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 le