2025 JC2 TJC Prelim P2 QP

1 [TURN OVER TEMASEK JUNIOR COLLEGE 2025 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CENTRE NUMBER S INDEX NUMBER BIOLOGY 9744/02 Paper 2 Part I 29 August 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 14 printed pages and 2 blank pages. For Examiner’s Use 1 / 10 2 / 10 3 / 10 4 / 11 5 / 9 6 / 10 7 / 11 8 / 8 9 / 11 10 / 5 11 / 5 Total / 100

2 Answer all questions. 1 Most membranes in a cell exist as phospholipid bila yers. Apart from the cell surface membrane, there are several organelles in the cell that are also enclosed by membranes. (a) The fluid mosaic model was devised by Singer and Nicolson in 1972 and was used to describe the membranes. Explain why membranes are described as fluid mosaic in structure. ……………………………………………………………………………………………………………….… ……………………………………………………………………………………………………………….… ……………………………………………………………………………………………………………….… ……………………………………………………………………………………………………………….… …………………………………………………………………………………………………………….... [2] Fig. 1.1 shows a cross-section of the nuclear membr ane. The arrow in Fig. 1.1 indicates the movement of substances towards a specific organelle Z. Fig. 1.1 (b) With reference to Fig. 1.1, match the letters A, B, and C to the following structures: (i) outer nuclear membrane …………………………………………………………… (ii) inner nuclear membrane …………………………………………………………… (iii) nuclear pore …………………………………………………………… [3] Z A C B

3 [TURN OVER (c) (i) State the name of the organelle Z and briefly describe its structure. …………………………………………………………… ………………………………….………………. …………………………………………………………… ………………….………………………………. ……………………………………………………… ……….………………………………………………. ………………………………………………..… …………………………………………………………… .…………………………………………………………… ……………………………………………… [2] (ii) With reference to the function of organelle Z, suggest the advantage of the proximity of organelle Z to the nuclear membrane. …………………………………………………………… ………………………………….………………. …………………………………………………………… ………………….………………………………. …………………………………………………………… ………………….………………………………. ……………………………………………………… ……….………………………………………………. ……………………………………………….……… ………………………………………………………. ……………………………….……………………… ………………………………………………………. ………………..…………………………………………… …………………………………………….. [3] [Total: 10]

4 2 Collagen is the most abundant protein found in the human body. Fig 2.1 shows the primary structure of collagen, which consists of a repeated sequence. Fig 2.1 (a) (i) Name amino acid E. ………………………………………………………………………………………………..... [1] (ii) With respect to collagen’s structure, explain the significance of amino acid E. ……………………………………………………………………………………………...….…………... ………………………………………………………………………………..…….……………………… ………………………………………………………………..……….…………………………………… .………………………………………………..………… ..……………………………………………….. .……………………………………………………………………………………………………….… [2] Collagen is an important structural protein found in our skin. Research has shown that the skin’s surface has a slightly acidic pH between 4.7 and 5.75. Various skincare products that contain acid derivatives can cause the skin surface to be more acidic. Certain skin conditions that cause inflammation or infection can also cause the skin’s surface pH to vary. Neutrophils and macrophages require oxygen when undergoing phagocytosis. (b) Suggest how inflammation can cause pH of the skin to be more acidic. …………………………………………………………… ………………………………….………………..… ……………………………………………………………………………….………………………………..… ………………………………………………………………. ………………………………………………..… ……………………………………………….………………………………………………………………..… …………………………….................................................................................................................. [ 2]

5 [TURN OVER (c) Explain how a decrease in pH can affect the structure and stability of collagen. …………………………………………………………… …………………………………….……………….. …………………………………………………………… …………………….……………………………….. …………………………………………………………… …….……………………………………………….. ………………………………………………….………… …………………………………………………….. ………………………………….………………………… …………………………………………………….. .………………….………………………………………… …………………………………………………..... ………………….……………………………………………… …………………………………………….. [3] Aside from collagen, another structural molecule that can be found in nature is cellulose. (d) Compare the structures of collagen and cellulose. …………………………………………………………… ………………………………….………………..… ……………………………………………………………………………….………………………………….. ………………………………………………………… …….………………………………………………….. ……………………………………………….…………… …………………………………………………….. …………………………….................................................................................................................. [ 2] [Total: 10]

6 3 Acetylcholine is an essential neurotransmitter. A neurot ransmitter is a signalling molecule secreted by a neuron that affects other cells. They are import ant to the function of complex neural systems. Acetylcholine is involved in various physiological processes, including voluntary and involuntary muscle contraction, learning and memory. Acetylcholine is synthesised by the enzyme, choline acetyltransferase (CHAT). Fig. 3.1 shows the structure of CHAT. Fig. 3.1 (a) With reference to Fig 3.1, name the secondary structure of protein that is most observed. ………………………………………………………………………………………………………….... [1]

7 [TURN OVER Fig. 3.2 shows the mechanism involved in the sy nthesis of acetylcholine. Boxes have been drawn around the names of the molecules. Fig. 3.2 (b) With reference to Fig. 3.1 and 3.2, describe the mechanism of action of CHAT enzyme in terms of induced fit hypothesis. ……………………………………………………………………………………………….….…………….… ……………………………………………………………………………….….…………………………….… ……………………………………………………………… ..……………………………………………….… ……………………………………………….….… ………………………………………………………….… …………………………….................................................................................................................. [ 2]

8 Some people choose to take choline and acetyl-CoA supplements to improve brain health and nerve signalling. (c) Explain how these supplements impact the action of CHAT. …………………………………………………………… ………………………………….….…………….… ……………………………………………………………………………….….…………………………….… ………………………………………………………… …….….…………………………………………….… ……………………………………………….….…… ……………………………………………………….… ……………………………….….…………………………………………………………………………….… ……………….….…………………………………… …………………………………………………………. ….………………………………………………………… …………………………………….….…………… ……………………………………………………… ……………………… .................................................. .......................................................................................................................................................... [4] Acetylcholine is hydrolysed by acetylcholinesterase (ACHE). Once hydrolysed, the neuro-signalling pathway is terminated. Thus, ensuring proper signal transmission and preventing overstimulation. A lethal polypeptide toxin from a green mamba snake binds irreversibly to the active site of ACHE. (d) (i) Identify what type of inhibitor the toxin is.