TJC 2023 JC1 H1 EOY ANS

1 JC1 2023 H1 PROMOTIONAL EXAMINATION ANSWERS SECTION A: MCQ 1 A 6 A 11 D 2 B 7 D 12 B 3 D 8 A 13 B 4 A 9 D 14 D 5 C 10 B 15 B 1 Fig.1.1 shows a cell releasing insulin in response to glucose uptake. The uptake of glucose through Glucose Transporter 2 (GLUT2) causes a rise in ATP levels in the cell. This closes the potassium channel and in turn causes calcium channel to open. The influx of calcium ions leads to the release of insulin. Fig. 1.1 (a) (i) With reference to Fig. 1.1., describe two differences in the way insulin and glucose are transported across the cell surface membrane. [2] Any 2 1. Transport of insulin involves the secretory vesicles , but the transport of glucose involves transport / carrier proteins. 2. Insulin is released when the secretory vesicles fuse with the cell surface membrane, but glucose enters the cell when they bind to [QF] GLUT2 which undergoes conformational change to facilitate the transport of glucose. 3. Glucose is transported down a concentration gradient but not insulin. 4. Transport of insulin requires energy from ATP (R: active transport) but not the transport of glucose.

Feedback / comment 1. Candidates had difficulty recalling the different types of transport across the membrane. While most knew that glucose is transported via facilitated diffusion, most did not realize from the Fig. that insulin is released / secreted via exocytosis (i.e., involving secretory vesicles). 2. Transport protein could either be channel protein or carrier protein. Note that glucose is transported into the cell via carrier protein and not channel protein. (ii) Explain how the membrane proteins in Fig. 1.1 are able to transport the substances across the cell surface membrane. [2] 1. The membrane proteins are transmembrane proteins 2. with hydrophilic channel to shield polar molecules (e.g., glucose) and charged ions (e.g., calcium ions) [1] Note: If no reference to glucose / potassium ions / calcium ions = ½ mark 3. from hydrophobic core of phospholipid bilayer / cell surface membrane. This helps to transport them across the membrane. Extra point: 4. Potassium channels have binding sites for ATP to bind to such that they are closed and prevent K+ ions from leaving the cell. This will help calcium channels to open. Feedback / comment 1. Candidates were mostly unable to relate to the property of membranes and the properties of substances that are transported across the membrane. 2. Candidates should use the information presented in the figure to answer (i.e., QF the types of substances in Fig. 1.1). (b) Suggest with a reason how a secretory cell will differ in terms of organelles from a non-secretory cell. [1] Any one 1a) There will be more mitochondria. 1b) Reason: To produce more ATP for the synthesis of proteins / movement of vesicles / exocytosis [any 1 example] 2a) There will be more rough