2025 SAJC H2Bio PE P2 (A)

1 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations Civics Group Index Number Name (use BLOCK LETTERS) ST. ANDREW’S JUNIOR COLLEGE 2025 JC2 PRELIMINARY EXAMINATIONS H2 BIOLOGY 9744/2 Paper 2 Wednesday 3rd September 2025 2 hours Materials: Question Paper 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. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiners’ Use 1 /10 2 /12 3 /10 4 /10 5 /10 6 /6 7 /9 8 /10 9 /8 10 /10 11 /5 Total /100 This document consists of x printed pages and 0 blank page. [Turn over H2

2 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations QUESTION 1 Fig. 1.1 shows the structure of the dipeptide consisting of cysteine and tryptophan. Fig.1.1 Picture credits : https://linkinghub.elsevier.com/retrieve/pii/S0039602810003869 (a) Complete the diagram to show the hydrolysis of the dipeptide. ……………………………………………………………………………………………[2]

3 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations 1 Water used in the hydrolysis reaction ; 2 Cysteine amino acid with a - COOH group ; Tryptophan amino acid with a - NH2 group ; (No labels are needed) In bacteria like Escherichia coli, tryptophan is incorporated into polypeptides during protein synthesis. The availability of tryptophan within the cell is tightly regulated by the trp operon which is known as a repressible operon. Fig. 1.2 summarises the structure and control of the trp operon. 1. + H2O + Cysteine Tryptophan 2. 3.

4 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations Fig. 1.2 Picture modified from 9700/W22/42 (b) Suggest and explain the advantage of having repressible operons in prokaryotes. …………………………………………………………………………………………....[2] 1 [Suggest] Essential enzymes / proteins are continuously produced ; 2 [Explain] End product inhibition occurs when enzymes / proteins are synthesized until product / tryptophan concentrations are high ; to prevent wastage of resources; A number of mutations have been found in the trp operon. One of these mutations results in a mutant operator (OC) (c) Predict and explain the likely effect of the O C mutation on the synthesis of tryptophan in E. coli. …………………………………………………………………………………………....[3] [Predict] 1 no repression of tryptophan synthesis / tryptophan synthesized continuously (even when in abundance); [Explain] 2 trp repres