2025 VJC H2 Biology Prelim P2 Answer

1 VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2025 HIGHER 2 NAME : ……………………………………………………….………………. CT CLASS: ………………...……… BIOLOGY Paper 2 Structured Questions 9744 / 02 16/09/2025 2 hour Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name and CT class 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. Answer all questions in the spaces provided on the Question Paper. Use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in bracket [ ] at the end of each question or part question. Question Marks 1 2 3 4 5 6 7 8 9 10 11 Total This document consists of 28 printed pages. [Turn over]

2 Answer all questions. 1 In most cell types, ribosomes are the most abundant organelles by number. They are present in both prokaryotic and eukaryotic cells, although their sizes and structures differ. (a) (i) State one structural feature of ribosomes that is common to both prokaryot ic and eukaryotic cells. [1] [Any one] • Composed of ribosomal RNA (rRNA) and proteins; • Consist of a large and a small subunit; (ii) Suggest how the difference in ribosome size between prokaryotic and eukaryotic cells can be exploited in medicine. [2] • Prokaryotic ribosomes are 70S (50S + 30S), eukaryotic ribosomes are 80S (60S + 40S); • Certain antibiotics bind specifically to 70S ribosomes without affecting 80S ribosomes in the cytosol of eukaryotic cells; (b) Unlike prokaryotic and eukaryotic cells, viruses such as SARS -CoV-2 lack ribosomes entirely. Fig. 1.1 shows the structure of the SARS-CoV-2. Fig. 1.1

3 With reference to the information provided, (i) explain how the structural features of SARS-CoV-2 show that it does not fully conform to the cell theory. [2] • Identify at least one missing cellular feature (e.g., no ribosomes, no cytoplasm, no membrane- bound organelles, no plasma membrane enclosing metabolic machinery); • Viruses are more basic than a cell, which contradicts the cell theory that that cells are the smallest unit of life; • Viruses are not made of cells / acellular, which contradicts the cell theory that all living things are made of cells; • Viruses cannot carry out life processes independently as they require a host cell for reproduction, which contradicts the statement that all cells come from pre-existing cells; (ii) compare the genetic material between SARS-CoV-2 and prokaryotic cells. [3] • Both have a single molecule of nucleic acid that carries hereditary information; • For both, genetic material is not enclosed in a membrane-bound nucleus; features SARS-CoV-2 prokaryotic cell type single-stranded RNA double-stranded DNA shape linear RNA circular DNA number of copies 1 copy of viral RNA 1 copy of bacterial chromosome with possible presence of plasmids

4 2 Proteins are large macromolecules that comprise one or more long chains of amino acid residues. A linear chain of amino acid residues is known as a polypeptide. A polypeptide is formed by ribosomes in a process called translation, in which amino acids are added to an elongating polypeptide sequentially. Collagen is an example of a protein with a quaternary structure. It is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25– 35% of protein content. It is mostly found in cartilage, bones, tendons, ligaments, and skin. Vitamin C is viral for collagen synthesis. Fig. 2.1 shows the general structure of an amino acid. Fig. 2.1 (a) (i) Draw a circle in Fig. 2.1 to indicate the part of the amino acid that is bonded to the elongating polypeptide. [1] (ii) Draw a labelled diagram in the space provided below to show how a dipeptide is formed. [3] • 2 amino acids drawn, with carboxyl group of one facing the amino group of the other; • Dipeptide drawn with peptide bond labelled; • Water drawn with condensation reaction indicated; (b) Other than peptide bonds, other bonds are also found in collagen. These bonds function to maintain the structure of collagen. Describe how these bonds help to maintain the quaternary structure of collagen. [4] • Hydrogen bonds between C=O and N=H of amino acids on adjacent polypeptides; • Maintain the structure of tropocollagen by holding 3 polypeptides together in a triple helix; • Covalent cross-linkages / bonds between lysine residues on adjacent tropocollagens; • Maintain the structure of collagen fibrils by holding the assembly of tropocollagens together;

5 (c) In recent years, collagen hotpot has been gaining popularity among diners. Unlike other hotpots, collagen hotpot contains an additional ingredient, with lumps of beige- coloured collagen jelly melted into the soup. Available at food courts and restaurants in Singapore, it has been attracting patrons, who hope that the soup would give their skin a lift while tantalising their taste buds. However, most health experts are sceptical about the claim that such collagen- infused hotpots help to increase the amount of collagen in our bodies. Using your knowledge of collagen, suggest two reasons for the scepticism of the health experts. [2] • Collagen is large and insoluble in water – collagen jelly melted in soup may not actually contain collagen / may not contain intact collagen / may contain collagen that has already been broken down; • Collagen is too large to be absorbed directly into the body by the small intestines / digestive system; • Collagen is digested in the stomach and / or small intestines / by the digestive system; • We cannot control how much collagen is produced and secreted by cells in the body;

6 3 Cellulase is an enzyme produced in plants where it hydrolyses cellulose in the cell walls, playing a role in processes such as fruit ripening and leaf abscission. Fig. 3.1 shows the effect of temperature on the activity of cellulase in ripening fruits of Musa acuminata (banana) and Mangifera indica (mango). Fig. 3.1 (a) (i) With reference to Fig. 3.1, compare the effects of temperature on cellulase in ripening fruits of banana and mango. [3] • Both rise and then fall; • Banana (enzyme) has higher activity (at all temperatures) + paired QV; • Banana (enzyme) has higher maximum activity + 3.3 (banana) vs 2.5 (mango) arbitrary units; • Banana (enzyme) has higher optimum temperature + 70° (banana) and 60° (mango); (ii) With reference to the types of bonding in proteins, suggest how differences in the tertiary structure of cellulase in ripening fruits of banana and mango could explain the differences in their activities shown in Fig. 3.1. [3] • Thermal stability arises from more bonds in banana cellulase / mango cellulase may have more H bonds in the tertiary structure; • Stronger bonds / more disulfide linkages in banana cellulase / hydrogen bonds are weaker; • Need more KE to break the bonds / more easily disrupted by heat; • Tertiary structure / active site of banana cellulase is altered less by high temperature, forming more enzyme-substrate complexes thus higher enzyme activity;

7 (b) Juices extracted commercially from fruits can be made less cloudy by the breakdown of the cell wall using the enzymes cellulase, pectinase and xylanase: • pectinase hydrolyses pectin • xylanase hydrolyses hemicellulose. An investigation was carried out into the effect of ultrasound on the activity of cellulase, pectinase and xylanase used in fruit juice manufacture. For each enzyme, the effect of ultrasound w