TMJC 2023 H2 P2 Ans

1 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Biology H2 BIOLOGY 9744/02 Paper 2 Structured Questions 14 September 2023 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 2023 JC2 Preliminary Examination H2 Biology QUESTION 1 [CELL/ TRANSPORT/ BIOMOLECULES] The table below compares the features of typical eukaryotic and prokaryotic cells. (a) Complete the table below by placing either a tick ( ), a cross ( ) or the words ‘sometimes present’ as appropriate in each empty box. [KU1] [3] Features Eukaryotic cell Prokaryotic cell nuclear envelope   cell wall sometimes present  chloroplast sometimes present  ribosomes   Golgi apparatus   flagellum sometimes present sometimes present carries out respiration   Active transport and facilitated diffusion are two ways by which substances cross the cell surface membranes. (b) State one similarity and one difference between active transport and facilitated diffusion.[KU1] similarity [1] • Both require proteins/ transmembrane/ transport proteins • Both transports hydrophilic molecules/ charged / polar Difference [1] • Active transport against concentration gradient while facilitated diffusion down a concentration gradient. • Active transport requires energy / ATP while facilitated diffusion does not. • Active transport uses a pump while the other uses carrier/channel Vitamins C and D are essential illness-fighting nutrients, which safeguard our health and boost immunity. They are therefore, taken into cells but take different routes across the cell surface membrane. Vitamin C is water-soluble while Vitamin D is lipid soluble. (c) Explain how Vitamin C and D is transported across the cell surface membrane. [HI2] [3] Vitamin C • require protein carriers or channel proteins which provide a hydrophilic passageway • Vitamin C is hydrophilic, hence, cannot pass through hydrophobic fatty acid/ hydrocarbon of phospholipid bilayer Vitamin D • Hydrophobic can diffuse directly across the phospholipid bilayer • ..it can interact with hydrophobic fatty acids via hydrophobic interactions

3 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Biology A vitamin C drink is thought to contain glucose. Excess glucose consumed is stored as glycogen in muscles. (d) Explain how the structure of glycogen is related to its role in living organisms. [KU-2] [3] • [Structure] α-1,4 glycosidic bond between monomers angles at 109 ° to form helices  [Property] form a compact structure so more glucose can be stored per unit volume. • [Structure] α-1,6 glycosidic bond form branch points  [Property] greater number of free terminal ends for enzymes to bind, resulting in glycogen being hydrolysed more quickly. • [Structure] OH groups forms bonds with other groups, hence, unavailable for H bonding with water • [Property] insoluble in water, can be stored in large quantities without affecting the water potential of the cells. • [Function] [compulsory] Hence, good energy storage molecule. [Total:11]

4 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Biology QUESTION 2 [ENZYMES] (a) Enzymes speed up the rate of reaction by lowering the activation energy of the reaction. Most enzymes are specific to one reaction. [KU1] Outline how enzymes lower the activation energy of a reaction. [2] 1. During catabolic reactions, an enzyme stresses/strains the bonds within substrates to slightly distort the substrate molecule bound to the active site. 2. During anabolic/catabolic reactions, an enzyme maintains the precise orientation of the substrates at the active site, such that these bonds are exposed to the catalytic residues. 3. During catabolic/anabolic reactions, an enzyme can increase the substrate reactivity/ as the R groups on the enzyme can change the charges of the substrate / alter the distribution of electrons within the bonds of the substrate/cause other chemical changes. 4. Enzymes provide a favourable microenvironment for enzymatic reaction to take place. A tyrosine kinase receptor (TKR) is a protein complex found in the cell surface membrane of mammalian cells. TKR has two components involved in the process of cell signaling: • a receptor for the signalling molecule (ligand) • an enzyme that catalyses the transfer of a phosphate group from ATP to an intracellular protein. Fig. 2.1 is a diagram to show how TKR is involved in cell signalling. Fig. 2.1

5 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Biology (b) Describe how the signalling molecule shown in Fig. 2.1 is able to trigger a response inside the target cell. [HI1] [3] • S ignalling molecule is complementary in shape with and binds to the extracellular domain of the receptor. • Binding induces a conformational change to the receptor protein. • ATP and intracellular protein binds to the enzyme active site • This results in the phosphorylation and activation of the intra