2025 JC2 TJC Prelim P3 QP

1 [TURN OVER TEMASEK JUNIOR COLLEGE 2025 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CENTRE NUMBER S INDEX NUMBER BIOLOGY 9744/03 Paper 3 17 September 2025 2 hours Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name 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. DO NOT WRITE IN ANY BARCODES. Answer all questions in the spaces provided in the Question Paper. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 24 printed pages and 0 blank pages. For Examiner’s Use 1 / 30 2 / 10 3 / 10 4 OR 5 / 25 Total / 75

2 Section A Answer all questions. 1 Myeloid stem cells in the human bone marrow undergo repeated proliferation and differentiation once they receive external signals to produce more white blood cells. White blood cells are critical in fighting infections from pathogens. Such stem cells will go through cell cycles in different stages and are regulated tightly by various proteins and checkpoints found along the way. Fig. 1.1 shows the various stages of the cell cycle and how it is regulated at the various checkpoints. The important control points of the cell cycle lie at the end of the G2 phase (G2/M transition), in mitosis (metaphase/anaphase transition) and in G1 phase (restriction point). Controls are shown in both solid and broken arrows. Fig. 1.1 (a) Describe the function of metaphase/anaphase transition control and how this may prevent the development of cancer. ………………………………………………………………………………………………….…………….. .…..………………………………………………………………………………….………………………... ………..………………………………………………………………….…………………………………… …………..………………………………………………….………………………………………………… ……………..………………………………….……………………………………………………………… ………………...………………….…………………………………………………………………………... ……………….....………………….…………………………………………………………………….. [3] Metaphase/anaphase transition Restriction point G2/M transition DNA replication complete? DNA intact? Mitosis completed?

3 [TURN OVER Spindle fibres are polymers made from tubulin monomers. The removal of tubulin monomers causes spindle fibres to shorten. Scientists investigated the effect of the rate of tubulin removal on the speed of movement of chromatids during mitosis. Fig. 1.2 shows the results of the investigation. Fig. 1.2 (b) (i) Describe how these results support the role of spindle fibres in mitosis. ……………………………………………………………………………………………….………….. .…….……………………………………………………………………………….…………………… ………….……………………………………………………………….………………………………. ……………….………………………………………………..………………………………………… …………………….………………………………………………………………………………… [2] (ii) Paclitaxel, also known as Taxol, is a microtubule structure-stabilizing drug that is commonly used to treat both early-stage breast cancer and advanced, or metastatic breast cancer. Explain why drugs such as Paclitaxel are effective as an anti-cancer therapeutic. ……………………………………………………………………………………………….………….. .…….……………………………………………………………………………….…………………… ………….……………………………………………………………….………………………………. ……………….………………………………………………..………………………………………… …………………….………………………………………………………………………………… [2] Rate of tubulin removal Speed of movement of chromatids

4 Chronic myeloid leukemia (CML) is a cancer of the white blood cells. Patients with CML suffer from shortness of breath and have increased risk of infection. This slow-growing cancer arises from a disorder in the myeloid stem cells found in bone marrow. Myeloid stem cells are responsible for maintaining the red blood cell and white blood cell populations in the body. CML patients are diagnosed via a complete blood count test, which will identify abnormal numbers of different types of blood cells in a fixed volume of blood. Fig. 1.3 shows the blood cells in 100 ml of blood from a healthy person and a CML patient. Fig. 1.3 (c) Explain what is meant by cancer. ………………………………………………………………………………………………….…………….. .…..………………………………………………………………………………….………………………... ………..………………………………………………………………….…………………………………… …………..………………………………………………….………………………………………………… ……………..………………………………….……………………………………………………………… ………………...………………….…………………………………………………………………………... ……………….....………………….…………………………………………………………………….. [3]

5 [TURN OVER (d) With reference to Fig. 1.3, explain how abnormal myeloid stem cells change the red blood cell and white blood cell populations. ……………………………………………………………………………………………….….……………. ………………………………………………………………………………….….………………………… ….………………………………………………………………….….……………………………………… …….………………………………………………….….…………………………………………………… ……….………………………………….….………………………………………………………………… ………….………………….….……………………………………………………………………………… ……………….….…………………………………………………………………………………………… ….….……………………………………………………………………………………………................... ...................................................................................................................................................... [4] Changes to ABL and BCR genes are normally associated with CML cancer. A genetic study that screens for the presence and length of ABL and BCR genes in specific chromosomes reveal that abnormal myeloid stem cells arise from a mutation event. The mutation results in mutant chromosome 22, also known as the Philadelphia chromosome. Fig. 1.4 shows the results of the genetic study. Chromosome 2 is known to not carry ABL and BCR genes. Fig. 1.4 (e) (i) Describe the mutation event that gives rise to Philadelphia chromosome. ……………….………………………………………………..………………………………………… ……….……………………………………………………………………….……………………… [1]

6 (ii) Suggest the purpose of screening chromosome 2. ……………….………………………………………………..………………………………………… ……….……………………………………………………………………….……………………… [1] Further studies revealed that CML patients that have the Philadelphia chromosome express an altered form of tyrosine kinase receptor, known as BCR -ABL. BCR -ABL is a receptor in a cell signaling pathway that stimulates cell growth. BCR-ABL receptor is observed to have a higher than normal level of activity, and abnormality in its ligand-receptor interaction. (f) (i) Describe how a receptor tyrosine kinase receptor (RTK) such as the BCR -ABL is activated in a cell signalling pathway. ……………………………………………………………………………………………….…………... …...….……………………………………………………………………………….…………………... ………….….……………………………………………………………….……………………………. ….……………….………………………………………………..……………………………………… ……………………….………………………………………………………….…………………… [2] (ii) Suggest how the presence of a Philadelphia chromosome may lead to the development of cancer. ……………………………………………………………………………………………….…………... …...….……………………………………………………………………………….…………………... ………….….……………………………………………………………….……………………………. ….……………….………………………………………………..……………………………………… ……………………….………………………………………………………….…………………… [2]

7 [TURN OVER In the regulation of cell cycles, roles of proteins such as cyclin-dependent kinases (CDK) and cy