HCI 2023 JC2 9744 H2 Bio Prelim P2 QP (Sharing)

© Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 HWA CHONG INSTITUTION JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 22S7__ CENTRE NUMBER INDEX NUMBER BIOLOGY Paper 2 Structured Questions Candidates answer on the Question Paper. No Additional Materials are required. 9744/02 21 August 2023 2 hours INSTRUCTIONS TO CANDIDATES There are five question booklets ( I - V) to this paper. Write your name and CT group in the spaces provided at the top of this cover page and on the lines provided at the top of the cover pages of Booklets II, III, IV and V. There are ten questions. Answer all questions in the spaces provided on the Question Paper. INFORMATION FOR CANDIDATES 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. You are reminded of the need for good English and clear presentation in your answers. This document consists of 27 printed pages. For Examiners' Use 1 / 11 2 / 10 3 / 12 4 / 10 5 / 12 6 / 13 7 / 12 8 / 10 9 / 5 10 / 5 Total / 100

2 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 QUESTION 1 Bacterial cells are prokaryotic. The cells of plants are described as eukaryotic. Both the bacterial cell and the plant cell have a cell wall, but the main component of the bacterial cell wall is peptidoglycan and not cellulose. (a) Protoplasts are plant cells that have had their cell walls removed by treatment with enzymes. Scientists often use protoplasts when researching ways to improve the yield of crop plants. Fig. 1.1 is a scanning electronmicrograph of protoplasts of cells from the tobacco plant, Nicotiana tabacum. Fig. 1.1 (a) Explain why scientists keep the protoplasts in a solution that has the same water potential as the cell. [2] (a external solution at same water potential as protoplasts cell surface membrane magnification x256

3 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 After protoplast treatment, the cells can be stimulated to synthesise new cell wall material. Fig. 1.2 is at a higher magnification than Fig. 1. 1 and shows a scanning electronmicrograph of part of a protoplast in an early stage of cell wall synthesis. Fig. 1.2 (b) The cellulose microfibrils visible in Fig. 1.2 will form cellulose fibres. Each cellulose molecule is a polymer of β-glucose. (i) Define the term polymer. [1] (ii) Explain how the structure of a cellulose molecule allows for the formation of the cellulose microfibrils and fibres. [3] magnification x3075 cellulose microfibrils chloroplasts visible below the cell surface membrane

4 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 Two main forms of bacteria V. cholerae, O1 and O139, are able to colonise the small intestine and cause cholera. These two forms are able to produce a toxin, choleragen, which causes the symptoms of diarrhoeal disease. V. cholerae has flagella that aid in its motility. Monoclonal antibodies (mAbs) can be designed to act against components of the cell wall of bacteria. The cell wall has an outer membrane with lipopolysaccharide (LPS) molecules, shown in Fig. 1.3. Fig. 1.3 The core polysaccharide and the lipid A components of the LPS molecules are the same in both V. cholerae O1 and V. cholerae O139. However they have different O-polysaccharides. (c) Laboratory tests were carried out using two different monoclonal antibodies that had been designed and produced to act against the LPS of bacterial cultures of V. cholerae O1: • mAb 2D6 acts against the O-polysaccharide • mAb ZAC-3 acts against the core polysaccharide and lipid A components. (i) Explain why the mAb ZAC -3 produced against the core polysaccharide and lipid A components will not act against the O-polysaccharide of the LPS molecules. [2]

5 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 (ii) The results of the tests showed that both mAbs were effective in causing agglutination (clumping) of bacteria and in preventing their motility. This suggests they may be useful for preventing cholera and for treating the disease. Justify the claim that mAb 2D6 and mAb ZAC -3 are useful for preventing cholera and for treating the disease. [3] [Total: 11]

6 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 QUESTION 2 Genetic information encoded in DNA is transcribed to different types of RNA. An example is the transfer RNA (tRNA) that is needed during translation. Fig. 2.1 shows two representations of a tRNA molecule. Fig. 2.1 (a) Name the structures labelled X and Y in Fig. 2.1. X Y [2] (b) Compare the structure of Z with the structure of DNA. [3] Y 5’ 3’ X 3’ 5’ Z Z

7 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 (c) With reference to Fig. 2.1, explain how the tRNA acts as an adaptor molecule for translation. [4] There are around 45 different tRNAs in a typical eukaryotic cell. There are 20 amino acids used in the process of translation. (d) Suggest why each amino acid can be carried by more than one type of tRNA. [1] [Total: 10]

8 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 QUESTION 3 In the bacterium Escherichia coli , the repressible system of operon regulation serves as a means of controlling the synthesis of a wide variety of enzymes involved in anabolic pathways. An example is the trp operon, which contains a group of structural genes that are transcribed together. Fig. 3.1 shows the trp operon when tryptophan is absent. Fig. 3.1 (a) Suggest why the structural genes in trp operon are transcribed together. [1] (b) trpR is a regulatory gene located upstream of the trp operon. Describe the differences between the functions of trpR and trpE. [2]

9 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 (c)(i) On Fig. 3.2, draw the positions of RNA polymerase and the repressor molecule when tryptophan is present. Fig. 3.2 [2] (ii) Explain the significance of your answer in (c)(i). [3]

10 © Hwa Chong Institution 2023 9744 H2 Biology / JC2 Preliminary Examinations / Paper 2 Another operon found in E. coli is the lac operon, which produces the enzyme β-galactosidase. E. coli can use glucose or disaccharides, such as lactose, in its metabolism. Lactose needs to be hydrolyzed by the enzyme β-galactosidase to form glucose and galactose, which can then be used by E. coli. In an investigation into the growth of E. coli , a sample of the bacterium was grown in a medium that contained limited concentrations of glucose and lactose. The population size of E. coli was measured at regular intervals. Fig. 3.3 shows the population growth curve obtained for this investigation. Fig. 3.3 (d) Describe and explain the population growth curve shown in Fig. 3.3. [4] [Total: 12]