2026 NYJC J2 H2 Biology Prelims P3 QP

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: 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 2 3 Section B Total 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. [3] (b) Compare the symbiont cell density between colonies with group C and colonies with group D Symbiodinium during the bleaching event. [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]

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. [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. [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. [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 [2] (ii) adenylyl cyclase [2] Prolonged exposure of coral cells to signalling molecule S may result in a reduced response to the signal. Fig. 1.3 shows how prolonged binding of signalling molecule S results in a G -protein- coupled receptor kinase (GRK) binding to and phosphorylating several sites on the receptor. An intracellular protein, arrestin, subsequently binds to the phosphorylated receptor. This prevents further activation of the G -protein and causes desensitisation of the coral cell to signalling molecule S. Fig 1.3

7 9477 / H2 Biology / 03 (h) With reference to Fig. 1.3, explain why the GRK phosphorylation sites must be located on the cytoplasmic side of the cell surface membrane for desensitisation of the receptor to occur. [2] In addition to responses leading to bleaching, heat stress alters the expression of several genes in coral cells. One of these genes encodes heat -shock protein 70 (HSP70), a molecular chaperone that assists proteins in maintaining their functional three- dimensional structures. Scientists found that heat -tolerant and heat-sensitive colonies of Pocillopora damicornis differed in the amount of HSP70 protein produced during heat stress. Heat stress results in an increase in the expression of the HSP70 gene. (i) Explain how transcriptional control could result in increased expression of the HSP70 gene. [3]

8 9477 / H2 Biology / 03 One hypothesis is that, in addition to differences in the regulation of gene expression, heat-tolerant and heat-sensitive corals may possess different alleles of the HSP70 gene. The HSP70 gene consists of several exons and introns. Mutations have been identified at several positions within exon 2. Researchers considered the following approach to investigate these mutations: • polymerase chain reaction (PCR) to amplify exon 2 of the HSP70 gene, followed by • gel electrophoresis to determine the length of the amplified DNA. Fig. 1.4 shows part of the HSP70 gene. The positions of two previously identified mutations are indicated by asterisks (*). Fig 1.4 (j) Describe the role of PCR primers in this context. [1] (k) Discuss if PCR followed by gel electrophoresis can detect all types of mutations in exon 2 of the HSP70 gene. [3] ** key: PCR primers exon 2 exon 3 exon 4 exon 5 exon 1

9 9477 / H2 Biology / 03 (l) Differences in cellular responses to heat stress may affect the ability of corals to survive periods of elevated seawater temperature. However, as global temperatures continue to rise, bleaching events are predicted to become more frequent and severe. Prolonged or repeated bleaching may result in coral mortality and a decline in coral populations. Using your knowledge of climate change, suggest why widespread coral reef loss is a concern. [2] [Total: 29]

10 9477 / H2 Biology / 03 2 In most plants, carbon dioxide is fixed by the Calvin cycle in mesophyll cells. These plants are known as C3 plants. Some plants found in hot, dry environments use a diff