2026 NYJC J2 H2 Biology Prelims P3 MS

NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS BIOLOGY 9477/03 Paper 3 Long Structured and Free-response Questions 21 September 2026 Additional Materials: Insert, Answer booklet 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question on the separate Answer Booklet. 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 no use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 29 2 10 3 16 Section B 20 Total 75 This document consists of 18 printed pages and 2 blank pages. [Turn over

2 9477 / H2 Biology / 03 Section A Answer all the questions in this section. 1 Reef-building corals harbour algal symbionts from the genus Symbiodinium. This relationship between the two organisms is mutually beneficial for both coral and algae. However, the relationship can break down under certain environmental conditions, resulting in coral bleaching. The term is attributed to the normally colourful corals losing their colouration due to the loss of algal symbiont. A study was conducted on 50 colonies of corals of the species Pocillopora damicornis to investigate the environmental factors that affect coral bleaching susceptibility. It was found that colonies of P. damicornis are dominated by Symbiodinium from genetically distinct groups, C or D. Fig. 1.1 shows the symbiont cell densities (algal cell mass per gram of coral tissue) in colonies dominated by group C and group D at each time point during the warming period and bleaching event. The bleaching event is where 80% or more of all corals (including other species) are bleached. The mean water temperature experienced by the corals over the 14 -day period preceding each sampling point are shown as the middle line of the boxplots. Fig 1.1

3 9477 / H2 Biology / 03 (a) Describe and explain the relationship between mean water temperature and the trend observed for symbiont cell densities during the warming period. 1. Increase in mean temperature from 23.5°C to 28.0°C during the warming period saw a corresponding increase in symbiont cell density from 0.06a.u.to 0.15a.u for colonies with group D/ 0.04a.u. to 0.07a.u. for colonies with group C; 2. Quote values correctly; 3. Increase in temperature leads to higher metabolism for the algal cells due to greater enzyme activity/rate of photosynthesis/respiration, hence greater growth rates and higher cell density; [3] (b) Compare the symbiont cell density between colonies with group C and colonies with group D Symbiodinium during the bleaching event. Similarities 1. Both show a decreasing trend; 2. Decrease was more gradual from 13 Aug to 18 Aug/ decrease was more steep from 14 Jun to 13 Aug; Differences 3. Cell density for group D was much higher at all sampling dates; 4. Cell density decreased to 0.00a.u. for colonies with group C/fully bleached but colonies with group D did not fully bleach (Reject: just stating cell densities without emphasizing that colonies with group D did not fully bleach)/ decrease in symbiont cell densities in colonies with group C was greater than in colonies with group D. 5. Standard deviation was greater for colonies with group D [2] (c) Suggest a possible reason for the decrease in symbiont cell density, although there was no change in temperature between 13 and 18 August. 1. Prolonged exposure to elevated temperatures caused corals to undergo prolonged period of stress resulting in bleaching; 2. 31°C is already beyond the thermal tolerance; 3. There were additional stress factors due to climate change like i ncreased bacterial infection, lower pH due to ocean acidification [1]

4 9477 / H2 Biology / 03 The algal symbionts from the genus Symbiodinium are eukaryotic cells containing chloroplasts in which photosynthesis occurs. The endosymbiotic theory proposes that chloroplasts evolved from free -living photosynthetic prokaryotic cells that were engulfed by ancestral cells and subsequently developed a permanent endosymbiotic relationship with their host cells. (d) Evaluate the extent to which features of chloroplasts support the endosymbiotic theory. Any two: 1. chloroplasts have their own circular DNA ; 2. chloroplasts contain 70S ribosomes ; 3. chloroplasts are similar in size to bacteria ; 4. chloroplasts have double membranes ; 5. * yes the features provides strong evidence that supports the theory [3] (e) High temperatures can damage components of the photosynthetic electron transport chain in the chloroplasts of Symbiodinium. Explain how this may affect ATP synthesis. 1. Ref to named proteins (name at least 1: electron carriers, proton pump) being denatured/ bonds broken, 3D structure damaged; 2. Damage to the photosynthetic electron transport chain reduces electron transfer. 3. Reduces the transfer of H⁺ into the thylakoid lumen, resulting in a smaller/ less steep/ no, proton gradient across the thylakoid membrane. 4. Therefore, fewer H⁺ ions diffuse through ATP synthase, providing less energy for phosphorylation of ADP to ATP, thus reducing ATP synthesis. [3]

5 9477 / H2 Biology / 03 Researchers investigated how heat stress may trigger cellular responses associated with bleaching in the corals P. damicornis. Under heat stress, the algal symbionts, Symbiodinium , experience cellular stress. Researchers proposed the signalling pathway shown in Fig. 1.2 to explain how heat stress in the algal symbionts may trigger responses in coral cells. In this proposed pathway, stress in the symbionts results in the release of signalling molecule S, which binds to a receptor on the plasma membrane of the coral cell. This initiates a multi -step signal transduction pathway that results in an increase in cytosolic Ca²⁺ concentration. Increased cytosolic Ca²⁺ contributes to cellular responses associated with the loss of algal symbionts from coral cells. Fig 1.2 (f) Explain how the structural features of the receptor shown in Fig. 1.2 enable it to function in cell signalling. 1. Receptors have 7 transmembrane α-helices being essential for embedding into membrane; 2. [ligand binding site] : Ref to extracellular / N- terminus hydrophilic region binding to ligand 3. Ref to cytoplasmic/ intracellular/ C-terminus hydrophilic region binding to G- protein [2]

6 9477 / H2 Biology / 03 (g) Explain the significance of the following proteins in transmitting the signal from signalling molecule S into the coral cell: (i) G-protein 1. Ligand binds and activates receptor, resulting in GDP bound to G -protein being displaced by GTP; 2. Resulting in a change in conformation of G protein, causing the β - and g- subunits to dissociate from α subunit; 3. ref to activated α subunit binds and activates adenylyl cyclase / relaying of signal from receptor to specific downstream effector; 4. ref to relaying extracellular signal into the cell; [2] (ii) adenylyl cyclase 1. Ref to activation by G protein; 2. ref to synthesis large number of cAMP molecules; 3. Thus small number of extracellular ligands is sufficient for signal amplification; 4. Ref to activation of phosphorylation cascade; [2] Prolonged exposure of coral cells to signalling molecule S may result in a red