2025 CJC H2Bio PE P3 (A)

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 20 printed pages and 0 blank page. [Turn over For Examiner’s Use Section A 50 1 2 3 Section B 25 4 or 5 Total 75 Suggested Answers

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] 1. Benzo[a]pyrene / ethidium bromide / 5’-Bromouracil / AVP. 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] 1. Tumour suppressor genes 2. (The loss-of-function mutation of BRCA 1 increases the risk of developing breast and ovarian cancers implies that ) this gene codes for gene products that inhibit growth without the appropriate conditions (OWTTE).

3 2025 Prelim/ 9744/ 03 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 (c) With reference to Fig. 1.1, (i) describe the effect of BRCA 1 mutations on the risk of developing ovarian cancer. ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [1] 1. The risk of developing ovarian cancer in female by age 70 increases from 1.5% (accept: 1% - 1.5%) in general population to 36% (accept: 36% - 36.5%) in individuals with BRCA 1 mutations (ii) describe the effects of BRCA 2 mutations on the risk of developing breast cancer. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [2] 1. The risk of developing breast cancer in female by age 70 increases from 12.5% (accept: 12% - 13%) in general population to 43.5% (accept: 43.5% - 44%) in individuals with BRCA 2 mutations. 2. The risk of developing breast cancer in male by age 70 increases from 0.1% (accept 0.1% - 0.3%) in general population to 7.6% (accept: 7.5% - 8%) in individuals with BRCA 2 mutations.

4 2025 Prelim/ 9744/ 03 (iii) compare the effects of BRCA 1 mutations and BRCA 2 mutations on the risk of developing breast cancer. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………….. [3] 1. The risk of developing breast cancer in female and male by age 70 increases in individuals with either BRCA 1 or BRCA 2 mutations as compared to the general population. 2. The risk of developing breast cancer in female by age 70 increases more in individuals with BRCA 1 mutations than in individuals with BRCA 2 mutations as compared to the general population, where the increase is 47.5% (accept: 47% - 48%) and 31% (accept: 30% - 32%) respectively. 3. The risk of developing breast cancer in male by age 70 increases more in individuals with BRCA 2 mutations than in individuals with BRCA 1 mutations than as compared to the general population, where the increase is 7.5% (accept 7.2% - 7.9%) and 1.4% (accept: 0.1% - 1.4%) respectively. (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] Any of the following: 1. Differences in gene functions and protein activities. 2. BRCA 1 may be more highly expressed in female or more critical for maintaining the genomic stability of female breast cells. 3. BRCA 1 may influence hormone regulation differently than BRCA 2, affecting the breast environment and contributing to cancer risk. 4. AVPs 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.

5 2025 Prelim/ 9744/ 03 Fig. 1.2

6 2025 Prelim/ 9744/ 03 (d) With reference to Fig. 1.2, (i) identify molecule X. …………………………………………………………………………………………………….. [1] 1. dGMP / deoxyguanosine monophosphate / deoxyribonucleoside monophosphate with guanine base (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] 1. The (free 3’) end of the growing daughter DNA strand / leading strand was moved from polymerase domain into the exonuclease domain. 2. At the exonuclease domain, the enzyme catalysed the hydrolysis of phosphodiester bond between the leading strand and the last deoxyguanosine monophosphate / deoxynucleoside monophosphate / molecule X. 3. Molecule X / deoxyguanosine monophosphate is released from the complex. 4. The (free 3’) end of the growing daughter DNA strand / leading strand was moved back from the exonuclease domain into polymerase domain. 5. The polymerase catalyses the formation of phosphodiester bond between the correct deoxythymidine triphosphate / nucleotide with a thymine base and the growing daughter DNA strand / leading strand and through complementary base pairing. (iii) suggest the directionality of the activity the exonuclease domain on the leading strand . Justify your answer. …………………………………………………………………………………………………………