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