TJC 2023 H2 BIO P3 QP

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] (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] 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]

3 [TURN OVER The HIV/AIDS pandemic has had a very large impact on life expectancy in many African countries. Table 1.1 shows the average life expectancy of individuals without and with HIV/AIDS and the percentage of the population tested positive for HIV in five African countries. Table 1.1 country average life expectancy / years percentage of population tested positive for HIV / % without HIV/AIDS with HIV/AIDS Botswana 72.4 33.9 35.8 Côte d’Ivoire 55.6 42.8 10.8 Kenya 65.6 45.5 14.0 South Africa 66.3 48.8 19.9 Zimbabwe 69.0 40.2 25.1 (iii) Using the data shown in Table 1.1, calculate the percentage decrease in average life expectancy for patients with HIV/AIDS in Zimbabwe. Show your working and give your answer to the nearest whole number. percentage decrease: ……………………….. % [2] (iv) After studying the data in Table 1.1, a student concluded that: “The higher the percentage of population tested positive for HIV, the greater the decrease in life expectancy with HIV / AIDS”. With reference to Table 1.1, discuss the validity of the student’s conclusion. .…………….….………………………………………………………………………………………. ……..…………….….……………………………………………………………………………..…. ……………..…………….….……………………………………………………………………...… .……………………..…………………….…………………………………………………………… .…………………………….……………….…..………………………………..……………..… [2]

4 (c) Another common infectious disease in developing nations is cholera. Cholera is caused by consuming food or water contaminated with a bacterium called Vibrio cholerae. Fig. 1.1 shows a transmission electron micrograph of Vibrio cholerae. ×30 000 Fig. 1.1 The symptoms of cholera are caused by the protein, cholaregen. Choleragen is a protein made up of six polypeptides: • a single copy of a polypeptide known as the A subunit that includes an extended alpha helix • five polypeptides that together make the B subunit. The B subunit of choleragen binds to a cell surface membrane component, known as GM1, of an intestinal epithelial cell. The complete choleragen protein then enters the cell by endocytosis. Once inside the cell, the A subunit of the protein acts as an enzyme, disrupting normal functions of the cell. (i) List the levels of protein structure present in choleragen. .…………………………….……………….…..………………………………..……………..… [1] Fig. 1.2 shows the ctxAB operon which contains the structural genes that code for choleragen. Fig. 1.2 H-NS and ToxT are proteins that are coded for by separate regulatory genes found upstream of the operon. It is found that: • high levels of H-NS would reduce the expression of the operon, • high levels of ToxT would increase the expression of the operon, • the operon has similar regulation as lac operon.

5 [TURN OVER (ii) State the role of H-NS and ToxT proteins in the regulation of ctxAB operon. H-NS: ……………..…………………….…………………………………………………………… ToxT: ……………..…………………….………………………………………………………… [2] (iii) In the laboratory, it is possible to produce a form of choleragen consisting of only B subunit as a vaccine against cholera. Suggest why B subunit, rather than A subunit, is used in the production of the vaccine. .……………………..…………………….…………………………………………………………… .…………………………….……………….…..………………………………..……………..… [1]

6 Infection by V. cholerae causes severe watery diarrhea, which leads to dehydration (loss of water and ions) and even death if untreated. Fig. 1.3 shows the signaling pathway activated by choleragen. Fig. 1.3 (iv) With reference to Fig. 1.3, outline how choleragen A subunit can result in diarrhea after chloragen binds to receptor GM1. .…………….….………………………………………………………………………………….…… ……..…………….….……………………………………………………………………………..…. ……………..…………….….……………………………………………………………………...… .……………………..…………………….…………………………………………………………… .…………….….………………………………………………………………………………….…… ……..…………….….……………………………………………………………………………..…. .…………………………….……………….…..……………………………………………….… [3]

7 [TURN OVER (d) Measles is a highly contagious, serious disease caused by the measl es virus. The virus is normally spread through direct contact and through the air when an infected person coughs or sneezes. Nine out of ten people who are not immune will become infected when they share living space with an infected person. The measles-containing vaccine (MCV) was developed in 1963 and is extremely effective at preventing the disease. Fig. 1.4 shows the global annual reported cases of measles and MCV coverage from 1980 to 2009. Immunization coverage refers to the percentage of population who receive one or more vaccines of interest in relation to the overall population. Fig. 1.4 (i) Comment on the relationship between immunization coverage and number of global annual reported cases. .……………………..…………………….…………………………………………………………… .…………………………….……………….…..………………………………..……………..… [1] (ii) With reference to Fig. 1.4, evaluate if the changes in global annual cases can be attributed to the changes in immunization coverage. .…………….….………………………………………………………………………………………. ……..…………….….……………………………………………………………………………..…. ……………..…………….….……………………………………………………………………...… .……………………..…………………….…………………………………………………………… .………