2025 SAJC H2Bio PE P3 (A)

SAJC / H2 Biology 9744/3 JC2 Prelim 2024 Civics Group Index Number Name (use BLOCK LETTERS) ST. ANDREW’S JUNIOR COLLEGE 2025 JC2 PRELIMINARY EXAMINATIONS H2 BIOLOGY 9744/03 Paper 3 Wednesday 17th September 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name, civics group and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagram, graph or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. Write your answers in the spaces provided on the question paper. All working for numerical answers must be shown. Conceptual error (C) Data Quoting (D) Expression (E) Misreading the question (Q) For Examiners’ Use 1 /30 2 /12 3 /8 4 or 5 /25 Total /75 This document (Booklet A) consists of 18 printed pages. [Turn over] H2

1 SAJC / H2 Biology 9744/3 JC2 Prelim 2025 Answer all questions. QUESTION 1 Control of processes in cells must be heavily regulated, failure which results in diseases. Circadian rhythm, the body’s internal clock that regulates sleep and wake cycle over a 24 - hour period, is one such process. It synchronizes body cells with external cues like light and darkness to influence sleep-wake cycles, hormone release and body temperature Clock proteins CLK, BMAL1, PER and CRY are essential proteins that help regulate the circadian rhythm. Proteins CLK and BMAL1 form a complex, which acts like transcriptional activators. Fig. 1.1 shows how these proteins, encoded by “clock genes”, oscillate in control of the circadian rhythm. Fig. 1.1 Daytime Night time

2 SAJC / H2 Biology 9744/3 JC2 Prelim 2025 (a) With reference to Fig. 1.1, state and explain the level at which the CRY and PER proteins are regulated during the night to establish the circadian rhythm. Level of regulation: ……………………………………………….. Explain: ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. …………………………………………………………………………………………[3] (b) A dysregulation of the circadian rhythm leads to various effects on the body, for example, the feeling of jetlag, where the body's core biological processes are "out of sync" with the new environment. Light exposure helps to reset the circadian rhythm by influencing the transcription of PER and CRY through melanopsin signaling. Melanopsin is a light -sensitive photoreceptor. Fig. 1.2 shows the cell signaling process involving melanopsin. Fig. 1.2 G α

3 SAJC / H2 Biology 9744/3 JC2 Prelim 2025 With reference to Fig. 1.2 and your theoretical knowledge, (i) identify the type of receptor for melanopsin. ……………..…………………………………………………………...………………..… [1] (ii) describe how the shining of light on the receptor leads to restoration of the circadian rhythm. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………..…………………..…………………………………...………………..… [6] (c) The dysregulation of PER2 gene may be associated with cancer. Fig. 1.3 shows the data of PER2 gene expression against different parameters.

4 SAJC / H2 Biology 9744/3 JC2 Prelim 2025 Fig. 1.3 PER2 expression levels in normal and cancerous tissues are analysed by reverse transcription-quantitative polymerase chain reaction. Reverse transcription -quantitative polymerase chain reaction is primarily used to measure the amount of a specific mRNA molecule in a sample over time. (i) With reference to the trends from Fig. 1.3, explain if PER2 gene promotes or inhibits progression of cancer. (No quoting of numerical data is required). …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………...………………………..…..[3] (ii) Suggest why reverse transcription-quantitative polymerase chain reaction is used instead of the standard polymerase chain reaction to study gene expression. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………...……………………………………………………………..…..[2] (iii) GAPDH (Glyceraldehyde -3-phosphate dehydrogenase) is a "housekeeping" protein, being expressed commonly in all cells and tissues at relatively high levels. GAPDH is usually analysed together with PER2 expression in Fig.1.3. Suggest why. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………...…………………………………………..…..[1]

5 SAJC / H2 Biology 9744/3 JC2 Prelim 2025 (d) Mutations to proto-oncogenes are also crucial in cancer development. One example is the ras protein. Fig.1.4 shows the Western blot analyses of ras protein in normal tissues and a cancerous tissue. A western blot measures the presence, amount, and sometimes size of specific proteins within a sample Fig. 1.4 (i) With reference to Fig. 1.4, tick against the appropriate the method(s) of conversion of ras to an oncogene. [1] (ii) Explain your choice(s) in (d)(i) and describe how this/these method(s) promote(s) cancer. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... Method of conversion to oncogene Tick if appropriate (√ ) Point mutation to the ras gene Insertion of a more active viral promoter ahead of the ras gene Ras protein

6 SAJC / H2 Biology 9744/3 JC2 Prelim 2025 …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………...…………………………………………………..…..[3] (e) While cancer is a leading cause of death, cardiovascular diseases, including heart conditions, are also major causes of death. Angiotensin converting enzyme (ACE ) inhibitors are a class of medications primarily used to treat high blood pressure and heart failure. They work by blocking the enzyme that converts angiotensin I to angiotensin II, a substance that narrows blood vessels. By reducing the amount of angiotensin II in the body, ACE inhibitors help relax blood vessels, lower blood pressure, and reduce the workload on the heart. Fig. 1.5 shows the structures of the real substrate and some proposed inhibitors for ACE. Fig. 1.5 (i) Describe the mode of enzyme inhibition based on the structures of the inhibitors shown in Fig. 1.5 …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………...

7 SAJC / H2 Biology 9744/3 JC2 Prelim 2025 …………………………………………………………………………………………………... …………………………………………………………………………………...………..…..[3] (ii) Describe the effect of high substrate concentrations on these kind of inhibitors. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …...………………………………………………………………………………………..…..[3] (iii) Suggest why the same