2025 CJC H2Bio PE P3 (QP)

NAME: ___________________________________________ CLASS: _________ INDEX: __________ CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Higher 2 BIOLOGY 9744/03 Paper 3 Long Structured and Free-Response Questions 16 September 2025 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 on all the work you hand in. Write in dark blue or black pen on both sides of the paper. [PILOT FRIXION ERASABLE PENS ARE NOT ALLOWED] You may use a soft pencil for any diagrams, graphs, or rough working. 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 in this section. Write your answers in the writing 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. This document consists of 17 printed pages and 1 blank page. [Turn over For Examiner’s Use Section A 50 1 2 3 Section B 25 4 or 5 Total 75

2 2025 Prelim/ 9744/ 03 Section A Answer all the questions in this section. 1 Based on the statistics by World Health Organisation (WHO), cancer is a leading cause of death worldwide, accounting for nearly 10 million deaths in 2020, or nearly one in six deaths. Many causative factors, including chemical carcinogens may increase the chances of cancerous growth. (a) Name one chemical carcinogen. ……………………………………………………………………………………………………………. [1] Studies showed that individuals inheriting BRCA 1 gene that underwent loss-of-function mutation have an increased risk of developing breast and ovarian cancers. (b) Based on the information above, identify the type of gene BRCA 1 belongs to and justify your answer. ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………. [2] Mutations in another gene, BRCA 2, was shown to increase the risk of developing breast and ovarian cancers. Fig. 1.1 shows the percentage risk of developing these cancers in general population, individuals with BRCA 1 mutations, and individuals with BRCA 2 mutations. Fig. 1.1

3 2025 Prelim/ 9744/ 03 (c) With reference to Fig. 1.1, (i) describe the effect of BRCA 1 mutations on the risk of developing ovarian cancer. ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [1] (ii) describe the effects of BRCA 2 mutations on the risk of developing breast cancer. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [2] (iii) compare the effects of BRCA 1 mutations and BRCA 2 mutations on the risk of developing breast cancer. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [3] (iv) suggest an explanation for the differences in the effects of BRCA 1 mutations and BRCA 2 mutations on the risk of developing breast cancer. ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [1] DNA replication is an important process prior to cell division. Base-pairs mismatch may sometimes occur during DNA replication. This base-pair mismatch can often be rectified during the elongation stage by the proofreading activity of DNA polymerase. Fig. 1.2 briefly illustrates the mechanism of proofreading activity in eukaryotic DNA polymerase δ.

4 2025 Prelim/ 9744/ 03 Fig. 1.2

5 2025 Prelim/ 9744/ 03 (d) With reference to Fig. 1.2, (i) identify molecule X. …………………………………………………………………………………………………….. [1] (ii) describe the events that occurred to enable the correct base to be incorporated by DNA polymerase δ when there was a base-pair mismatch. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [5] (iii) suggest the directionality of the activity the exonuclease domain on the leading strand . Justify your answer. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [2] If the proofreading activity of DNA polymerase a nd other DNA repair mechanisms fail to rectify errors during DNA replication, mutations occur. Mutation in t he Kirsten rat sarcoma (K-Ras) proto-oncogene is commonly found in patients with colorectal cancer. (e) Mutation in K-Ras gene is not passed down to the offsprings. Name this type of mutation. ……………………………………………………………………………………………………………. [1]

6 2025 Prelim/ 9744/ 03 In one of the studies, the resulting mutant K-Ras protein was purified from colorectal cancer cells and crystallography was performed to determine the structure of the protein. Fig. 1.3 shows the structure of the mutant K-Ras protein in the presence and absence of growth factors. Fig. 1.3 (f) With reference Fig. 1.3, identify the level of protein structure of K-Ras protein. ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………. [3] (g) Based on the information provided above and Fig. 1.3, suggest how mutation in K-Ras gene contributes to the development of colorectal cancer. ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………. [4]

7 2025 Prelim/ 9744/ 03 Cancer cells and stem cells are similar in many ways. One of the similarities is their abilities to maintain the length of telomere despite multiple rounds of successive DNA replication. (h) Apart from their ability to maintain the length of telomere, c ompare the features of cancer cells and embryonic stem cells. ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………. [2] (i) “Telomerase prevents end-of-replication problem in both cancer and stem cells”. Comment on the accuracy of the statement. ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………...... ……………………………………………………………………………………………………………. [3] [Total: 31] 2 Polymerase Chain Reaction (PCR) possesses the potential to generate billions of copies of target DNA from a single copy. One of the requirements of this method is having information on at least partial sequences of the target DNA, which is needed to design primers that hybridise specifically t