Control and coordination

5(a) 6 ion direction of movement of ion action resulting from movement of ion co-transport / secondary active transport, of, from lumen of proximal amino acids / glucose Na+ convoluted tubule into proximal or convoluted tubule cell osmosis of water ; K+ ; into guard cell opening of stoma(ta) Na+ ; into presynaptic knob depolarisation of presynaptic membrane Ca2+ ; into presynaptic knob exocytosis of acetylcholine from intermembrane space into H+ ATP synthesis ; matrix of mitochondrion binds to troponin / troponin shape changes / tropomyosin moves / from sarcoplasmic reticulum to actin binding site on myosin head exposed / Ca2+ cytoplasm of muscle fibre binding of myosin head to actin / allows power stroke / sarcomere contracts ; 5(b)(i) Ca2+ / calcium ions ; 1 5(b)(ii) to avoid wasting energy 1 or idea of avoid closing, due to a single contact / by an object such as water drop ; 5(b)(iii) exocytosis ; 1 5(b)(iv) not enough, nitrogen / nitrate, in the soil 1 or poor mineral content of the soil ; R nutrients © UCLES 2021 Page 13 of 22

6(a) any five from: 5 1 chemicals, stimulate / bind to / enter, (receptor cells) ; 2 Na+ enters (receptor cells) via microvilli ; 3 membrane depolarised ; 4 ref. to receptor potential ; 5 ref. to threshold ; 6 voltage-gated Ca2+ channels open / Ca2+ ions enter, cytoplasm / cell ; 7 vesicles (of neurotransmitter), move towards / fuse with, (cell surface) membrane ; 8 exocytosis of neurotransmitter / AW ; 9 neurotransmitter binds to receptor ; 10 (receptor cell) acts as a transducer ; 6(b) any two from: 2 1 non-invasive / safe ; 2 quick / immediate results / saves time / early detection ; 3 can be done at home / no equipment ; 4 cheap / cost effective ; © UCLES 2021 Page 14 of 22

5(a)(i) any three from: 3 1 wider / thicker / larger diameter  increases / higher, speed ; 2 large(r) membrane surface area so more ion movement ; 3 myelin  increases / faster / higher, speed ; 4 saltatory conduction (in myelinated) ; 5 pairwise data comparison ; 5(a)(ii) any one from: 1 1 impulses, for touch / in Aβ neurones, travel faster ; 2 (Aβ neurones) inhibit, spinal cord / relay / projection, neurones ; 3 AVP ; 5(b)(i) any four from: 4 1 endorphins bind to (endorphin) receptors ; 2 stop, calcium ions / Ca2+, entering presynaptic knob ; 3 no / fewer, vesicles, move towards / fuse with, (presynaptic) membrane ; 4 no / less, acetylcholine / ACh, released ; 5 no / less, binding of ACh to postsynaptic receptors ; 6 no / less, depolarisation of postsynaptic, neurone / membrane ; 7 no / fewer, action potentials / impulses, to, pain centre / brain ; 5(b)(ii) any one from: 1 1 (drug) dependency / addiction / tolerance ; 2 (drug) side-effects ; 3 expensive ; 4 work more slowly ; © UCLES 2021 Page 10 of 16

1(a)(i) A – sodium potassium pump ; CON if channel mentioned 3 B – potassium ions ; A K+ D – sodium ions ; A Na+ max 2 if no ref. to ions 1(a)(ii) ATP ; 1 1(b) any five from: 5 drugs could be in any order curare 1 less / no, ACh binds to receptors ; I neurotransmitter 2 fewer / no, (ligand gated) Na+ channels open or fewer / no, Na+ can enter sarcomere / sarcoplasm or no / less, depolarisation of, sarcolemma / muscle cell membrane ; nerve gas 3 no / less, ACh broken down or ACh remains bound to receptor ; 4 (ligand gated) Na+ channels remain open / Na+ continue to enter post synaptic neurone or permanent / AW, depolarisation (of post synaptic membrane) ; A sarcolemma alcohol 5 no / less, binding of, neurotransmitter / ACh, to receptors ; © UCLES 2021 Page 5 of 22 1(b) 6 fewer / no, (ligand gated) Na+ channels open or fewer / no, Na+ can enter post synaptic neurone or no / less, depolarisation (of post synaptic membrane) ; A sarcolemma Question Answer Marks

1(a) A – binding site ; 4 B – tropomyosin ; C – troponin ; D – myosin head ; A ATPase 1(b) any four from: 4 1 ref. to release from, sarcoplasmic reticulum / SR ; 2 bind to, troponin / C ; 3 tropomyosin / B, moves / AW ; A changes shape 4 binding site / A, exposed / AW ; 5 myosin head / D, binds to actin or ref. to formation of cross bridge ; allow ecf from 1(a) 1(c) no / little, ATP, produced / available ; 2 (so) no breaking of cross bridges / myosin head not released ; © UCLES 2021 Page 5 of 22

10(a) any seven from: 7 selective reabsorption – sodium ions 1 active transport of Na+, out of (pct) cells / into blood ; 2 Na+ ion concentration, gradient (produced) / reduced in cell ; 3 Na+ enters (pct) cells from, lumen / tubule / filtrate ; 4 by facilitated diffusion / using carrier protein ; 5 cotransport of, glucose / amino acids / ions ; 6 glucose diffuses into blood ; synapse – calcium ions 7 (when) presynaptic membrane depolarised ; 8 calcium (ion) channels / voltage-gated channels, open ; 9 calcium ions enter presynaptic neurone ; 10 stimulate vesicles of ACh to, move towards / fuse with, presynaptic membrane ; 11 causing exocytosis of ACh ; © UCLES 2021 Page 21 of 22 10(b) any eight from: 8 differences nervous endocrine 1 communication action potential / impulse and hormone ; 2 nature of communication electrical (and chemical) and chemical ; 3 mode of transmission neurone / nerve cell and blood ; 4 response destination muscle / gland and target, organs / tissue / cells ; 5 transmission speed fast(er) and slow(er) ; 6 effects specific / localised and (can be) widespread ; 7 response speed fast(er) and slow(er) ; 8 duration short-lived / temporary and can be long-lasting / permanent ; 9 receptor location on cell surface membrane and either on cell surface membrane or within cell ; similarities 10 cell signalling both involve cell signalling ; 11 detail both involve signal molecule binding to receptor ; 12 chemicals both involve chemicals ; © UCLES 2021 Page 22 of 22

5(a) embryo ; 1 5(b)(i) any two from: 2 1 as water potential increases the germination index increases ; ora 2 water potential in MPa and index figure given for two points ; 5(b)(ii) any three from: 3 1 low / negative, water potential decreases water, uptake / in, seed ; ora 2 water, needed / used, to activate embryo / produce gibberellin ; 3 water, needed / used, for hydrolysis (reactions) ; 4 starch to maltose / maltose to glucose ; 5 water, needed / used, as a medium for reactions ; 6 solutes (lowering water potential) may, be toxic / inhibit enzymes ; 7 AVP ; 5(c) enzyme 2 amylase / maltase / protease ; location aleurone layer ; 5(d)(i) less, energy / resources, to make stem so, more to / larger, flowers or less likely to be damaged by, wind / storm / heavy rain 1 or takes less, water / fertiliser / time to flower ; © UCLES 2021 Page 12 of 21 5(d)(ii) any three from: 3 short / dwarf, plants: 1 are, homozygous recessive / lele ; 2 le / recessive allele, codes for, non-functional / no, enzyme ; 3 le / recessive allele / non-functional enzyme, gives inactive gibberellin ; 4 DELLA proteins, not broken down / stay bound to PIF ; 5 PIF cannot, bind to promoter / start transcription ; 6 of gene(s) that promote, growth / cell division / cell elongation ; Question Answer Marks

10(a) any nine from: 9 1 Na+ / sodium ion, channels open ; 2 Na+ / sodium ions, enter, neurone / axon / (nerve) cell ; 3 membrane (potential) becomes, positive / +40 mV / depolarised ; 4 (repolarisation / after peak) Na+ / sodium ion, channels close ; 5 K+ / potassium ion, channels open ; 6 K+ / potassium ions, leave / move out (of cell) ; 7 membrane (potential) becomes, negative / –90 mV / repolarised ; 8 local circuits ; 9 myelin sheath / Schwann cells, insulates / stops ion movement ; 10 action potential / depolarisation, only occurs at nodes of Ranvier ; 11 saltatory conduction ; 12 fast transmission (of, action potential / impulse) ; 13 one-way transmission (of, action potential / impulse) ; 14 AVP ; © UCLES 2021 Page 20 of 21 10(b) any six from: 6 1 maintain / keep / regulate, internal, environment / conditions ; 2 within, narrow / set, limits or around, optimum value / set point / norm ; 3 low (body) temperature and consequence ; 4 high (body) temperature and consequence ; 5 low blood glucose (concentration) and consequence ; 6 high blood glucose concentration and consequence ; 7 low, (blood) water potential / ψ, and consequence ; 8 high, (blood) water potential / ψ, and consequence ; © UCLES 2021 Page 21 of 21

3(a) any three from: 3 1 seed / embryo, absorbs water ; 2 (stimulates) embryo to produce gibberellin ; 3 gibberellin moves to aleurone layer ; 4 gene coding for amylase, expressed / transcribed ; 5 translation of mRNA (to produce amylase) ; 6 AVP ; e.g. gibberellin binds to receptor / ref. destruction of DELLA protein 3(b)(i) endosperm ; 1 © UCLES 2021 Page 9 of 24 3(b)(ii) any four from: 4 1 amylase activity increases ; 2 as (seeds) produce more amylase ; 3 percentage of starch decreases ; 4 amylase, hydrolyses / breaks down, starch ; 5 idea of a change at an increasing rate (for either) ; A exponential change 6 data quote: amylase or starch at two different days ; time / days amylase activity / au percentage of starch remaining 0 0.0 100 1 0.2 99 2 0.8 98 3 2.4 95 4 5.0 91 5 8.4 82 accept manipulated data © UCLES 2021 Page 10 of 24 3(c)(i) any three from: 3 1 enzyme, denatured / deactivated / inactivated ; 2 changes, tertiary structure / 3D shape, of amylase ; A enzyme 3 changes shape of active site ; 4 active site, no longer complementary / does not bind, to starch / substrate or no, ESC / enzyme-substrate complexes, formed ; 5 AVP ; e.g. removes water from embryo for gibberellin synthesis / removes water from endosperm for hydrolytic reactions 3(c)(ii) any one from: 1 1 stops, sugars / glucose, from being used ; ora 2 ensures (enough) sugars for beer production ; © UCLES 2021 Page 11 of 24

10(a) any seven from: 7 1 (dip stick) has immobilised enzymes ; 2 (dip stick) dipped in urine ; A person, urinates / AW, on stick 3 glucose oxidase and peroxidase ; 4 glucose reacts to give hydrogen peroxide ; 5 (hydrogen peroxide reacts with) colourless substance / chromogen ; 6 to give, colour change / coloured substance ; 7 compare with colour chart ; 8 more glucose gives darker colour / colour intensity gives glucose quantity ; 9 AVP ; e.g. doesn’t give current blood glucose concentration / not numerical / semi-quantitative © UCLES 2021 Page 23 of 24 10(b) any eight from: 8 1 dominant allele / Le, codes for, functional enzyme ; ora 2 (enzyme) produces active gibberellin (GA) ; 3 DELLA (protein) inhibits, transcription factor / PIF or DELLA (protein) prevents transcription ; 4 gibberellin / GA, binds to receptor (complex) ; ignore cell surface membrane 5 ref. to enzyme involved ; 6 causes DELLA (protein) destruction ; R GA breaks DELLA (protein) 7 transcription factor / PIF / RNA polymerase, binds to, DNA / promoter ; 8 (growth) genes, switched on / expressed / transcribed or transcription occurs ; 9 cell walls loosen / acid growth (described) ; 10 (so) cells can expand when water enters ; 11 ref. to cell, elongation / division ; 12 increases internode length ; 13 AVP ; e.g. ref. to expansins / interaction with auxin / ref. to XET © UCLES 2021 Page 24 of 24

5(a) embryo ; 1 5(b)(i) any two from: 2 1 as water potential increases the germination index increases ; ora 2 water potential in MPa and index figure given for two points ; 5(b)(ii) any three from: 3 1 low / negative, water potential decreases water, uptake / in, seed ; ora 2 water, needed / used, to activate embryo / produce gibberellin ; 3 water, needed / used, for hydrolysis (reactions) ; 4 starch to maltose / maltose to glucose ; 5 water, needed / used, as a medium for reactions ; 6 solutes (lowering water potential) may, be toxic / inhibit enzymes ; 7 AVP ; 5(c) enzyme 2 amylase / maltase / protease ; location aleurone layer ; 5(d)(i) less, energy / resources, to make stem so, more to / larger, flowers or less likely to be damaged by, wind / storm / heavy rain 1 or takes less, water / fertiliser / time to flower ; © UCLES 2021 Page 12 of 21 5(d)(ii) any three from: 3 short / dwarf, plants: 1 are, homozygous recessive / lele ; 2 le / recessive allele, codes for, non-functional / no, enzyme ; 3 le / recessive allele / non-functional enzyme, gives inactive gibberellin ; 4 DELLA proteins, not broken down / stay bound to PIF ; 5 PIF cannot, bind to promoter / start transcription ; 6 of gene(s) that promote, growth / cell division / cell elongation ; Question Answer Marks

10(a) any nine from: 9 1 Na+ / sodium ion, channels open ; 2 Na+ / sodium ions, enter, neurone / axon / (nerve) cell ; 3 membrane (potential) becomes, positive / +40 mV / depolarised ; 4 (repolarisation / after peak) Na+ / sodium ion, channels close ; 5 K+ / potassium ion, channels open ; 6 K+ / potassium ions, leave / move out (of cell) ; 7 membrane (potential) becomes, negative / –90 mV / repolarised ; 8 local circuits ; 9 myelin sheath / Schwann cells, insulates / stops ion movement ; 10 action potential / depolarisation, only occurs at nodes of Ranvier ; 11 saltatory conduction ; 12 fast transmission (of, action potential / impulse) ; 13 one-way transmission (of, action potential / impulse) ; 14 AVP ; © UCLES 2021 Page 20 of 21 10(b) any six from: 6 1 maintain / keep / regulate, internal, environment / conditions ; 2 within, narrow / set, limits or around, optimum value / set point / norm ; 3 low (body) temperature and consequence ; 4 high (body) temperature and consequence ; 5 low blood glucose (concentration) and consequence ; 6 high blood glucose concentration and consequence ; 7 low, (blood) water potential / ψ, and consequence ; 8 high, (blood) water potential / ψ, and consequence ; © UCLES 2021 Page 21 of 21

2(a)(i) any two from: 2 1 no / less, ATP for the, sodium-potassium pump / active transport of Na+ and K+ ; 2 reduces / prevents, (re-establishment of) resting potential ; 3 reduces transmission of action potential (along the axon) ; 2(a)(ii) any two from: 2 1 decreases (speed) / lower (speed than expected) ; 2 in both, nerves / median and peroneal / arm and leg ; 3 processed data quote ; e.g. median mean 43 m s–1 / peroneal mean 31.3 m s–1 4 AVP ; e.g. person 1 not affected so much 2(a)(iii) any two from: 2 1 takes longer for impulses to reach, neuromuscular junction / muscles ; 2 fewer / slower, muscle contractions ; 3 walking problem described ; e.g. reduced muscle control / walks slower / stumbles / trips 4 slower reflexes ; © UCLES 2022 Page 7 of 22 2(b) accept ‘neurone activity’ for ‘balance time’ throughout 4 (had benefit is justified because): 1 (mice with therapy) rate of decline of balance time, slower / less steep, from, 18 to 20 months / initially / at the start or (mice with therapy) have a longer balance time ; (not cure is justified since): 2 (mice with therapy and mice with no therapy) have, same / similar, balance time, at 23 months / at the end or mice with therapy have a, downwards trend / decrease in balance time or mice with therapy have shorter balance time (compared to mice without GAN) ; (results are not affected by age is not justified because): 3 mice without GAN increase balance time, during the experiment / with age or balance time decreases for mice with GAN, during the experiment / with age ; 4 comparative figures to support any marking point or ref. to need for statistical test ; © UCLES 2022 Page 8 of 22

10(a) A – chloroplast ; 3 B – vacuole ; C – cell wall ; A cell surface membrane 10(b) any four from: 4 1 abscisic acid binds to receptors on cell surface membrane (of guard cell) ; 2 proton pumps are inhibited / AW ; 3 stimulates Ca2+ uptake / opens Ca2+ channels ; 4 Ca2+ acts as second messenger ; 5 K+ diffuses out of the (guard) cell ; 6 water potential of (guard) cell increases ; 7 water leaves (guard) cell, by osmosis / down water potential gradient ; 8 (guard) cell becomes flaccid / cell volume decreases (so stoma closes) ; © UCLES 2022 Page 22 of 22

1(a)(i) Eukarya ; 2 Animalia ; 1(a)(ii) any one from: 1 warning to predators / to deter predators ; AVP ; 1(b) any three from: 3 1 Ca2+ (stays) in, cytoplasm / sarcoplasm ; 2 Ca2+, binds / bound, to troponin ; 3 tropomyosin, shifted / does not cover (myosin) binding sites (on actin) ; 4 myosin-actin, cross bridges / bonds, exist / remain ; 5 sarcomere(s) / muscle, contracted / shortened / paralysed ; 1(c) any three from: 3 1 Ca2+, enters / diffuses into, synaptic knob ; 2 through (voltage-gated) calcium (ion) channels ; 3 vesicles containing acetylcholine ; 4 move to / fuse with, presynaptic membrane ; 5 exocytosis of acetylcholine ; © UCLES 2022 Page 7 of 19

10(a) 3 motor sensory 1 transmits impulses from CNS to effector transmits impulses from, receptors / (named) sense and ; organs, to CNS plus two from: motor sensory 2 cell body at end of, neurone / axon cell body, in middle of / part-way along, neurone OR cell and ; body not at end of, neurone / axon 3 cell body in, CNS / brain / spinal cord and cell body in (dorsal root) ganglion ; 4 long axon OR short axon OR and ; axon axon and dendron 5 dendrites attached to cell body and dendrites attached to dendron ; 10(b) any three from: 3 1 no myelin slow and myelin fast(er) / myelin increases speed ; 2 no myelin = 0.5–2 m s–1 and with myelin > 5 / up to 120 m s–1 ; 3 as axon diameter increases speed increases ; 4 diameter (+ units once) and speed (+ units once) for two neurones ; © UCLES 2022 Page 18 of 19 10(c) any three from: 3 A – any one reason from: 1 Na+ / sodium, channels already open OR Na+ has already entered neurone OR no more Na+ channels to open OR less Na+ outside to diffuse in OR less steep Na+ concentration gradient ; B – any one reason from: 2 sodium channels are, inactive / unresponsive OR potassium channels are open OR membrane is, impermeable / less permeable, to Na+ OR membrane is more permeable to K+ ; C – any one reason from: 3 harder to reach threshold OR potassium channels are (still) open OR sodium-potassium pumps need to restore the resting potential ; 4 hyperpolarisation at C ; © UCLES 2022 Page 19 of 19

6(a) G – embryo to aleurone layer ; 2 A – aleurone layer to endosperm ; 6(b) any three from: 3 1 hydrolyses / breaks down / digests / converts, starch / amylose ; 2 in endosperm ; 3 to, maltose / glucose ; 4 (glucose) used by embryo ; 5 (glucose used) for, respiration / growth ; © UCLES 2022 Page 15 of 22 6(c) any four from: 4 accept distilled water for A, 500mg dm-3 for B and 1000mg dm-3 for C. 1 seeds of B and C germinated before seeds of A or seeds soaked in gibberellin germinated before seeds soaked in distilled water ; ora 2 rate of (increase in percentage) germination was, highest in C or higher in C than, B / A or higher as the concentration of gibberellin increases ; ora 3 final / day 10 / maximum (percentage) germination was, highest in C or higher in C than, B / A or higher as the concentration of gibberellin increases ; ora 4 data quote between two groups ; mp1 – A by day 6 and B and C by day 2 mp1 – A germinates four days after B and C ora mp2 – A – 2.2 B – 5.2 C – 9.2, percentage germination day-1 mp3 – A – 22% B – 52% C – 92% mp3 – A to C = 70% more, A to B = 30% more, B to C = 40% more 5 percentage germination in C levels off after 9 days ; 6 AVP ; e.g. no seeds germinate by day 1 © UCLES 2022 Page 16 of 22

8(a) microvilli ; A brush border 1 8(b) no movement of, chemicals / substances / ions, between the, 1 chemoreceptor / cells / (cells) A ; Ignore food A named dissolved substance © UCLES 2022 Page 18 of 22 8(c) any seven from: 7 1. Na+ ions enter, (chemo)receptor cell / A, through, microvilli / Y / channel (proteins) ; 2 cell surface membrane depolarised ; 3 receptor potential ; 4 ref. to threshold ; 5 (voltage-gated) Ca2+ / calcium, channels open ; 6 Ca2+ ions enter, cytoplasm / cell / A ; A presynaptic knob 7 vesicles (of neurotransmitter), move towards / fuse with, cell surface membrane / presynaptic membrane ; 8 exocytosis (described) / secretion, of (named) neurotransmitter ; 9 neurotransmitter binds to receptor on, postsynaptic / (sensory) neurone / B, membrane ; 10 Na+ / sodium, channels open or Na+ enter (sensory) neurone / B ; 11 postsynaptic membrane / (sensory) neurone membrane, depolarised ; 12 ref. to threshold ; allow either mp4 or mp12 © UCLES 2022 Page 19 of 22

6(a) 1 microvilli ; A brush border I papillae 3 2 increase surface area ; 3 (so), more (Na+) channels / more Na+ enter ; © UCLES 2022 Page 15 of 23 6(b) any six from: 6 1 vesicles of neurotransmitter are stimulated to move ; 2 vesicles fuse with, cell surface membrane / presynaptic membrane ; 3 exocytosis (described) / secretion, of (named) neurotransmitter ; 4 neurotransmitter diffuses across, synapse / (synaptic) cleft / gap between cells A and B ; 5 neurotransmitter binds to receptors ; 6 on, cell surface / postsynaptic / (sensory) neurone / B, membrane ; 7 Na+ / sodium, channels open ; 8 Na+ enter, (sensory) neurone / B ; 9 postsynaptic membrane / (sensory) neurone membrane, depolarised ; 10 ref. to threshold ; © UCLES 2022 Page 16 of 23

9(a) A – axon / axoplasm ; 2 B – Schwann cell nucleus ; 9(b) 1 myelinated has faster speed (of transmission of action potential) ; 4 plus any three from: 2 (myelinated) Na+ channels only occur at nodes of Ranvier or (non-myelinated) Na+ channels occur along length of neurone ; 3 (myelinated) depolarisation only occurs at nodes or (non-myelinated) depolarisation occurs along length of neurone ; 4 (myelinated) long local circuits or (non-myelinated) short local circuits ; 5 (myelinated) saltatory conduction / described ; 6 AVP ; e.g. 100 ms–1 v 2 ms–1 © UCLES 2022 Page 21 of 23

9(a) any four from: 4 motor / neurone 1 resting potential higher ; 2 –70 mV (motor) versus –90 mV (muscle) ; 3 smaller change in membrane potential / smaller depolarisation ; 4 110 mV (motor) versus 130 mV (muscle) ; 5 action potential / depolarisation, takes less time / is faster ; 6 (action potential) 2.7 ms (motor) versus 4 ms (muscle) or (depolarisation) 1 ms (motor) versus 2 ms (muscle) ; 7 hyperpolarisation / relative refractory period, occurs ; 9(b)(i) any three from: 3 1 transverse / T- , tubules depolarised ; 2 Ca2+ diffuse out of sarcoplasmic reticulum ; 3 Ca2+ bind to troponin ; 4 tropomyosin, moves from / exposes, binding sites ; 5 for myosin on actin ; 6 cross-bridges form / myosin (head) binds to actin ; © UCLES 2022 Page 18 of 19 9(b)(ii) any one from: 1 1 cross bridges break / myosin heads detach, at different times ; 2 AVP ; Question Answer Marks

9(a) 3 phase of action potential state of voltage-gated channels A 2 C 1 E 3 F 3 G 2 ;;; 5 correct = 3 marks 3/4 correct = 2 marks 1/2 correct = 1 mark 9(b) any three from: 3 1 Schwann cells, wrap around the axon / form the myelin sheath ; 2 insulates (axon) / prevents movement of ions ; 3 depolarisation / action potentials, can only occur at nodes (of Ranvier) ; 4 ref. to long(er) local circuits / (nodes are) 1–3 mm apart ; 5 action potentials, move by saltatory conduction / jump from node to node ; 6 speed of transmission is, fast(er) / 100 m s–1 ; © UCLES 2022 Page 18 of 19

9(a) any four from: 4 motor / neurone 1 resting potential higher ; 2 –70 mV (motor) versus –90 mV (muscle) ; 3 smaller change in membrane potential / smaller depolarisation ; 4 110 mV (motor) versus 130 mV (muscle) ; 5 action potential / depolarisation, takes less time / is faster ; 6 (action potential) 2.7 ms (motor) versus 4 ms (muscle) or (depolarisation) 1 ms (motor) versus 2 ms (muscle) ; 7 hyperpolarisation / relative refractory period, occurs ; 9(b)(i) any three from: 3 1 transverse / T- , tubules depolarised ; 2 Ca2+ diffuse out of sarcoplasmic reticulum ; 3 Ca2+ bind to troponin ; 4 tropomyosin, moves from / exposes, binding sites ; 5 for myosin on actin ; 6 cross-bridges form / myosin (head) binds to actin ; © UCLES 2022 Page 18 of 19 9(b)(ii) any one from: 1 1 cross bridges break / myosin heads detach, at different times ; 2 AVP ; Question Answer Marks

7(a) any four from: 4 1 0.1 g dm–3 chemoreceptor (membrane), is not depolarised / does not release neurotransmitter / remains at resting potential ; 2 so, dendrite / sensory neurone, is not depolarised / remains at resting potential / has no action potential ; 3 1.0 g dm–3 / 10.0 g dm–3, chemoreceptor (membrane), is depolarised / releases neurotransmitter ; 4 so, depolarisation / action potential / impulse, in, dendrite / sensory neurone ; 5 receptor / generator, potential qualified ; 6 ref. to threshold / all or nothing law (in context of either cell) ; 7(b) any three from: 3 sensory motor 1 cell body, between dendron and and cell body, at end / in CNS ; axon / in ganglion 2 has dendron and axon and has (long) axon ; 3 no dendrites from cell body and dendrites extend from cell body ; 4 carries impulses from receptor and carries impulses from, to, CNS / intermediate neurone CNS / intermediate neurone, to effector ; © UCLES 2023 Page 15 of 20

9(a)(i) P pointing to thin filament ; 2 R pointing to thick filament ; 9(a)(ii) A-band – stays the same ; 2 I-band – gets narrower ; © UCLES 2023 Page 17 of 20 9(b)(i) any four from: 4 1 competes with, acetylcholine / neurotransmitter or acetylcholine cannot bind to receptors or blocks receptors ; 2 Na+ channels do not open or no / fewer, sodium ions enter (muscle fibre) ; 3 so, no / less, depolarisation of sarcolemma ; 4 no / fewer, action potentials / impulses (spread across muscle fibre) ; 5 Ca2+ (voltage-gated) channels do not open in sarcoplasmic reticulum or no / fewer, Ca2+ ions released by sarcoplasmic reticulum ; 6 no / fewer, Ca2+ ions bind to troponin or no exposing of binding sites or no / fewer, cross bridges / AW ; 9(b)(ii) any two from: 2 1 affects, rib muscles / intercostal muscles / diaphragm, so unable to breathe ; 2 affects cardiac muscle so, stops blood circulation / heart failure / attack ; 3 cannot move so unable to escape from predators ; 4 cannot eat so starves ; © UCLES 2023 Page 18 of 20

7(a) (pyruvate) – serine ; 2 (oxaloacetate) – asparagine ; 7(b)(i) 1 chloride (ions) / Cl –, not, sodium ions / Na+ (enter post-synaptic neurone) ; 2 2 glycine not choline (re-enters / recycled to, pre-synaptic neurone) OR glycine not, broken down / hydrolysed, but acetylcholine is (in synaptic cleft) ; 7(b)(ii) any two from: 2 1 Cl – decreases, membrane / resting, potential (difference) / voltage ; 2 harder / need more depolarisation, to reach threshold ; 3 glycine is inhibitory ; 7(b)(iii) any four from: 4 1 sodium-potassium pump / active transport ; 2 Na+, out / leaves and K+, in / enters ; 3 three Na+ for two K+ ; 4 some K+ can diffuse out of neurone OR (20) more K+ diffuses out than Na+ diffuses in OR membrane is (20) more permeable to K+ (than Na+) ; 5 inside of, axon / neurone, is more negative (than outside) OR outside of, axon / neurone, is more positive (than inside) ; © UCLES 2023 Page 15 of 17

7(a) any four from: 4 1 respiration rate decreases / less ATP produced ; 2 reduces activity of (named) enzymes / description ; 3 reduces movement of, Ca2+ / Na+ / ACh / neurotransmitter ; 4 (in neuromuscular junction) less / no, acetylcholine broken down acetylcholine remains attached to receptors acetylcholinesterase, less active / inactive ; 5 (in sarcomere) fewer / no, Ca2+ bind to troponin fewer / no, cross bridges formed fewer / no, power stokes ; 6 (in sarcomere) less / no, detachment of myosin heads (from actin) fewer / no, cross bridges broken ATPase / myosin head, less active / inactive hydrolysis of ATP, slower / stops ; 7 AVP ; e.g. shivering / reduced blood flow to muscle / energy diverted for thermoregulation (idea) © UCLES 2023 Page 20 of 25 7(b) any three from: 3 1 Na+ channels don’t open A Na+ do not, diffuse / move, into neurone or stay open ; A Na+ always, diffuse / move, into neurone 2 (axon) membrane, cannot be depolarised or (axon) membrane stays depolarised ; 3 no action potentials, generated / transmitted (along motor neurone) or continuous action potentials, generated / transmitted (along motor neurone) ; 4 Ca2+ does not enter presynaptic knob / vesicles not stimulated to move / no ACh release (at neuromuscular junction) or Ca2+ always enters presynaptic knob / vesicles always stimulated to move / ACh continually released (at neuromuscular junction) ; 5 consequence e.g. paralysis / described or continued muscle contraction ; © UCLES 2023 Page 21 of 25

7(a) any three from: 4 1 opens (voltage-gated) Ca2+ channels in sarcoplasmic reticulum or calcium ions leave sarcoplasmic reticulum ; 2 calcium ions bind to troponin ; 3 troponin changes shape / tropomyosin moves ; 4 exposes binding site on actin ; 5 myosin head, binds to (binding) site / forms cross bridge ; plus 6 myosin head, tilts / AW ; 7 pulls actin / power stroke (so sarcomere shortens) ; © UCLES 2023 Page 18 of 24 7(b) any two from: 4 1 young mice have more (muscle fibres) that are smaller (in diameter) ; ora 2 young mice have smaller range (of diameters of muscle fibres) ; ora 3 comparative data quote ; e.g. number of muscle spread of fibres at mean diameters / m diameter / m young mice 35 at 30 16–44 adult mice 16 at 50 20–80 plus any two from: young mice 4 fewer, (muscle) fibres / myofibrils / sarcomeres ; ora 5 less, muscle protein / actin and myosin ; ora 6 so, weaker contraction / AW ; ora © UCLES 2023 Page 19 of 24

9(a)(i) any four from: 4 1 (dopamine) diffuses across synaptic cleft ; 2 binds to receptors ; 3 on postsynaptic membrane ; 4 Na+ channels open R voltage gated channels or influx of Na+ into post synaptic neurone ; 5 depolarisation of postsynaptic membrane ; 6 ref. threshold ; 9(a)(ii) dopaquinone ; A melanin 1 9(b) any three from: 3 1 Cl – influx makes (inside of postsynaptic neurone) more negative / stays negative ; 2 hyperpolarisation / remains polarised ; 3 (not enough Na+ enter so) less likely to reach threshold ; 4 no depolarisation of (postsynaptic) membrane ; 5 (so) no action potential ; © UCLES 2023 Page 22 of 24

7(a)(i) any four from: 4 both 1 acetylcholine, in / from, vesicles ; 2 many mitochondria ; 3 have presynaptic and postsynaptic membranes ; 4 (synaptic) cleft / gap ; 5 have receptor(s) (for ACh / neurotransmitter) ; 6 presynaptic, Ca2+, entry / channels or postsynaptic Na+, entry / channels ; 7(a)(ii) any three from: 3 1 few(er) Ca2+ ions, leave sarcoplasmic reticulum / enter sarcoplasm ; 2 few(er) Ca2+ ions bind to troponin ; 3 few(er) troponin molecules change shape ; 4 few(er) tropomyosin molecules move ; 5 few(er) myosin-binding sites, uncovered / exposed ; 6 few(er), actin-myosin cross bridges form / myosin (heads) bind to actin ; 7 AVP ; e.g. lack of P leads to less ATP formed i 8 AVP ; e.g. myosin-actin cross-bridges do not break / myosin heads do not reset 7(b) A: adenylyl cyclase ; 2 B: protein kinase A ; Question Answer Marks

7(a) any four from: 4 1 mitochondria produce ATP ; presynaptic knob 2 for production of, acetylcholine / ACh ; 3 for, making / moving, vesicles ; A exocytosis sarcomere 4 active transport of Ca2+ into, sarcoplasmic reticulum ; 5 detachment of myosin heads / break cross bridge or allows myosin head to move back to original position ; 6 AVP ; e.g. ref. to sodium potassium pump / active transport of Ca2+ out of synaptic knob 7(b) X – agree, because Na+ influx leads to depolarisation ; 3 Y – disagree, because Cl– influx leads to hyperpolarisation / description or disagree, because no Na+ influx so no depolarisation ; X and Y – agree, because Na+ (influx) is balanced by Cl– (influx) / AW ; 7(c) any two from: 2 1 decrease in transmission speed ; 2 ref. to shorter local circuits ; 3 no / less, saltatory conduction / described ; © UCLES 2023 Page 14 of 18

7(a)(i) any four from: 4 both 1 acetylcholine, in / from, vesicles ; 2 many mitochondria ; 3 have presynaptic and postsynaptic membranes ; 4 (synaptic) cleft / gap ; 5 have receptor(s) (for ACh / neurotransmitter) ; 6 presynaptic, Ca2+, entry / channels or postsynaptic Na+, entry / channels ; 7(a)(ii) any three from: 3 1 few(er) Ca2+ ions, leave sarcoplasmic reticulum / enter sarcoplasm ; 2 few(er) Ca2+ ions bind to troponin ; 3 few(er) troponin molecules change shape ; 4 few(er) tropomyosin molecules move ; 5 few(er) myosin-binding sites, uncovered / exposed ; 6 few(er), actin-myosin cross bridges form / myosin (heads) bind to actin ; 7 AVP ; e.g. lack of P leads to less ATP formed i 8 AVP ; e.g. myosin-actin cross-bridges do not break / myosin heads do not reset 7(b) A: adenylyl cyclase ; 2 B: protein kinase A ; Question Answer Marks

9(a) any four from: 4 1 (blue) light decreases germination / AW ; 2 as intensity of (blue) light increases percentage germination decreases ; 3 data quote ; light intensity percentage / arbitrary units (au) germination 0 (dark) 98.0 36 76.9 48 45.0 57 14.7 4 (blue) light increases (the concentration of) ABA ; 5 ABA inhibits gibberellin (synthesis / activity) ; 6 any further valid suggestion of ABA action ; e.g. DELLA not broken down / promotes dormancy / stops gene expression © Cambridge University Press & Assessment 2024 Page 18 of 21 9(b) any seven from: 7 1 auxin binds to receptor on the cell surface membrane ; 2 stimulates proton pumps ; 3 protons move from, cytoplasm / cell, to cell wall ; 4 pH of cell wall decreases ; 5 expansins activated ; 6 loosens linkage between cellulose microfibrils ; 7 by breaking hydrogen bonds ; Ignore weakening bonds 8 K+ channels open ; 9 K+ diffuse into, cytoplasm / cell ; 10 water potential (of cytoplasm / cell) decreases ; 11 water enters by osmosis ; 12 increase in turgor pressure / volume of cell increases ; © Cambridge University Press & Assessment 2024 Page 19 of 21

10(a) any four from: 4 1 troponin binds Ca2+ and changes shape ; 2 (so) tropomyosin moves away from the binding sites on actin ; 3 myosin heads, bind to / form cross-bridges, with actin ; 4 myosin head, pulls actin / performs power stroke, to, either shorten / contract, sarcomere or cause Z lines to move closer together / Z lines move closer to M lines ; 5 myosin head, is ATPase / binds to ATP, to allow detachment ; 10(b) any three from: 3 1 succinylcholine binds to ACh receptors or succinylcholine acts as a competitive inhibitor ; R if binds to active site of receptor 2 (sodium ions) channel proteins do not open ; R if voltage gated 3 sodium ions do not enter, muscle cell / sarcoplasm ; 4 sarcolemma / post-synaptic membrane, not depolarised ; © Cambridge University Press & Assessment 2024 Page 20 of 21 10(c) any three from: 3 1 sex-linked / gene on X chromosome ; 2 recessive (allele) ; 3 males only have one, copy of gene / allele / X chromosome ; 4 female heterozygotes, do not have DMD / are carriers or only homozygous females have DMD ; © Cambridge University Press & Assessment 2024 Page 21 of 21

2(a)(i) 1 similarity: both involve a (signalling), chemical / ligand / molecule ; 2 2 difference: endocrine chemical / hormone, travels in blood / circulatory system (but paracrine chemical travels by diffusion) ; 2(a)(ii) 1 (ACh) travels a short distance by diffusion ; 2 2 across, synapse / synaptic cleft / neuromuscular junction ; 2(b) any three conclusions from: 3 1 palmitate-exposed cells, release / secrete, molecule / chemical / substance ; 2 (this) molecule switches on stress genes in, new / other, muscle cells ; 3 molecule is not, destroyed / denatured, by, boiling / high temperature ; 4 (so) molecule is not a protein ; 5 molecule is, lipid / lipid-soluble / hydrophobic / non-polar ; 6 AVP ; 2(c) any three from: 3 1 less actin ; 2 less myosin ; 3 less troponin ; 4 less tropomyosin ; 5 fewer / smaller, sarcomeres / myofibrils / myofilaments / mitochondria / ribosomes ; 6 less of other named protein ; Question Answer Marks

10 any six from: 6 1 sucrose binds to, receptor protein / (chemoreceptor) cell surface receptor ; 2 ref. to second messenger ; 3 (chemoreceptor cell) Na+ entry / membrane depolarises ; 4 receptor / generator, potential ; 5 Ca2+ ions enter (chemoreceptor cell) ; 6 (named) neurotransmitter vesicles, move towards / fuse with, (presynaptic) membrane ; 7 (named) neurotransmitter, release / exocytosis, into (synaptic) cleft ; 8 (named) neurotransmitter binds to receptor on, sensory neurone / postsynaptic membrane ; 9 Na+ enters (through ligand-gated channel) → depolarisation ; 10 ref. to threshold for action potential ; 11 AVP ; © Cambridge University Press & Assessment 2024 Page 15 of 15

8(a)(i) receptor ; 1 8(a)(ii) intermediate neurone ; A relay neurone / motor neurone 1 8(a)(iii) Schwann ; 1 8(b) any four from: 4 differences myelinated neurone 1 faster (impulse transmission) ; ora explanation 2 myelin (sheath), insulates (the axon) / prevents movement of ions ; 3 nodes of Ranvier / gaps with no myelin sheath, have voltage-gated channels or nodes of Ranvier / gaps with no myelin sheath, allow movement of ions ; 4 depolarisation / action potential, occurs only at nodes of Ranvier / gaps with no myelin sheath; ora 5 action potentials jump from node to node / saltatory conduction ; ora 6 longer local circuits / local circuits occur between nodes ; ora 8(c)(i) 1 A voltage-gated and B ligand-gated / not voltage-gated 2 or A opens in response to, depolarisation / arrival of an action potential and B opens in response to binding of, acetylcholine / neurotransmitter ; 2 A for calcium ions and B for sodium ions ; © Cambridge University Press & Assessment 2024 Page 16 of 20 8(c)(ii) any four from: 4 1 no Ca2+ enter (presynaptic, knob / neurone) ; 2 vesicles do not, move towards / fuse with, presynaptic membrane ; 3 no, ACh / neurotransmitter, released or no exocytosis of, ACh / neurotransmitter ; 4 ACh / neurotransmitter, does not bind to, receptor / ion channel B ; 5 Na+ does not enter postsynaptic neurone / ion channel B does not open ; 6 postsynaptic membrane not depolarised or no action potential generated or impulse not transmitted ; 8(c)(iii) any two from: 2 1 inside more negative (charge) or membrane hyperpolarised / membrane potential decreases / potential difference increases ; 2 harder to / cannot, reach threshold ; 3 no depolarisation of membrane / harder to depolarise membrane or no / fewer / harder to generate, action potentials / impulses ; © Cambridge University Press & Assessment 2024 Page 17 of 20

10(a) 2 K ; A ; © Cambridge University Press & Assessment 2024 Page 19 of 20 10(b) any four from: 4 1 sodium (ion) channels open or Na+ enters (axon) ; 2 (so) membrane depolarised ; 3 ref. to threshold (potential) reached (for action potential to occur) ; 4 potassium (ion) channels open or K+ moves out (of axon) ; 5 (causes) repolarisation (of membrane) ; 6 ref. to hyperpolarisation (of membrane) ; 7 return to resting potential ; 8 AVP ; e.g. entry of sodium ions causes more sodium channels to open 10(c) any four from: 4 description 1 myelinated axon / myelination, produces faster transmission speed (than unmyelinated) ; 2 a larger the diameter (for unmyelinated) results in a faster transmission speed ; ora 3 myelination has a greater effect on transmission speed than axon diameter ; explanation 4 (myelinated faster due to) saltatory conduction or action potential jumps from node (of Ranvier) to node ; 5 axons with wider diameter have, less ion leakage / larger surface area / lower resistance ; © Cambridge University Press & Assessment 2024 Page 20 of 20

1(a)(i) A = dendrite(s) ; 3 B = nuclei ; C = synaptic knob(s) ; 1(a)(ii) 1 rat has, myelin sheath / Schwann cell / myelinated axon / myelinated neurone ; 2 2 (rat has) saltatory conduction OR (rat) impulse / action potential, jumps / leaps / AW, from (one) node of Ranvier to, the next / another ; 1(b) any three from: 3 snail / Fig. 1.3 1 greater depolarisation OR (membrane potential) gets more positive / has higher increase / has higher peak ; 2 action potential, slower / takes longer / takes more time OR longer time to return to resting potential ; 3 longer (absolute / relative) refractory period ; 4 longer hyperpolarisation ; 5 AVP ; © Cambridge University Press & Assessment 2024 Page 6 of 15

2(a) any three from: 3 1 open in, day / light ; 2 to take in carbon dioxide for, photosynthesis / light-independent stage / Calvin cycle ; 3 close in, night / dark ; 4 to decrease water loss by transpiration ; 2(b) any six from: 6 1 hydrogen ions / protons / H ions / H+, leave (cell) using, energy / ATP ; 2 low H+ (in cell) / more negative charge ; 3 K+ / potassium ion, channel (proteins) open OR K+, move into / enter, cell (by facilitated diffusion) ; 4 Cl – ions, move into / enter (cell) ; 5 water potential of cell decreases ; 6 water moves in (to cell) by osmosis ; 7 (cells) become turgid / swell / increase in volume / expand ; 8 (guard cell) inner wall thicker / outer wall thinner, so cells, bend / curve ; 2(c) 1 (environment) light needed, to keep cycle normal / to achieve same peak % of stomata opening ; 2 2 genes have a role as (regular), rhythm / pattern / cycle, continues, in darkness / without light ; © Cambridge University Press & Assessment 2024 Page 7 of 15

8(a)(i) X – Schwann (cell) ; Ignore myelin sheath (as not a cell) 2 Y – cell body ; A cytoplasm 8(a)(ii) intermediate neurone ; A relay neurone / sensory neurone 1 8(b) 4 correct order letter of stage 1 C 2 F 3 A 4 E 5 J 6 I 7 G 8 B 9 H 10 D C F A E all above J ; C F A E in correct order ; I G B H between J and D ; I G B H in correct order ; © Cambridge University Press & Assessment 2024 Page 15 of 19 8(c) any four from: 4 allow ‘no’ for ‘less’ or ‘fewer’ 1 less / fewer, Ca2+ enter (pre)synaptic knob ; 2 less / fewer, vesicles, move to / fuse with, presynaptic membrane ; 3 less, ACh released / exocytosis of ACh ; 4 less binding of ACh to receptors (on sarcolemma) ; 5 fewer, Na+ channels open / Na+ enter (muscle fibre) ; 6 less depolarisation of sarcolemma / threshold potential not reached / fewer action potentials generated ; Ignore postsynaptic membrane 7 less Ca2+ released from SR / less binding of Ca2+ to troponin / fewer sites exposed / fewer cross bridges ; Question Answer Marks

1(a)(i) A = dendrite(s) ; 3 B = nuclei ; C = synaptic knob(s) ; 1(a)(ii) 1 rat has, myelin sheath / Schwann cell / myelinated axon / myelinated neurone ; 2 2 (rat has) saltatory conduction OR (rat) impulse / action potential, jumps / leaps / AW, from (one) node of Ranvier to, the next / another ; 1(b) any three from: 3 snail / Fig. 1.3 1 greater depolarisation OR (membrane potential) gets more positive / has higher increase / has higher peak ; 2 action potential, slower / takes longer / takes more time OR longer time to return to resting potential ; 3 longer (absolute / relative) refractory period ; 4 longer hyperpolarisation ; 5 AVP ; © Cambridge University Press & Assessment 2024 Page 6 of 15

2(a) any three from: 3 1 open in, day / light ; 2 to take in carbon dioxide for, photosynthesis / light-independent stage / Calvin cycle ; 3 close in, night / dark ; 4 to decrease water loss by transpiration ; 2(b) any six from: 6 1 hydrogen ions / protons / H ions / H+, leave (cell) using, energy / ATP ; 2 low H+ (in cell) / more negative charge ; 3 K+ / potassium ion, channel (proteins) open OR K+, move into / enter, cell (by facilitated diffusion) ; 4 Cl – ions, move into / enter (cell) ; 5 water potential of cell decreases ; 6 water moves in (to cell) by osmosis ; 7 (cells) become turgid / swell / increase in volume / expand ; 8 (guard cell) inner wall thicker / outer wall thinner, so cells, bend / curve ; 2(c) 1 (environment) light needed, to keep cycle normal / to achieve same peak % of stomata opening ; 2 2 genes have a role as (regular), rhythm / pattern / cycle, continues, in darkness / without light ; © Cambridge University Press & Assessment 2024 Page 7 of 15

10(a) any four from: 4 1 Na+ (ions) enter cell ; 2 through channels / by facilitated diffusion ; 3 depolarisation of cell surface membrane ; 4 reference to, receptor potential / threshold ; 5 Ca2+ channels open / Ca2+ enter cell ; 6 vesicles with neurotransmitter move towards cell surface membrane ; 7 vesicles fuse with cell surface membrane and release neurotransmitter / exocytosis ; 10(b) any three from: 3 1 albino / albinism or described ; e.g. no pigment or melanin in skin / pale skin / white hair 2 poor vision or described ; e.g. red or pink eyes / irises, eyes sensitive to light / jerky eye movements 3 tyrosinase, non-functioning / not produced ; 4 tyrosine not converted to, DOPA / dopaquinone ; 5 no melanin produced ; © Cambridge University Press & Assessment 2025 Page 19 of 19

8 any six from: 6 1 gibberellin binds to (gibberellin) receptor (-enzyme-complex) ; 2 DELLA (protein) destroyed ; 3 transcription factor / PIF, released / free / no longer bound to DELLA ; 4 transcription factor / PIF / RNA polymerase, binds to, DNA / promoter ; 5 growth / expansion / XET / xyloglucan endotransglucosylase, gene, switched on / expressed / transcribed ; 6 loosens cell walls / breaks bonds between cellulose ; 7 water enters (cells) by osmosis causing cell elongation ; 8 AVP ; © Cambridge University Press & Assessment 2025 Page 15 of 17

10(a) causing X / –70 (mV) any three from: 7 1 active transport / sodium-potassium pump ; 2 moves three Na+ out of and two K+ in (to neurone) ; 3 more K+ diffuses out than Na+ diffuses in ; 4 makes outside of membrane (relatively) more positive ; 5 maintaining / establishing, resting potential ; causing Y / +40 (mV) any two from: 6 depolarisation ; 7 Na+ / sodium ion, channels open ; 8 Na+, moves / diffuses, in (to neurone) ; causing Z / –90 (mV) any two from: 9 hyperpolarisation ; 10 (voltage-gated) K+ / potassium ion, channels open ; 11 K+, moves / diffuses, out (of neurone) ; 10(b) 1 local, circuit / current ; 2 2 from, depolarised / positive, area to, resting / negative, area ; 10(c) any three from: 3 1 speeds up (nerve) impulse / impulse transmission faster ; 2 (as) myelin sheath / Schwann cells, act(s) as an insulator ; 3 (as) local circuits flow between, nodes of Ranvier / gaps in sheath ; 4 saltatory conduction ; 5 fast(er), (described) response / muscle contraction ; © Cambridge University Press & Assessment 2025 Page 17 of 17

7(a) any six from: 6 1 sodium–potassium pumps (in axon membrane) ; 2 transport, sodium ions / Na+, out and, potassium ions / K+, in ; 3 by active transport / uses ATP ; 4 three, sodium ions / Na+, and two, potassium ions / K+ ; 5 sets up an electrochemical gradient ; 6 potassium ions / K+, diffuse out through channels ; 7 membrane more permeable to K+ / membrane has more K+ channels ; 8 (so) more, potassium ions / K+, move out of axon than, sodium ions / Na+, move in ; 9 ref. to anions / negatively charged ions / negatively charged proteins, inside ; 10 inside negative (relative to outside) ; 11 -60 mV to -70 mV ; © Cambridge University Press & Assessment 2025 Page 20 of 25 7(b)(i) any three from: 3 hypokalaemia ora for normal 1 longer, action potential / depolarisation / repolarisation or larger depolarisation ; 2 longer hyperpolarisation or more negative / smaller, hyperpolarisation ; 3 longer refractory period ; 4 more negative / lower, resting potential ; 5 data quote ; normal hypokalaemia mp1 longer action potential 2.6 ms 3.25 ms mp1 longer depolarisation 1.0 ms 1.25 ms mp1 longer repolarisation 1.0 ms 1.3 ms mp1 larger depolarisation 110 mV 140 mV mp2 longer hyperpolarisation 0.7 ms 1.0 ms mp2 more negative –92 mV –112 mV hyperpolarisation –22 mV –12 mV mp2 smaller hyperpolarisation mp4 resting potential –70 mV –100 mV © Cambridge University Press & Assessment 2025 Page 21 of 25 7(b)(ii) any two from: 2 1 harder stimulus / larger stimulus / larger depolarisation, needed, to reach threshold required / to generate an action potential ; 2 fewer, impulses / action potentials, transmitted or lower frequency of impulses ; 3 slower, nervous coordination / reaction times / responses / cognition or weaker, sensation / muscle contraction ; allow named examples Question Answer Marks

9(a) any four from: 4 1 use (named) sense organs to detect prey ; 2 faster transmission of, impulses / signals ; 3 (so) faster reaction to stimuli ; 4 ref. to control centre / brain / CNS (decision making) ; 5 faster response or ref. reflexes ; 6 (by) muscles ; 9(b) (if a letter is used more than once, all must be correct) 3 correct position of label and letter for: R ; S ; T ; S S R R T © Cambridge University Press & Assessment 2025 Page 18 of 20 9(c)(i) any three from: 3 increase in curve 1 cross bridges form / myosin heads bind to actin ; 2 power stroke / actin filaments slide over myosin filaments ; 3 bands get, smaller / shorter or decrease in width of sarcomere ; decrease in curve 4 breaking of cross bridges / detachment of myosin heads from actin ; 5 bands get, bigger / longer or increases width of sarcomere ; 9(c)(ii) increase 3 1 calcium ions / Ca2+, released by sarcoplasmic reticulum ; 2 calcium ions / Ca2+, bound to troponin ; decrease 3 calcium ions / Ca2+, pumped back into sarcoplasmic reticulum ; © Cambridge University Press & Assessment 2025 Page 19 of 20

8(a) P to light area ; A on Z line 3 Q to medium area ; A on M line R to darker area ; P R Q P in I band Q in H lightest zone R either side of H zone in A band – darkest – overlap © Cambridge University Press & Assessment 2025 Page 23 of 27 8(b) any four from: 4 1 (at rest) tropomyosin, covers / AW, the binding sites on actin ; R active sites 2 Ca2+ binds to troponin ; 3 troponin changes shape ; 4 (causing) tropomyosin to move ; 5 (so) exposes binding site ; 6 (so) myosin head, binds (to binding sites) / forms crossbridge ; 8(c) any two from: 2 1 no / less, Ca2+ ; 2 no / less, ATP ; 3 no / less, glucose / glycogen ; 4 no / less, oxygen ; 5 build-up / presence of, lactate / lactic acid ; 6 AVP ; e.g. no / less, creatine phosphate © Cambridge University Press & Assessment 2025 Page 24 of 27

5(a) 3 feature ADH glucagon insulin binds to receptors on cell surface ✓ ✓ ✓ ; membranes results in molecules moving from ✓ ✓  ; cells into the blood is secreted as a result of detection by ✓   ; osmoreceptors 5(b) any four from: 4 1 impulses / action potentials / neurotransmitters, in nervous system and hormones in endocrine system ; 2 electrical in nervous system and chemical in endocrine system ; 3 neurones / nerve cells, in nervous system and blood in endocrine system ; 4 effects are / target is, specific / localised, in nervous system and (can be) widespread in endocrine system ; 5 effect / response, happens quickly in nervous system and slowly in endocrine system ; 6 effect / response, lasts a short time in nervous system and long time in endocrine system ; 7 AVP ; 5(c)(i) C ; 1 5(c)(ii) B ; 1 © Cambridge University Press & Assessment 2025 Page 13 of 18 5(c)(iii) 1 (D / it), shortens / contracts / decreases ; 4 and any three from: 2 calcium ions / Ca2+, bind to troponin ; 3 tropomyosin, moves / shifts position / exposes binding sites on actin ; 4 myosin (head) binds to actin / myosin-actin cross-bridges form ; 5 power stroke / myosin head, pulls actin ; 6 more actin, enters / overlaps with, A band / B or more overlap between actin and myosin ; Question Answer Marks

1(a) A oxygen ; 3 B ethanol ; C aerenchyma ; 1(b) ref. to ethanol dehydrogenase (to break it down) ; A alcohol dehydrogenase 1 1(c)(i) as gibberellin concentration increases, the length of stem increases 2 or positive correlation between concentration of gibberellin and length of stem ; data quote – two concentrations and two lengths with units ; conc gibberellin / au length of stem / mm ± 0.5 mm 1 3 2 19 3 27 4 45 5 52 © Cambridge University Press & Assessment 2025 Page 8 of 23 1(c)(ii) any three from : 3 1 ethylene causes break down of ABA, so gibberellin, active / stimulated / functional ; 2 plants grow tall(er) / stems increase in length / stem elongation / increase in internodal length ; 3 (so) leaves / flowers, held above the water ; 4 (so) photosynthesis can occur / increased access to light / AW or (so) gas exchange / reproduction, can occur ; Question Answer Marks

7(a)(i) any one from : 1 soil contains few (named mineral) ions ; located in, shaded areas / areas of low light intensity ; 7(a)(ii) to attract insects ; 1 7(a)(iii) energy / ATP, not wasted (responding to a non-edible object) ; 1 7(a)(iv) (time) for, digestion / enzyme action / absorption / assimilation ; 1 7(b) any three from : 3 1 impulses / action potentials, are discrete events / AW ; 2 impulses / action potentials, are unidirectional ; 3 determines / limits, the frequency of, impulses / action potentials ; 4 AVP ; e.g. 200-300 action potentials per second © Cambridge University Press & Assessment 2025 Page 18 of 23

10(a) any three from : 3 1 myelin sheath / Schwann cells, acts as an insulator / prevents movement of ions ; 2 depolarisation / action potential, only occurs at the nodes ; I impulses 3 action potentials jump from node to node / saltatory conduction ; I impulses 4 long(er) local circuits ; 5 AVP ; e.g. wide axon diameter 10(b) any four from : 4 1 ACh binds to receptors on sarcolemma ; 2 (ligand-gated) Na+ channels open or Na+ enters, muscle cell / sarcoplasm ; 3 sarcolemma depolarised ; 4 depolarisation / action potential, spreads, to / down, T-tubules ; 5 voltage-gated Ca2+ channels open ; 6 Ca2+, diffuse / move, out of sarcoplasmic reticulum (and bind to troponin) ; © Cambridge University Press & Assessment 2025 Page 22 of 23 10(c) any three from : 3 1 (decreased rate of respiration so), no / less, ATP produced ; 2 no / less, Ca2+ pumped back into sarcoplasmic reticulum ; 3 no / less, release of myosin heads from actin / cross bridges broken or no / less, hydrolysis of ATP by myosin head / return of myosin head to original position ; AW 4 sarcomere, permanently contracted / cannot relax ; A paralysis 5 slower sarcomere contraction / less sarcomere shortening / weaker power stroke ; © Cambridge University Press & Assessment 2025 Page 23 of 23

5(a) 3 feature ADH glucagon insulin binds to receptors on cell surface ✓ ✓ ✓ ; membranes results in molecules moving from ✓ ✓  ; cells into the blood is secreted as a result of detection by ✓   ; osmoreceptors 5(b) any four from: 4 1 impulses / action potentials / neurotransmitters, in nervous system and hormones in endocrine system ; 2 electrical in nervous system and chemical in endocrine system ; 3 neurones / nerve cells, in nervous system and blood in endocrine system ; 4 effects are / target is, specific / localised, in nervous system and (can be) widespread in endocrine system ; 5 effect / response, happens quickly in nervous system and slowly in endocrine system ; 6 effect / response, lasts a short time in nervous system and long time in endocrine system ; 7 AVP ; 5(c)(i) C ; 1 5(c)(ii) B ; 1 © Cambridge University Press & Assessment 2025 Page 13 of 18 5(c)(iii) 1 (D / it), shortens / contracts / decreases ; 4 and any three from: 2 calcium ions / Ca2+, bind to troponin ; 3 tropomyosin, moves / shifts position / exposes binding sites on actin ; 4 myosin (head) binds to actin / myosin-actin cross-bridges form ; 5 power stroke / myosin head, pulls actin ; 6 more actin, enters / overlaps with, A band / B or more overlap between actin and myosin ; Question Answer Marks

1(a) 1 A ; 4 2 C ; 3 F ; 4 B ; 1(b) any four from: 4 1 no / less, Ca2+ / calcium ions, enter (synaptic knob / presynaptic neurone) ; 2 no / less, vesicles of acetylcholine, move towards / fuse with / do exocytosis at, presynaptic membrane ; 3 no / less, acetylcholine / ACh, binds to receptors (on postsynaptic membrane) ; 4 no / less, Na+ / sodium ions, enter (postsynaptic neurone) or no / less, depolarisation of postsynaptic membrane ; 5 no / fewer, actions potentials ; Question Answer Marks

5(a) ALLOW one mark if only letters stated in correct order 5 Table 7.1 part of sarcomere description H zone / band ; only myosin present A band ; actin and myosin present I band ; only actin present M line ; attachment for myosin Z disc / line ; attachment for actin © Cambridge University Press & Assessment 2026 Page 15 of 25 5(b) any four from: 4 1 fewer calcium ions absorbed by muscle (fibres) from the blood ; 2 fewer calcium ions released by sarcoplasmic reticulum ; 3 fewer calcium ions bind to troponin ; 4 fewer, myosin head binding sites exposed on actin / myosin heads bind to actin / cross bridges formed ; 5 weaker / fewer / slower, power strokes ; A described 6 weaker / fewer / slower, muscle contraction / sarcomere shortening ; 7 AVP ; e.g. fewer calcium ions so less transmission at neuromuscular junction / release of neurotransmitter © Cambridge University Press & Assessment 2026 Page 16 of 25

3(a)(i) any four from: 4 IGNORE refs. to K+ ions ALLOW mp 3 either in context of 3a or 3b but not twice (morning / opening / width increasing, context) 1 width increases from 1 to 6.5 mm between 06.00 and 1 ALLOW 6.9 for 6.5 mm 11.00 ; 2 so (more) carbon dioxide can, enter / diffuse in ; 3a high / rising, light intensity → high / more, photosynthesis ; (afternoon / night / closing / width decreasing, context) 3b ALLOW in dark / at night / before 06.00, no 3b low / decreasing, light intensity → low / less, photosynthesis photosynthesis ; 4 ECF from mp 1 if peak time or width wrong 4 width decreases from 6.5 to 3 mm between 11.00 and 5 CON prevent / stop, for ‘decrease’ 17.00 ; 5 to, decrease / limit, transpiration / water loss ; 3(a)(ii) any three from: 3 ALLOW ORA throughout 1 K+ ions enter (guard) cell ; 1 CON stoma for ‘cell’ 2 water enters cell, by osmosis / down water potential 2 CON stoma for ‘cell’ but ECF from mp 1 gradient → increase in volume / increase in turgor / cell 3 ALLOW opens for ‘widens’ becomes turgid ; 3 CON guard cell for ‘stoma’ 3 action in mp 1 or 2 causally linked to: widens 3 IGNORE statement of correlation aperture / opens stoma(ta) ; 3(b) any three from: 3 If answer is about when ABA will decrease (not answering question), CON 1 mark then apply ECF after first error ABA concentration is more likely to increase when light If answer states that ABA rises when light intensity is intensity is decreasing because: increasing, CON 1 mark then apply ECF after first error 1 ABA stops H+ moving, out of cell / into cell wall ; 2 (ABA) causes Ca2+ ions to enter, cytoplasm / cell ; 3 (ABA) causes K+ to leave (cytoplasm / cell) ; 3 IGNORE prevent K+ from entering 4 (ABA) leads to, water leaving (cell) / guard cell becoming 4 DO NOT ALLOW guard cell closing flaccid / stomatal closing ; 4 IGNORE prevent stomata from opening © Cambridge University Press & Assessment 2026 Page 11 of 23 Trace ID: PC-791D658355 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a00p/4a1 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9700/41 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

1(a) F ; 4 A ; B ; B and C ; 1(b) any four from: 4 1 (voltage-gated) Na+ channels open and Na+ move in (to axon / neurone) ; 2 (so) depolarisation (of membrane) ; 3 ref. to reaching threshold (potential / value / level / voltage) ; R frequency 4 (voltage-gated) K+ channels open and K+ move out (of axon / neurone) ; 5 (so) repolarisation (of membrane) ; 6 ref. to hyperpolarisation (of membrane) ; Question Answer Marks

6(a) facilitated diffusion ; 1 6(b) 480 ; 2 max 1 if not as a whole number 479.5918367 If standard form incorrect allow max 1 if evidence of 4.7 divided 9.8 6(c) any four from: 4 1 ref. to, many, impulses / action potentials (occurring) or many synapses / many connections between neurones ; 2. ref. to sodium potassium pump / active transport of Na+ and K+ ; R channel 3 setting up / maintaining, ion gradient(s) ; 4 setting up / maintaining, resting potential(s) ; 5 production / recycling, of, neurotransmitters / acetylcholine / ACh ; 6 production / recycling / movement, of vesicles or exocytosis (of neurotransmitter) / endocytosis ; R exocytosis of vesicles 7 production of acetylcholinesterase ; © Cambridge University Press & Assessment 2026 Page 15 of 23 Trace ID: PC-913B5F5E92 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a00p/4a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9700/42 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/ 6(d) any three from: 3 1 (caffeine) binds to (adenosine) receptors ; R active site or inhibits / blocks, binding of adenosine to receptors / AW ; 2 less ATP made during sleep / more ATP made whilst awake ; 3 postsynaptic (neurone) activity is not inhibited / can occur / AW ; 4 (less adenosine bound to receptors) cannot promote sleep / promotes wakefulness / AW ; © Cambridge University Press & Assessment 2026 Page 16 of 23 Trace ID: PC-913B5F5E92 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a00p/4a2 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9700/42 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

1(a) F ; 4 E ; C ; D ; 1(b) any five from: 5 1 ref.to muscles need a large ATP supply / muscles have high respiration rate ; 2 glucose used up / glucose (concentration) becomes low(er) ; 3 glucagon released (by alpha cells in pancreas) ; 4 glycogenolysis / gluconeogenesis (in liver cells) ; A description 5 glucose released into blood / blood glucose (concentration) increases ; 6 ref. to water loss through sweating ; 7 idea of ADH reducing water loss ; A vasopressin 8 AVP ; e.g. adrenaline (on muscle cells / liver cells) causes, glycogenolysis / gluconeogenesis e.g. cortisol causes gluconeogenesis in liver cells / supresses insulin release © Cambridge University Press & Assessment 2026 Page 8 of 20 Trace ID: PC-C51CA5D8F2 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a00p/4a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9700/43 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

8(a) 4 function part of seed gibberellin synthesis embryo ; starch store endosperm ; amylase synthesis aleurone layer ; maltose production endosperm ; 8(b)(i) any three from: 3 1 protons / H+ ions, pumped / actively transported (into cell wall) ; 2 (so) pH (in cell wall) decreases / (cell wall) becomes more acidic ; 3 expansins, activated / AW ; 4 microfibrils (in cellulose) loosen (to allow elongation) ; Ignore weaken 8(b)(ii) any three from: 3 1 K+ / potassium ions, enter, cell / cytoplasm ; R active transport 2 water potential of, cell / cytoplasm, decreases or water potential of the cell wall increases ; 3 water enters (cell through aquaporins) by, osmosis / down the water potential gradient ; 4 cell volume increases / cell expands / increase in turgor pressure (inside cell) ; © Cambridge University Press & Assessment 2026 Page 17 of 20 Trace ID: PC-C51CA5D8F2 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a00p/4a3 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9700/43 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

2(a) 4 ion direction of movement of ion and type of cell action that results from movement of ion K+ into guard cells ; opening of stoma(ta) depolarisation (of presynaptic membrane) Na+ into synaptic knob of presynaptic neurone or action potential generated ; vesicles, move towards / fuse with, (presynaptic) membrane Ca2+ into synaptic knob of presynaptic neurone or exocytosis of acetylcholine / described ; from sarcoplasmic reticulum to sarcoplasm of cell Ca2+ / calcium ion ; binding to troponin of striated muscle 2(b) any four from: 4 1 Na+ concentration in cells, decreases / is low or Na+ concentration gradient formed ; 2 Na+ enter cells from, filtrate / lumen ; 3 ref. to cotransport of glucose (from, filtrate / lumen) into cells ; 4 glucose concentration in cells increases ; 5 glucose moves (out of cells) into the blood ; © Cambridge University Press & Assessment 2026 Page 10 of 22 Trace ID: PC-C13BFDE7F5 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a00p/4a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9700/44 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/

9(a)(i) any four from: 4 1 H+ pumped out of, hinge / midrib, cells or H+ pumped into cell walls ; 2 cell wall, loosens / cross-links broken ; 3 calcium pectate dissolves ; 4 Ca2+ enter cells ; 5 water enters by osmosis ; 6 cells, expand / become turgid ; 7 (lobes) change from convex to concave ; 9(a)(ii) idea that soil contains few, nitrates / (named) ions ; 1 9(b) 4 feature nervous system endocrine system signal impulse hormone ; how neurone ; in blood signal is transmitted type of electrical chemical ; communication duration of short(er) long(er) ; effect © Cambridge University Press & Assessment 2026 Page 20 of 22 Trace ID: PC-C13BFDE7F5 Re-uploading, mirroring or re-hosting this file on any other website or domain is unauthorised and traceable. Licensed for hosting on papacambridge.com only. P97a00p/4a4 CMaarkm Scbhermide gJuene 2·0 2p6 a| Spoaurccea: mpapbarciadmgbreid.gceo.comm 9700/44 Mark Scheme June 2026 Downloaded from PapaCambridge - https://papacambridge.com/