2025 SAJC H2Bio PE P2 (QP)

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 Set A and Set B 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 16 printed pages and 0 blank page. [Turn over H2

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

3 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations 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. (b) Suggest and explain the advantage of having repressible operons in prokaryotes. …………………………………………………………………………………………………..…. …………………………………………………………………………………………………..…. …………………………………………………………………………………………….……….. …………………………………………………………………………………………….……….. ………………………………………………………………………………………………… ..[2] 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] Fig. 1.2 Picture modified from 9700/W22/42

4 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations (d) Describe three differences in the structure and organisation of prokaryotic and eukaryotic genomes. ………………………………………………………………………………………………….…. ………………………………………………………………………….…………………………. …………………………………………………………………………….………………………. …………………………………………………………………………….………………………. ……………………………………………………………………………….……………………. ……………………………………………………………………………….……………………. ……………………………………………………………………………….……………………. ………………………………………………………………………………….…………………. ………………………………………………………………………………….……………….[3] [Total: 10]

5 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations QUESTION 2 (a) In chickens, feather color is either white, black or speckled. The alleles for black feathers and white feathers are denoted by “ C B ” and “ C W ” respectively. A cross between a white chicken and a black chicken gave rise to a speckled chicken. White Black Speckled Fig. 2.1 (i) Using the information provided, explain the appearance of the speckled chicken. …………………………………………………………………………………………………..…. …………………………………………………………………………………………………..…. …………………………………………………………………………………………….……….. …………………………………………………………………………………………….……….. ………………………………………………………………………………………………… ..[2] (ii) Using the symbols provided, draw a genetic diagram to show the results of a sibling mating between two speckled chickens. [3]

6 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations (b) Drosophila melanogaster, commonly known as the fruit fly, has been a cornerstone of genetic research for over a century. The practical benefits of using Drosophila are numerous and contribute significantly to its widespread adoption in laboratories. (i) Suggest why fruit flies are good experimental organisms for carrying out crosses in genetic research. …………………………………………………………………………………………….……….. ………………………………………………………………………………………………… ..[1] The purple gene is known for its impact on eye color in Drosophila. The recessive allele results in a characteristic "purple eye" phenotype, a clear deviation from the normal, wild - type red eyes typically observed in fruit flies The vestigial gene controls wing development in Drosophila. The recessive allele leads to a distinctive "short, 'vestigial' wings" phenotype. Flies exhibiting this mutation are unable to fly, representing a significant morphological and functional alteration from the normal, long wings of wild-type flies. Pure breeding flies with red eyes and long wings were crossed with pure breeding flies with purple eyes and vestigial wings. All the F1 flies show red eyes and long wings. These F1 flies undergo a test cross and the following results were obtained in this F2 generation. Phenotype of F2 flies Observed number red eyes and long wings 305 red eyes and vestigial wings 41 purple eyes and long wings 39 purple eyes and vestigial wings 315 Total 700 (ii) A chi-squared (2) test was carried out. Fill in the blanks in the table below to reflect the expected ratio and expected numbers for each class of phenotype. Calculate the 2 value. 2 =  E )EO( 2− v = c – 1 where  = ‘sum of…’ O = observed ‘value’ v = degrees of freedom E = expected ‘value’ c = number of classes

7 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations A chi-squared table. degrees of freedom probability, p 0.10 0.05 0.02 0.01 0.001 1 2.71 3.84 5.41 6.64 10.83 2 4.61 5.99 7.82 9.21 13.82 3 6.25 7.82 9.84 11.35 16.27 4 7.78 9.49 11.67 13.28 18.47 Classes Observed number (O) Expected ratio Expected number (E) 2d.p. red eyes and long wings 305 red eyes and vestigial wings 41 purple eyes and long wings 39 purple eyes and vestigial wings 315 Total 700 [1] Calculated 2 = ……………………………………[1] (iii) Using the probability that the difference between observed and expected results is due to chance for the calculated 2, state the conclusions that can be drawn. …………………………………………………………………………………………………..…. …………………………………………………………………………………………………..…. …………………………………………………………………………………………….……….. …………………………………………………………………………………………….……….. ………………………………………………………………………………………………… ..[2] (iv) Explain the conclusion derived from (iii). …………………………………………………………………………………………………..…. …………………………………………………………………………………………………..…. …………………………………………………………………………………………….……….. …………………………………………………………………………………………….……….. ………………………………………………………………………………………………… ..[2] [Total: 12]

8 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations QUESTION 3 Translation is a fundamental biological process involving several key macromolecules. One such macromolecule is ribosomal RNA (rRNA) which is a structural component of ribosomal subunits. (a) Use an arrow on Fig. 3.1 to indicate the location where ribosomal RNA (rRNA) and proteins are assembled to form ribosomal subunits. Identify the organelle. Fig. 3.1 Picture modified from https://commons.wikimedia.org/wiki/ [1]

9 St Andrew’s Junior College 2025 9744/02/Preliminary Examinations Fig. 3.2 shows the two eukaryotic ribosomal