Homeostasis

6(a) 4 response explanation blood vessels near the surface of the skin constrict less heat lost as, less / slower, blood (flow) at, skin / surface ; (narrow) shivering occurs muscle contraction, creates / generates / produces, heat ; hairs rise trapped air, insulates / reduces thermal gradient ; reduction in the production of sweat to stop / decrease, heat loss by evaporation ; 6(b) decrease / less, surface area to, conserve / retain heat 1 or decrease / less, surface area so less heat lost ; 6(c)(i) any three from: 3 1 Sitatunga’s (core / body) temperature (fairly) constant ; 2 Nile monitor’s / lizard’s, (core / body) temperature rises as environmental temperature rises ; 3 figures for two animals at one temperature with units or one animal at two temperatures with units ; 4 AVP ; 6(c)(ii) problem with, catching prey / feeding / avoiding predation ; 1 6(d) 1 ref. to set point / norm(al) / ideal value ; 3 2 rise / fall / change / fluctuation ; 3 reversed / corrected / counter-acted ; © UCLES 2021 Page 11 of 16

6(a)(i) (glyco / lipo) protein ; 1 6(a)(ii) blood ; 1 6(b) glycogenolysis / described ; 2 gluconeogenesis / described ; e.g. glucose from, amino acids / fatty acids 6(c) to reduce ingestion of food 1 or binds to receptor(s) in brain ; 6(d) any three from: 3 1 change in a parameter ; 2 detected by receptor ; 3 coordination / described ; 4 (corrective) action taken by effector ; 5 return to, set point / norm / optimum ; © UCLES 2021 Page 14 of 22 6(e) any two from: 3 1 frameshift / described ; 2 different primary structure / shortened polypeptide ; 3 TF non-functional / TF cannot bind to, DNA / promoter or TF not produced ; 4 gene coding for GLP-1 not expressed ; plus 5 less / no, GLP-1, produced / secreted ; Question Answer Marks

6(a)(i) idea of heat transfer from artery to veins ; 1 6(a)(ii) any one from: 1 vasodilation / description ; R capillaries / blood vessels move to skin surface behavioural response ; e.g. dive down to cooler waters before surfacing for air 6(b)(i) any four from: 4 1 concentration of insulin (relatively) constant for all groups before being fed ; 2 (fasting dolphins) insulin concentration very little change ; 3 (fed dolphins) insulin concentration increases then decreases ; 4 (fed dolphins) for 11 g / kg dolphins steep, increase / decrease, in insulin concentration ; 5 (fed dolphins) for 11 g / kg dolphins high(est) peak in insulin concentration ; 6 data quote for mp3 or mp4 with time in min ; 3 kg 21 at 0 min 30 at 180 min 20 at 240 min 11 kg 10 at 0 min 79 at 90 min 18 at 480 min 6(b)(ii) 79−10 2 ; 90 = 0.77 ; © UCLES 2021 Page 14 of 22 6(c) any three from: 3 1 change in a parameter ; 2 detected by receptor ; 3 coordination / described ; 4 (corrective) action taken by effector ; 5 return to, set point / norm / optimum ; © UCLES 2021 Page 15 of 22

1(a) 4 description letter efferent blood vessel B ; part of nephron containing cells that respond to ADH F, G ; part of nephron where podocyte cells are located C ; part of nephron containing cells that are located in the medulla E, G ; 1(b) any five from: 5 1 microvilli / basal membrane folds, increase / give large, surface area ; 2 for / many, (named) transport proteins ; 3 Na+ / sodium ions, and, glucose / amino acids, move / co-transported, into cell (from filtrate / lumen) ; 4 Na+ / sodium ions, pumped / move (out of cell) to, blood / tissue fluid ; 5 ref. to active transport ; 6 many mitochondria, give / for, energy / ATP ; 7 tight junctions and reason ; 1(c)(i) any two from: 2 1 as water potential (of blood) increases concentration of ADH (in the blood) decreases ; 2 two ADH figures related to two % change in water potential figures ; 3 between 0% and (+)10% change in water potential, ADH (concentration), does not change / is constant / stays the same / plateaus ; © UCLES 2021 Page 5 of 21 1(c)(ii) blood, volume / pressure, decreases ; 1 Question Answer Marks

1(a) 4 feature letter glomerular filtrate E ; basement membrane C ; podocyte cells D ; capillary endothelial cell A ; 1(b) any five from: 5 1 afferent arteriole, (lumen) wider / has larger diameter, than efferent ; 2 causes high, blood / hydrostatic, pressure in, glomerulus / capillaries ; 3 pores / gaps / fenestrations, in capillary endothelium ; I holes in cells 4 basement membrane acts as a filter / AW ; 5 detail of podocytes ; e.g. finger-like structures / folds / slit pores 6 correct ref. to passage of substances ; e.g. basement membrane stops, blood cells / large proteins / molecules above RMM 68 000–70 000 or allows urea / glucose / amino acids / ions / water 7 idea of network of capillaries ; 1(c)(i) any two from: 2 1 as (mean arterial blood) pressure increases the GFR increases, levels off and increases / AW ; 2 (plateau occurs) at 100 cm3 min–1 / between 10 and 20 kPa ; 3 AVP ; e.g. plateau is normal or healthy value © UCLES 2021 Page 5 of 24 1(c)(ii) any one from: 1 1 kidney, damage / disease / cancer ; 2 dehydration ; 3 low, blood / hydrostatic, pressure or blood loss ; 4 AVP ; e.g. other (relevant) disease Question Answer Marks

9(a) any nine from: 9 1 hypothalamus / osmoreceptors, detects changes in water potential of blood ; 2 (causes) posterior pituitary gland ; 3 (to) release ADH into blood ; 4 ADH binds to receptors ; 5 on cell surface membrane of collecting duct (cells) ; 6 stimulates enzyme cascade / phosphorylase enzyme produced ; 7 vesicles, move towards / fuse with, cell surface membrane ; 8 (vesicles have) aquaporins ; 9 collecting duct, membranes / cells / walls, more permeable to water ; 10 water moves, down water potential gradient / by osmosis ; 11 into, (collecting duct) cells / tissue fluid / blood ; 12 water potential (of blood) returns to set point ; © UCLES 2021 Page 21 of 24 9(b) any six from: 6 1 dendrites attached to cell body ; 2 nucleus in, cell body / soma ; 3 many mitochondria ; 4 much rough endoplasmic reticulum / Nissl’s granules (in cell body) ; 5 long axon ; 6 synaptic knobs / synaptic bulbs / terminal branches / axon terminals ; 7 Schwann cells / myelin sheath / myelinated ; 8 nodes of Ranvier ; 9 cell body in, CNS / brain and spinal cord ; accept from labelled diagram if sensory neurone described – max 5 © UCLES 2021 Page 22 of 24

1(a) 4 description letter efferent blood vessel B ; part of nephron containing cells that respond to ADH F, G ; part of nephron where podocyte cells are located C ; part of nephron containing cells that are located in the medulla E, G ; 1(b) any five from: 5 1 microvilli / basal membrane folds, increase / give large, surface area ; 2 for / many, (named) transport proteins ; 3 Na+ / sodium ions, and, glucose / amino acids, move / co-transported, into cell (from filtrate / lumen) ; 4 Na+ / sodium ions, pumped / move (out of cell) to, blood / tissue fluid ; 5 ref. to active transport ; 6 many mitochondria, give / for, energy / ATP ; 7 tight junctions and reason ; 1(c)(i) any two from: 2 1 as water potential (of blood) increases concentration of ADH (in the blood) decreases ; 2 two ADH figures related to two % change in water potential figures ; 3 between 0% and (+)10% change in water potential, ADH (concentration), does not change / is constant / stays the same / plateaus ; © UCLES 2021 Page 5 of 21 1(c)(ii) blood, volume / pressure, decreases ; 1 Question Answer Marks

3(a) any five from: 5 max four from mp1–mp6: 1 (sickle cell anaemia is) homozygous recessive ; 2 ref. to beta / β, globin / polypeptide or HBB (allele / gene) ; 3 base / nucleotide, substitution or mis-sense mutation or change in, triplet / codon or GAG to GTG / A to T ; 4 causes, change in amino acid (sequence) / glutamic acid to valine ; 5 valine is non-polar ; 6 causes change in, 3D shape / tertiary structure / quaternary structure / globular structure (of haemoglobin) ; 7 haemoglobin has lower affinity for oxygen ; 8 (in red blood cells) haemoglobin, less soluble / sticks together / forms fibres ; 9 (red blood) cells become sickle shaped ; © UCLES 2022 Page 9 of 22 3(b)(i) decrease (in ADH) (accept no ADH secreted) 1 and reduce water reabsorption (in the collecting duct) or decrease (in ADH) and increased volume of / more dilute, urine (formed) ; 3(b)(ii) idea that fluid / water, is forced (from blood) into alveoli ; R diffusion / osmosis 1 3(c) any four from: 4 describe: 1 having kidney disease increases the risk of TACO ; ora 2 AKI has highest risk (of TACO) ; 3 data quote to support mp1 (comparison) ; reasons: 4 kidney disease reduces ability to remove excess water ; 5 more water retained increases blood volume ; 6 AVP ; e.g. CKD + D less risk as dialysis helps to restore water volume © UCLES 2022 Page 10 of 22 3(d) any two from: 3 1 fewer sodium (ions) reabsorbed / more sodium (ions) in filtrate ; 2 decreases water potential of filtrate or increases water potential of the medulla ; 3 less water reabsorbed, by osmosis / down water potential gradient ; 4 increases volume of urine ; plus: 5 so blood volume (from transfusion) is reduced ; © UCLES 2022 Page 11 of 22

6(a) homeostasis / negative feedback ; 1 6(b)(i) blood(stream) / circulation ; 1 6(b)(ii) A – adenyl,(-yl) / (-ate), cyclase ; 2 B – cyclic AMP / cAMP ; 6(b)(iii) amplifies signal / expands message ; 1 6(b)(iv) break down glycogen / glycogen  glucose / glycogenolysis ; 1 6(c) any four from: 4 1 blood on, pad / strip, inserted into, biosensor / glucometer ; 2 glucose oxidase ; 3 (glucose)  gluconic acid and hydrogen peroxide ; 4 (electric) current / flow of electrons / voltage ; 5 (current) proportional to glucose, quantity / concentration ; 6 digital / numerical, reading (on screen) ; © UCLES 2022 Page 13 of 19

9(a) to generate a high, blood pressure / hydrostatic pressure ; 2 Ignore to increase the blood pressure to force, plasma / fluid / water, through basement membrane / into the Bowman’s capsule / into lumen ; R osmosis / diffuse Ignore named substance e.g. glucose 9(b)(i) A – basement membrane ; 2 B – podocyte ; 9(b)(ii) any three from: 3 A basement membrane 1 acts as a, filter / filtration barrier ; 2 only, named molecules / ions / molecules less than 68 000–70 000 (R)MM, can pass through or red blood cells / large proteins, cannot pass through ; B podocyte 3 has, gaps / slits / projections / pores ; 4 allows, fluid / water / filtrate, to pass into the, lumen / Bowman’s capsule ; 5 produces, A / basement membrane ; © UCLES 2022 Page 20 of 22

1(a)(i) 1 loop of Henle ; 2 2 collecting duct ; 1(a)(ii) antidiuretic hormone / ADH ; A vasopressin 1 1(a)(iii) 1 as the RMT increases the concentration of urine increases ; A positive correlation 4 2 two pairs of comparative figures ; RMT urine conc. beaver 1.4 0.90 kangaroo rat 8.6 10.50 any three from: kangaroo rat 3 little water available / AW ; Ignore desert Ignore rivers & lakes for ora 4 loop of Henle / collecting duct, is longer ; 5 (so) more reabsorption of water occurs ; Ignore retaining more water 6 (so) urine (of kangaroo rat) more concentrated / small volume of urine ; allow ora for beaver © UCLES 2022 Page 5 of 23 1(b) any two from: 2 1 ref. to metabolic water / water from respiration ; 2 it obtains water through the (named) food it eats ; 3 AVP ; e.g. behavioural response / no or less sweating © UCLES 2022 Page 6 of 23

10(a)(i) any three from: 3 1 as the, blood glucose / glucose concentration, increases the, blood insulin / insulin concentration, increases ; A positive correlation 2 data quote with unit ; data quote for mp1 time of day blood glucose conc / mmol dm–3 time of day blood insulin conc / pmol dm–3 ±1.5 min ±0.025 ±1.5 min ±1 07.00 4.3 07.15 30 08.00 6.2 08.00 280 data quote for mp5 time of day blood glucose conc / mmol dm–3 time of day blood insulin conc / pmol dm–3 ±1.5 min ±0.025 ±1.5 min ±1 08.00 6.2 08.00 280 09.00 4.45 09.00 120 3 increase in, blood glucose / glucose concentration, causes release of insulin (from pancreas) ; ora 4 insulin stimulates the conversion of glucose to glycogen / glycogenesis or insulin increases permeability (of liver / muscle) cells to glucose / AW ; 5 insulin causes, blood glucose / glucose concentration, to return back to set point ; 6 ref. to negative feedback ; © UCLES 2022 Page 22 of 23 10(a)(ii) any three from: 3 max 2 if only glucose or insulin curve mentioned 1 ref. to delay before both graphs increase / AW ; 2 peaks for both would be lower ; 3 both curves would take longer to decrease ; 4 time is needed for starch to be, broken down / converted (to glucose) ; 5 to glucose ; 10(b) any four from: 4 1 ref. to adenylyl cyclase ; 2 formation of, cyclic AMP / cAMP ; 3 cAMP acts as a second messenger ; 4 activation of (protein) kinase ; 5 enzyme cascade ; 6 amplification of signal ; 7 glycogenolysis / gluconeogenesis / described ; 8 glucose released into blood ; © UCLES 2022 Page 23 of 23

8(a) A – distal convoluted tub(ul)e ; 3 B – cortex ; C – loop of Henlé ; © UCLES 2022 Page 16 of 19 8(b) any three from: 3 1 as ADH concentration increases urine concentration increases ; 2 as ADH concentration increases urine flow rate decreases ; 3 as urine flow rate decreases urine concentration increases ; 4 data quote with units ; 5 AVP ; 8(c) any five from: 5 1 ADH binds to cell, surface / membrane, receptor (of collecting duct cells) ; 2 ref. G protein / adenyl(ate) cyclase ; 3 second messenger / cAMP ; 4 protein kinase activated ; 5 vesicles, move towards / fuse with, cell (surface) membrane ; 6 correct ref. aquaporins ; 7 collecting duct / cells / membrane, (more) permeable to water ; 8 more water, leaves, lumen / nephron or more water enters, blood / medulla ; © UCLES 2022 Page 17 of 19

10 1 internal ; 5 2 negative feedback ; 3 receptor(s) ; 4 endocrine / islets of Langerhans /  and  ; 5 glycogen ; © UCLES 2022 Page 19 of 19

8(a) C pointing to the microvilli adjacent to the proximal convoluted tubule lumen ; 2 P pointing to the basal membrane adjacent to the blood capillary ; label line must touch a membrane (not a space) 8(b) any five from: 5 1 microvilli for large surface area (for reabsorption) ; 2 (large surface area) for many, cotransporters / carrier proteins ; 3 cotransporter (proteins) to absorb sodium ions with, glucose / amino acids ; A idea of secondary active transport 4 tight junctions between cells so substances have to pass through the cells / AW ; 5 many mitochondria to produce ATP ; 6 (ATP) for the sodium (potassium) pumps or (ATP) to pump / actively transport, sodium ions (into the blood) ; 7 folded basal membrane for many sodium (potassium) pumps ; 8(c) 2.00 2 ; 0.03 67 ; 2.00–0.03 if given then accept 66 ecf for second mark point only 0.03 © UCLES 2022 Page 17 of 19

10(a) any four from: 4 1 decreasing / low, blood glucose concentration causes, increase in glucagon concentration / glucagon secretion ; 2 glucagon acts on liver cells ; 3 glycogenolysis / described ; R is glucagon breaks down glycogen 4 gluconeogenesis / described ; 5 so, glucose is released into the blood / blood glucose concentration increases ; 6 ref. to negative feedback ; 10(b) complementary ; 3 G-protein ; adenyl(yl) cyclase ; © UCLES 2022 Page 19 of 19

8(a) A – distal convoluted tub(ul)e ; 3 B – cortex ; C – loop of Henlé ; © UCLES 2022 Page 16 of 19 8(b) any three from: 3 1 as ADH concentration increases urine concentration increases ; 2 as ADH concentration increases urine flow rate decreases ; 3 as urine flow rate decreases urine concentration increases ; 4 data quote with units ; 5 AVP ; 8(c) any five from: 5 1 ADH binds to cell, surface / membrane, receptor (of collecting duct cells) ; 2 ref. G protein / adenyl(ate) cyclase ; 3 second messenger / cAMP ; 4 protein kinase activated ; 5 vesicles, move towards / fuse with, cell (surface) membrane ; 6 correct ref. aquaporins ; 7 collecting duct / cells / membrane, (more) permeable to water ; 8 more water, leaves, lumen / nephron or more water enters, blood / medulla ; © UCLES 2022 Page 17 of 19

10 1 internal ; 5 2 negative feedback ; 3 receptor(s) ; 4 endocrine / islets of Langerhans /  and  ; 5 glycogen ; © UCLES 2022 Page 19 of 19

1(a) 4 region of kidney location of loops of Henle C ; location of Bowman’s capsules A ; location of glomeruli A ; contains urine at final concentration B + D ; 1(b) any three from: 3 1 (aquaporins are) water channel (proteins) ; 2 (more) aquaporins increase (cell surface) membrane permeability (to water) ; ora 3 of collecting duct (cells) ; I distal convoluted tubule cells 4 allow water to, be reabsorbed / move into tissue fluid or blood ; 1(c) any three from: 3 1 detected by osmoreceptors ; 2 in hypothalamus ; 3 (osmoreceptors send) fewer impulses to posterior pituitary ; I signals 4 less ADH, released / produced ; I no ADH released © UCLES 2023 Page 5 of 20

5(a)(i) A = glomerulus ; 2 B = Bowman’s capsule ; 5(a)(ii) any four from: 4 1 ultrafiltration ; 2 high(er) pressure due to afferent arteriole wider than efferent arteriole ; 3 capillary endothelium has, fenestrations / gaps / holes / pores ; 4 small molecules / (named) ions / glucose / amino acids / urea / water, and EITHER leave, blood / plasma / capillary / glomerulus OR enter, capsule / filtrate / tubule ; 5 basement membrane forms, (main) filtration / selective, barrier ; 6 (R)MM / M, limit of, 68 000 to 70 000 (Da) / 68–70 kDa ; r 7 podocytes, form slit pores / support basement membrane ; 5(b)(i) C adenyl(yl) cyclase ; 2 D c(yclic) AMP ; 5(b)(ii) any four from: 4 1 in both as Na+ concentration increases ADH concentration increases (after a, certain / stated, point) ; 2 in, type C / SIAD, ADH rise occurs at a lower Na+ concentration ; 3 comparative figures ; 4 (ADH ) more aquaporins / greater permeability to water, in collecting duct / DCT ; 5 (C / SIAD / ADH ) more water reabsorbed, at collecting duct / at DCT / into blood ; 6 (C / SIAD / ADH ) small(er) volume of / (more) concentrated, urine ; 7 type C / SIAD, causes, high blood water potential / low blood Na+ concentration ; Question Answer Marks

6(a) 2 F P 6(b)(i) 11852 11852 11852 3 or or ; 60 69 51 1.1 or 1.0 or 1.3 ; cm3 min–1 y–1 ; A cm3 min–1 / year A year(s) –1 R yr or yrs or mins © UCLES 2023 Page 17 of 25 6(b)(ii) any three from: 3 1 high(er), hydrostatic / blood, pressure causes higher GFR ; ora 2 water / solute, potential gradient between glomerulus and Bowman’s capsule affects GFR ; 3 kidney disease / named, decreases GFR ; e.g. damage to nephron or basement membrane / cancer 4 dehydration / lower water potential of blood, decreases GFR ; ora 5 high altitude decreases GFR ; ora 6 drugs / named, affects GFR ; e.g. diuretics / beta blockers / vasodilators / NSAIDS / ACE inhibitors 7 larger difference between afferent arteriole lumen and efferent causes higher GFR ; ora © UCLES 2023 Page 18 of 25 6(c) any seven from: 7 1 Na+, actively transported / pumped, out of cells ; 2 Na+ enter blood ; 3 Na+ concentration in cells decreases or Na+ concentration gradient (between pct lumen and cytoplasm) / described ; 4 Na+ enter cells from, filtrate / lumen ; 5 by facilitated diffusion ; 6 cotransport of, glucose / amino acids ; I secondary active transport 7 water potential of cells decreases ; 8 water enters cells from (filtrate / lumen) by, osmosis / down the water potential gradient ; 9 glucose / amino acids, leave cells by, (facilitated) diffusion / described ; 10 glucose / amino acids, reabsorbed or move into , tissue fluid / blood ; 11 AVP ; e.g. other named ions reabsorbed © UCLES 2023 Page 19 of 25

9(a) glands ; 6 cell surface membrane / plasma membrane ; A liver (cells) second messenger / cAMP ; A enzyme cascade / phosphorylation of enzymes / signalling cascade (striated) muscles ; collecting duct ; homeostasis ; 9(b)(i) 1 insulin, produced / released ; 3 2 increase in uptake of glucose into cells ; 3 detail of uptake ; e.g. increase permeability of cell surface membrane (to glucose) / GLUT added to cell surface membrane 4 increase / stimulates, respiration of glucose (in cells) / phosphorylation of glucose ; 5 (stimulates) glycogenesis / conversion of glucose to lipids ; 9(b)(ii) ref. glucagon ; 1 © UCLES 2023 Page 24 of 25

6(a) A – endothelial cell ; 3 B – basement membrane ; C – podocyte ; © UCLES 2023 Page 15 of 24 6(b) any two from: 2 1 acts as the filter ; 2 prevents molecules more than 68 000 – 70 000 MM from passing through ; ora 3 stops, large (plasma) proteins / red blood cells ; 6(c) 1801.4 2  100 180 or 178.6  100 ; 180 99.2 ; © UCLES 2023 Page 16 of 24 6(d) any seven from: 7 1 ADH, acts as / is, a cell signalling molecule ; 2 ADH binds to receptors ; 3 on cell surface membrane (of collecting duct cells) ; I activates G protein 4 cAMP / second messenger, produced ; 5 enzyme cascade / activation of kinase ; 6 vesicles / aquaporins, phosphorylated / activated ; 7 vesicles (with aquaporins) move towards cell surface membrane ; 8 aquaporins added to (cell surface) membrane ; 9 increases, cell / membrane, permeability to water ; 10 water moves out (of collecting duct), by osmosis / description ; 11 into, (collecting duct) cells / tissue fluid / blood ; I water is reabsorbed as in Q © UCLES 2023 Page 17 of 24

3(a) 1 (q2 = 440 or q2 = 0.4 ) 3 1100 q = √0.4 or q = 0.632455532 ; 2 (p = 1 – 0.632455532 or p = 0.367544468) 2pq = 2 x 0.632455532  0.367544468 or 2pq = 0.4649110641 ; 3 (heterozygotes = 2pq  1100 e.g. 511.4 or 511.5 or 511.6672 ) 511 / 512 ; 3(b) any two from: 2 1 colours / shades / categories / phenotypes, not distinct / not discrete / overlap / form a (gradual) range / include intermediates ; 2 >1 / 4 / several / many, genes ; 3 environment affects, it / colour / phenotype ; 3(c)(i) any two from: 2 1 (as climate changes) increase in CO concentration causes, stomatal aperture to decrease / stomata to be less open ; 2 2 less water, lost / evaporated / transpired (though stomata) ; 3 compensates for / allows survival in, low water availability / dry conditions ; © UCLES 2023 Page 9 of 16 3(c)(ii) any four from: 4 1 (abscisic acid / ABA) binds to receptor on, (guard) cell surface membrane ; 2 H+ stops moving, out of cell / into cell wall ; 3 Ca2+ ions enter, cytoplasm / cell or Ca2+ ions act as second messenger ; 4 K+ ions leave cell ; 5 water leaves cell, by osmosis / down water potential gradient ; 6 less turgid / flaccid, guard cell(s) close stoma(ta) ; 3(d)(i) any two from: 3 1 0.1, (mol) increases / gives higher, rate (compared to control / normal) ; 2 1(.0) and 10(.0), (mol) decrease / give lower, rate (compared to control / normal) ; 3 10(.0) (mol) rate, stays (approx.) constant / plateaus / does not increase, over, time / (6) days ; 4 data quote comparing rate at two concentrations on one day or data quote comparing rate on two different days for 10 mol ; 3(d)(ii) 1 protons / H+ (ions) ; 2 2 cellulose ; Question Answer Marks

6(a)(i) P: receptor ; 4 Q: adenyl(yl) cyclase ; R: G-protein ; S: cyclic AMP / cAMP ; © UCLES 2023 Page 12 of 18 6(a)(ii) 3 process effect on rate of process when blood glucose concentration decreases glycogenolysis increase glycogenesis decrease glycolysis decrease fatty acid synthesis decrease ;;; 4 correct = 3 marks 3 correct = 2 marks 1/2 correct = 1 mark 6(b) any four from: 7 1 strip contains glucose oxidase and peroxidase ; 2 strip dipped into urine ; 3 glucose (and oxygen) reacts with glucose oxidase to produce hydrogen peroxide ; 4 hydrogen peroxide reacts with peroxidase to produce a colour change ; 5 colour is matched with a colour chart to give, reading / estimate, of glucose concentration ; any three from: 6 quick(er) ; 7 (more) sensitive / accurate / precise ; 8 gives immediate reading ; 9 results can be stored electronically / can be connected to smart phone / AW ; 10 numerical / digital / quantitative / objective ; 11 reusable ; © UCLES 2023 Page 13 of 18

9(a) any four from: 4 1 (drink of water causes) increase in blood water potential / AW ; 2 detected by, osmoreceptors / hypothalamus ; 3 causes decrease in release of ADH (into blood in first hour) ; 4 less water reabsorbed (from collecting ducts) ; 5 (so) decrease in blood water potential / blood water potential returns to set point ; 6 causes increase in release of ADH ; 7 negative feedback ; © UCLES 2023 Page 16 of 18 9(b) any four from: 4 nervous system endocrine system 1 communication action potential / impulse and hormone ; 2 nature of electrical (and chemical) and chemical ; communication 3 mode of neurone and blood ; transmission 4 response muscle and target, organs / tissue / cells ; destination 5 transmission fast(er) and slow(er) ; speed 6 location of specific / localised and (can be) widespread ; effect 7 response speed fast(er) and slow(er) ; 8 duration of short-lived / temporary and can be long-lasting / permanent ; effect © UCLES 2023 Page 17 of 18

3(a) 1 (q2 = 440 or q2 = 0.4 ) 3 1100 q = √0.4 or q = 0.632455532 ; 2 (p = 1 – 0.632455532 or p = 0.367544468) 2pq = 2 x 0.632455532  0.367544468 or 2pq = 0.4649110641 ; 3 (heterozygotes = 2pq  1100 e.g. 511.4 or 511.5 or 511.6672 ) 511 / 512 ; 3(b) any two from: 2 1 colours / shades / categories / phenotypes, not distinct / not discrete / overlap / form a (gradual) range / include intermediates ; 2 >1 / 4 / several / many, genes ; 3 environment affects, it / colour / phenotype ; 3(c)(i) any two from: 2 1 (as climate changes) increase in CO concentration causes, stomatal aperture to decrease / stomata to be less open ; 2 2 less water, lost / evaporated / transpired (though stomata) ; 3 compensates for / allows survival in, low water availability / dry conditions ; © UCLES 2023 Page 9 of 16 3(c)(ii) any four from: 4 1 (abscisic acid / ABA) binds to receptor on, (guard) cell surface membrane ; 2 H+ stops moving, out of cell / into cell wall ; 3 Ca2+ ions enter, cytoplasm / cell or Ca2+ ions act as second messenger ; 4 K+ ions leave cell ; 5 water leaves cell, by osmosis / down water potential gradient ; 6 less turgid / flaccid, guard cell(s) close stoma(ta) ; 3(d)(i) any two from: 3 1 0.1, (mol) increases / gives higher, rate (compared to control / normal) ; 2 1(.0) and 10(.0), (mol) decrease / give lower, rate (compared to control / normal) ; 3 10(.0) (mol) rate, stays (approx.) constant / plateaus / does not increase, over, time / (6) days ; 4 data quote comparing rate at two concentrations on one day or data quote comparing rate on two different days for 10 mol ; 3(d)(ii) 1 protons / H+ (ions) ; 2 2 cellulose ; Question Answer Marks

1(a) A – label line to collecting duct ; 4 B – label line to inner part of Bowman’s capsule ; C – label line to, loop of Henle / part of collecting duct below level of convoluted tubules ; D – label line to wider blood vessel entering Bowman’s capsule ; 1(b) any four from: 4 1 microvilli, for large surface area / increases surface area (for reabsorption) ; 2 cotransporter (proteins) for movement of, glucose / amino acids (with sodium ions) ; 3 tight junctions / described, to, stop substances passing in between cells / cause substances to pass though cells ; 4 many mitochondria to provide ATP for, active transport / pumping of Na+ ; 5 folded basal membrane for many sodium (potassium) pumps ; © Cambridge University Press & Assessment 2024 Page 5 of 21

3(a) any four from: 4 1 protons / H+ ions, pumped, from guard cells / into guard cell wall ; 2 ref. to negative potential (inside cell) or Cl – ions enter (cell) ; 3 (voltage-gated) K+ channels open or K+ ions enter (guard) cells ; 4 water enters cell, by osmosis / down water potential gradient ; 5 (guard) cells, become turgid / swell / increase in volume ; © Cambridge University Press & Assessment 2024 Page 7 of 15 3(b)(i) any two from: 2 1 as abscisic acid concentration increases stomatal conductance decreases or negative correlation / inverse correlation / inversely proportional ; 2 two sets of x y figures to support mp 1 with units (at least once) ; 3 steep decrease in conductance to 100–150 ABA ; 4 no / little, effect on conductance above 250–425 ABA ; 3(b)(ii) any four from: 4 1 ABA causes stomata to close ; 2 ABA binds to receptor on guard cell ; 3 Ca2+ ions, enter (guard) cells / act as 2nd messenger ; 4 K+ ions leave (guard) cells ; 5 water leaves so cells become, flaccid / less turgid ; 6 AVP ; 3(c) DNA / promoter ; 1 Question Answer Marks

1(a)(i) hypothalamus ; 1 1(a)(ii) (changes in) water potential (of blood) ; A  1 1(a)(iii) posterior pituitary (gland) ; 1 1(b)(i) 61.5(%) ;; 2 61.538461 allow one mark for not rounding to one decimal place 1(b)(ii) any three from: 3 1 (increase in ADH results in) aquaporins added to, cell surface membrane / luminal membrane / plasma membrane ; 2 more water leaves, filtrate / collecting duct or more water reabsorbed / more water enters blood or tissue fluid ; 3 so urine, volume decreases / concentration increases ; 4 AVP ; e.g. ADH binds to receptor / increase in permeability of (cell surface) membrane / ref. to water moving, down a water potential gradient or by osmosis I descriptions © Cambridge University Press & Assessment 2024 Page 5 of 20

10(a) negative feedback ; 1 10(b) any three from: 3 1 (blood) glucose concentration decreases due to increased respiration or (blood) glucose concentration decreases due to glucose used to generate ATP for, muscle contraction / movement / exercise ; 2 glucagon released (from pancreas) ; 3 glucagon acts on liver cells ; 4 glycogenolysis occurs / description ; 5 glucose released into blood so (blood) glucose concentration, increases / returns to set point ; 6 AVP ; e.g. gluconeogenesis / ref. cell signalling 10(c)(i) A – gluconic acid / gluconolactone ; 2 B – chromogen ; 10(c)(ii) any two from: 2 1 measures, current / direct, blood glucose concentration ; 2 accurate reading / quantitative / numerical / digital ; 3 reusable ; 4 AVP ; e.g. can use regularly / convenient digital store of data / connected to phone or surgery © Cambridge University Press & Assessment 2024 Page 20 of 20

1(a) A – G protein ; 3 B – cyclic AMP / cAMP ; C – aquaporin ; I water channel 1(b) any three from: 3 1 dehydration / not drinking enough water ; 2 ingesting salty food / description ; 3 more, ions / glucose / amino acids / solute, (in blood) ; 4 sweating / perspiration / evaporation (of water) ; 5 AVP ; e.g. disease where ADH is not, made / secreted 1(c) any two from: 2 1 increase in / large, urine volume or more frequent urination or dilute / less concentrated, urine ; 2 fatigue ; 3 feelings of thirst / dry mouth ; 4 AVP ; e.g. dehydration change in blood pressure © Cambridge University Press & Assessment 2024 Page 6 of 20 1(d) any two from: 2 1 few / no, aquaporins added to membrane / P ; 2 reduced / low, permeability of, membrane / P, to water ; R impermeable to water 3 less water moves through, membrane / P ; ecf for mp1 if C named as water channels in 1(a) 1(e) (gene is on X chromosome) 2 X (chromosome with recessive allele) inherited from mother ; Y (chromosome) inherited from father ; © Cambridge University Press & Assessment 2024 Page 7 of 20

6(a) any three from: 3 1 need to open to obtain carbon dioxide for, photosynthesis / Calvin cycle ; 2 need to close to prevent water loss by, transpiration / described ; 3 can close, at night / when dark, (to save water) as no photosynthesis ; AW 4 must close to prevent water loss when, high light intensity / high temperatures / high wind speed / water stress / drought conditions ; © Cambridge University Press & Assessment 2024 Page 13 of 20 6(b) any six from: 6 1 H+, pumped / moved by active transport, out (of guard cells) ; 2 decrease in H+ inside (of guard cells) / proton gradient set up / AW ; 3 K+ channels open / K+ enters (guard cells) ; 4 water potential (in guard cells), decreases / lowers / becomes more negative ; 5 water enters (guard cells) by, osmosis / down the water potential gradient ; 6 cells, expand / become (more) turgid ; 7 outer wall thinner to allow (more), stretching / bending or inner wall thicker to allow less, stretching / bending ; 8 AVP ; e.g. light activates, ATP production / proton pump sentry of, chloride ions / Cl- (in addition to K+) / entry of water via aquaporins max 3 if stomatal closure described © Cambridge University Press & Assessment 2024 Page 14 of 20

6(a)(i) 1 (excess) amino acids, deaminated / have amino group removed ; 2 2 in the liver ; 6(a)(ii) any three from: 3 1 osmoreceptors in hypothalamus (detect change / are receptors) ; 2 effector(s): collecting duct / distal convoluted tubule / nephron ; 3 target cells: collecting duct (cells) ; © Cambridge University Press & Assessment 2024 Page 10 of 15 6(b) any three from: 3 1 ultrafiltration / forms glomerular filtrate ; 2 high, hydrostatic / blood, pressure in, glomerulus / capillaries ; 3 so, water / (named) solutes, move (out of glomerulus / into Bowman’s capsule) ; 4 through two of: fenestrae / fenestrations basement membrane slit pores / filtration slits / between podocytes ; 5 AVP ; 6(c) any three from: 3 1 high(er / est), U:P / ratio → can tolerate water shortage ; 2 high(er / est), U:P / ratio → much water reabsorbed / small volume of urine produced ; 3 high(er / est), U:P / ratio → can, concentrate urine / conserve water OR high(er / est), U:P / ratio → (well) adapted to dry environment ; 4 AVP ; Question Answer Marks

1(a)(i) A – podocyte ; 2 B – (capillary) endothelial cell ; 1(a)(ii) high(er), hydrostatic / blood, pressure ; Ignore ref. to water potential 2 basement membrane acts as a filter / only small molecules can pass through basement membrane ; 1(b) 3 component of component in component in blood plasma in newly formed urine glomerulus glomerular filtrate glucose same not present ; large proteins not present not present ; urea same increased ; 1(c) posterior pituitary gland – releases (more) ADH ; A secretes 2 kidney – reabsorbs more water / urine more concentrated / lower volume of urine ; OR (more) aquaporins added to membrane of collecting duct (cells) / membrane of collecting duct (cells) more permeable to water ; © Cambridge University Press & Assessment 2024 Page 5 of 19

10(a) any four from: 4 1 changes in factor / stimulus, detected by receptor ; 2 ref. to CNS / brain / coordinator ; 3 impulses / (named) hormone, sent to, (named) effector / muscle / gland ; 4 (named) effector / muscle / gland, carries out response ; 5 factor returns to, set point / norm ; 6 negative feedback ; 7 AVP ; e.g. cell signalling © Cambridge University Press & Assessment 2024 Page 18 of 19 10(b) any three from: 3 cell signalling carries on 1 / 2 two details ;; e.g. glucagon binds to receptors / adenylyl cyclase stimulated / G protein activated / cAMP formed / protein kinase A activated / enzyme cascade 3 no / less, (functioning) glycogen phosphorylase (produced) OR non-functioning glycogen phosphorylase (produced) OR no / less, glycogen phosphorylase activated ; 4 change in, tertiary structure / active site ; 5 (so) less / no, glycogen converted to glucose / glycogenolysis ; 10(c) any three from: 3 1 no / less, (functioning) glycogen synthase (produced) or non-functioning glycogen synthase (produced) or no / less, glycogen synthase activated ; 2 high / increase in, blood glucose concentration (following this meal) ; 3 (so) glucose (excreted) in urine ; 4 more lipid synthesis ; 5 inhibits release of glucagon ; 6 AVP ; e.g. affects blood water potential / dehydration / thirst / tiredness / coma / affects blood pressure © Cambridge University Press & Assessment 2024 Page 19 of 19

6(a)(i) 1 (excess) amino acids, deaminated / have amino group removed ; 2 2 in the liver ; 6(a)(ii) any three from: 3 1 osmoreceptors in hypothalamus (detect change / are receptors) ; 2 effector(s): collecting duct / distal convoluted tubule / nephron ; 3 target cells: collecting duct (cells) ; © Cambridge University Press & Assessment 2024 Page 10 of 15 6(b) any three from: 3 1 ultrafiltration / forms glomerular filtrate ; 2 high, hydrostatic / blood, pressure in, glomerulus / capillaries ; 3 so, water / (named) solutes, move (out of glomerulus / into Bowman’s capsule) ; 4 through two of: fenestrae / fenestrations basement membrane slit pores / filtration slits / between podocytes ; 5 AVP ; 6(c) any three from: 3 1 high(er / est), U:P / ratio → can tolerate water shortage ; 2 high(er / est), U:P / ratio → much water reabsorbed / small volume of urine produced ; 3 high(er / est), U:P / ratio → can, concentrate urine / conserve water OR high(er / est), U:P / ratio → (well) adapted to dry environment ; 4 AVP ; Question Answer Marks

6(a)(i) P – insulin ; 3 Q – muscle / liver ; R – glycogen ; 6(a)(ii) negative feedback ; 1 © Cambridge University Press & Assessment 2025 Page 12 of 19 6(b) any seven from: 7 1 glucagon ; 2 binds to receptor on cell surface membrane (of liver cell) ; 3 G-protein activated ; 4 adenyl(yl) cyclase activated ; 5 ATP converted to cAMP ; 6 second messenger ; 7 enzyme cascade / described ; 8 enzymes activated by phosphorylation ; 9 signal amplified ; 10 glycogen broken down into glucose / glycogenolysis ; 11 glucose enters blood ; 12 gluconeogenesis / described ; © Cambridge University Press & Assessment 2025 Page 13 of 19

6(a)(i) P: selective reabsorption ; 3 Q: osmoregulation ; R: ultrafiltration ; 6(a)(ii) P: proximal convoluted tubule ; 3 Q: collecting duct / distal convoluted tubule ; R: Bowman’s capsule ; 6(b) 1 B / interstitial fluid / tissue fluid / medulla, has more, salt / sodium chloride / Na+ / Cl–; 2 plus one from: 2 salt gradient helps reabsorb water from collecting duct ; 3 AVP ; Question Answer Marks

7(a) any four from: 4 1 insulin / it, is a hormone ; 2 (described) stimulus causes insulin to be secreted from (named) endocrine, gland / tissue / cells ; 3 insulin travels in blood ; 4 binds to receptors on (named) target cells ; 5 to cause (described) response ; 6 AVP ; 7(b)(i) any four from: 4 1 at 21 min, blood glucose concentration / it, rises to 110 mg 100 cm–3 ; 2 (high / increase in, blood glucose concentration) detected by pancreas / causes response in pancreas ; 3 insulin rises to 500 pmol dm-3 ; 4 (insulin) increase GLUT proteins in membrane / increases glucose uptake into cells / increases cell permeability to glucose or (insulin) increases rate of respiration of glucose ; 5 (insulin) causes / stimulates, glycogenesis / lipogenesis ; 6 (mean) blood glucose concentration / it, falls, to normal / within normal range / below starting point / to set point ; © Cambridge University Press & Assessment 2025 Page 14 of 17 7(b)(ii) any three from: 3 1 blood glucose concentration falls as glucose is respired ; 2 blood glucose concentration falls below, set point / normal ; 3 insulin, secretion / release, stops ; 4 glucagon (secreted / released / rises) ; 5 glycogen, (in cells) converted to glucose or glycogenolysis ; 6 (stored) protein / fat, converted to glucose or gluconeogenesis or (stored) protein / fat, used for respiration ; Question Answer Marks

6(a) any four from: 4 1 variable thickness of cell wall described ; 2 no plasmodesmata (between guard cell and other epidermal cells) ; 3 many, chloroplasts / mitochondria ; 4 chloroplasts have few grana ; 5 mitochondria have many cristae ; 6 cell surface membrane, often folded / contains many transport proteins ; 7 AVP ; e.g. cellulose microfibrils arranged in bands / shape description has several small vacuoles nucleus is relatively larger than in mesophyll cells 6(b)(i) 1 (more) stomata open at (mid)day 2 and (more) stomata closed, at (mid)night / in darkness – ora ; 2 data quote – two values of time of day and percentage of stomata open ; time of day percentage of mean stomata open percentage ( 0.5) 06:00 90 / 80 / 64 78 12:00 / midday 93 / 70 / 90 84.3 and 18:00 25 / 35 30 24:00 / midnight 10 / 15 / 10 11.7 © Cambridge University Press & Assessment 2025 Page 17 of 25 6(b)(ii) any two from: 2 1 water stress / drought ; 2 high temperature ; 3 low humidity / dry (atmosphere); 4 high carbon dioxide concentration in leaf (air spaces) ; 5 low light intensity ; 6 high wind speed ; © Cambridge University Press & Assessment 2025 Page 18 of 25 6(c) 4 correct order letter of event 1 D 2 E 3 G 4 B 5 F 6 J 7 I 8 A 9 H 10 C E G B between D and F ; E G B in correct order throughout table ; J I A H between F and C ; J I A H in correct order throughout table ; © Cambridge University Press & Assessment 2025 Page 19 of 25

6(a)(i) urea ; 1 6(a)(ii) deamination / ornithine cycle / urea cycle / converts ammonia (to urea) ; 1 6(a)(iii) liver ; 1 © Cambridge University Press & Assessment 2025 Page 14 of 20 6(b) any seven from: 7 1 blood enters glomerulus via afferent arteriole ; 2 afferent arteriole (lumen) diameter larger than efferent ; 3 (so) high, blood / hydrostatic, pressure ; 4 blood / hydrostatic, pressure greater than water potential gradient (between Bowman’s capsule and glomerulus) ; 5 fluid forced through pores / fenestrations in (blood vessel) endothelium ; 6 basement membrane acts as a filter ; 7 stops, large proteins / blood cells / molecules larger than 68 000–70 000 RMM ; 8 water / glucose / amino acids / urea / mineral ions, pass through ; 9 slit pores between podocytes ; 10 AVP ; e.g. GFR 125 cm–3 min–1 6(c) any two from: 2 1 collecting duct in medulla ; 2 thicker medulla has lower water potential ; 3 (so) more water reabsorbed ; 4 AVP ; e.g. ref. to loop of Henle © Cambridge University Press & Assessment 2025 Page 15 of 20

1(a) any three from: 3 1 osmoreceptors detect (decrease) or osmoreceptors, shrink / decrease in volume ; 2 ref. to hypothalamus ; 3 hypothalamus produces (more) ADH ; A neurosecretory cells produce ADH R secretion 4 posterior pituitary releases (more) ADH (into blood) ; A secretes R produces 1(b)(i) second(ary) messenger ; 1 1(b)(ii) adds aquaporins into, cell surface / luminal, membrane ; 2 (so) more permeable to water ; 1(b)(iii) arrow from lumen into cell and arrow from cell into capillary 1 or one arrow from lumen through cell and into capillary ; © Cambridge University Press & Assessment 2025 Page 9 of 27 1(c) any two from: 2 1 no / less, water reabsorbed or no / less, water absorbed into, capillary / blood ; I tissue fluid 2 water potential of blood, (remains) low / lower than set point ; 3 large(r) volume of urine / dilute urine / low(er) concentration of urine ; I amount / more water excreted / more urine 4 AVP ; e.g. feelings of thirst / dehydration / dizzy / fatigue / ADH release continues / decreased blood volume © Cambridge University Press & Assessment 2025 Page 10 of 27

9(a) (X =) (renal) pelvis ; 2 (Y =) medulla ; 9(b) any four from: 4 1 glucose oxidase (present / immobilised, in sensor / on strip) ; 2 glucose → hydrogen peroxide ; 3 hydrogen peroxide (oxidised) → oxygen / electrons ; 4 (magnitude of) e– flow / current / voltage, (generated) is proportional to, hydrogen peroxide / glucose, concentration ; 5 digital / numerical / quantitative, reading / result / value (on screen) ; 6 AVP ; © Cambridge University Press & Assessment 2025 Page 17 of 18

6(a) any four from : 4 1 less / no, PKB, activated / stimulated ; 2 fewer / no, vesicles, move to / fuse with, cell surface membrane ; 3 fewer / no, GLUT4 (transport proteins) added to (cell surface) membrane or (cell surface) membrane, less / not, permeable to glucose ; 4 less / no, glucose taken up by facilitated diffusion (into muscle cells) ; 5 blood glucose concentration, (remains) high(er) / does not decrease ; 6(b) any seven from : 7 1 (biosensor has) glucose oxidase (immobilised on recognition layer) ; 2 blood sample added ; 3 glucose (in blood) passes through, partially / selectively, permeable membrane ; 4 glucose oxidase, oxidises glucose / converts glucose / catalyses glucose reaction ; 5 gluconic acid and hydrogen peroxide formed ; 6 reaction converted to a current (by transducer) ; 7 current is amplified ; 8 digital / numerical / quantitative, reading ; 9 size of current is proportional to glucose concentration ; 10 instant result / accurate ; © Cambridge University Press & Assessment 2025 Page 17 of 23

9(a) (X =) (renal) pelvis ; 2 (Y =) medulla ; 9(b) any four from: 4 1 glucose oxidase (present / immobilised, in sensor / on strip) ; 2 glucose → hydrogen peroxide ; 3 hydrogen peroxide (oxidised) → oxygen / electrons ; 4 (magnitude of) e– flow / current / voltage, (generated) is proportional to, hydrogen peroxide / glucose, concentration ; 5 digital / numerical / quantitative, reading / result / value (on screen) ; 6 AVP ; © Cambridge University Press & Assessment 2025 Page 17 of 18

6(a)(i) 1 blood glucose concentration increases until 30 minutes ; 2 2 decreases to original value / returns to 5 mmol dm–3, by 90 minutes ; 6(a)(ii) 83.3 ; ; 2 6(a)(iii) any two from: 2 1 reduce intake of (named) carbohydrate ; 2 physical exercise ; 3 inject insulin ; 4 AVP ; © Cambridge University Press & Assessment 2025 Page 13 of 17 6(b) any seven from : 7 1 glucagon is, cell-signalling molecule / ligand / first messenger ; 2 binds to receptor on liver cell (surface) membrane ; 3 G-protein activated ; 4 aden(yl)yl cyclase activated / formation of cAMP ; 5 ref. to second messenger ; 6 enzyme cascade / signal amplified ; 7 glycogenolysis / glycogen hydrolysed to glucose ; 8 gluconeogenesis / amino acids → glucose / triglycerides → glucose ; 9 glucose released into blood ; 10 AVP ; Question Answer Marks

8(a) any four from: 4 1 Ca2+ act as second messenger ; 2 causes (K+) channel proteins to open ; 3 X = potassium ions / K+ (that leave the cell) ; 4 water potential of cell increases / water leaves cell by osmosis ; 5 (guard) cell, becomes flaccid / loses turgidity ; 8(b) any four from: 4 1 (stomata) open to take up carbon dioxide for photosynthesis ; 2 (stomata) close to prevent, transpiration / (excessive) water loss ; 3 e.g. conditions when stomata close ; 4 (water homeostasis needed to) maintain turgidity of cells / supply water for reactions ; 5 ref. to daily rhythm or open during, day / light, and close, at night / at low light intensity / in the dark ; 6 AVP ; Question Answer Marks

7(a) A – podocyte ; 3 B – basement membrane ; C – endothelial (cell) ; 7(b) any three from: 3 1 decreased, (glomerular) blood pressure / hydrostatic pressure ; 2 dehydration / reduced water potential of blood / loss of blood / heart failure ; 3 (named) kidney disease ; A diabetes 4 damage to, Bowman’s capsule / basement membrane / glomerulus / arterioles ; 5 ref. to, drugs / hormones, qualified ; A named or action described e.g. ADH / beta blockers / diuretics © Cambridge University Press & Assessment 2026 Page 19 of 25 7(c) any seven from: 7 1 maintain constant internal environment / AW ; e.g. within narrow limits 2 despite changes in the, internal / external, environment ; max two from: 3 named factor ; e.g. temperature / water potential / blood glucose concentration 4 changes in factor / stimulus, detected by (named) receptor ; 5 ref. to central control decision / AW ; e.g. ref. to, brain / CNS / hypothalamus 6 response carried out by effector ; 7 named effector ; e.g. muscle / gland 8 corrective action ; A correct example 9 factor returns to, set point / norm ; 10 negative feedback ; © Cambridge University Press & Assessment 2026 Page 20 of 25

2(a)(i) 1 initial receptors – osmoreceptors / hypothalamus ; 4 1 IGNORE osmoregulators 2 coordination systems – endocrine / hormonal ; 2 IGNORE ADH 3 final effectors – collecting, duct / tubule ; 3 IGNORE posterior pituitary gland 3 CON other parts of nephron 4 response – less urine produced / urine more concentrated / less watery urine OR more water, reabsorbed / taken up (into blood) OR (more) aquaporins added to membrane / membrane more permeable to water ; 2(a)(ii) any two from: 2 IGNORE flaccid / turgid / plasmolysed 1 if water potential, rises / high, cells, absorb 1 ALLOW if too much water in blood / blood dilute, for ‘high water / swell / burst / lyse ; water potential’ 2 ALLOW if too little water in blood / blood concentrated, for 2 if water potential, falls / low, cells, lose ‘low water potential’ water / shrink / crenate / shrivel ; ALLOW 1 mark for ‘so cells do not burst or shrink’ OR ‘so cells do not gain water or lose water’ if mps 1 and 2 not 3 water is a, solvent / medium / site, for, (named) reactions in given cells / metabolic reactions ; 3 e.g. water needed for hydrolysis (reactions) in cells 4 AVP ; 4 e.g. control / maintain / important for, blood volume / blood pressure / hydrostatic pressure / glomerular filtration ref. prevent oedema 2(b)(i) 180 (g) ; 1 calculation = 200  5  0.18 © Cambridge University Press & Assessment 2026 Page 9 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/ 2(b)(ii) any four from: 4 IGNORE ultrafiltration DO NOT ALLOW basement membrane for mps 2, 3, 4 but ECF after first error If Na+ / sodium ion, not stated CON once then ECF in, proximal convoluted tubule / PCT: max 3 if PCT not stated CON if wrong part of nephron stated then ECF to max 3 ECF if cell not stated or implied (e.g. cytoplasm) for mps 1 (glucose) reabsorbed / moves, into, blood / (peritubular) 2, 3 and 4 to max 3 capillary ; 2 Na+ leaves (epithelial / tubule) cell by active transport (at 2 ALLOW using ATP / pumped / by pumps, for ‘active basal / basolateral, membrane) ; transport’ 2 IGNORE transport protein 3 glucose moves into cell by co-transport with Na+ (at 2 DO NOT ALLOW channel protein luminal membrane) ; 3 ALLOW through co-transporter protein for ‘by co-transport’ 4 glucose leaves cell by facilitated diffusion (at, 4 ECF from mp 2 if basement membrane repeated basal / basolateral, membrane) ; 4 ALLOW diffuses through GLUT, proteins / channels, for ‘facilitated diffusion’ 5 AVP ; 5 mp 2 establishes, Na+, diffusion gradient / concentration gradient e.g. secondary active transport © Cambridge University Press & Assessment 2026 Page 10 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/

8(a) 4 location of Na+ / K+ pumps P ; Ignore Q location of cotransport proteins S ; Ignore P structures through which glucose P + S ; Ignore Q molecules pass prevents leakage of fluid R ; 8(b) any seven from: 7 1 increase in ADH released ; Ignore produced A secreted 2 (ADH released from) posterior pituitary ; 3 ADH binds to receptors ; 4 in, cell surface / basal, membrane, of collecting duct (cells) ; 5 cAMP / secondary messenger, produced ; 6 ref. to enzyme cascade / signal amplification / described ; 7 vesicles (with aquaporins) move to / fuse with, cell surface / luminal, membrane ; 8 more aquaporins in the, cell surface / luminal, membrane ; 9 increase in (cell / membrane / collecting duct) permeability to water ; 10 (more) water moves out of, lumen / collecting duct / filtrate, into, cell / tissue fluid / blood ; 11 by, osmosis / down the water potential gradient ; 12 (more) concentrated / small(er) volume, urine produced ; © Cambridge University Press & Assessment 2026 Page 19 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(a) any six from: 6 1 afferent arteriole is wider than efferent (arteriole) ; 2 (creates) high(er), hydrostatic / blood, pressure ; 3 in, glomerulus / capillaries ; 4 fluid / water / plasma, forced through gaps between endothelial cells ; 5 basement membrane acts as a (molecular) filter ; 6 only, named molecules / ions / molecules less than 68 000–70 000 (R)MM, can pass through (basement membrane) or red blood cells / large proteins, cannot pass through (the endothelium) ; 7 podocyte has, gaps / slits / projections / pores ; 8 fluid / water / filtrate, passes into the, Bowman’s capsule ; 6(b) any three from: 3 1 reduces secretion of ADH ; Ignore production 2 idea that less / no, ADH binds to receptors (at the collecting duct) ; 3 ref. to fewer / no, aquaporins, in / added to, membranes (of cells in collecting duct) ; 4 ref. to less water reabsorbed (at collecting ducts) ; 5 increase in blood pressure so increase, in GFR / volume of glomerular filtrate ; © Cambridge University Press & Assessment 2026 Page 14 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/

5(a)(i) 833.3 ;; © Cambridge University Press & Assessment 2026 Page 14 of 22 2 8 0 3 − 0 3 0 2  100 if answer incorrect award one mark for working 5(a)(ii) any four from: 4 1 insulin secreted by, pancreas / beta cells / Islets of Langerhans ; 2 binds to receptors on (cell surface membrane of), liver / muscle, cells ; 3 glucose transporter (proteins) added to muscle cell (surface membrane) or increases permeability of muscle cell (to glucose) ; 4 more glucose enters (cells) ; 5 increase in respiration of glucose ; 6 glycogenesis ; A described 5(b)(i) glucose oxidase ; 2 peroxidase ; 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/ 5(b)(ii) any three from: 3 identical to human insulin 1 no, allergy / immune response / antibody response / side effects / rejection ; 2 acts rapidly ; 3 do not, develop tolerance to it / need larger doses ; 4 no risk of, disease / infection ; 5 no / fewer, (named) ethical issues ; © Cambridge University Press & Assessment 2026 Page 15 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/