2024 TJC Prelim Biology P3 (A)

1 Section A Answer all questions in this section. 1 Tuberculosis (TB) is an infectious disease caused by the bacterium. (a) Define the term infectious disease. [1] 1. Infectious – caused by pathogens (bacteria/virus) passed from infected to uninfected person 2. Disease – cause health problems / illness / poor health / disorder (b) State the name of the pathogenic organism which causes TB and describe its m ode of transmission. Name of organism Mycobacterium tuberculosis [1] [1/2 mark if everything is correct but underlined together] Mode of transmission [1] 1. uninfected person inhales / breathes in; [1/2] 2. Infected person coughs / sneezes / spits and release aerosol / droplet containing the pathogen; [1/2] (c) One example of a defence mechanism against pathogens in the lung s involves the action of macrophages. (i) State the location in the body where macrophages are formed. [1] (ii) Outline the mode of action of a macrophage. [2] 1. Macrophage has receptors which recognize and bind pathogens OR macrophage has Fc receptors which recognize and bind Fc region of antibodies bound to pathogens [1/2] 2. Take in pathogen via receptor-mediated endocytosis / phagocytosis [1/2] 3. Forms phagosome with pathogen and lysosome fuse and hydrolytic enzymes breaks down pathogen [1/2] TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 2 BIOLOGY 9744/03 Paper 3 Long Structured and Free Response Questions ANSWERS 9 SEPTEMBER 2024 2 hours

2 4. Peptide antigen presented on cell surface / act as antigen presenting cell [1] 5. Involved in innate immunity [1/2] 6. Activate adaptive immune response. [1/2] (iii) It is sometimes possible for the pathogenic bacteria to survive within macrophages. Suggest one way in which these pathogenic bacteria may survive within a macrophage.[1] Any one [1 mark] 1. Bacteria inhibits fusion of phagosome with lysosome Note: Do not write macrophage fuse with lysosome 2. Bacteria inhibits the proton pump that acidifies the phagolysosome 3. Bacteria produce inhibitors to stop lysosomal enzymes from digesting. 4. Bacteria form spores which is resistant to digestive enzymes Reject: Bacteria mutate Reason: This is too general and vague and does not state how it can survive. (iv) The TB bacterium has many operons in its DNA. Suggest one advantage to the bacterial cell in having operons. [1] Any one [1 mark] 1 Operons allow for rapid response by bacteria to environmental change. 2 An operon consists of a cluster of structural genes that are of related functions which are transcribed at the same time since they are controlled by the same promoter and operator. 3 Allow for the rapid synthesis of important metabolites which are lacking in the environment, or the utilisation of substrates that are present. OR The cell conserves its energy and resources by producing the necessary enzymes only when they are needed. Table 1.1 shows recent information about TB cases reported during one ye ar in six different countries. Table 1.1 country region number of cases number of cases per 100 000 population Germany Europe 4000 5 India Asia 2 300 000 185 Japan Asia 27 000 21 South Africa Africa 490 000 981 Swaziland Africa 15 000 1287 United Kingdom Europe 7900 13 this is not average

3 (d) With reference to Table 1.1, explain the advantage of calculating the number of cases of TB per 100 000 population rather than stating the number of cases alone. [2] 1 mark each 1. Number of cases per 100000 shows the proportion infected in a population. 2. Easier to determine the severity of the problem OR Reliable for making comparisons between different countries OR More accurate representation of the seriousness of the infection in the country Reject: “standardisation” or “easy comparison” Reason: comparing number of cases is just as easy. 3. As countries with larger populations will usually have more cases / higher number of cases may just mean larger population of country ; 4. quote comparative data to support [MUST HAVE]; QF: any country with higher number of cases but lower number of cases per 100 000 population compared with a country with lower number of cases but higher number of cases per 100 000 population E.g. India with 2300 000 cases which is higher than Swaziland with 15 000 cases but Swaziland has 1287 number of cases per 100 000 population has higher than India with only 185 cases per 100 000 population Antibiotics are prescribed to people who have HIV for the treatment of secondary infections such as bacterial infections. (e) Explain why antibiotics are prescribed to treat secondary infections, but not for HIV infection. [2] 1 mark each 1. Antibiotics are only effective against bacteria Reject: microbes or micro-organisms instead of stating bacteria OR Antibiotics not effective against viruses. 2. Viruses do not have cell walls / ribosomes or named enzyme that antibiotic work on [must have at least 1 e.g. of the antibiotic target; RNA polymerase without qualifying what type – only 1/2] 3. Viruses are within cells, that antibiotics cannot reach them. Antibiotic rifampicin is observed to bind tightly to RNA polymerase molecule close to its active site. This affects the activity of the enzyme during the synthesis of RNAs, invo lving the action of RNA polymerase.

4 (f) Suggest two ways in which rifampicin can affect the activity of RNA polymerase. [2] Any Two: 1. Alters shape of / large blocks active site of RNA polymerase R enters / fits into, active site as it is not competitive R ref. to choice of competitive or non-competitive 2. Substrates / nucleotides cannot bind to the active site of RNA polymerase OR Lesser enzyme-substate complex formed. 3. Complementary base pairs cannot form / form less easily between DNA template and RNA nucleotides; 4. Prevents unwinding / uncoiling of DNA double helix 5. Prevents RNA polymerase from recognizing and binding to promoter 6. Prevents RNA polymerase from reading DNA template ; 7. Prevents RNA polymerase from joining RNA nucleotides 8. Prevents RNA polymerase from catalysing formation of phosphodiester bond 9. Prevents sigma factor from binding to RNA polymera se. (g) 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 gene result in strains of TB bacteria that are resistant to rifampicin.  In these strains, mutations often occur in two DNA triplets, in positions 526 and 531. Table 1.2 summarises the results of an investigation into seven rifampicin-resista nt strains, A to G, that have amino acid changes for positions 526 and 531. Table 1.2 includes:  the change in the mRNA codon for position 526 or position 531  the amino acid change that has occurred  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 gene. Table 1.2

5 With reference to Table 1.2, (i) complete Table 1.2 to show the amino acid changes that have occurred in st rains F and G; [1] (ii) list the strains of TB bacteria that show the greatest resistance to rifampicin; [1]  B D F G [in any order] (iii) suggest reasons to explain why strains C, D and E show different levels of resistance to rifampicin. [2] 1. QF: C has 2 other mutations and D and E have 3 [1/2] 2. Types of other mutations are different. [1/2] OR Other mutations may result in different changes to, structure β-subunit / enzyme, and result in different levels of resistance.