SGSS Pure Biology Prelim 2024 Paper 1 & Paper 2 Answer

1 Answer Scheme for Sec 4E Biology Prelims P1 & P2 2024, St Gabriel’s Secondary School Paper 1 1 2 3 4 5 6 7 8 9 10 A D C D A B B B B D 11 12 13 14 15 16 17 18 19 20 B D C B A D A C B A 21 22 23 24 25 26 27 28 29 30 C C A D B A B C C B 31 32 33 34 35 36 37 38 39 40 D A C A D B C A C D A: 10 B: 11 C: 10 D: 9 Paper 2 Section A No. Answer Remarks 1 (a) • Between 650 and 900 cells per ml 1 1 (b) • [D1] From the 2nd to the 4th hour, the concentration of Campylobacter protein decreased from 800 cells per ml to about 220 cells per ml, by about 580 cells per ml • [D2a] From the 2nd to the 3rd hour, the concentration of Campylobacter protein decreased steeply from 800 cells per ml to about 420 cells per ml, by about 380 cells per ml • [D2b] From the 3nd to the 4th hour, the concentration of Campylobacter protein decreased less steeply from 420 cells per ml to about 220 cells per ml, by about 200 cells per ml • [E1] Antibiotics kill / inhibit bacteria growth by interfering with bacterial growth & metabolic activities, • [E2] such as inhibiting cell wall synthesis / cell membrane function / protein synthesis in ribosomes / enzyme action in cytoplasm hence concentration of Campylobacter protein decreased • [E3] Time is needed for digestion of coating / absorption / transport to area of effect, hence takes 2-4 hours for effect to show (max 4) 4

2 1 (c) Any 2: • Cell wall • Cell membrane • (free) ribosome • flagellum • circular DNA • plasmid R DNA / genetic material 2 1 (d)i • Yes, Infectious diseases can be spread from person to person • Campylobacter spreads by contaminated food / ORA 2 1 (d)ii • A vaccine contains an agent that resembles Campylobacter • White blood cells binds to antigens on vaccine • Some white blood cells remain in the blood stream for a long time as memory cells. • In the future, when the Campylobacter enters the body, memory cells recognise the pathogen • produce the antibodies to destroy it (max 3) 3

3 2 ( a ) • Wilting occurs when rate of water loss by transpiration exceeds rate of water gained from roots • Thin / small leaves reduces surface area to volume ratio • Less water loss by transpiration • Reduces chances of rate of water loss by transpiration exceeding rate of water gained from roots / OWTTE 2 2 (b) • Correct xylem label (lignified vessels) • Correct phloem label (non-lignified vessels in the core) 2 2 (c) • M: oxygen; photosynthesis • P: carbon dioxide; respiration 2 2 (d) • active transport require energy from aerobic respiration. • Root is mostly submerge in water, where there is low concentration / level of dissolved oxygen in water available for aerobic respiration. 2

4 3a • Blocked vessel: Coronary artery • Vessel A: Aorta 2 3b • less oxygen and glucose delivered to heart muscles leads to reduced rate of aerobic respiration • Heart muscle cells die leading to heart attack 2 3c • Thinner muscular walls hence less able to withstand high pressure ; • Presence of valves, hence blood travel slower/ impede blood flow ; • Less elastic fibre / tissue hence less able to stretch and recoil; • Large lumen relative to diameter, hence speed of blood slows down (any 2) 2 R small walls, thin without mentioning about the walls ; treated as foreign body and rejected by immune system 3di • Fat deposit / cholesterol 1 3dii • Anti-platelets drug administered to prevents platelet release, prevents soluble fibrinogen to change to insoluble fibrin ; • prevents blood to clot due to damage or injury caused by insertion of the stent • prevents blood vessel to be further narrowed (any 2) 2 R prevents agglutination

5 4ai • Correct Shape • Correct Order of organisms 4aii • About 90% of energy is lost at each trophic level / when transferred from one trophic level to another; • through processes like heat loss during respiration, faeces egestion, uneaten body parts, and excreted substances like urea/ carbon dioxide (any 2 stated) 4bi • Number of light grey owls increase; • as light grey owls camouflage better than brown tawny owls; • light grey owls selected for / have selective advantage over brown tawny owls • Less light grey owls eaten; • More light grey owls survive to reproduce / becomes a reproductive adult • More light grey owls survive to pass on genes/alleles for brown coats to offspring; (max 3) 3 4bii Combustion of fossils/ deforestation /any activities that increase the release of carbon dioxide into atmosphere or destroy carbon sink (any 2) 2 4c • Decreased northern goshawk population will increase tawny owl population, due to presence of less predators, and decreases large fish population due to presence of more predators (at least 2 trophic levels mentioned correctly) • Decreased northern goshawk population disrupts balance of ecosystem / biodiversity / every trophic level downstream in the food chain / OWTTE 1 Kelp Marine invertebrates Small fish Large fish Tawny owl

6 5a • Aerobic respiration is the breakdown of glucose to release energy in the presence of oxygen. 1 5b • During exercise, muscles contract vigorously, requiring energy. • Muscle cells then carry out anaerobic respiration, producing lactic acid. • Lactic acid accumulates in the muscles, causing soreness and fatigue. The body now incurs an oxygen debt. (max 2) • Heart rate remains high to maintain fast transport of • lactic acid from muscles to liver and oxygen from lungs to liver • Deeper and faster breathing allows continuously fast oxygen uptake • In the liver, oxygen is required to remove lactic acid • In the liver, lactic acid is also converted to glucose • When all lactic acid is converted to glucose, oxygen debt is repaid. 4 5c Che mical electronic cigarettes traditional tobacco smoke Nicoti ne [1] • Both electronic cigarettes and traditional tobacco smoke contain nicotine that is an addictive drug that releases adrenaline [1] • increases heart rate and blood pressure / Makes blood clot/ narrows artery lumen easily, increasing risk of coronary diseases / affects fetal development, increase risk of miscarriage [1] Tar [1] • Both electronic cigarettes and traditional tobacco smoke have carcinogenic / cancer - causing effects [1] • due to fumes from the vaporisation of the electronic cigarettes liquids and tar in traditional tobacco smoke [1] • Both electronic cigarettes and traditional tobacco smoke causes inflammation [1] • due to propylene glycol in electronic cigarettes liquids and tar and irritants in traditional tobacco smoke [1] • that paralyses cilia lining the air passages causing inflammation from the dust-trapped mucus in the air passages [1] (any 5) 5

7 6a • When the blood glucose concentration becomes above threshold level / normal set point, • the cells in pancreas’ islets of Langerhans are stimulated • to secrete insulin into the bloodstream, to be transported to liver and muscle cells • At the liver and muscle cells, insulin causes cell membranes to be more permeable to glucose, so glucose uptake increases from the bloodstream to the cells • Insulin stimulates conversion of glucose to glycogen to be stored in the liver/ muscle cells • insulin stimulates increased respiration rate to oxidise more glucose • Blood glucose concentration then decreases to threshold level / normal set point (max 4) 4 6b • Age/ height and mass/ proportion of males and females or group size/(same) severity of diabetes/ (same) activity (during investigation)/ (same) type of meal/ dose of drug/ (similar) blood glucose concentrations at start/ other health conditions or other drugs being taken; 1 6c • Bar graph drawn • Axes drawn • Correct y-values • Equal width for bars and Equal width for separators; 4 Disagree with stateme