2025 FH Prelim BIO Paper 2 ANS

2025 FHSS 6093 Pure Biology Prelim Paper 2 Mark Scheme Section A (70m) Qn Mark Scheme Marks Examiner’s Comment 1 a • Chloroplast (reject chloroplasts) 1 Some students ignore the qn’s requirement of organelle and wrote chlorophyll b • As light intensity increases from 0 Wm-2 to 50 Wm-2, relative rate of photosynthesis increases from 0.0 to 0.8 a.u.(±0.1) by 0.8 a.u.; • As light intensity increases from 50 Wm-2 to 100 Wm-2, relative rate of photosynthesis remains constant at 0.8 a.u. (±0.1); • As light intensity increases from 100 Wm-2 to 455 Wm-2, relative rate of photosynthesis decreases from 0.8 a.u. (±0.1) to 0.0 a.u. by 0.8 a.u.; • Highest rate of photosynthesis between 50-100 Wm-2 at 0.8 a.u; 3 Students who performed poorly failed to provide the full descriptive data with processed data. ci • [idea] As light enters water some of it is absorbed hence light intensity decreases as depth increases as light cannot reach the bottom of the sea / ORA • At sea surface, light intensity is likely above 100 Wm-2 as rate of photosynthesis is not highest; • Just below sea surface, light intensity is between 50 to 100 Wm-2, therefore rate of photosynthesis is highest; • As depth increases, rate of photosynthesis decreases as there is insufficient light energy for absorption for photosynthesis; 4 Qn is poorly done as most students did not relate Fig. 1.2 and Fig. 1.3 cii • Below depth Y, rate of photosynthesis decreases below rate of respiration of Chlorella; • Insufficient glucose produced for respiration to release energy for cellular activities / metabolism / survival, leading to cell death; 2 Well done.

2 ai • There will be no change in level 1 and level 2. 1 Poorly done, students failed to appreciate qn context that starch is insoluble hence does not affect water potential Aii • Starch is insoluble in water therefore does not affect / has minimal effect on water potential. 1 b • Capillary action • Adhesion and cohesion forces between water molecules with the wall of the tube causes water to rise up the tube. 2 Poorly done. Students not familiar with capillary action and often confuse it with transpiration pull c • Solute A must be large enough (so that it cannot pass through the partially permeable membrane). 1 Well done 3 ai • Protease; 1 Well done aii • Digest proteins into peptides/polypeptides (reject amino acids) 1 Well done b • Bromelain / enzyme has a narrow optimal pH range / (idea) alkaline water causes pH to deviate from Bromelain optimum pH; • Marinating meat with alkaline water may denature Bromelain, loss of 3D shape of active site no longer complementary to shape of protein hence protein not digested / protein cannot fit and bind / no ES complex formed; 2 Well done c • Fresh pineapple contain active Bromelain which digest gelatin hence jelly is unable to solidify; • Bromelain in canned pineapple has been denatured due to high heat during the canning process; 2 Well done

4 a Any Two of the following: • pancreatic lipase • trypsin / protease • pancreatic amylase 2 Well done b • No lipase produced in mouth and stomach; • Lipid coating can only be digested in the small intestine in the presence of intestinal lipase. 2 Well done c • Enzymes only work in solution / when dissolved / in presence of water / inactive when dry; 1 Poorly done. Most students did not appreciate that enzyme only active when hydrated. di • Diabetes / diabetes mellitus; 1 Well done dii Any Two of the following: • Insulin injections • reduce carbohydrates intake in diet • regular exercise • AVP (e.g. pancreas transplant) Reject: ref. to organ transplant w/o specific reference 2 Well done 5 a • C, E, F 1 Poorly done. Most students were not cautious in identification of heart components. bi • 120 mmHg – Systole; 80 mmHg -Diastole 1 Well done bii Any four of the following: • During atrial systole and ventricular diastole; • Muscles in atrium contract and muscles in ventricle relax; • Pressure in atrium greater than pressure in ventricle; • Bicuspid / Atrioventricular valve forced open; • Blood in left atrium / G forced into left ventricle / H 4 Well done

c Any three of the following: • Mixing of oxygenated blood and deoxygenated blood between the left and right ventricles; • Oxygen transport becomes less efficient and tissue cells receive less oxygen for aerobic respiration and less energy released; • Heart has to pump harder resulting in fatigue; • Enlarged heart to increase volume of blood pumped to the lungs; • Increased pressure in lungs may cause capillaries in lungs to burst / pulmonary hypertension 3 Most students were only able to achieve credit for the 1st two points. Most did not elaborate on subsequent consequences. d 2 Poorly done. Most students were unable to relate data to pressure changes during systole and diastole 6 ai (E) urethra (F) urinary bladder (G) kidney (H) ureter 2 Well done aii • Tube E carries Semen / seminal fluid / sperm / AVP but Tube H does not; 1 Well done

b • Presence of glucose/proteins in fluid of diabetic person but absent in non-diabetic person. 1 Well done ci • Purple 1 Well done cii • Parental phenotype and genotype correctly represented; • Gametes correctly represented and circled; • Offspring genotype and phenotype correctly represented; • Phenotypic ratio given correctly; 4 Some students represented dominant and recessive allele using different alphapet assignment. This is wrong. During the choice of letter for allele representation, it is suggested that letter chosen should be clearly different for upper and lower case. E.g Q and q Most students did not provide phenotypic ratio to earn the full credit. ciii • Mutation; 1 Well done 7 a Describe: • The indicator turns yellow within 8 minutes for the small hamster whereas the large hamster took 14 minutes / small hamster turns the indicator yellow 6 minutes faster than the big hamster; Explain (Any Three of the following): • This implies that the small hamster releases more carbon dioxide and has a higher rate of respiration; • Small hamster has a larger surface area: volume ratio; 4 Well done for 1st two points. Most students were unable to score the remaining points to account for higher respiration rate for smaller hamster.

• Loses heat to the environment faster than big hamster; • Respiration rate higher to generate more heat to maintain its body temperature; bi • Increased energy demand due to vigorous muscle contraction at higher speed; • Anaerobic respiration occurs in the muscles to release extra / more / additional energy to meet demands of the exercise; OR Insufficient oxygen supply due to limit in breathing and heart rate resulting in anaerobic respiration • Lactic acid formed and accumulated in the body; 3 Well done bii Any Three of the following: • Heart rate remains high to transport lactic acid from muscles to liver; • Increase transport of oxygen to oxidise lactic acid into energy and glucose by liver / oxidises lactic acid to carbon dioxide and water; • So as to repay oxygen debt incurred during the vigorous exercise. • Increase transport of carbon dioxide to lungs to be expelled 3 Well done 8 a • A vaccine contains an agent that resembles a pathogen, prevents infectious diseases by stimulating white blood cells to quickly produce antibodies when the pathogen invades. 1 Poorly done, most students fail to achieve credit without stating purpose of vaccine to prevent infectious diseases. b • When viral protein is present in the bloodstream, they stimulate white blood cells / lymphocytes to produce antibodies against it. • Antibodies may stay in the blood /plasma for some time / when exposed to the virus, the same antibodies are produced readily / immunologi