2024 TMJC Prelim H2 Bio Paper 3 (A)

H2 BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 13 September 2024 2 hours SUGGESTED ANSWERS No Oh dear, where did I go wrong?  Affected Questions I can improve by doing the following! ☺ 1 I don’t understand what the question wants from me. • Identify topic(s) related to the question. • Analyse the preamble and/or diagram carefully. • Unpack the command term (e.g. explain, describe) 2 I don’t know / can’t remember the conceptual facts. • Review my study techniques – what is effective and what is not? • Approach my tutor / peers for advice. 3 I did not give the essential keywords / wrong keyword. • Reflect on why the missing words / phrases were essential in addressing the question. 4 My answers are incomplete / not of enough depth. 5 I misinterpreted the questions / data, hence wrote the wrong answer / out-of- point answer • Read the preamble carefully. • Paraphrase the question in my own words. • Unpack the command term (e.g. explain, describe) 6 I did not contextualize my answers to the question. That is, I did not make use of the information in the preamble / stimulus / figure. • When the question revolves around a specific example, use the contextual information to craft the answers. 7 I did not cite data / I did not include the units for data / did not cite meaningful data for both axes. • Cite complete data: both x & y axes, with units. • Examine the trend of the graph. If appropriate, divide the graph into  2 parts for meaningful citation of data. 8 I did not organize my answers properly, especially for comparison questions / essay questions. • For comparison questions, ensure each sentence focuses on one feature. Use comparative words (e.g. but, whereas, while) • For essay questions, organise each major idea in a separate paragraph. 9 I did not manage to attempt the question due to insufficient time. • Look through the whole paper and first attempt questions I am more confident in. • Be concise & succinct. Do not write excessively. • When I am stuck at a question, move on. 10 I was not able to apply the conceptual facts to this kind of ‘suggest’ questions. • Identify topic(s) that the question is related to and draw links to the concept. • Examine any hint(s) / information in the preamble to suggest biologically sensible ideas. TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION

2 Tampines Meridian Junior College 2024 JC2 Preliminary Examinations H2 Biology Section A Answer all questions in this section. 1. The movement of blood glucose across the cell surface membrane of mammalian cells involves a family of related proteins called glucose transporters (GLUT s). Different isoforms of GLUT are found in different tissues, as shown in Table 1.1. Several studies have measured the changes in rates of glucose uptake by different forms of GLUT as the concentration of glucose is increased. For each type of GLUT, the rate of transport levels off to a maximum value called Vmax. The glucose concentration at which the rate of transport is half Vmax is defined as the KM of the transporter. A lower KM is indicative of greater binding affinity of GLUT for glucose , which means that the GLUTs will be saturated at lower concentrations of glucose. The KM for the four forms of GLUT and the effect of increasing glucose concentration of the rate of glucose uptake are shown in Fig. 1.1. Table 1.1 isoform function location GLUT1 basal glucose uptake required to sustain respiration all cells GLUT2 act as a glucose sensor pancreatic β-cells, liver cells GLUT3 act as a scavenger for cells with high rate of glucose metabolism neuronal cells GLUT4 insulin-responsive isoform that translocate to cell surface membrane upon insulin stimulation skeletal muscle cells, adipose (fat) cells Fig. 1.1

3 Tampines Meridian Junior College 2024 JC2 Preliminary Examinations H2 Biology (a) State the process of glucose uptake by GLUT into a cell. [Transport, KU-1] [1] • facilitated diffusion (b) The rate of glucose transport at a given glucose concentration can be calculated using the formula: V = Vmax × [G] KM + [G] V = rate of glucose transport [G] = glucose concentration (mmol/l) The physiological range of blood glucose concentration in a healthy individual after fasting ranges from approximately 3.9 to 5.5 mmol/l. With reference to Fig. 1.1, c alculate the rate of glucose transport by GLUT2 when the blood glucose concentration is 5·5 mmol/l. Show your stepwise working and express your answer to 2 significant figures. [Data, HI-3] [2] Rate of glucose uptake at KM of 17 mmol/l = 0.02 mmol/min (read off from graph) Hence, Vmax = 0.02 x 2 = 0.04 mmol/min [1] 𝑉 = 0.04 × 5.5 17 + 5.5 = 0.0098 mmol/min [1] [allow ecf for incorrect Vmax used] rate of glucose uptake = 0.0098 mmol/min ERRORS: “Vmax = 17 x 2 = 34” Please read the definition of Km and Vmax carefully: The glucose concentration at which the rate of transport is half Vmax is defined as the Km of the transporter.

4 Tampines Meridian Junior College 2024 JC2 Preliminary Examinations H2 Biology (c) In pancreatic β -cells, GLUT2 acts as a glucose sensor. When blood glucose increases, glucose enters the β-cells through GLUT-2, leading to an increase in intracellular glucose concentration. This increase in glucose concentration triggers a series of events leading to the release of insulin, which helps to lower blood glucose levels. The amount of insulin released is dependent on the amount of glucose taken into the β-cells. (i) Explain why it is important that pancreatic β -cells contain the isoform (GLUT2) that has the highest KM. [Cell Comm, KU-3] [2] 1. Idea that Highest K M would mean that GLUT2 requires a high concentration of glucose before becoming saturated / reverse argument 2. Idea that Allows β-cells to sense changes in blood glucose concentrations over a wide range, from low to high. [reject: allow high glucose conc. to enter] 3. Idea that Enables β-cells to release the right amount of insulin in response to a range of elevated blood glucose levels. ERRORS: “Ensure that GLUT2 only transport glucose at high blood glucose concentrations.” “Ensures that insulin is released only when blood glucose is very high.” GLUT2 can transport glucose across a wide range of blood glucose concentrations, hence releasing appropriate amount of insulin proportional to the blood glucose concentration. • At lower elevated blood glucose, lesser glucose is transported into the β -cell, which leads to the secretion of little insulin. • At higher elevated blood glucose, more glucose is transported into the β-cell, which leads to the secretion of more insulin. A low Km GLUT would allow a lot of glucose to be transported into the β -cell even at lower elevated blood glucose. This will lead to an excessive insulin being secreted that lead s to hypoglycemia (overly low blood glucose levels) that can be fatal.

5 Tampines Meridian Junior College 2024 JC2 Preliminary Examinations H2 Biology (ii) Fig. 1.2 shows the series of events that happen after glucose molecules enter the β- cells through GLUT2. Fig. 1.2 Outline the roles of the cell surface membrane in the release of insulin after the entry of glucose into the β-cell. [Transport, HI-2] [3] 1. ATP–gated K+ channel (on the cell surface membrane ) closes when ATP increases, preventing K+ from diffusing out. 2. Voltage–gated Ca2+ channel (on the cell surface membrane) o