NYJC 2023 H2 Biology 9744 P3 MS

9744 / H2 Biology / 03 NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME CLASS BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 20 Sept 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions in the spaces provided on the Question Paper Section B Answer any one question on the separate Answer Paper. 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 no use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 29 2 12 3 9 Section B (a) 13 (b) 12 Total 75 This document consists of 14 printed pages. [Turn over

9744 / H2 Biology / 03 2 Section A Answer all the questions in this section. 1 (a) Tuberculosis (TB) is a major cause of ill health worldwide. Prokaryotic Mycobacterium tuberculosis is the causative agent of TB. Fig. 1.1 shows the longitudinal section of M. tuberculosis , viewed under the transmission electron microscope, with a scale bar representing 500nm. Source: Muhsin Özel, Gudrun Holland/RKI Fig. 1.1 (i) List two features visible in Fig. 1.1 that identify these cells as prokaryotes. Presence of (peptidoglycan) cell wall; Unicellular; [2] (ii) Outline the process by which M. tuberculosis reproduce. Binary fission; semi-conservative replication of parental DNA begins at the origin of replication each origin moves rapidly toward the opposite end of the cell and adhere to the cell surface membrane. cell elongates. Elongation of the cell also separates the two identical copies of the chromosomes. cell surface membrane invaginates, and deposits new c ell wall materials. Two daughter cells are formed which are genetically identical to the parent cell.

9744 / H2 Biology / 03 3 [4] (iii) Identify and explain one problem of trying to classify prokaryotes such as M. tuberculosis. P1 hard to classify prok on, phenotype / morphology / appearance ; R1 as, small / simple / single-celled / share similar cell structure / have limited range of cell shapes OR P2 idea that (biological) species concept does not apply to bacteria ; R2 as they reproduce asexually ; [2] (b) The World Health Organization (WHO) introduced a strategy in 2015 to end the global TB epidemic. An important part of the strategy is to: • identify people at risk of becoming infected with TB • use methods to prevent transmission of TB. (i) State the mode of transmission of M. tuberculosis to humans. Ref to airborne droplets ; [1]

9744 / H2 Biology / 03 4 (ii) The BCG vaccination is one method of prevention recommended for use in countries where TB is common. The BCG vaccine contains a non-pathogenic, living form of the microorganism that causes TB. Complete Table 1.1 by using a tick (✓) to identify the type of immunity that develops in a person who has been given the BCG vaccination Table 1.1 artificial active immunity ✓ artificial passive immunity natural active immunity natural passive immunity [1] (c) The treatment for people with active tuberculosis (TB) lasts six months and involves a combination of antibiotics. This is usually very effective if the person has a susceptible (non-resistant) strain of M. tuberculosis. Table 1.2 summarises one recommended treatment strategy that involves a combination of antibiotics. Table 1.2 antibiotic length of treatment mode of action of antibiotic rifampicin (R) 6 months enters bacterial cells and inhibits protein synthesis isoniazid (H) 6 months prevents the synthesis of cell wall components known as mycolic acids ethambutol (E) first two months prevents mycolic acids from being added to the cell wall pyrazinamide (Z) first two months prevents the synthesis of fatty acids Susceptible strains of M. tuberculosis will be killed using any one of the antibiotics listed in Table 1.2. However, combination treatment is preferred as it is one method that can be used to reduce the impact to society of antibiotic resistance.

9744 / H2 Biology / 03 5 (i) Explain how antibiotic resistance in M. tuberculosis develops. [4]

9744 / H2 Biology / 03 6 (ii) With reference to Table 1.2, explain how combination treatment for TB can help to reduce the impact of antibiotic resistance compared to single antibiotic treatment. [3] Rifampicin binds tightly to an RNA polymerase molecule close to its active site. This affects the activity of the enzyme. (d) (i) Outline briefly the main role of RNA polymerase in M. tuberculosis. Transcription + forming mRNA using one of the DNA strand as template; Catalyse phosphodiester bonds between ribonucleotides;

9744 / H2 Biology / 03 7 [2] (ii) Suggest the effect of rifampicin on RNA polymerase. [2]

9744 / H2 Biology / 03 8 (e) RNA polymerase is composed of five different polypeptides. Gene rpoB codes for one of these polypeptides known as the β-subunit. One or more mutations in a specific region of rpoB result in strains of M. tuberculosis that are resistant to rifampicin. In these strains, mutations often occur in two DNA triplets in this region, in positions 526 and 531. Table 1.3 summarises the results of an investigation into seven rifampicin-resistant strains, A to G, that have amino acid changes for positions 526 and 531. Table 1.3 includes: • the change in the mRNA codon for position 526 or position 531 • the amino acid change that has occurred as a result of the mutation • the minimum concentration of rifampicin required to inhibit growth of the bacterial strain (MIC) • the number of other mutations occurring within the specific region of rpoB. Table 1.3 (i) Complete Table 1.3 to show the amino acid changes that have occurred in strains F and G. [1]

9744 / H2 Biology / 03 9 (ii) With reference to Table 1.3, list the strains of M. tuberculosis that show the greatest resistance to rifampicin. B, D, F, G [1] (iii) Suggest reasons to explain why strains C, D and E show different levels of resistances to rifampicin. [3]

9744 / H2 Biology / 03 10 (f) WHO Global Tuberculosis Report for 2019 published data on the estimated number of deaths from TB and HIV/AIDS in 2018. All deaths of people from TB who were infected with HIV were also counted as deaths of people with HIV/AIDS. Fig. 1.2 shows these data. The dark grey boxes show the estimated number of deaths of people from TB who were also counted as deaths of people with HIV/AIDS. Fig. 1.2 A student used the data in Fig. 1.2 to predict that measures to control the spread of HIV will decrease the number of deaths from TB. Discuss whether the data in Fig. 1.2 support this prediction. [3] [Total: 29]