JPJC 2023 J2 H2 BI Prelim P2 ANS

9744 / 02 [Turn over NAME : CLASS : JURONG PIONEER JUNIOR COLLEGE JC2 Preliminary Examination 2023 BIOLOGY Higher 2 9744/02 29 August 2023 Paper 2 Structured Questions 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your class 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. 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 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. For Examiner’s Use 1 2 3 4 5 6 7 8 9 10 11 Total This document consists of 19 printed pages and 1 blank page.

2 JPJC/JC2 H2 Biology/Prelims/2023 Answer all questions. 1 Fig. 1.1 shows a diagram of a cell surface membrane. Fig. 1.1 (a) The structure of the cell surface membrane is described as a fluid mosaic. Explain what is meant by the term fluid mosaic. ............................................................................................................................... [2] Fluid: 1. “Fluid” means that the phospholipids and proteins are free to move within the membrane ; 2. Phospholipids are held by weak hydrophobic interactions and hence move about rapidly by diffusion in their own layers ; [Max 1] Mosaic: 3. Proteins are embedded within the phospholipid bilayer in a random manner ;

3 JPJC/JC2 H2 Biology/Prelims/2023 [Turn over (b) Outline the functions of the following components of the cell surface membrane. K ................................................................................................................................. L ................................................................................................................................. M ................................................................................................................................ N ................................................................................................................................. [4] 1. K: channel proteins that help to regulate the movement of polar molecules or charged ions across membranes, via facilitated diffusion ; 2. L: involved in cell- cell recognition where the carbohydrate chain of (glyco)proteins serves as markers/identification tags, that distinguishes one cell from another ; 3. M : the hydrophobic core of membranes acts as a selective barrier , restricting the movement of charged ions or polar molecules across the membrane into the cell ; 4. N: maintains membrane fluidity / increases the stability and flexibility of membranes ; OR 5. N: acts like a plug, reducing the escape or entry of charged ions and small polar molecules through the membrane ;

4 JPJC/JC2 H2 Biology/Prelims/2023 (c) In an investigation, animal cells were exposed to different concentrations of glucose. The rate of uptake of glucose into the cells across the cell surface membrane was determined for each concentration. Fig. 1.2 shows the results. Fig. 1.2 Using the information in Fig. 1.2, explain how the results of the investigation support the idea that glucose enters cells by active transport. 9700/02/M/J/07 ................................................................................................................................. [2] 1. (Active transport because) As concentration of glucose increases from 1 arbitrary unit to 9 arbitrary units, rate of uptake of glucose increases from 18 arbitrary units to 20 arbitrary units and levels off ; 2. R ate shown is independent of concentration (except at low concentration) ; 3. Not facilitated diffusion because the rate of uptake did not start at 0 arbitrary unit and increase with increasing glucose concentration up to a plateau/constant rate (because no more transport proteins available/all proteins in use) ; 4. Not passive diffusion as rate would continue to rise ; (d) Active transport also involves other water -soluble substances such as Na + and K+, and the use of ATP to provide the energy needed for their transport through carrier proteins. Outline other features of active transport. 9700/22/M/J/22 ................................................................................................................................. [2] 1. Movement of substances against concentration gradient / from lower to higher concentration ; 2. Carrier protein has specific binding site(s) ; 3. Binding causes protein to undergo conformational change / change of shape ; [Total: 10]

5 JPJC/JC2 H2 Biology/Prelims/2023 [Turn over 2 Fibroblasts are one of the cell types of connective tissue s. The cells synthesise and secrete collagen, which forms part of the supporting external cellular environment, known as the extracellular matrix. Fig. 2.1 shows the primary structure of a section of a polypeptide chain of collagen. Fig. 2.1 (a) Explain how the primary structure shown in Fig. 2.1 indicates that the structure of the polypeptide is suited to be a component of a collagen molecule. ............................................................................................................................... [3] 1. every third / high proportion of, amino acid in the polypeptide is glycine ; 2. glycine is small/smallest amino acid / has H as R-group ; 3. glycine allows the (three helical) polypeptides to (lie close together and) form a tight coil, resulting in a tropocollagen/triple helix ; A glycine presence allows a, compact / AW, triple helix 4. gly (-NH) can form hydrogen bonds with (C=O in pro of) other polypeptides of triple helix ; 5. Three helical polypeptides (wind tightly around each other, and) are bound to one another by intermolecular hydrogen bonds, forming a tropocollagen / triple helix ; 6. AVP (from CIE) ; pro / ala, also small amino acids (for tight coiling) high proportion of smaller amino acids / amino acids with small side chains A high proportion of glycine if mp1 not given and mp2 is pro can form hydroxyproline for stability ref. insoluble and (some), amino acids with non-polar R-groups (e.g. ala) A: gly for glycine (b) After final processing in the Golgi body, collagen is released to the outer surface of the cell by exocytosis. Describe the process of exocytosis. ............................................................................................................................... [3] 1. Secretory vesicles containing collagen ( bud off from cisternae at trans face of Golgi body) move towards the cell surface membrane ; 2. The membrane of the secretory vesicles fuses with the cell surface membrane ; 3. vesicles moved by microtubules / cytoskeleton (to cell surface membrane) ; 4. ATP required/active process ; 5. releasing insulin out of the fibroblasts via exocytosis.

6 JPJC/JC2 H2 Biology/Prelims/2023 (c) Hydrolytic enzymes, known as collagenases, are secreted by cells in an inactive form. Cells also secrete inhibitors of collagenases. The activity of the enzymes and inhibitors is regulated so that the development and maintenance of the extracellular matrix is controlled. (i) State and explain what the outcome will be for the composition of the extracellular matrix if collagenase inhibitor activity is needed. ..................................................................................................................