(a) Describe how a nerve impulse crosses a cholinergic synapse. [9](a) 1. action potential / depolarisation, reaches presynaptic membrane ; 2. calcium (ion) channels open / presynaptic membrane becomes more permeable to Ca2+ ; 3. Ca2+ flood into presynaptic neurone ; R membrane 4. this causes vesicles of (neuro)transmitter to move towards presynaptic membrane ; 5. ref. acetylcholine / ACh ; 6. vesicle fuses with presynaptic membrane / exocytosis ; 7. ACh released into synaptic cleft ; 8. ACh diffuses across (cleft) ; 9. ACh binds to receptor (proteins) / AW ; 10. on postsynaptic membrane ; R neurone 11. proteins change shape / channels open ; 12. sodium ions rush into postsynaptic neurone ; R membrane 13. postsynaptic membrane depolarised ; 14. action potential / nerve impulse ; 15. AVP ; e.g. action of acetylcholinesterase

(b) Explain the roles of synapses in the nervous system. [6]B) 16. ensure one-way transmission ; 17. receptor (proteins) only in postsynaptic, membrane / neurone ; ora 18. vesicles only in presynaptic neurone ; ora 19. ref. adaptation ; 20. increased range of actions ; 21. due to interconnection of many nerve pathways ; 22. ref. inhibitory synapses ; 23. involved in memory / learning ; 24. due to new synapses being formed ; 25. AVP; e.g. summation / discrimination

(a)Describe the structure of a chloroplast. [9] (a) 1. biconvex disc ; 2. 3-10 m diameter ; 3. double, membrane / envelope ; 4. internal membrane system ; 5. flattened or fluid-filled sacs / thylakoids ; 6. arranged in stacks / grana ; 7. hold pigments / named pigment ; 8. ref. clusters of pigments / AW ;

9. (membrane of grana) hold ATP synthase ; 10. intergranal lamellae ; 11. stroma / ground substance ; 12. lipids / starch grains ;

13. contains enzymes of Calvin cycle ; 14. stroma contains ribosomes / DNA etc ; 15. AVP ; e.g. variation in shape between species [9 max

(b) Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis. [6(b) 16. closely packed -- to absorb more incident light / AW ;

17. palisade mesophyll near upper surface of leaf -- to maximize light interception ;

18. arranged at right angles to leaf surface -- to reduce number of light absorbing walls ;

19. cylindrical cells -- producing air spaces between cells ;

20. air spaces -- act as reservoir of carbon dioxide ;

21. large surface area -- for gas exchange ;

22. cell walls thin -- so short diffusion pathway ;

23. large vacuole -- pushes chloroplasts to edge of cell ;

24. chloroplasts on periphery -- to absorb light more efficiently ;

25. large number of chloroplasts -- to maximise light absorption ;

26. chloroplasts can move within cells -- towards light ;

27. chloroplasts can move away from high light intensity -- to avoid damage ;

(a) Describe the structure of photosystems and explain how a photosystem functions in

cyclic photophosphorylation. [9]arranged in light harvesting clusters ; A system

primary pigments / chlorophyll a ;

at reaction centre ;

P700 / P1, absorbs at 700(nm) ;

P680 / P11, absorbs at 680(nm) ;

accessory pigments / chlorophyll b / carotenoids ; ignore ref to chlorophyll a

surround, primary pigment / reaction centre / chlorophyll a ;

absorb light ; linked to 6

pass energy to, primary pigment / reaction centre / ; chlorophyll a ;

P700 / PI, involved in cyclic photophosphorylation ;

(light absorbed results in) electron excited / AW ;

emitted from chlorophyll ;

chain of electron carriers / ETC ;

ATP synthesis ;

electron returns to, P700 / P1 ;

(b)Explain briefly how reduced NADP is formed in the light-dependent stage of photosynthesis and is used in the light-independent stage. [6]photolysis of water ;

releases H+ ; R H / hydrogen atoms by, P680 / PII ; e- released ; by, P700 / PI ; both combine with NADP ; (reduced NADP) reduces, GP / PGA ; to TP ; ATP used ; NADP, regenerated / oxidized

(a)Explain how meiosis and fertilisation can result in genetic variation amongst offspring.

chiasma / crossing over ; between non-sister chromatids ; of, homologous chromosomes / bivalent ; in prophase 1 ; linked to 1 exchange of genetic material / AW ; R genes unqualified linkage groups broken ; new combination of alleles ; independent assortment ; R random assortment metaphase 1 ; linked to 8 detail of independent assortment ; possible mutation ; random mating ; random fusion of gametes ; (b)Explain, using examples, how the environment may affect the phenotype of an organism.phenotypic variation results from interaction of genotype and environment / VP = VG + VE ; environment may limit expression of gene(s) / AW ; e.g. for size / mass / height ; because, food / nutrients / ion, missing / malnutrition ; named, nutrient / ion / mineral, missing ; environment may, trigger / switch on, gene ; ref. low temperature and change in animal colour ; ref. high temperature and, curled wing in Drosophila / gender in crocodiles ; ref. UV light and melanin production ; ref. wavelength of light and, flowering / germination / fruit colour ; other named trigger plus example ; environment effect usually greater on polygenes / ora ; environment may induce mutation affecting phenotype ;

Q)Describe the structure of a kidney, including its associated blood vessels.1. (outer) cortex ; 2. medulla ; 3. pelvis ; 4. renal artery ; 5. renal vein ; 6. nephron / (kidney) tubule ;7. renal capsule / proximal convoluted tubule (pct) / distal convoluted tubule (dct), in cortex ; 8. loop of Henle / collecting duct (cd), in medulla ; 9. glomerulus ;10. afferent & efferent arterioles; 11. capillary network, surrounds tubule / in medulla ;

Q)Describe the mechanisms involved in reabsorption in the proximal convoluted tubule and describe how the epithelial cells of the proximal convoluted tubule are adapted to carry out this process. [9]

mechanisms 12. active transport ; A actively pumped / uses ATP 13. Na+ , out of pct cells / into blood ; 14. (sets up) Na+ ion gradient ; 15. facilitated diffusion ; 16. using protein carrier ; A transport protein 17. cotransport (from lumen to pct cell); 18. of, glucose / amino acids / ions; 19. osmosis ;

20. down water potential gradient ; 21. diffusion (in correct context) ; 22. down a concentration gradient ; max 7adaptations 23. microvilli ; A brush border 24. many mitochondria ;25. tight junctions ; 26. folded, basal membrane / described ; 27. many, transport proteins / cotransporters / pumps;28. AVP ; e.g. many aquaporins

A)Explain the role of ATP in active transport of ions and in named anabolic reactions. [7](a) Active transport or anabolic reactions 1. ATP provides energy (linked to either) ; ignore ref. to energy currency aloneactive transport2. movement against concentration gradient ;3. carrier / transport, protein (in membrane) ; ignore pump 4. binds to (specific) ion ; 5. protein changes shape ; anabolic reactions 6. synthesis of complex substances from simpler ones ; 7. starch / cellulose / glycogen, from, monosaccharides / named monosaccharides / named sugar ; 8. glycosidic bonds ;9. lipid / triglyceride, from fatty acids and glycerol ; 10. ester bonds ; 11. polypeptides / proteins, from amino acids ; 12. peptide bonds ;13. other named polymer from suitable monomer ; 14. appropriate named bond ;

Outline the process of anaerobic respiration in both mammal and yeast cells. [8]general15. reduced NAD produced in glycolysis ; A glycolysis described16. small amount of ATP produced in glycolysis ; in yeast cells 17. pyruvate converted to ethanal ;18. carbon dioxide released / decarboxylation ;19. ethanal, reduced / accepts H ;20. by reduced NAD ;21. ethanol formed ; in mammalian cells22. pyruvate converted to lactate ; 23. by reduced NAD ;24. in, liver / muscle, cells ; 25. AVP ;;26. e.g. reversible in mammal / irreversible in yeast / single step in mammal / more than 1 in yeast / reoxidised NAD allows glycolysis to continue / named enzyme only award either mp19 or mp23 [

(a) Outline, with reference to blood glucose concentration, the principles of homeostasis in mammals. [6](a) 1. (homeostasis is) maintenance of, constant / stable, internal environment ;2. irrespective of changes in external environment ;3. negative feedback ;4. receptor /appropriate named cell, detects change in, parameter / blood glucose concentration ; 5. (receptors are) / , cells ;

6. in, Islets of Langerhans / pancreas ;7. insulin / glucagon, released ;8. action taken by effector / correct action described (liver / muscle, cell) ;9. restoration of, norm / set point / AW ; 10. ref. fluctuation around the norm ;

(b) Describe the roles of the endocrine and nervous systems in control and coordination in mammals.

(b) endocrine 11. hormones ; 12. chemical messengers ; A chemicals that transfer information 13. ductless glands / (released) into blood ; 14. target, organs / cells ; 15. ref. receptors on cell membranes ; 16. example of named hormone and effect ; nervous17. impulses / action potentials ; R electrical, signals / current 18. along, neurones ; R nerves 19. synapse (with target) / neuromuscular junction ; 20. ref. receptor / effector or sensory / motor, neurones ; differences endocrine21. slow effect / ora ; 22. long lasting effect / ora ; 23. widespread effect / ora ; 24. AVP ; e.g. extra detail of synapse

(a)Outline the ways in which the endocrine and nervous systems carry out their roles in control and coordination in animals. [8]

(a) endocrine1. hormones ; 2. chemical messengers ; A chemicals that transfer information

3. ductless glands / (released) into blood ; 4. target, organs / cells ; 5. ref. receptors on cell membranes ; 6. example of named hormone and effect ;nervous 7. impulses/ action potentials ; R electrical, signals / current 8. along, axon / neurones / nerve fibres ; R nerves R across 9. synapse (with target) / neuromuscular junction ; 10. ref. receptor / sensory neurones ; 11. ref. effector / motor neurones ; differences endocrine 12. slow effect / ora ; 13. long lasting effect / ora ; 14. widespread effect / ora ; 15. AVP ; e.g. extra detail of synapse / hormone changes triggered within cells [8 max]

Describe the part played by auxins in apical dominance in a plant shoot.[7]

(b) 16. IAA / plant growth regulator ; R plant hormone 17. synthesised in, growing tips / apical buds / meristems ; R root tip 18. moves by diffusion ; 19. moves by active transport ; 20. from cell to cell ; 21. also, mass flow / in phloem ; 22. stimulates cell elongation ; R cell enlargement 23. inhibits, side / lateral, buds / growth ; A inhibits branching 24. plant grows, upwards / taller ; A stem elongates 25. auxin not solely responsible or interaction between auxin and other plant growth regulators ; 26. AVP ; e.g. role of ABA and lateral bud inhibition 27. AVP ; e.g. cytokinins antagonistic to IAA / gibberellins enhance IAA [7 max]

(a)Describe how non-cyclic photophosphorylation produces ATP and reduced NADP. [9](a) 1. photosystem I (PI) and photosystem II (PII) involved ; 2. light harvesting clusters ; 3. light absorbed by accessory pigments ; 4. primary pigment is chlorophyll a ; 5. energy passed to, primary pigment / chlorophyll a ; 6. electrons, excited / raised to higher energy level ; 7. (electrons) taken up by electron acceptor ; 8. (electrons) pass down electron carrier chain (to produce ATP) ; 9. PII has (water splitting) enzyme ; 10. water split into protons, electrons and oxygen ; A equation 11. photolysis ; 12. electrons from PII pass to PI / electrons from water pass to PII ; 13. to replace those lost ; give either in relation to PI or PII 14. protons and electrons combine with NADP (to produce reduced NADP) ;can award these marking points from a diagram [9 max]

(b)Outline the steps of the Calvin cycle. [6](b) 15. RuBP combines with carbon dioxide ; 16. rubisco ; 17. forms unstable 6C compound ; 18. produces two molecules of, GP / PGA ; 19. GP / PGA, converted to TP ; 20. by reduced NADP and ATP ; 21. from light dependent stage ; 22. TP used to regenerate RuBP ; 23. using ATP ; 24. TP can form, hexose / fatty acids / acetyl CoA [6 max]

(a) Describe the photoactivation of chlorophyll and its role in cyclic photophosphorylation.[8](a) 1. (photosynthetic pigments) arranged in light harvesting clusters ;

2. primary pigments / chlorophyll a ; 3. at reaction centre ; 4. P700 / Pl, absorbs light at 700nm ; 5. accessory pigments / chlorophyll b / carotenoids ; 6. surround, primary pigment / reaction centre / chlorophyll a ; 7. absorb light ; 8. pass energy to, primary pigment / reaction centre / chlorophyll a ; 9. (light absorbed results in) electron excited / AW ; 10. emitted from, chlorophyll / primary pigment / reaction centre ; 11. passes to electron, acceptor / carrier ; 12. (electron) passes along, chain of electron carriers / ETC ; 13. ATP (synthesis) ; 14. electron returns to, P700 / Pl ; [8 max]

(b)Explain briefly how reduced NADP is formed in the light-dependent stage and how it is used in the light-independent stage. [7](b) 15. photolysis of water ; 16. releases H+ ; R H / hydrogen atoms 17. by, P680 / PII ; 18. e released from, P700 / PI ; 19. e (from PI) and H+ combine with NADP ; 20. used in Calvin cycle ; 21. reduces, GP / PGA ; 22. to TP ; 23. ATP used (during reduction of GP) ; 24. NADP, regenerated / oxidised ;

(a) Describe the role of abscisic acid (ABA) in the closure of a stoma. [8]

(a) accept ABA for abscisic acid 1. stress hormone ; 2. plant secretes ABA in, high temperatures / dry conditions ; 3. ABA binds to receptors ; 4. on plasma membranes of guard cells ; 5. inhibits proton pump / H+ not pumped out of cell ; 6. high H+ conc / positive charge, inside cell ; 7. K+ diffuses out of cell ; 8. water potential of cell increases ; A increase in solute potential 9. water moves out of cell by osmosis ; 10. volume of guard cells decreases ; 11. guard cells become flaccid ; 12. response very fast ; [8 max]

(b)Describe the role of gibberellins in the germination of barley seeds. [7]

(b) 13. (barley) seed is, dormant / metabolically inactive ; 14. seed absorbs water ; 15. embryo produces gibberellin ; 16. gibberellin stimulates aleurone layer ; 17. to produce amylase ; 18. amylase hydrolyses starch ; 19. in endosperm ; 20. to maltose / glucose ; 21. embryo uses sugars for respiration ; 22. energy used for growth ; 23. gibberellins affect, gene / transcription of mRNA, coding for amylase ; [7 max]

(a) Describe how the structure of a chloroplast is related to its functions. [9](a) 1. ground substance / stroma ;2. for, light independent stage / Calvin cycle ;3. contains enzymes / named enzyme e.g. rubisco ;4. also, sugars / lipids / starch / ribosomes / DNA ;5. internal membrane system ;6. for, light dependent stage ;7. fluid-filled sacs / thylakoids ;8. grana are stacks of thylakoids ;9. (grana) hold (photosynthetic) pigments ;10. (grana) have large surface area for (maximum) light absorption ;11. (pigments are arranged in), light harvesting clusters / photosystems ;

12. primary pigment / reaction centre / chlorophyll a, surrounded by accessory pigments ;13. (accessory pigments) pass energy to, primary pigment / reaction centre / chlorophyll a ;14. different photosystems absorb light at different wavelengths ;15. membranes hold, ATP synthase / electron carriers ;

16 for, photophosphorylation / chemiosmosis ; [9 max]

(b)

Describe how you would separate chloroplast pigments using chromatography. [6](b) 17. grind leaf with solvent ;18. example of solvent ; e.g. propanone19. leaf extract contains mixture of pigments ;20. ref. concentrate extract ;21. further detail ; e.g. pencil line drawn / extract placed on chromatography paper / repetitive spotting / drying between spots22. paper placed (vertically) in jar of (different) solvent ;23. solvent rises up paper ;24. each pigment travels at different speed ;25. pigments separated as they ascend ;26. distance moved by each pigment is unique ;27. Rf value ;28. two dimensional chromatography ;29. better separation of pigments ; [6 max]

(a) Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis. [8]

(b) (a) 1 closely packed to absorb maximum light ;(c) 2 vertical/at right angles to surface of leaf to reduce number of cross walls ;(d) 3 large vacuole pushes chloroplasts to edge of cell ;(e) 4 chloroplasts at edge short diffusion path for carbon dioxide ;(f) 5 chloroplasts at edge to absorb maximum light ;(g) 6 large number of chloroplasts to absorb maximum light ;(h) 7 cylindrical cells or air spaces to circulate gases/provide a reservoir of CO2 ;(i) 8 large surface area for diffusion of gases ;(j) 9 moist cell surfaces for diffusion of gases ;(k) 10 cell walls thin for maximum light penetration/diffusion of gases ;(l) 11 chloroplasts can move towards light ;(m)12 chloroplasts can move away from high light intensity to avoid damage ; [8 max]

(c) Outline the light-independent stage of photosynthesis. [7](d)(b) 13 Calvin cycle/stroma ;(e)14 carbon dioxide fixed by RuBP ;(f) 15 rubisco ;(g)16 2 molecules of GP formed ; A PGA(h)17 (GP) forms TP ; A GALP/PGAL(i) 18 use of ATP ;(j) 19 use of, reduced NADP/NADPH ;(k)20 from light dependent stage ;(l) 21 some TP forms, hexose/sucrose/starch/cellulose/glycerol ;(m)22 some TP converted to acetyl CoA ;(n)23 some TP used to regenerate RuBP ;(o)24 using ATP ;(p)allow either mp 18 or mp 24(q) marks can be awarded on a diagram [7 max

(a) Describe the structure of a kidney nephron and its associated blood vessels. [7](b)(a) 1 renal/Bowmans, capsule ;(c)2 ref. podocytes ;(d)3 (proximal convoluted tubule/distal convoluted tubule/capsule) in cortex ;(e)4 proximal convoluted tubule ;(f) 5 loop of Henle ;(g)6 (loop) in medulla ;(h)7 distal convoluted tubule ;(i) 8 afferent arteriole ;(j) 9 glomerulus ;(k)10 efferent arteriole ;(l) 11 capillary network around/proximal convoluted tubule/loop/distal convoluted tubule ;(m)12 collecting duct ;(n) accept points on a labelled diagram [7 max]

Explain how glomerular filtrate is formed. [8](b) 13 endothelium of, blood capillaries/glomerulus ;14 more/large, gaps between endothelial cells ;15 podocytes ;16 large gaps between podocytes/filtration slits ;17 basement membrane, selective barrier/acts as a filter ;18 prevents, large protein/RMM > 68 000, passing through ;19 no cells pass through ;20 named molecule which is filtered ; e.g. urea/water/glucose/uric acid/creatinine/Na+/K+/Cl- ;21 high, blood/hydrostatic, pressure in glomerulus ;22 afferent arteriole wider than efferent arteriole ;23 lower pressure in, renal/Bowmans, capsule ;24 fluid forced into capsule/ultrafiltration ; [8 max]

[

(a) Describe the structure of photosystems and explain how a photosystem functions incyclic photophosphorylation. [8]

(a) 1 arranged in light harvesting, clusters/system ;2 primary pigments/chlorophyll a ;3 at reaction centre ;4 P700/P1, absorbs at 700(nm) ;5 P680/P11, absorbs at 680(nm) ;6 accessory pigments/chlorophyll b/carotenoids, surround, primary pigment/reactioncentre/ chlorophyll a ;7 pass energy to, primary pigment/reaction centre/chlorophyll a ;8 P700 / PI, involved in cyclic photophosphorylation ;9 (light absorbed results in) electron excited/AW ;10 emitted from, chlorophyll/photosystem ;11 flows along, chain of electron carriers/ETC ;12 ATP synthesis ;13 electron returns to, P700/P1 ; [8 max]

(b) Explain briefly how reduced NADP is formed in the light-dependent stage and how it isused in the light-independent stage. [7]

(b) 14 photolysis (of water) ;15 releases H+ ; R H/hydrogen atoms16 by, P680/PII ;17 e- released ;18 by, P700/PI ;19 both combine with NADP ;(reduced NADP)20 reduces, GP ; A PGA21 to TP ; A PGAL / GALP22 ATP used ;23 NADP, regenerated/oxidised ; [7 max]

(a) Describe the structure of a myelinated sensory neurone. [7]

1 nucleus in cell body ;2 (long) dendron ; R plural3 (shorter) axon ;4 many mitochondria (in cell body) ;5 many RER/nissls granules, (in cell body) ;6 synaptic knobs ;7 detail of synaptic knob ;8 (terminal) dendrites ;9 Schwann cells ;10 detail of myelin sheath ;11 nodes of Ranvier ;accept points on labelled diagram [7 max](b) Explain how an action potential is transmitted along a sensory neurone. [8]

12 Na+ channels open ; A sodium channels13 Na+ enter cell ; R enter membrane14 inside becomes, less negative/positive/+40mV or membrane depolarised ;15 Na+ channels close ; A sodium channels16 K+ channels open ; A potassium channels17 K+ move out (of cell) ; R of membrane18 inside becomes negative or membrane repolarised ; A negative figuremax 519 local circuits/description ;20 (myelin sheath/Schwann cells) insulate axon/does not allow movement of ions ;21 action potential/depolarisation, only at nodes (of Ranvier)/gaps ;22 saltatory conduction/AW ;23 one-way transmission ;24VP ; e.g. hyperpolarisation/refractory period [8 max]

Describe a reflex arc and explain why such reflex arcs are important. [7]strong stimulus in receptor / AW ;action potential / impulses, along sensory neurone ;dorsal root of spinal nerve ;into spinal cord ; synapse with intermediate neurone ;(then) motor neurone ;action potential / impulses, to effector ;action potential / impulses, to brain ;response ; e.g. knee jerk 5 max can be on diagramfast / immediate ;stops / limits, damage / danger ;automatic / no conscious thought ;innate / stereotyped / instinctive ; [7]

Describe the structure of a myelin sheath and explain its role in the speed of transmissionof a nerve impulse. [8]

Schwann cells ;wrap around axon ;sheath mainly lipid ;(sheath) insulates axon (membrane) ;Na+ / K+, cannot pass through sheath / can only pass throughmembrane at nodes ;depolarisation (of axon membrane) cannot occur where there issheath / only at nodes of Ranvier ;local circuits between nodes ;action potentials jump between nodes ;saltatory conduction ;increases speed / reduces time, of impulse transmission ;up to 100 ms-1 ;speed in non-myelinated neurones about 0.5 ms-1 ;

(a) Outline the main features of the Krebs cycle. [9]acetyl CoA combines with oxaloacetate ;to form citrate ;4C to 6C ;decarboxylation / CO2 released ;dehydrogenation / oxidation / release of hydrogen ;reduced NAD produced / NAD accepts hydrogen ;reduced FAD produced / FAD accepts hydrogen ;ATP produced ;substrate level phosphorylation ;series of, steps / intermediates ; A many named steps off a diagramenzyme catalysed reactions ;oxaloacaetate regenerated ;occurs in mitochondrial matrix ;

Explain the role of NAD in aerobic respiration. [6]

coenzyme ;for dehydrogenase ;reduced ;carries, electrons and protons / hydrogen / NADfrom Krebs cycle ;and glycolysis ;to ETC / electron carrier chain / oxidation ;reoxidised / regenerated hydrogen removed ;ATP produced ; [6 max]

Explain the roles of synapses in the nervous system. [6]

ensure one-way transmission;receptor (proteins) only in postsynaptic, membrane / neurone ; oravesicles only in presynaptic neurone ; oraadaptation / ACh amount reduces due to overuse of synapse ;wide range of responses ;due to interconnection of many nerve pathways ;inhibitory synapses affect other synapses ;involved in memory / learning ;due to new synapses being formed ;summation / discrimination ;

Describe and explain how a stoma is opened.

1 ref. ABA absence ;2 H+ transported out of guard cells, actively / using ATP ;3 low H+ conc / negative charge, inside cell ;4 K+ channels open / K+ diffuses into cell ;5 water potential of cell falls ; A decrease in solute potential6 water moves into cell by osmosis ;7 volume of guard cells increase / turgor increases ;guard cells:8 have hoops of cellulose microfibrils which ensure increase in length rather thandiameter ;9 have ends that are joined together ;10 have, thicker inner walls / thinner outer walls ;

11 curve apart / bend, (to open stoma) ;

Describe the part played by the proximal convoluted tubules in the functioning of thekidneys. [8]

1 selective reabsorption ;2 (pct cells have) villi / microvilli / large surface area ;3 (pct cells have) many mitochondria ;4 Na+ leave pct cells ;5 by active transport ;6 Na+ concentration falls in (pct) cells / Na+ concentration gradient ;7 Na+ (diffuse) from lumen into (pct) cells ;8 through, transporter / carrier, proteins ; ignore channel proteins9 cotransport ;10 of, glucose / amino acids / vitamins / chloride ions ;11 (from pct cells) into intercellular fluid ; linked to 1012 (then) diffusion into blood ; linked to 1013 (normally) all glucose reabsorbed ;14 some water reabsorbed ;15 some urea reabsorbed ;16 AVP ; e.g. creatinine secreted into lumen [8 max]accept sodium ions but reject sodium or Napenalise once only

Explain how the collecting ducts in the kidneys may reduce the loss of water from thebody. [7]

17 ADH affects collecting duct ;18 binds to receptor on membrane ;19 increase membrane permeability (to water) / more water channels ;20 ref. enzyme controlled reactions ;21 produces (active) phosphorylase ;22 (which causes) vesicles with, water channels / aquaporins ; must be linked to 2323 to, move to / fuse with, (plasma) membrane ;24 more water flows out of collecting duct ;25 down / along, water potential gradient ;26 (then) into blood ;27 urine (more) concentrated / small volume of urine ;28 ref. negative feedback ;29 AVP ; e.g. role of loop of Henle in creating water potential gradientmovement of urea increases water potential gradient

9 (a) Explain how changes in the nucleotide sequence of DNA may affect the amino acidsequence in a protein. [7]

(a) 1 code is three, bases / nucleotides ; A triplet code2 (gene) mutation ; R chromosome mutation3 base, substitution / addition / deletion ;4 addition / deletion, large effect (on amino acid sequence) ;

5 frame shift ;6 completely new code after mutation / alters every 3 base sequence which follows ;7 (substitution) often has no effect / silent mutation ;8 different triplet but same amino acid / new amino acid in non-functional part of protein ;9 (substitution) may have big effect (on amino acid sequence) ;10 could produce stop codon ;11 sickle cell anaemia / PKU / cystic fibrosis ;12 reference to transcription or translation in correct context ; A description12a AVP ; e.g. protein produced, is non-functional / not produced / incomplete [7 max]

(b) Explain how natural selection may bring about evolution. [8]

13 individuals in population have great reproductive potential / AW ;14 numbers in population remain roughly constant ;15 variation in members of population ;16 environmental factors / named factor (biotic or abiotic) ; linked to 17 and 1817 (cause) many, fail to survive / die / do not reproduce ;18 those best adapted survive / survival of the fittest ;19 (reproduce to) pass on alleles ; R genes20 genetic variation leads to change in phenotype ;21 ref: changes in, gene pool / allele frequency ;22 over time produces evolutionary change ;23 new species arise from existing ones / speciation ;24 directional / stabilising, selection ; [8 max]

9 (a) Outline the behaviour of chromosomes during meiosis. [9]do not credit marking points out of sequencedo not credit marking points out of sequenceprophase 11 idea of condensation of chromosomes ;2 homologous chromosomes pair up / bivalent formed ;metaphase 13 homologous chromosomes / bivalents, line up on equator ;4 of spindle ;5 by centromeres ;6 independent assortment / described ;7 chiasmata / described ;8 crossing over / described ;anaphase 19 chromosomes move to poles ;10 homologous chromosomes / bivalents, separate ;11 pulled by microtubules ;12 reduction division ;metaphase 213 chromosomes line up on equator ;14 of spindle ;

anaphase 215 centromeres divide ;16 chromatids move to poles ;17 pulled by microtubules ;9 (a)18 ref. haploid number ;allow 4 or 14allow 11 or 17 [9 max]Describe the ways by which gene mutations can occur. [6]

19 change in, base / nucleotide, sequence (in DNA) ;20 during DNA replication ;21 detail of change ; e.g. base, substitution / addition / deletion22 frame shifts / AW ;23 different / new, allele ;24 random / spontaneous ;

25mutagens ;26ionising radiation ;27UV radiation

11 (a) Explain how changes in the nucleotide sequence of DNA may affect the amino acidsequence in a protein.

11 (a) 1. (amino acid) code is three, bases / nucleotides ; A triplet code2. (gene) mutation ; R chromosome mutation3. base / nucleotide, substitution / addition / deletion4. addition / deletion, has large effect (on amino acid sequence) ;5. frame shift ;6. completely new code after mutation / alters every 3 base sequence which follows ;7. substitution may have little or no effect / silent mutation ;8. different triplet but same amino acid / new amino acid in non-functional part of protein ;9. substitution may have big effect (on amino acid sequence) ;10. could produce stop codon ;11. sickle cell anaemia / PKU / cystic fibrosis ;

12. reference to transcription or translation in correct context ; A description [8 max

(b) Explain how the allele for haemophilia may be passed from a man to his grandchildren.You may use genetic diagrams to support your answer. [7]

(b) 13. (haemophilia) allele on X chromosome ; A gene14. sex-linked ;15. (haemophilia) allele recessive ;16. man, homogametic / has one X chromosome ;17. Y chromosome does not have blood clotting gene ;18. only daughter(s) get his X chromosome ;19. daughter(s) carrier(s) of (haemophilia) allele ;20. grandson(s) 50% chance of having, (haemophilia) allele / haemophilia ;21. granddaughter(s) 50% chance of carrying, (haemophilia) allele ;allow following marks from diagram22. correct symbols ; e.g. XH and Xh explained23. mans genotype ; e.g. XhY ignore partners genotype24. F1 (daughters) genotype ; e.g. XHXh ignore her partners genotype25. F2 (grandsons) genotypes ; e.g. XhY XHY both required

26. F2 (granddaughters) genotypes ; e.g. XHXH XHXh both required or XhXh XHXh [7 max]

9 (a) Describe how crossing over and independent assortment can lead to genetic variation.[9]

(a) 1 occur during meiosis I ;crossing over2 between non-sister chromatids ;3 of, (a pair of) homologous chromosomes / a bivalent ;4 in prophase 1 ;5 at chiasma(ta) ;6 exchange of genetic material / AW ;R genes unqualified7 linkage groups broken / AW ;8 new combination of alleles (within each chromosome) ;independent assortment9 of homologous chromosomes pairs / bivalents ;10 each pair lines up independently of others ;11 line up on equator ;12 (during) metaphase 1 ;13 results in gametes that are genetically unique / AW

(a) Describe the first division of meiosis (meiosis I) in animal cells. [6]1. reduction division / (to) halve number of chromosomes / diploid to haploid / AW ; 2. homologous chromosomes pair up / bivalents form ; 3. ref. chiasmata / ref. crossing over ; 4. homologous chromosome pairs / bivalents, line up on equator ; 5. independent assortment ; 6. spindle / microtubules, attached to centromeres ; 7. chromosomes of each pair pulled to opposite poles ; 8. by shortening of, spindle / microtubules ; 9. nuclear envelopes re-form ; 10. cytokinesis / AW ; [6 max]

(b) Discuss the link between the frequency of sickle cell anaemia and the number of cases

of malaria. [9]accept alternative symbols for alleles throughout 11. frequency of sickle cell anaemia is highest in areas where malaria is common ; 12. sickle cell anaemia red blood cells cannot carry oxygen very well / AW ; A sickling blocks capillaries

13. homozygous HS / HSHS, have sickle cell anaemia / may die ; 14. homozygous HN / HNHN, have normal, Hb / red blood cells ; 15. heterozygotes, have sickle cell trait or (sickle cell trait) red blood cells not (severely) affected ;

16. malaria parasite / Plasmodium, affects red blood cells ; 17. malaria lethal ; 18. sickle cell trait people / heterozygotes, less likely to suffer from (severe effects of) malaria ; 19. have selective advantage ; 20. pass on both HN and HS ; 21. malaria selects against, homozygous HN / HNHN ; 22. sickle cell anaemia selects against, homozygous HS / HS HS; 23. idea that sickle cell allele is maintained within population because of sickle cell trait individuals ; [9 max]

11 (a) Explain how changes in the nucleotide sequence of DNA may affect the amino acidsequence in a protein. [8]

1. (amino acid) code is three, bases / nucleotides ; A triplet code2. (gene) mutation ; R chromosome mutation3. base / nucleotide, substitution / addition / deletion4. addition / deletion, has large effect (on amino acid sequence) ;5. frame shift ;6. completely new code after mutation / alters every 3 base sequence which follows ;7. substitution may have little or no effect / silent mutation ;8. different triplet but same amino acid / new amino acid in non-functional part of protein ;9. substitution may have big effect (on amino acid sequence) ;10. could produce stop codon ;11. sickle cell anaemia / PKU / cystic fibrosis ;12. reference to transcription or translation in correct context ; A description [8 max

(b) Explain how the allele for haemophilia may be passed from a man to his grandchildren.You may use genetic diagrams to support your answer. [7]

(b) 13. (haemophilia) allele on X chromosome ; A gene

14. sex-linked ;15. (haemophilia) allele recessive ;16. man, homogametic / has one X chromosome ;17. Y chromosome does not have blood clotting gene ;18. only daughter(s) get his X chromosome ;19. daughter(s) carrier(s) of (haemophilia) allele ;20. grandson(s) 50% chance of having, (haemophilia) allele / haemophilia ;21. granddaughter(s) 50% chance of carrying, (haemophilia) allele ;allow following marks from diagram22. correct symbols ; e.g. XH and Xh explained23. mans genotype ; e.g. XhY ignore partners genotype24. F1 (daughters) genotype ; e.g. XHXh ignore her partners genotype25. F2 (grandsons) genotypes ; e.g. XhY XHY both required26. F2 (granddaughters) genotypes ; e.g. XHXH XHXh both required or XhXh XHXh [7 max]

9 (a) Explain the need to maintain biodiversity in an ecosystem such as a tropical rainforest.[7]

(a) 1. cultural/aesthetic / leisure, reasons;2. moral/ethical, reasons ; e.g. right to exist/prevent extinction;3. resource material ; e.g. wood (for building)/fibres for clothes/food forhumans/(herbal) medicine4. (eco)tourism;5. economic benefits;6. ref. resource / species, may have use in future/AW;e.g. medical use7. maintains, food webs / food chains;A description8. nutrient cycling;9. protection against erosion;10. climate stability;11. maintains, (large) gene pool/genetic variation;12. scientific research;

(b) Discuss the advantages and the disadvantages of captive breeding programmes formammals. [8](b) advantages (max 5)13. can monitor health of mother;14. can monitor development of foetus;15. storage of, sperm/eggs/gametes;16. artificial insemination;17. IVF;18. ref. surrogate mothers;19. international cooperation;20. genetic records kept;21. can prevent extinction/extend range of a species/used in restoringecosystem;

disadvantages (max 5)22. unnatural environment;23. stress in captivity;24. behavioural changes;25. reproductive cycles disrupted;26. may reject selected mate;27. examples of problems with release ;;28. difficulty in finding foodmay not integrate into groupsmore susceptible to diseasevery little natural habitat left to release animals into[max 8][Total: 15]

9 (a) Bacteria are members of the kingdom Prokaryota. Describe the main features of abacterial cell. [8](a) 1. DNA not surrounded by nuclear membrane / no nucleus;2. (prokaryote) DNA is circular;3. DNA not associated with histones; A naked DNA4. plasmids (may) be present;5. no (double) membrane-bound organelles; A no, mitochondria / chloroplasts6. no, ER / Golgi; A ribosomes not attached to membranes7. ribosomes,70S / 18 nm / smaller (than eukaryotic cells);8. cell wall made of, peptidoglycan / murein / amino sugars / AW;9. (usually) unicellular;10. 0.5 to 5.0 m diameter; A any value between 0.5 and 5.0 as long as m is used11. AVP; (may) have, flagella / pili / capsule / slime layer [8 max]

(b) Outline the use of bacteria in the extraction of metals from ores. [7](b) 12. ores (may) contain metal sulfides;13. example; e.g. iron / copper / zinc / cobalt / lead14. insoluble in water so difficult to extract;15. bacteria oxidise metal sulfide;16. to soluble sulfate;17. bioleaching;18. example of bacteria; e.g. A.ferrooxidans19. bacteria need to survive in acidic conditions;20. mixture of bacteria required (in bioheap);21. (in order to) survive a wide range of temperatures / range of bacteria with differenttemperature optima;

22. advantage;23 e.g. low grade ores / spoil heaps, can be exploitedcan get metal from industrial wastedoes not produce sulfur dioxidecan be done in situlow energy demandless (heavy) machinerynot labour intensive

relatively cheaper (than other mining methods)24. AVP; e.g. ref. gold / uranium [7 max]