NJC 2023 H2 Biology Prelim P2 QP

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination [Turn over NATIONAL JUNIOR COLLEGE, SINGAPORE Senior High 2 Preliminary Examination Higher 2 CANDIDATE NAME BIOLOGY CLASS 2bi2_____ REGISTRATION NUMBER Biology Paper 2: Structured Questions Candidates answer on the Question Paper. No Additional Materials are required. 9744/02 24 August 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name, Biology class and registration number on all the work you hand in. Write in dark blue or black pen. You may use an HB for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the 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 your workings 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 of question. For Examiner’s Use 1 /10 2 /9 3 /11 4 /11 5 /9 6 /12 7 /10 8 /8 9 /10 10 /5 11 /5 Total /100 This document consists of 24 printed pages.

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination 2 Section A Answer all the questions in this section. 1 Triglycerides are transported via lipoproteins such as low-density lipoproteins (LDL). LDL are taken up by target cells as shown in Fig. 1.1. Fig. 1.1 (a) Name the structures labelled A in Fig. 1.1. [1] (b) Explain the roles of B in the synthesis of LDL receptor. [2]

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination [Turn over 3 (c) With reference to Fig. 1.1, describe how an LDL particle is taken up by a target cell. [3]

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination 4 Lipoproteins are made up of proteins and lipids. Their function is to transport cholesterol, triglycerides, and other lipids in the bloodstream. Fig. 1.2 represents the structure of a lipoprotein. Fig. 1.2 (d) (i) With reference to Fig. 1.2, describe the arrangement of phospholipids in lipoproteins. [2] (ii) Suggest why lipoproteins are needed to transport cholesterol, triglycerides and other lipids in the bloodstream. [2] [Total: 10]

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination [Turn over 5 2 Collagen serves as the main structural protein in various connective tissues in animals. These tissues include bone cartilage, blood vessels, gum, and skin. (a) Describe the primary structure of collagen. [2] (b) Explain how the structure of collagen differs from cellulose. [3]

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination 6 Fig 2.1 show the main steps involved in the synthesis and assembly of collagen. Fig 2.1 (c) Suggest why the assembly of collagen takes place outside the cell. [2] (d) Vitamin C is necessary in aiding the hydroxylation of amino acids to form hydroxyproline and hydroxylysine in Step 2. A deficiency in Vitamin C can lead to scurvy, a disease associated with symptoms such as loss of teeth and easy bruising. Suggest why vitamin C deficiency can lead to scurvy. [2] [Total: 9] Step 1 Step 2 Step 3 Step 4 Step 5

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination [Turn over 7 3 In eukaryotes, transcription of a gene produces RNA transcripts that must be successfully processed before they can be exported out of the nucleus into the cytoplasm for translation. This process is illustrated in Fig. 3.1. Fig. 3.1 (a) With reference to Fig. 3.1, (i) describe the process occurring at stage X that results in the formation of a continuous coding sequence in mRNA. [2] (ii) suggest why the cap-binding complex and poly -A-binding proteins are essential for stage Y. [1] (b) Describe three differences between eukaryotic and prokaryotic translation. [3]

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination 8 (c) The development of a mouse, from a fertilised egg into an adult, is regulated by variations in DNA methylation. Fig. 3.2 shows the developmental stages of a mouse with corresponding levels of DNA methylation. R, S and T represent the zygote, inner cell mass of blastocyst, and embryo respectively. Fig. 3.2 (i) State the level of potency of the inner cell mass of blastocyst. [1] (ii) With reference to Fig. 3.2, suggest reasons for the different relative levels of DNA methylation at R, S and T. [3] (iii) Although the inner cell mass of blastocyst has low levels of DNA methylation, many genes are not transcribed. Suggest how the levels of transcription is kept low in blastocyst. [1] [Total: 11]

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination [Turn over 9 4 Influenza and COVID-19 are both contagious respiratory diseases caused by different viruses. COVID-19 is caused by infection with a coronavirus, SARS-CoV-2, first identified in 2019. Flu is caused by infection with an influenza virus. Fig. 4.1 shows the structure of the SARS-CoV-2. Fig. 4.1 (a) Compare the structures of SARS-CoV-2 and influenza virus. [2] (b) Both influenza virus and SARS -CoV-2 have viral genes coding for viral RNA polymerases. Explain why such genes coding for viral RNA polymerase are needed by these viruses despite the availability of host RNA polymerases. [2]

©NJC 2023 9744/02/SH2/H2/Biology/Preliminary Examination 10 The subtypes of the influenza virus that infect birds, human and pigs in one area of the world in recent times are shown in the Table 4.1 below. Table 4.1 time period influenza virus subtypes present humans pigs 1918-1957 H1N1 H1N1 1958-1970 H2N2 1971-present day H3N2 H1N1 H3N2 H2N3 (c) Based on the above information, discuss the plausibility that an antigenic shift of the influenza virus can occur from H2N2 combining with H1N1 or H3N2 in present human populations. [3]