2024 ASRJC H2 Bio P2 MS

ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P2 [Turn over H2 ANDERSON SERANGOON JUNIOR COLLEGE HIGHER 2 ANSWERS 2024 JC2 PRELIMINARY EXAMINATIONS CANDIDATE NAME CLASS INDEX NUMBER BIOLOGY 9744/02 PAPER 2 SHORT STRUCTURED QUESTIONS Candidates answer on the Question Paper. No Additional Materials are required. 12 SEPTEMBER 2024 THURSDAY 2 HOURS READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graph Do not use paper clips, highlighters, glue or correction fluid. Answer all questions. The 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. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 13 printed pages and 1 blank page For Examiner’s Use 1 / 7 2 / 10 3 / 11 4 / 11 5 / 12 6 / 10 7 / 10 8 / 8 9 / 12 10 / 4 11 / 5 Total /100

2 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM//P2 Answer all the questions. 1 Starch and cellulose are carbohydrates that are found in most plants. (a) Compare between structures of amylose and amylopectin of starch. Similarity (max 1) 1. Both are composed of α-glucose monomers. 2. Both contain α(1,4) glycosidic bonds between monomers. Difference (max 1) 1. Amylopectin contain α(1,4) glycosidic bonds and α(1,6) glycosidic bonds while amylose only contain α(1,4) glycosidic bonds. (A: amylopectin contain α(1,6) glycosidic bonds while amylose do not.) 2. Amylopectin is branched while amylose is unbranched. [2] (b) Juices that are extracted commercially from fruits can be made less cloudy by the breakdown of the cellulose cell wall using the enzyme cellulase. In the space below, show how the bonds in a short section of cellulose that is made up of three monomers may be broken by cellulase. Add appropriate labels to your drawing. 1. Structures of cellulose with indication of ‘continuity’ for polymer + correct rotation + correctly labelled glycosidic bond 2. Correct structure of 3 -glucose monomer correctly drawn including H 3. Type of reaction labelled (hydrolysis) + 2 water molecules indicated as reagents [3]

3 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P2 [Turn over Fig. 1.1 is an electron micrograph showing parts of two plant cells. The middle lamella is a layer, composed largely of a polysaccharide known as pectin, that cements together the cell wall of two adjacent plant cells. Pectins can also be found in the cell wall of plant cells. Fig 1.1 Fig. 1.2 shows a diagrammatic representation of the complex structure of the plant cell wall. Pectins are hydrophilic structures and interact with both cellulose and cross-linking glycans to hold cell walls close together. Glycans are carbohydrate molecules. Fig. 1.2 (c) With reference to Fig. 1.2, suggest how the structure of the cell wall facilitates the passage of water between plant cells. 1. cellulose microfibrils arranged in a crisscross pattern/ interwoven structure that creates large intermolecular spaces or pores between the microfibrils to allow movement of water or small molecules 2. Presence of hydrogen bond cross-linking between cellulose microfibrils to form a strong network of cellulose fibres (maintaining the interwoven structure) 3. presence of pectins that are able to interact and form hydrogen bonds with water / hydrophilic molecules 4. AVP (crosslinking glycans linking two or more cellulose microfibrils to strengthen network [2] Easy: 4, Moderate: 3, Challenging: 0 [Total: 7]

4 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM//P2 2 The walls of alveoli in the lungs contain some specialised epithelial cells called type II epithelial cells. These cells secrete surfactant. Surfactant helps to prevent the alveoli collapsing during breathing. Surfactant is composed of phospholipid, cholesterol and protein. The components of surfactant are synthesised in the rough endoplasmic reticulum and smooth endoplasmic reticulum and then passed to the Golgi body. (a) Ribosomes are found on the surface of rough endoplasmic reticulum. Describe the structure of a ribosome. 1. Composed of rRNA and proteins 2. Each ribosome consists of a large (60S) and a small subunit (40S) (making up a 80S ribosome) 3. Each ribosome has 1 mRNA and 3 tRNA (A, P, E) binding sites. ( reject merely saying A,P,E site) 4. Contains ribozyme / peptidyl transferase in the large ribosomal subunit ( An rRNA molecule complex (of the large ribosomal subunit) ) [3] (b) Identify the component(s) of surfactant that is (are) synthesised in the smooth endoplasmic reticulum. Phospholipid and cholesterol [1] (c) Fig. 2.1 shows part of a type II epithelial cell. Fig. 2.1

5 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P2 [Turn over Both the Golgi body and the smooth endoplasmic reticulum are part of the internal network of membranes in cells. Describe structural features shown in Fig. 2.1 that identify G as the Golgi body and not the smooth endoplasmic reticulum. 1. Cisternae/ membrane-bound sacs are not interconnected / independent 2. Cisternae are more elongated (than tubular) 3. Cisternae/ sacs are stacked 4. presence of vesicles at the end of the sacs/ cisternae 5. more uniform in shape [3] (d) The surfactant that is produced is stored in secretory organelles called lamellar bodies. Each lamellar body is surrounded by a single membrane. The surfactant in the lamellar bodies is released onto the surface of the alveolar epithelium by exocytosis. Scientists studying the production and secretion of lung surfactant have discovered that a reduction in cholesterol in the cell surface membrane of type II epithelial cells reduces the secretion of surfactant. Explain why secretion of surfactant is affected by a reduction in cholesterol in the cell surface membranes of type II epithelial cells. Without cholesterol, (any 2) 1. movement of phospholipids are not restricted 2. because there are less cholesterol molecules for phospholipids to bump into to lose their kinetic energy 3. absence (of spacer ) to separate phospholipids / so that they pack closely together / more hydrophobic interactions between phospholipids AND 4. membrane becomes too fluid / too rigid / solidify such that is cannot fuse with the membrane of lamellar body during exocytosis [3] Easy: 8, Moderate: 2, Challenging: 0 [Total: 10]

6 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM//P2 3 Keratin is the structural protein in feathers of birds. Keratin polypeptides are composed of a high proportion of cysteine