SAJC 2023 H2 BIO P3 QP

1 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 Civics Group A Level Index Number Name (use BLOCK LETTERS) ST. ANDREW’S JUNIOR COLLEGE 2023 JC2 PRELIMINARY EXAMINATIONS H2 BIOLOGY 9744/03 Paper 3 Friday 15th September 2023 2 hours 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. All working for numerical answers must be shown. For Examiners’ Use 1 /40 2 /10 4 or 5 /25 Total /75 This document consists of 21 printed pages. [Turn over] H2

2 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 Answer all questions. QUESTION 1 On October 14, 2021, the World Health Organization (WHO) released the Global Tuberculosis Report 2021, which showed that 9.87 million new cases of tuberculosis and 1.5 million people died of tuberculosis in 2020. Among them, the estimated number of new cases of tuberculosis in China in 2020 was 842,000 (833,000 in 2019), and the estimated incidence of tuberculosis was 59/100,000 (58/100,000 in 2019). Among the 30 countries with a high burden of tuberculosis, China ranks second in the number of estimated cases of tuberculosis and has over 30,000 deaths due to tuberculosis. (a)(i) In Fig. 1.1 below, label X and Y appropriately, to reflect the pathogenesis of tuberculosis. Fig. 1.1 [2] (ii) With reference to a cellular organelle in the macrophages, describe how macrophages usually attempt to process engulfed bacteria. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… .……..………………………………………………………………..…………………..……....[2]

3 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 Fig. 1.2 shows the cell wall of the bacteria causing tuberculosis and its unique make up of fatty acids which are slightly different from those used in the synthesis of triglycerides in eukaryotes. Fig. 1.2 (iii) With reference to Fig. 1.2, explain how the bacteria causing tuberculosis can evade the mechanisms of the macrophage host cells. ……………………………………………………………………………………………………… ……..…………………………………………………………………...……………….…….....[1] (iv) Complete and annotate on the diagram below to show the production of a triglyceride from its constituents in eukaryotes. …………………………………………………………………..………..………………..….….[2]

4 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 Most infections are latent and do not have symptoms. Latent infections can progress to active form of the disease which, if left untreated, kills about half of those infected. The most common classic symptoms of active TB include chronic cough with blood - containing sputum, chest pain and shortness of breath. (v) Explain the cause of the shortness of breath symptom of TB in its active stage. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……..……………………………………………………………………..………..…………....[2] Bacteria causing tuberculosis is able to acquire genes coding for antibiotic resistance through various ways, leading to multi-drug resistant tuberculosis. An example is bacteria that are resistant to rifampicin, a key drug in the treatment of tuberculosis. The mode of action of rifampicin in bacteria is by binding to the beta (β)-subunit of the RNA polymerase, inhibiting the elongation of messenger RNA. In about 96% of bacteria resistant to rifampicin, there are mutations in the so-called “hot- spot region” of DNA transcribing into codons 507–533 of the rpoB gene, which codes for the beta (β)-subunit of bacterial RNA polymerase. [edited from Palomino JC, Martin A. Drug Resistance Mechanisms in Mycobacterium tuberculosis. Antibiotics (Basel). 2014 Jul 2;3(3):317-40] (vi) Calculate the length of the DNA in the “hot-spot region”. Represent your answer in bp. …………………. bp [2]

5 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 (vii) Explain why a mutation to the rpoB gene can lead to resistance to rifampicin. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……..……………………………………………………………………..………..…………....[3] (viii) Discuss how natural selection could have led to the evolution of antibiotic rifampicin resistance in bacteria causing tuberculosis. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……..……………………………………………………………………..………..…………....[4]

6 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 (b) Table 1 below shows the effect of a newly discovered antibiotic X on the survival of bacteria causing tuberculosis. The same volume of bacteria causing tuberculosis was plated on nutrient medium plates and incubated at 37°C overnight. For control plates, there was no antibiotic added to the nutrient medium plates, while test plates contains the antibiotic. For each condition, 4 readings from 4 plates were measured to obtain replicate readings. At the end of incubation, the number of bacterial colonies are counted and presented in Table 1. Table 1: Effect of antibiotic X on the number of bacterial colonies after incubation Number of colonies Condition Count 1 Count 2 Count 3 Count 4 Average (whole number) Standard deviation (3 s.f.) Control 55 61 58 73 Test plates (antibiotic added) 13 20 7 12 (i) Calculate the average and complete Table 1. Express your answers to nearest whole number. [1] (ii) Using the formula below, calculate the standard deviations of bacterial colony count, in the presence and absence of antibiotic X. Complete Table 1. Express your answers to 3 significant figures. [1] Legend ∑ is summation of x is observed values x is the mean n is the sample size (number of observations per condition)

7 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 (iii) With reference to Table 1’s calculations for test plates (with antibiotic added), explain what is standard deviation and its implications. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………..……….[2] (iv) Using the average and standard deviation values calculated in ( b)(i) and (ii), as well as critical t-values in Table 2, Calculate the t calculated value. ………………………………………………………………………………………………..[1] T calculated value = ……………………………… (v) Determine if there is a significant difference in the number of colonies after the addition of antibiotic X. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………..………………………………………………..[2]

8 SAJC / H2 Biology 9744/3 JC2 Prelim 2023 Table 2: Student’s t-test table of t critical values (vi) Bacteriophages called mycobacteriophages is another treatment method for tuberculosis, as an alternative to administration of antibiotics. Suggest a limitation for using mycobacteriophages against bacteria causing tuberculos