KSS EOY 2026 3G3 Biology Answer

1 Kranji Secondary School 3G3 BIOLOGY End-of-Year Examination 2026 Suggested Answers Note: A (Accept possible answer) R (Reject) Section A (30 m): 1 2 3 4 5 6 7 8 9 10 D C D D C D D C D A 11 12 13 14 15 16 17 18 19 20 A B B A C B B B C D 21 22 23 24 25 26 27 28 29 30 B D C B A A C B D C Section B (40 m): 1 (a) structure P: mitochondrion R: mitochondria (Plural) function: Carry out aerobic respiration to release energy R: produce energy structure Q: cell membrane function: Control movement of substances into and out of the cell R: enter only / move only in 1 direction 1 1 1 1 (b) • Ribosomes attached to the Rough Endoplasmic Reticulum/RER synthesise mucin glycoproteins which are packaged into vesicles • Vesicles transported to and fuse with golgi body where it undergoes chemical modification and are packaged into secretory vesicles • Secretory vesicles pinch off golgi body and fuse with the cell membrane, releasing the mucin glycoproteins out of the cell 1 1 1

2 (c) • Tar in smoke paralyses the cilia • Cilia unable to sweep the mucus, with trapped pathogens and dust, out of the air passages • Results in persistent/ vigorous coughing • causing break down/ damage of partitions / walls of alveoli R: other effects not leading to emphysema 1 1 1 1 2 (a) Soil has higher water potential than cell sap of root hair cell / vice versa Water molecules diffuse into root hair cell by osmosis and diffuse / move across the partially permeable cell membrane R: water concentration / up water potential gradient 1 1 1 (b)(i) • at X, as the oxygen concentration increases, there is a low rate / no increase/ constantly low inion uptake • At Y , increase in oxygen concentrations lead to increase in rate of uptake of ions • at Z, further increase in oxygen concentration leads to no increase/ remain constant in rate of uptake of ions R: remain unaffected/ same/ unchanged 1 1 1 (b)(ii) X: diffusion Y: active transport Y: increase in concentration of oxygen, increases rate of aerobic respiration, more energy is released for active transport, resulting in increased rate of ion uptake. R: produce energy 1 1 1 3 (a) From 0 to 30 min, the blood alcohol concentration increases from 5-10 mg/100mL to 50 - 55 mg/100mL. / Increase by or by 40 o4 45 mg/100mL/ increase by 10 times From 30 to 120 min, the blood alcohol concentration decreases gradually from 50 mg/100mL to 5 mg/100mL. Note: If only trend stated with no data quoted: award only 1m overall 1 1

3 (b) • From 0 to 30 min, alcohol is absorbed/ diffuse into the bloodstream in the capillaries found in the villi /ileum/ small intestine causing an increase in blood alcohol concentration • From 30 to 120 min, alcohol in blood is transported to the liver by hepatic portal vein* • where detoxification occurs OR alcohol is broken down/ converted into harmless products, hence the blood alcohol concentration decreases. 1 1 1 (c) Individual A: alcohol is being absorbed into the bloodstream/ small intestine at a faster rate A: drank a higher volume/ higher concentration of alcohol/ liver is not functioning well 1 4 (a) Person ate a carbohydrate rich meal/ meal high is sugars/ starch/ specify foods with high starch content, eg. bananas R: heavy / full meal 1 (b) Blood glucose level remain high and decrease slowly 1 (c) Islets of Langerhans in the Pancreas detect the change Insulin is secreted into the blood stream by the Islets of Langerhans Any one point: Insulin stimulates the liver to convert excess glucose into glycogen and store in the liver / Insulin increases the permeability of cells to increase uptake of glucose / Insulin increases the rate of aerobic respiration R: insulin convert excess glucose into glycogen 1 1 1 5 (a) Q: proximal convoluted tubule R: wrong spelling 1 1 2 time / h X blood glucose concentration

4 (b) Diameter of B is wider / larger than A A: thicker Creates a high (hydrostatic) pressure for ultrafiltration/ to force the blood plasma / any named substances out of the glomerulus R: pressure to diffuse 1 1 (c)(i) All the amino acids are reabsorbed back into the blood at the proximal convoluted tubule 1 (c)(ii) Proteins are too large to pass through the partially permeable membrane of the glomerulus 1 (c)(iii) Hypothalamus is stimulated by/ detect the increase in blood water potential above normal Hypothalamus produce less ADH / pituitary glands would release less ADH R: Pancreas produce/ secrete Cells in the walls of collecting duct/ R become less permeable to water and less water reabsorbed Amount of water in R would increase R: volume of urine increase (need to answer the question ‘amount of water in R’) 1 1 1 1

5 Section C (30 m): 6 (a) Correct Axis Label Correct Plots (allow 1 error) Best fit line Correct Scale 1 1 1 1 (b) Depends on the the student’s graph Estimated value is between 35-40°C No units -1 m 1 (c) • Lipase (R: enzyme) is the lock, fats is the key (R: milk, substrate) • At temperatures above 70°C, lipase is denatured and loses/changes the shape of its active site • Fats can no longer bind and fit into the active site to form enzyme-substrate complex • Hence fatty acids not formed, hence pH did not decrease, so the phenolphthalein remains pink. 1 1 1 1 (d) Time taken for phenolphthalein to turn pink would decrease Bile can emulsify the fat/ large fat globules into tiny fat droplets Increases the surface area to volume ratio for faster digestion by lipase enzyme 1 1 1 0 50 100 150 200 250 300 350 0 20 40 60 80 temperature/ oC time taken for Phenolphthalein to turn colourless / s

6 7 (a) (i) label pulmonary vein (ii) label either tricuspid valves or the semi lunar values on the right side of the heart 1 1 (b) (i) 0.24 – 0.26 s (R: 0.30) (ii) At Y , ventricular muscles start to relax the pressure in the left ventricle drops below the aortic pressure. Aortic valve/semi lunar valves is forced close (R: closed shut) to prevent backflow of blood into the ventricle. MPV 1 1 1 (c) • The excess fats will be deposited in the inner walls of the coronary arteries forming plague. • This narrows the lumen (A: blockage, occlusion) of the coronary arteries, reducing the blood flow through these vessels. • Less/insufficient glucose and oxygen can be transported to the heart cells • Lower rate of aerobic respiration resulting in less energy released • Less energy can be released by heart muscles cell to contract which can lead to heart attack OR • Increase blood pressure caused by blood clot due to rough inner surface OR • Blood clot in arteries in brain can lead to a stroke OTHER ACCEPTED EFFECTS: • Excess glucose will be converted to fats for storage • Can lead to weight gain/ obesity • Overstimulation of pancreas/ islets of Langerhans leading to insulin resistance • Can lead to diabetes in the patient 1 1 1 1 1 1 1 1 1

7 8 (a) • During vigorous exercise, body cells carry out anaerobic respiration which produces lactic acid • After the exercise, heart rate remains high to transport more oxygen and lactic acid to the liver • Lactic acid is removed + using oxygen / oxygen debt is repaid. (R: detoxify) 1 1 1 (b) • During exercise, the body/ blood temperature increases above normal • Thermoreceptors in Hypothalamus/ skin detects the increase in temperature and sends nerve impulses to stimulate the start of corrective mechanism • Vasodilation of arterioles/ arteriole lumen widens so more blood flow to the capillaries on the surface of the skin to lose heat/ increase heat loss • Sweat glands become more active, producing more sweat. Water in sweat evaporat