2022 J2 ASRJC H2 Biology Prelims Paper 2 (QP)

ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P2 [Turn over H2 ANDERSON SERANGOON JUNIOR COLLEGE HIGHER 2 2022 JC2 PRELIMINARY EXAMINATIONS CANDIDATE NAME CLASS INDEX NUMBER BIOLOGY 9744/02 PAPER 2 SHORT STRUCTURED QUESTIONS Candidates answer on the Question Paper. No Additional Materials are required. 13 SEPTEMBER 2022 TUESDAY 2 HOURS READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graph Do not use paper clips, highlighters, glue or correction fluid. Answer all questions. 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. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 29 printed pages and 3 blank pages. For Examiner’s Use 1 / 10 2 / 11 3 / 9 4 / 10 5 / 10 6 / 10 7 / 10 8 / 10 9 / 10 10 / 5 11 / 5 Total /100

2 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM//P2 Answer all the questions. 1 Chitin, the second most abundant organic polymer after cellulose on Earth, is found in the cell walls of fungi and the exoskeleton of insects. Both chitin and cellulose serve as structural polysaccharides. The chitin polysaccharide consists of N-acetylglucosamine. Fig. 1.1 shows the structure of chitin. Fig. 1.1 (a) With reference to Fig. 1.1, (i) name the covalent bond between two monomers in a chitin molecule and describe how this bond is formed. …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... [3]

3 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P2 [Turn over (ii) explain how the structure and property of chitin are related to its role as a structural polysaccharide in fungi and insects. …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... [4] (c) Chitinase is an enzyme found in plants. It degrades chitin in fungal cell walls and exoskeletons of insects, protecting the plants against a range of pathogens. Describe the mode of action of chitinase. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… [3] [Total: 10]

4 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM//P2 2 Fig. 2.1 is an electronmicrograph of a human cell during mitosis. Fig. 2.1 (a) Describe the events that take place in the stage of mitosis before that seen in Fig. 2.1. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. .………………………………………………………………………………………………… …………………………………………………………………………………………………. [3]

5 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P2 [Turn over (b) The normal diploid number of chromosomes for a human cell, such as that shown in Fig. 2.1, is 46. The cell in Fig. 2.1 has 92 DNA molecules. Explain the presence of 92 DNA molecules in this cell and why it is important to have this number. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. .………………………………………………………………………………………………… …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. [4]

6 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM//P2 (c) Fig. 2.2 shows DNA replication occurring in a human cell (A) and in an Escherichia coli (B). Diagrams are not shown to scale. A B Fig. 2.2 (i) State one visible difference in the structure of these two DNA molecules during DNA replication and account for this difference. …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... [2] (ii) Explain why there is both continuous and discontinuous synthesis of daughter strands during DNA replication. …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... …………………………………………………………………………………………... [2] [Total: 11]

7 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P2 [Turn over Question 3 starts on page 8

8 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM//P2 3 Fig. 3.1 shows a diagram of protein synthesis. Fig. 3.1 (a) With reference to Fig. 3.1, outline the synthesis of the polypeptide chain from its mRNA. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ……………………………………………………………………………………………….…... …………………………………………………………………………………………………… …………………………………………………………………………………………………… [4] Y

9 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P2 [Turn over (b) During protein synthesis in cells of an embryo, all molecules Y in Fig. 3.1 are observed to be attached to the arginine amino acid instead of lysine. (i) Suggest how the attachment of the wrong amino acid , arginine, to molecule Y may arise. …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... [2] (ii) Suggest and explain the effect of attachment of the wrong amino acid, arginine, to molecule Y on the embryo. …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... …………………………………………………………………………………………..... [3] [Total: 9]

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