2024 TMJC Prelim H2 Bio Paper 2 (A)

1 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Biology H2 BIOLOGY 9744/02 Paper 2 Structured Questions 11 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 Examination H2 Biology Answer all questions. 1. Cholesterol is synthesized in the smooth endoplasmic reticulum (SER) in liver cells by a series of enzyme-catalyzed reactions. Within the SER, molecules of cholesterol and triglycerides are surrounded by proteins and phospholipids to form lipoproteins. These lipoprotein particles enter the Golgi apparatus where they are packaged into vesicles and released into the bloodstream. Fig. 1.1 is an electron micrograph of parts of two liver cells showing lipoprotein particles within the Golgi apparatus. Fig. 1.2 shows the structure of a lipoprotein particle. Fig. 1.1 Fig. 1.2

3 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Biology (a) State the number of phospholipid layers formed when a lipoprotein particle is packaged into a vesicle by the Golgi apparatus. [Cell, HI-2] [1] • 3 GENERAL COMMENTS: • You need to learn to READ preambles and figures. (b) (i) Explain why cholesterol and triglycerides need to be packaged into lipoproteins before they are released from liver cells into the bloodstream. [Cell, KU-2] [3] 1. Cholesterol/triglycerides are hydrophobic / lipid-soluble / not water-soluble. 2. Lipoprotein is a phospholipid monolayer 3. Its hydrophobic fatty acid tails interact with cholesterol/triglycerides. 4. Its hydrophilic phosphate heads allow cholesterol/triglycerides to be transported in aqueous blood. (ii) State two roles of cholesterol in cells. [Cell, KU-1] [2] 1. A component of cell membranes. 2. Regulate membrane fluidity. 3. The starting molecule to synthesize bile salts / steroid hormones / vitamins / named molecules ERRORS: “Provide insulation for the cell”, “source of energy”, “converted into glucose” Undiscovered roles of cholesterol currently discovered by you? 😊

4 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Biology (c) Cholesterol is also packaged into vesicles by the SER and then secreted from the cell into small fluid-filled spaces between the liver cells. These spaces form ducts that drain into the gallbladder to form bile. Describe how cholesterol is secreted into ducts, such as the duct shown in Fig. 1.1. [Cell, KU-1] [2] 1. SER vesicles move to the cell surface membrane / space between liver cells. 2. Vesicles fuse with the cell surface membrane. 3. Cholesterol released/secreted into the duct via exocytosis. ERRORS: “budding”, “endocytosis”, “pseudopodia” Seems like you didn’t really learn anything from the Afternoon Practice. (d) Other than the packaging of substances into vesicles for transport, the Golgi apparatus also modifies proteins into their active form. State two ways in which a protein can be modified into its active form. [Cell, KU-1] [2] 1. Glycosylation / adding oligosaccharides to protein 2. Phosphorylation / adding phosphate group to protein 3. Hydroxylation / adding hydroxyl group to protein 4. Cleavage of protein into active form 5. Assembly of protein subunits into its quaternary structure ERRORS: “removal of 1st amino acid methionine” The removal of 1st amino acid methionine determines the half-life of the protein. Even with methionine, the protein is already active. “folding of the polypeptide into its 3D conformation” Folding is not considered as protein modification. Furthermore, the polypeptide has already folded in the rough ER upon translation. “hydrolysis of the protein” This sounds like the protein is degraded into individual amino acids or smaller peptides. [Total: 10]

5 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Biology 2. (a) The major constituent of plant cell walls is cellulose. Selected parts of the cell wall contain another type of polysaccharide called callose. Fig. 2.1 is a simplified diagram showing the structure of callose. Not all hydrogen atoms are shown. Fig. 2.1 Compare the structure of a callose molecule with a cellulose molecule. [Biomol, HI-2] [3] feature callose cellulose monomer β-glucose branching unbranched shape straight / linear type of glycosidic linkage 1,3-glycosidic bond 1,4-glycosidic bond orientation of monomer adjacent glucose molecules same way up / AW alternate glucose molecules rotated by 180° ERRORS: “Cellulose is formed by 1,6-glycosidic bond.” Confusion with starch/glycogen? (b) Amino acids are the building blocks of proteins. Fig. 2.2 shows the R-groups of two amino acids, phenylalanine and serine. Fig. 2.2 (i) In the space below, draw a dipeptide formed from the condensation reaction between phenylalanine and serine. [Biomol, KU-1] [3]

6 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Biology GENERAL COMMENTS: • If you drew some weird diagrams, I suggest you r