2025 DHS H2 Prelim Paper 3 (with answers)

© DHS 2025 9744/03 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 BIOLOGY 9744/03 Paper 3 Long Structured and Free-Response Questions 26 September 2025 2 hours Candidates answer on the Question Paper and Answer Booklet. Additional Materials: Answer Booklet READ THESE INSTRUCTIONS FIRST: Write your name, centre number, index number and class 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. Sections A Answer all questions in the spaces provided on the Question Paper. Sections B Answer any one free-response question in the Answer Booklet provided. 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 Section A / 50 1 32 2 9 3 9 Section B / 25 4 / 5 25 Total 75 This document consists of 18 printed pages and 2 blank pages.

2 © DHS 2025 9744/03 Section A: Long Structured Questions Answer all questions. 1 Hawaii is located in the central Pacific Ocean, approximately between 19° and 22° North latitude, placing it within the tropics. It experiences a warm tropical climate all year round. This positioning influences its unique ecosystems and diverse flora and fauna, including native species like the Hawaiian honeycreepers. Epidermal cells of Hawaiian honeycreepers possess the Epidermal Growth Factor Receptor (EGFR), which plays a crucial role in their feather development. Like in other birds, EGFR helps in regenerating damaged tissues and maintaining feather quality, which is essential for their survival and adaptation to environmental changes. Fig. 1.1 shows EGF binding to EGFR on the surface of a cell. A specific region on each EGFR functions as an enzyme. Fig. 1.1 (a)(i) Name the enzyme found on EGFR and describe the reaction catalysed by the enzyme. Be as precise as possible. [2] (ii) Suggest why having a mutated EGFR can increase the susceptibility of the Hawaiian honeycreepers to infections by pathogens. [1]

3 © DHS 2025 9744/03 [Turn over The EGFR and insulin receptor exhibit a high degree of similarities. (b)(i) Describe the insulin signaling pathway after the insulin receptor is fully activated. [2] RAF and RAS are two examples of proteins involved in signal transduction. RAF can be activated by phosphorylation, or by direct interaction with its allosteric site. RAS protein is known to activate RAF by direct interaction instead of phosphorylation. (ii) Suggest why RAS does not activate RAF by phosphorylation. [1]

4 © DHS 2025 9744/03 In some Hawaiian honeycreepers, slower feather regeneration was observed. Scientists hypothesised that this may be due to reduced EGFR expression caused by increased histone deacetylation. To test this, they measured histone acetylation levels and EGFR mRNA expression in four populations of honeycreepers exposed to varying levels of feather damage through moulting. Table 1.1 shows the level of histone acetylation in the four populations and Fig. 1.2 shows the mRNA expression in each population. Table 1.1 population histone acetylation level / a.u. A 1.23 B 2.56 C 4.39 D 4.38 Fig. 1.2 (c)(i) With reference to Table 1.1 and Fig. 1.2, explain how histone acetylation may regulate the expression of the EGFR gene in Hawaiian honeycreepers. [3]

5 © DHS 2025 9744/03 [Turn over (ii) Discuss whether the data in Table 1.1 and Fig. 1 .2 fully support the hypothesis that histone deacetylation is responsible for reduced EGFR expression in some populations. [3] The FEGF1 gene, located downstream of EGFR, contains non-coding sequences believed to regulate EGFR gene expression in Hawaiian honeycreepers. Fig. 1.3 shows the schematic representation of the F EGF1 gene. In a recent study, scientists found that some birds with rapid feather regrowth had mutations in intron 2 of FEGF1, allowing regulatory proteins to bind. These regulatory proteins control the transcription of the EGFR gene. Fig. 1.3 (d) Suggest how mutations to intron 2 of the FEGF1 gene could result in faster feather regrowth. [4]

6 © DHS 2025 9744/03 In the forests of Hawaii, climate change has led to warmer temperatures and increased rainfall, which in turn has expanded the range of Plasmodium relictum , a parasitic protozoan that causes avian malaria. Avian malaria is a mosquito- borne disease of birds. The local Hawaiian honeycreeper birds, especially the Iiwi and Apapane, are particularly susceptible to this pathogen due to their long- term isolation and lack of prior exposure to such diseases. This outbreak of avian malaria exhibits symptoms such as anemia, respiratory distress, and organ failure in the honeycreeper population. Table 1.2 shows the mean rate of oxygen consumption per gram of body mass in Hawaiian honeycreepers infected and uninfected with P. relictum, measured over a 12-hour period at a constant ambient temperature of 27 oC. Table 1.2 Time (h) Mean rate of oxygen consumption / a.u. Uninfected Hawaiian honeycreepers Infected Hawaiian honeycreepers 0 33.27 23.13 4 33.48 22.92 8 33.65 22.71 12 33.70 22.63 (e) Using Table 1.2, explain how infection with P. relictum may affect the metabolism of Hawaiian honeycreepers. [3]

7 © DHS 2025 9744/03 [Turn over The immune system of Hawaiian honeycreepers responds to P. relictum by identifying the parasite as non-self antigens. Fig. 1.4 is a diagram of a protein in the cell surface membrane of a macrophage from the Hawaiian honeycreepers. Macrophages use these proteins in antigen presentation. Non- self antigens bind to these proteins and are involved in the activation of specific T lymphocytes during the immune response. Fig. 1.4 (f)(i) Explain what is meant by a non-self antigen. [1] Macrophages partially digest these pathogens and present antigens to T lymphocytes during immune responses. (ii) With reference to Fig. 1. 4, explain how a specific immune response against these pathogens is possible. [4]

8 © DHS 2025 9744/03 Hawaiian honeycreepers do not occur naturally in other parts of the world. Although at least 56 species of Hawaiian honeycreepers have been documented, only 18 of them survive today with the most recent extinction occurring in 2004. Fig. 1. 5 shows the phylogenetic tree of the Hawaiian honeycreeper species , including the Hawaii Creeper, that was constructed based on their mitochondrial genomes . The four grey vertical bars indicate the times when the four Hawaiian Islands were formed. Fig. 1.5

9 © DHS 2025 9744/03 [Turn over (g)(i) The Hawaii Creeper, while endemic to Hawaii, did not originate there. With reference to Fig. 1.5, explain how the Hawaii Creeper appears in Hawaii. [3]

10 © DHS 2025 9744/03 A spectrogram shows the frequencies that make up a sound and how they change over time. The courtship songs of four Hawaiian honeycreeper species were recorded. Fig. 1.6 shows the spectrograms of common rosefinc