2025 JPJC H2Bio PE P2 (A)

9744 / 02 [Turn over NAME : CLASS : JURONG PIONEER JUNIOR COLLEGE JC2 Preliminary Examination 2025 BIOLOGY Higher 2 9744/02 2 September 2025 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. 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/PE/2025 Section A Answer all questions. 1 Alveoli are tiny air sacs in the lungs that are crucial for gas exchange. The walls of alveoli contain some specialised epithelial cells called type II epithelial cells. These cells secrete surfactant, which helps to prevent the alveoli collapsing during breathing. The components of surfactant are synthesised in the rough endoplasmic reticulum and smooth endoplasmic reticulum and then passed to the Golgi body. The surfactant that is produced is stored in secretory organelles called lamellar bodies. The surfactant in the lamellar bodies is released onto the surface of the alveolar epithelium, as shown in Fig. 1.1. Fig. 1.1 (a) The cell surface membrane of type II epithelial cells has a fluid mosaic structure. Describe what is meant by the term fluid mosaic. ................................ ................................ ................................ ............................ [3] 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 ; 3. Unsaturated fatty acid tails of phospholipids have kinks that keep the molecules from packing together, enhancing membrane fluidity ; (least important) Mosaic: 4. Proteins are embedded within the phospholipid bilayer in a random manner ; (b) Each lamellar body is surrounded by a single membrane. Draw a diagram to show the arrangement of phospholipid molecules in the membrane surrounding the lamellar body. [2] 1. phospholipid with a head and two tails ; 2. bilayer shown ;

3 JPJC/JC2 H2 Biology/PE/2025 [Turn over (c) (i) Suggest the components present in the surfactant. ................................ ................................ ................................ ................... [2] 1. lipids/phospholipids /(cholesterol) ; 2. proteins ; (ii) Describe how the surfactant is released from the cell. ................................ ................................ ................................ ................... [3] 1. lamellar bodies containing surfactant move towards the cell surface membrane of the type II epithelial cells via the use of microtubules ; 2. membrane of the lamellar bodies fuses with the cell surface membrane ; 3. surfactant is secreted/released out of the type II epithelial cells via exocytosis ; 4. active process which requires ATP ; (iii) 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. Suggest why secretion of surfactant is affected by a reduction in cholesterol in the cell surface membranes of type II epithelial cells. ................................ ................................ ................................ ................... [2] 1. cholesterol regulates the fluidity of the membrane ; 2. a reduction in cholesterol, decreases membrane fluidity/making the cell surface membrane more rigid ; 3. cell surface membrane less able to fuse with the membrane of lamellar body ; [Total: 12]

4 JPJC/JC2 H2 Biology/PE/2025 2 Proteins have diverse roles that arise from their three -dimensional structures, which are determined by the sequence of amino acids and the nature of bonds formed between them. The structure-function relationship in proteins is critical to life, and disruption to this relationship may result in diseases. Fig. 2.1 shows two examples of proteins: • G-protein-linked receptors (GPLRs), which are membrane proteins that are involved in majority of cell signalling processes in the body. • Collagen, a fibrous protein that forms structural scaffolds in connective tissues like skin, bone, and tendons. Fig. 2.1 (a) With reference to Fig. 2.1, describe how the bonding and amino acid composition contribute to the shape of each protein. ................................ ................................ ................................ ............................ [2] GPLR: 1. Ionic bonds and hydrogen bonds between charged/polar amino acid residues stabilise, extracellular / intracellular. domains ; 2. Hydrogen bonds, ionic bonds, disulfide bonds, and hydrophobic interactions between R groups of amino acid residues maintain the globular/3D shape of the GPLR ; 3. (intramolecular) hydrogen bonds between the O of C=O group and the H of the - NH group of every fourth peptide bond in the main chain of the polypeptide stabilise/form the α-helices ; Collagen: (A!tropocollagen/ triple helix) 4. High proportion of glycine / Almost every third amino acid in each polypeptide chain is glycine, (the small size of glycine) allows the three (helical) polypeptide chains to form a tight coil/ a tropocollagen ; 5. (Intermolecular) h ydrogen bonds form between the three helical polypeptide chains, forming/stabilising the tropocollagen ; R: covalent cross-links, no fibrils shown

5 JPJC/JC2 H2 Biology/PE/2025 [Turn over (b) (i) Explain how the molecular structure of the G-protein linked receptor relates to its function. ................................ ................................ ................................ ................... [3] 1. made up of a single polypeptide chain with seven transmembrane α-helices , allowing it to be embedded in and span the cell surface membrane (to transmit signal) ; 2. has an extracellular region (which may be glycosylated) to serve as a specific binding site for ligand ; 3. has an intracellular / cytoplasmic region to serve as a specific binding site for G- protein ; (ii) A mutation in the GPLR gene leads to the substitution of a non -polar amino acid for an essential charged residue in the third intracellular loop, disrupting signal transduction. Explain how this change alters the structure and function of the GPLR protein. ................................ ................................ ................................ ................... [2] 1. Substitution of a non -polar amino acid for a charged residue disrupts ionic bonds / hydrogen bonds, in the intracellular loop ; 2. Alters the conformation of the intracellular loop, prevents binding of G-protein (and prevents triggering downstream signalling pathways / signal transduction pathways) ; (iii) Mutations affecting collagen can lead to severe diseases such as osteogenesis imperfecta (OI) which is characterised by fragile bones that break easily. OI is often caused by a missense mutation in the COL1A1 or COL1A2 genes encoding collagen type I. One such mutation replaces glycine with a bulkier amino acid such as cysteine in the collagen chain. Explain how