. Stearic has no double bonds (in hydrocarbon chain/double C-C bonds) or converse. Stearic acid is a straight hydrocarbon chain/not kinked/bent or converse. 1 (iii) Stearic acid/saturated (fatty acid). 1 Total 5 marks 2 Question 3. Answer/Explanatory Notes Marks Available Genetic fingerprinting Q mark scheme (a) (b) (c) (i) Genetic/DNA fingerprinting/DNA profiling. 1 (ii) blood/saliva/skin/hair/semen any 2 (not: fingerprints/body fluids/urine/sweat) 1 (iii) suspect 2 1 (iv) it is the only one which has the banding pattern which exactly matches the one at the scene of the crime. (allow: samples are the same) 1 (i) Used to cut the DNA (into sections.) (not: genes) 1 (ii) Separation of DNA fragments. 1 Paternity suits/eq 1 Total 7 marks 3 Question 4. Answer/Explanatory Notes Marks Available Cell division mark scheme (a) Correct ID of LS root zone of cell division. (not: cross in vascular bundle/across all diagram) Correct ID of TS anther zone of cell division. (allow: to top of root cap but not in root cap) 2 Root labelled MITOSIS (correct spelling only). Anther labelled MEIOSIS (correct spelling only). (b) 2 Correct drawings as below. (number must be consistent) 3 On equator As bivalent, labelled. deleted) (c) (Allow: at right angles if poles Correct label for centriole, drawn. Centromere Bivalent One mark each 3 Total 10 marks 4 Question 5. Answer/Explanatory Notes Marks Available Beetroot Q mark scheme (i) {very little increase/0-7 units} up to {40ºC/first 4 temperatures; rapid rise at 50ºC/rise from 7 to 80 at 50ºC; small rise from 80 to 100 units from 50 to 70ºC. higher temperature, darker solution/higher reading (ii) 2 Membrane (proteins) are stable between 10 and 40ºC/at low temperatures; (Appearance of the red pigment means that) the (tonoplast and) cell membrane has been damaged between 40 and 50ºC/ at high temperatures; (meaning) pigment has leaked out of cells/sap vacuole/ change in membrane permeability/damaged membrane; proteins change shape/denature and come out of bilayer; phospholipids bilayer has become too fluid/cannot retain proteins. (iii) 3 Dissolves phospholipids/destroys cell membrane structure; (So) pigment leaks out. (not: ref. to higher or lower readings) 1 Total 6 marks 5 Question 6. Answer/Explanatory Notes Marks Available DNA Q mark scheme (a) (i) A DNA B RNA 1 (ii) Ribose (not: pentose) 1 (iii) Nucleus/nucleolus/mitochondria/chloroplasts 1 (iv) Hydrogen 1 (v) RNA/B is a short molecule, DNA/A is a long molecule; Pentose in DNA contains one less oxygen. RNA/B is much shorter than DNA/A; A is helix, B is straight molecule/not helix. (b) Uracil replaces thymine in RNA/B. (not: DNA has deoxyribose and RNA has ribose) 1 (i) A bond/base pairs with T and C with G. 1 (ii) Any suitable figure from table indicating A approx = T/C approx = G (data and species) 1 Purines. 1 (iii) Total 8 marks 6 Question 7. Answer/Explanatory Notes Marks Available Immobilised enzyme mark scheme (a) (i) (ii) 2(mm) (because) it gives the highest percentage of product (not: converse) 1 smaller beads give a larger total area (exposed to the milk/substrate); (not: smaller beads have large surface area) or smaller beads will pack more closely (so there is more enzyme:subtrate); the milk will have longer contact/flow more slowly around small, close packed beads; or gives more time for the enzyme and subtrate to come into contact. (iii) (iv) 2 Percentage product would increase/get more product; More time for enzyme-substrate complexes to occur/ for reaction. 1 temperature/milk type/source (not: pH) 1 (b) glucose and galactose 1 (c) Can tolerate/more stable condition/temps/pH qualified; in a wider range of Product not contaminated with enzyme/pure product/easily reused qualified; Several enzymes (requiring different conditions) may be used together; Enzymes easily added/removed = more control. (allow: ref. to continuous production qualified, not: ref. to cost) 2 Total 8 marks 7 Question 8. Answer/Explanatory Notes Marks Available Cystic fibrosis mark scheme (a) protein/capsid nucleic acid/DNA/RNA 2 (b) gene therapy 1 (c) Use of liposomes; Transfer of non CF gene (into plasmid); Coated in (spheres of) phospholipids/lipid (bilayer); Breathed into lung via aerosol/inhaler. (d) 3 Gets into nucleus; Insertion into genome/chromosome; Transcription/eq; (in context) Translation/eq. (in context) (e) 2 Activation of oncogenes; Unexpected disease caused/leukaemia; Allergic response. (not: side effects unqualified) 1 Total 9 marks 8 Question 9. (a) Answer/Explanatory Notes Enzyme essay mark scheme a Biological catalysts/speed up a chemical reaction (not: catalyst unqualified) b By lowering activation energy/labelled diagram c Globular protein/labelled diagram/tertiary structure or eq. d With active site/specific shape e Into which substrate(s) fits and is converted to product(s) f Correct reference to lock and key/induced fit or suitably labelled diagrams PH g Enzymes have a narrow optimum pH range h Large deviations from this optimum may result in denaturation/shape change i Small pH changes cause reversible changes (which may inactivate the enzyme) Temp j Rate of reaction increases with increasing temperature k Because of increased number of collisions of active site and substrate l Enzymes are denatured by higher temperatures above 45C Optimum for most (mammalian) enzymes approx 37C m At low temperatures enzymes are inactive/eq Inhibitors n Description of the 2 types of inhibitors competitive p Non-competitive/labelled diagrams q Correct egs cyanide for non-comp, malonic acid for comp Must mention pH, temp and inhibitors to get 10 marks. If one or more missing Max. 9 marks. 9 Marks Available Question 9. (b) Answer/Explanatory Notes Marks Available DNA replication/transcription essay mark scheme DNA replication a DNA replication has to occur prior to cell division/during interphase b (Parental) DNA helix unwinds (has to be clear that this is all the DNA, not just a section) c Complementary strands separate due to breaking of (weak) H-bonds (could be given in transcription) d Base pairing (AT, CG) occurs between the bases of the both template strands and free nucleotides e DNA polymerase separates the 2 DNA strands/joining of DNA nucleotides f Produces pair of identical helices/strands g Semi-conservative replication/one new chain, one original h Mention of Meselson and Stahl expt/correct details of experiment Transcription i Occurs during protein synthesis j Base sequence of a (cistron) gene is converted to mRNA (not: DNA is converted) k Gene (only)/short section (eq) unwinds l RNA polymerase nucleotides c DNA unzips/c from replication if not already given m One strand acts as a template n Free RNA nucleotides align themselves opposite the complementary base/mention of uracil instead of thymine, uracil pairs with adenine p Complete mRNA peels off and exits (nucleus) through a nuclear pore/DNA zips back up attaches to the DNA/joins RNA Total 10 marks 10 ASSESSMENT UNIT BI 2 Question 1. Answers/Explanatory Notes Marks Available (a) diaphragm; 1 (b) diffusion; 1 (c) emphysema; 1 (d) asthma; 1 (e) tidal; 1 [5] 2. (a) 1:1; 2 0.75:1/3:4/1:1.3; (b) ratio of surface area to volume large; diffusion sufficient to meet requirements/shorter diffusion path; oxygen for respiration/removal of carbon dioxide; as cells/organisms become larger, surface area to volume ratio smaller; diffusion can't supply oxygen/nutrients/remove carbon dioxide; 3 max (comparison needed) [5] 11 Question 3. (a) Answers/Explanatory Notes (i) (ii) 21060 x 100; 1,700,000 1.24(%); Marks Available 2 reflected; passes straight through the leaf/transmission through leaf (not: transmission unqualified) misses photosynthetic parts/leaves; wrong wavelength; 3 max absorbed by water; not present because of season; (b) (c) (d) (e) (i) 4; 1 (ii) energy at last/4th trophic level only 21 units; insufficient to pass on/support another level; 2 death/decay; excretion/urine; faeces/egestion; 2 max bacteria; fungi/saprophytes; 2 producer floats out/removed from, ecosystem/fishing/ migration qualified; 1 [13] 12 Question 4. (a) Answers/Explanatory Notes Marks Available nutrient content /three named nutrients decreases; named example plus figures from table; lack of leaves/trees to decompose; less nutrients released into soil; increased leaching; no trees to hold soil/reduce run off of water; 3 max (Any figures quoted require units) (b) increased daytime soil temperature (after clearing); rate of respiration/enzyme activity of decomposers increases; 2 [5] 13 Question 5. Answers/Explanatory Notes (a) Marks Available arteries have thicker walls; arteries have more muscle in walls; (not: veins have no muscle) more elastic in walls; veins have valves; 3 max arteries have smaller lumen; (accept reverse points) (b) (i) artery; 1 (ii) 5 0.5kPa; 1 (iii) contraction of ventricle/ventricular systole; 1 (iv) ventricle relaxes/diastole; 1 (v) further away from heart; friction/more resistance; increased cross sectional area of vessels; (c) (i) 2 max separate systemic/body; and pulmonary/lungs systems; blood passes through heart twice during one complete circuit (ii) 2 max blood contained in vessels; 1 [12[ 14 Question 6. (a) Answers/Explanatory Notes (i) Marks Available stomata open earlier/close later/open longer, on a sunny day; lighter earlier/later/longer; stomata open wider/aperture increases on a sunny day; more/higher light intensity; rate of opening/closing greater on a sunny day; higher light intensity/more light; (ii) (b) 4 max excessive transpiration/too much water lost/plant tries to conserve water/prevents wilting; 1 (i) xerophytes; 1 (ii) feature explanation feature explanation (iii) long root; large surface area for absorption/reaches down to water deposits; (not: ref. to anchorage) few/small leaves/foliage close to ground; less transpiration/reduce water loss; thick cuticle; sunken stomata; rolled leaves; hairs on leaves; (not: hairs unqualified) leaves reduced to spines; water storage organs 2 2 2 max [12] 15 Question 7. (a) Answers/Explanatory Notes Marks Available (i) E; 1 (ii) C-D; 1 (b) decreases; blood enters/forced into aorta; (forced) out of ventricle; (c) (i) point where the two lines diverge; (ii) pressure falls in ventricle; 2 max 1 below that in aorta; blood tries to flow back; forces valves to close; (d) 2 max sino atrial node; (not: SAN) 1 [8] 16 Question 8. (a) Answers/Explanatory Notes (i) A loading of sucrose; B into sieve tube cells/at source C by active transport/ATP/energy dependent; D sucrose lowers water potential (of sieve tube cell); E water moves down water potential gradient; F by osmosis; G (high) hydrostatic pressure generated; H sucrose unloaded/removed at sinks/roots; I used for respiration/storage/converted to starch; J water passes out of sieve tube cell; K low hydrostatic pressure at sink/root; L pressure gradient from source to sink/along sieve tube; M water plus dissolved substances/sucrose/assimilates flow down gradient; (ii) N ref to bidirectional flow; O ref to no apparent role for sieve plates/companion cells; P ref to different rates of movement; Q cytoplasmic streaming observed; Marks Available 8 max 2 max (Incorrect use of 'glucose' penalised once) [10] 17 Question (b) Answers/Explanatory Notes A birth rate and death rate; B population grows if birth rate higher; (ORA) C immigration and emigration; D population grows if immigration exceeds emigration; (ORA) E increased predation decreases population; F disease will reduce size of a population; G effect of weather/temperature qualified; H availability of food qualified; I availability of living space qualified; J human involvement/intervention; K specific example of human involvement; L ref. density dependent/ factors; Marks Available M ref. to carrying capacity; N labelled diagram/description of a growth curve (3 of 4 phases needed); O ref. to some factors can cause a population to crash; 18 10 ASSESSMENT UNIT BI 4 Question 1. (a) (b) Answers/Explanatory Notes Marks Available (i) chloroplasts 1 (ii) dehydrogenases 1 (iii) lacteal 1 (iv) inflammation 1 (i) endemic present but a low/constant level in population/ area, 1 epidemic spreading to larger number in population/same area (ii) bacteriostatic stops bacteria growing/multiplying/reproducing bactericidal kills bacteria 1 [6] 2. (a) (b) (c) (i) to prevent overheating / remove heat generated by process 1 (ii) to maintain optimum / constant pH 1 (iii) to prevent contamination with unwanted microbes (not: purifying air) 1 contains nitrogen; 1 microbe needs nitrogen to synthesise proteins/nucleic acids 1 Penicilliun produces penicillin during stationary phase 1 Resources become scarce during overcrowding (in stationary phase) / ref. to competition/secondary metabolite 1 [7] 19 Question 3. Answers/Explanatory Notes (a) (b) Marks Available B circled on drawing 1 (i) Temperature (kept at 37ºC) / pH (2) / level of acidity 1 (ii) no microbes / sterile / denature proteases or enzymes in beef 1 in stomach churning / mechanical digestion / separates fibres 1 presents large surface area (for enzyme to act upon) / more ES complexes 1 (c) continuous enzyme production (not: ref. to HCl) (d) (i) (ii) (iii) 1. trypsin(ogen) / chymo~ (not: peptidases) 1 2. pancreas 1 gut wall / organs made of protein / secreting cells 1 active enzyme would digest wall / organ / cells / prevents autolysis (not: cell wall) 1 removal of amino group/excess cannot be stored / ref. to urea 1 so that remainder of molecule may be stored / utilised / converted to carbohydrate. 1 [12] 20 Question 4. (a) Answers/Explanatory Notes (i) (ii) (b) Marks Available A glycolysis 1 C Krebs / citric acid cycle 1 D electron transfer / respiratory chain (not: ETC/ TCA / electron transfer) 1 P carbon dioxide 1 Q ethanol / alcohol 1 R oxygen 1 S water 1 (iii) NAD / nicotinamide adenine dinucleotide / NADH2 1 (i) use energy from the electrons 1 to pump protons into intermembrane space / across membrane 1 (ii) R S (allow: Oxygen to water) 1 (ii) it takes up / removes hydrogen / protons / forms water 1 (iv) protons flow down gradient / diffusion; 1 through (a channel in) ATP synthetase / ATPase / stalked particles; 1 the energy is used to make ATP (from ADP). 1 [15] 21 Question 5. (a) (b) Answers/Explanatory Notes Marks Available (i) oxygen 1 (ii) 27 mm / 2.7 cm (allow: consequential error) 1 (iii) 40.69 mm3 – no units 1 mark only (allow: 40.5 to 40.7) 81.3 to 81.5 2 (i) collect bubbles of gas (over a fixed time period) (use syringe to move bubble) and measure its length / volume; 1 insert coloured filters (between lamp and pondweed) and repeat (not: different colours) 1 steps to avoid stray light / temperature change; max 3 (c) (i) (at low light intensities) increasing light intensity increases rate / volume of gas produced; 1 at higher light intensities / quoting values increasing light intensity does not affect rate. (not: ref. to time/levels off) 1 (ii) 0.9 to 0.4m 1 (iii) the temperature / carbon dioxide level / volume NaHCO3 1 (iv) when a process is affected by more than one factor or description 1 the overall rate is limited by that factor which is closet to its minimum value. (not: factor in least supply) (i.e. within not between factors) 1 [13] 22 Question 6. (a) (b) (c) (d) Answers/Explanatory Notes Marks Available (i) spherical / round 1 (ii) coccus 1 (i) (cell wall) contains peptidoglycan / murein / glycoprotein 1 do not have outer layers with / have little lipoprotein / lipopolysaccharide 1 (ii) cell wall / cross links in the wall 1 (iii) don't have (cell) wall (not: no metabolic pathways) 1 (i) A, D and F (must get all 3) 1 (ii) which are methicillins 1 (iii) E 1 cover skin lesions / sores with (clean, dry) dressings 1 don't share towels / bed linen with family / friends prevent direct physical contact / stay in quarantine 1 wash hands before touching objects others might use 1 tell others to wash hands after touching you / your dressings / objects you might have contaminated; Any 3 (not: stay away from infected person / multiples of same suggestion) [12] 23 Question 7. (a) Answers/Explanatory Notes Marks Available A energy source is (a photon) of light, pigments / chlorophyll absorb light energy / light energy changed to chemical energy 1 B pigments include chlorophyll a and b, carotene and xanthophylls 1 C to absorb different wavelengths / parts of spectrum 1 D reference to antennae complex / photosystems (embedded in (thylakoid) membranes) 1 E energy transferred between pigment molecules and to reaction centre (chlorophyll) 1 F emission of electrons by reaction centre (chlorophyll) / P700 / photosystems 1 G electron acceptors 1 H electron transfer chain (between PSII and PSI) 1 I reference to proton pumps ATPase / chemiosmosis 1 J electrons (emitted from PS II) replaced from water – photolysis / correct description of photolysis 1 K photolysis takes place inside thylakoid space / mopping up of protons in stroma by NADP 1 L therefore contributes to electrochemical gradient 1 M NADP is reduced / NADPH2 end product or final electron acceptor 1 N reference to cyclic phosphorylation 1 O Energy is stored in the form of ATP 1 Maximum 10 marks from available 15. [10] 24 Question 7. (b) Answers/Explanatory Notes Marks Available A humoral response involves production of proteins (globulins) called antibodies 1 B they are specific to the antigen 1 C antibodies are Y shaped / formed from 4 polypeptide chains 1 D the antibody antigen complex inactivates the antigen 1 E an example of how / identifying for phagocytosis / agglutination / lysis / immobilisation / neutralisation 1 F humoral response involves (lymphoid tissue to form) B lymphocytes / B cells 1 G each B cell (or T cell) has receptors for its specific antigen 1 H antigen stimulates proliferation of plasma cells and memory cells 1 I memory cells remain ready to divide if same antigen is encountered again (i.e. increase number rather than output) 1 J cell mediated response involves T lymphocytes / T cells 1 K T cells develop / mature in thymus gland 1 L there are 3 types of T cell/ref. To killer cells, helper cells and memory or suppressor cells 1 M function of killer cells, directly kill pathogen/ bacterium cell infected by virus 1 N function of helper cells, stimulate phagocytosis / make T or B cells competent / assist killer cells 1 O role for suppressor cells - suppress B cells / lymphocyte action after infection / switch off immune system when antigen not present Maximum 10 marks from available 15. [10] All points may be awarded for a suitably annotated diagram, but marking points must be explicit. 25 ASSESSMENT UNIT BI 5 SECTION A Question 1. Answers/Explanatory Notes (a) 2, 5, 4, 7, 6, 1, 3 (b) Protoctista; Marks Available [1] Fungi; [4] Animalia; Plantae; (c) Cell Wall of murein / not cellulose; (not: chitin) No nuclear membrane/nucleus; Circular DNA; DNA not associated with histones; [Max 3] No membrane bound cell organelles /mitochondria/ chloroplasts etc.; Small ribosomes/70S ribosomes (not: large) No meiosis; Plasmids (d) Offspring infertile [1] 26 Question 2. (a) Answers/Explanatory Notes Marks Available (i) Both alleles express themselves. [1] (ii) Form of a gene/ref. to same locus [1] (iii) Parental genotypes: C C LL; Gamete L; C F1 genotypes: all C L F1 phenotypes: all Chevron with pale patch; (F1 genotypes and phenotypes 1 mark) Gametes: C L F2 genotypes: CC CL C L; CL LL F2 phenotypes chevron chevron with pale patch pale patch; (F2 phenotypes and genotypes 1 mark) [1] [1] Ratio 1 : 2 : 1 (b) Accept other symbols if key given. Accept gametes if on Punnett square. [5] (i) Continuous [1] (ii) Tall [1] (iii) Tt x Tt Parental genotype [1] Gametes; TT Tt Tt tt Genotype offspring 3 tall l:1 Dwarf (Both for 1 mark) (c) (d) Ratio; (allow: 75%, 25%) (i) 9:3:3:1 [1] (ii) 1:1:1:1 [1] Named characteristic; Named environmental factor. (not: examples of selection) [1] [1] 27 Question 3. Answers/Explanatory Notes (a) Marks Available A = glomerulus/malpighian corpuscle; B = Bowman's capsule; C = proximal/first convoluted/coiled tubule A. PCT; D = Loop of Henle, A. descending limb; (b) (i) (ii) E = collecting duct; [5] The longer the loop of Henle the lower the water potential of the urine/more concentrated urine/solute potential higher. [1] Sodium (ions) pumped out; of ascending limb; creates a region of low water potential around collecting ducts; water moves out of collecting duct/descending limb; by Osmosis; ref. counter current. (c) [Max 3] (i) Hypothalmus (1); brain (1); osmoreceptors. Any 2. [2] (ii) (posterior) pituitary; [1] (iii) first/proximal convoluted tubule; [1] (iv) (distal convoluted tubule) collecting ducts. [1] 28 Question 4. (a) Answers/Explanatory Notes (i) (ii) Mutation; Marks Available [1] Selective advantage (if Warfarin being used); (not: just ref. to natural selection and survival of the fittest) more resistant rats survived; formed breeding population; Max. 3 passed on beneficial allele to offspring/more resistant alleles in gene pool. (iii) (Sexual) reproduction/interbreeding; [2] migration. (b) If Warfarin not used there is no selective advantage/ description; Disadvantage rats with allele need large amounts of vitamin K; therefore selected against/die out. 2 from 3 (not: more rats survive therefore greater selection pressure) 29 [2] Question 5. Answers/Explanatory Notes (a) A. Fibre, Myofibril. B. Sarcolemma, sarcoplasm, large numbers mitochondria, SR. T tubules, multinucleate, nuclei. 3 from. C. Sarcomere qual. D. Tin Actin/Thick Myosin E. Ref. Z line. Correct position. F. Ref. A band. Myosin G. Ref I band actin only. H. Ref. H zone. I. Ref. M line. Max. 5 J. Sliding. K. evidence for sliding. L. Cross bridges. M. Myosin head binds to actin. N. Details of ratchet mechanism. O Function of ATP. Breaks bond between actin and myosin. Ref. SR. P Role of Calcium. Change of shape of tropomyosin exposing binding site Max. 5 30 Marks Available Question Answers/Explanatory Notes (b) A. Pollen tube growth controlled by tube nucleus. (A Diag) B. Generative nucleus. C. Mitosis. D. 2 male gametes/nuclei. E. Embryo sac A ref. 8 nuclei. F. Micropyle, ref. pollen tube entry. G. Double fertilisation. H. One male gamete fuses with egg cell nucleus. I. To produce a zygote. J. One male gamete fuses with polar nuclei. K. To produce primary endosperm nucleus/triploid cell. L. Develops into endosperm M. Integuments become testa. N. Zygote becomes embryo. O (cotyledons) plumule and radicle. P. Ovule becomes seed. 31 Marks Available Question 6. Answers/Explanatory Notes (a) (b) (c) (i) (ii) (d) (e) Genetically identical; from small groups of cells/ meristems/explants/individual cells; artificial medium/agar [3] No nucleus/mitosis cannot take place/differentiated cells. [1] Genetically identical; grow at same rate; look same; same size; same flavour; preserves favoured alleles or converse. Genetically same (if not above); no resistance because no variation; no variation to survive climate change owtte; reduction in gene pool; high cost or difficulties in production. (not: cost unqualified) (i) Chromosome. (ii) Break down of spindle fibres, during mitosis/nondisjunction/increased DNA replication/chromatids don't separate. (iii) Marks Available [Max 2] [Max 2] [1] Pairing of homologous chromosome cannot take place; no meiosis; no gametes/haploid cells produced [Max 1] [Max 2] Reversion of virus to disease causing form; Virus could be changed into different form; Bacteria/virus could be toxic to humans or insects; Virus/bacterium could transfer to another species; Accept ref. ethical reasons qualified e.g. Why change colour of leaves when there is no nutritional value? Accept ref. increase cost of plants putting financial burden on farmers; Accept other valid points e.g. unknown future side effects. (not: playing God/genes escaping) 32 [Max. 3] Question 7. Answers/Explanatory Notes (a) (b) Marks Available E.g. of intracellular, described e.g. named respiratory (allow: digestive if stated as lysosomal) [1] E.g. of extracellular, described e.g. named digestive [1] DNA, code for primary structure/amino acid sequence. Ribosomes, translation/joining a. acids together/site of protein synthesis. Golgi body, assembly and packaging/modify proteins. Lysosomes, contain (proteolytic) enzymes; Exocytosis, membrane. (c) (i) release/export of enzymes across cell [5] Competitive (similar shape to substrate), binds to active site; [2] Non-competitive binds to enzyme but not at active site; (not: ref. to non-reversible/reversible) (ii) (iii) Competitive, (reversible) inhibitor; binds to active sites in enzyme; prevents ethylene glycol entering; slows production of oxalic acid/less acid produced; can leave active site. [Max. 4] Enzymes work at optimum pH/specific pH; Changes secondary/tertiary structure of enzyme; Affects H bonds/ionic bonds/disulphide bridges; Active sites destroyed/distorted; Shape of enzyme changes/configuration; Slight pH change causes inactivation/extreme causes denaturation. 33 [Max. 4] Question (d) Answers/Explanatory Notes Marks Available Enzymes always proteins/hormones proteins or steroids; Hormones produced by endocrine glands/ductless glands; Hormones transported in blood to site of action; Enzymes often work inside cell in which produced, hormones target cells; Enzymes more lower activation energy; Ref. speed of action; Enzymes more susceptible to pH/temp changes (not: ref. active site/hormones homeostatic and enzymes catalysts) (comparative statements not necessary) GCE Biology Markscheme (June 2005)/HJ 34 [Max. 2] Welsh Joint Education Committee 245 Western Avenue Cardiff. CF5 2YX Tel. No. 029 2026 5000 Fax. 029 2057 5994 E-mail: exams@wjec.co.uk website: www.wjec.co.uk/exams.html