TJC 2023 H2 BIO P3 ANS

1 [TURN OVER READ THESE INSTRUCTIONS FIRST Write your Center number, index number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question in spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show any working or if you do not use appropriate units. The number of marks is given in the brackets [ ] at the end of each question or part question. TEMASEK JUNIOR COLLEGE 2023 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CENTRE NUMBER S INDEX NUMBER BIOLOGY 9744/03 Paper 3 Long Structured and Free Response Questions PART I 12 SEPTEMBER 2023 2 hours Candidates answer on the Question Paper. No Additional Materials are required. For Examiner’s Use 1 / 29 2 / 11 3 / 10 4 / 5 / 25 Section A This document consists of 9 printed pages and 3 blank pages.

2 Answer all questions in this section. 1 There are a variety of infectious diseases that can affect humans. (a) Explain what is meant by an infectious disease. [2] Infectious Diseases Part III Lecture Notes p.2 1. [Infectious] Infectious diseases are caused by pathogens (A: bacteria, viruses, fungi, protozoa) that can spread from one organism / host to another (i.e. transmissible, communicable). [1] 2. [Disease] The pathogens cause damage or injury to the host that impairs the normal function of the body. [1] (b) The human immunodeficiency virus (HIV) causes the infectious disease known as autoimmune deficiency syndrome (AIDS). (i) Compare the structures of HIV and a typical bacterium. [2] Similarities: 1. Both have genetic material. 2. Both have phospholipid bilayer (envelope for HIV, cell membrane of bacteria) 3. Both have glycoproteins. 4. Both do not have membrane-bound organelles. Differences: Feature HIV Bacteria 1. Genetic material Linear, single stranded (+) RNA Circular, double- stranded DNA 2. Presence of peptidoglycan cell wall No Yes 3. Presence of reverse transcriptase / HIV integrase / HIV protease (Any 1) Yes No 4. Presence of ribosomes No Yes 5. Presence of plasmid No Yes 6. Presence of flagellum No Yes HIV can integrate its genome into the host cell chromosome, thus forming a provirus. The provirus may remain transcriptionally silent for decades. (ii) Suggest and explain one way in which the provirus can remain transcriptionally silent. [3] Any one modification 1. DNA methylation [1] 2. Causes DNA to bind more tightly to histones and