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 du