ACJC 2023 H2 Bio Prelim P3_ANSWERs

This document consists of 21 printed pages. [Turn over Anglo-Chinese Junior College JC2 Biology Preliminary Examination Higher 2 CANDIDATE NAME FORM CLASS TUTORIAL CLASS INDEX NUMBER BIOLOGY Paper 3 Long Structured and Free-response Questions Candidates answer on the Question Paper. Additional Materials: Writing paper(s) 9744/03 29 August 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your Name, Class and Index number 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. Section A Answer all questions. Section B Answer any one question on the separate writing paper(s) provided. 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. At the end of the examination, fasten all the writing paper(s) used securely together. For Examiners’ use only Section A 1 / 30 2 / 10 3 / 10 Section B 4 or 5 / 25 Total / 75

2 Anglo-Chinese Junior College 2023 J2 H2 9744 Paper 3 Preliminary Examination For Examiner’s Use Section A Answer all the questions in this section. 1 Polyethylene terephthalate (PET) is one of the common polymers used to make plastic bottles. A bacterial species, Ideonella sakaiensis, was found to have the ability to break down PET through a two-step process catalysed by two enzymes. Fig. 1.1 shows the first step in which the enzyme PETase resulted in the degradation of PET into monohydroxylethyl terephthalate (MHET), and Fig. 1.2 shows the second step where the enzyme MHETase breaks down MHET into ethylene glycol (EG) and terephthalic acid (TPA). Fig. 1.1 Fig. 1.2 The structures of PETase and MHETase are shown in Fig. 1.3 and Fig. 1.4 respectively. Fig. 1.3 Fig. 1.4

3 [Turn over Anglo-Chinese Junior College 2023 J2 H2 9744 Paper 3 Preliminary Examination For Examiner’s Use (a) (i) With reference to Fig. 1.1 and Fig. 1.2, state the type of reaction that PETase and MHETase catalyse. 1. hydrolysis; …………………………………………………………………………………………. [1] (ii) Describe the secondary structures present in PETase and MHETase in Fig. 1.3 and Fig. 1.4. 1. Alpha helices and beta-pleated sheets can be found within the polypeptide; ………………………………………….…………………………………………………. 2. In an alpha helix, each N-H forms hydrogen bond with C=O four amino acids apart in the same polypeptide backbone; ……………………………………