2026 CJC H2 Biology 9477 P2 ANS

CATHOLIC JUNIOR COLLEGE JC2 PRELIM EXAMINATION Higher 2 CANDIDAT E NAME CLASS 2T INDEX NUMBE R BIOLOGY 9477/02 Paper 2 Structured Questions 31 st August 2026 2 hours Candidates answer on the Question Paper No Additional Materials are required READ THESE INSTRUCTIONS FIRST Write your name (as per NRIC), class, and index number in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Total 90 1 [9] 2 [8] 3 [12] 4 [11] 5 [11] 6 [16] 7 [10] 8 [7] 9 [6]

2 This document consists of 25 printed pages and 1 blank page. [Turn over Answer all questions. 1 Fig. 1.1 shows an electron micrograph of a steroid-producing endocrine cell. Fig. 1.1 With reference to Fig. 1.1, (a) Identify organelles A and B . Organelle A ………………………………..….… Organelle B ……………………………………… [2] A: Mitochondrion (accept plural) B: Smooth endoplasmic reticulum (b) Describe one structural feature of each organelle, A and B , and explain how each feature adapts the cell for its function in steroid hormone production. ………………………………………………………………………………………………………………. [4] 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 2

3 Mitochondrion feature 1: Double membrane with highly folded inner membrane / cristae Explanation: Provides a large surface area for membrane-bound enzymes required for the conversion of cholesterol to steroid precursors. OR Generates large amounts of ATP via aerobic respiration to supply the energy needed for steroid biosynthesis. OR Inner membrane that is impermeable to movement of protons / H + ions due to hydrophobic core of the cell membrane, to allow generation of proton gradient so that chemiosmosis can happen leading to ATP synthesis needed to supply the energy for steroid biosynthesis. SER feature 2: Extensive network of interconnected tubular membranes Explanation: Provides a large surface area for enzymes specifically involved in lipid and steroid hormone synthesis. (c) Explain the significance of the close proximity between organelle A and organelle B during the synthesis of steroid hormones. ………………………………………………………………………………………………………………. [1] Any 1 1. Reduces the diffusion distance for hydrophobic / lipophilic intermediate molecules moving between the two organelles. 2. Reduces diffusion distance for direct ATP supply to reach energy-requiring active transport or enzymatic steps in the SER / Structure B 3. Prevents insoluble / non-polar lipid intermediates from being exposed to / aggregating in the aqueous cytosol / Prevents cytosol exposure (d) Steroid hormones are synthesised on demand and pass out of endocrine cells immediately upon production. Explain why the physical properties of steroid molecules allow them to leave the cell by simple diffusion, and why they cannot be released by exocytosis. ………………………………………………………………………………………………………………. [2] 1. Steroids are non-polar / hydrophobic / lipophilic, so they can readily dissolve in and pass directly through the hydrophobic phospholipid bilayer down a concentration gradient. 2. Steroids cannot be packaged / cannot be stored within membrane-bound secretory vesicles , as they would freely diffuse across the vesicle membrane. [Total: 9] 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 2

4 2 Researchers isolated a sucrase enzyme from the bacterium Bacillus subtilis. They immobilised the enzyme in alginate beads. The researchers investigated the effects of pH on the activity of the immobilised sucrase compared with the activity of the same enzyme free in solution. The results are shown on Fig. 2.1. Fig. 2.1 (a) With reference to Fig. 2.1 (a) state the optimum pH for both the immobilised sucrase and free sucrase. …………………………………………………………………………………………………………. [1] pH 4.3 - pH 4.45 (ii) compare the effect of increasing pH above 5.5 on the percentage of maximum enzyme activity for immobilised sucrase and free sucrase. …………………………………………………………………………………………………………. [2] 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 2

5 1. Above pH 5.5 , the percentage activity of both immobilised and free sucrase decreases , but the activity of free sucrase decreases much more steeply / rapidly than immobilised sucrase. 2. [Evidence Data at any pH > 5.5.] At pH 6.0 , free sucrase retains only 22% activity while immobilised sucrase retains 95% activity OR activity of free sucrase decreases from (76)% to 0% whereas activity of immobilised sucrase decreases from 98% to 40%, between pH5.5 to pH8. (b) In order to measure enzyme activity at each pH, the researchers measured the rate of product formation using an excess concentration of sucrose solution over a fixed duration. With reference to the molecular mechanism of enzymes, explain why maintaining an excess substrate concentration was essential to ensure valid results when comparing enzyme activity across different pH values. ………………………………………………………………………………………………………………. [3] 1. Substrate concentration must be a controlled variable so that rate of reaction is limited only by pH / enzyme conformation, not by substrate availability. 2. Excess substrate ensures all active sites are fully saturated with substrate ( is reached / 𝑉 𝑚𝑎𝑥 enzyme is the limiting factor). 3. Prevents the rate of effective collisions / enzyme-substrate complex (ESC) formation from decreasing over time due to substrate depletion during the assay. (c) In food manufacturing, the enzyme