TMJC 2023 H2 P3 Ans

H2 BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 18 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 Section A Answer all questions in this section. QUESTION 1 (a) The pituitary gland is located in the brain of mammals. Prolactin, a hormone from the pituitary gland, stimulates cells in the mammary glands of female mammals so that the cells are able to secrete milk. (i) State the potency of the stem cells that produce pituitary cells. [1] [Stem cell] [HI-1] • Multipotent (ii) With reference to the information provided, explain how the stem cells in pituitary gland stimulate cells in the mammary gland to secrete milk. [3] [Stem cell and context] [HI-2] 1. Stem cells in the pituitary gland undergo cell division and differentiation to produce specialized cells that secrete hormones / prolactin. 2. the hormones travel via bloodstream… 3. …and bind to prolactin receptor on mammary cells to lead to signal transduction to stimulate the mammary cells to secrete milk. (iii) Cells in the mammary glands that have been stimulated by prolactin need more glucose. State one reason why those cells need more glucose. [1] [Resp] [HI-2] 1. Glucose is a respiratory substrate used to synthesise ATP for the production/secretion of milk. (reject: synthesise/produce energy) 2. Glucose is a substrate to form milk sugar/ lactose. 3. Glucose is a component found in milk

3 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Biology (b) Female mammals produce milk to feed new-born offspring. Secretory Immunoglobulin A ( SIgA) is the main antibody found in breast milk of humans. It is secreted from IgA-producing plasma cells into cavities within the mammary glands to form milk with other components. (i) Explain how newly synthesi sed SIgA in the IgA -producing plasma cells reach the cavities within the mammary glands. [4] [Cell] [KU-2] 1. Newly synthesi sed SIgA antibody enters the ER lumen for biochemical modifications 2. ER vesicles carrying SIgA bud off from rER… 3. … and travel towards the cis face of Golgi apparatus and fuse with the membrane of the Golgi apparatus. 4. SIgA may undergoes further biochemical modification in GA. 5. Through repeated budding and fusion of vesicles to transport SIgA from the cis face to trans face 6. At the trans face of the Golgi apparatus, SIgA is sorted and packaged into a secretory vesicle which buds off from the Golgi apparatus. 7. The secretory vesicle moves towards the cell surface membrane and fuse with it to secrete SIgA out of the cell via exocytosis. (ii) The antibodies and other components in the breast milk provide immediate protection to newborns in fighting infections. However, this is not a long-term protection. Explain why antibodies such as SIgA in breast milk will not produce long-term protection to newborns. [2] [Immunity] [KU-1] 1. Passive immunity 2. which does not elicit immune response Or Antibodies came from other source/the mother 3. Antibodies remains in the blood only for a short time / eventually degraded

4 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Biology (c) β-catenin signal ling pathway involving WNT as a ligand is important in regulating cell proliferation during mammary gland development. When WNT binds to the Frizzled receptor embedded on the cell surface membrane, β-catenin is activated which translocates into the nucleus to upregulate the transcription of target genes. Fig. 1.1 shows the signal ling pathway with and without WNT. Fig. 1.1 (i) The shape of Frizzled receptor is characteristic of a particular group of transmembrane receptor proteins. Name this group of proteins. [signalling] [HI-1] [1] • G-protein linked receptors / G -protein coupled receptors (ii) Suggest how β-catenin is degraded in the absence of WNT. [2] [OCGE] [HI-2] 1. β-catenin is tagged by ubiquitin… 2. Which is then recognised and degraded by proteasome (iii) Cell surface membrane is made up of phospholipid molecules. Explain why triglycerides are not suitable as a component of cell surface membranes. [2] [Bio Mol] [KU-2] 1. Triglyceride is hydrophobic/non-polar 2. Hence it is unable to form hydrogen bonds with water 3. Idea of Both cytoplasm and extracellular matrix are aqueous, triglyceride cannot form a bilayer to interact with

5 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Biology (d) One of the target genes in WNT/β-catenin signalling pathway is cyclin D1 gene. Fig. 1.2 shows the percentage of β-catenin activity and cyclin D1 protein level during the mitotic cell cycle of a mammary gland cell. Fig. 1.2 With reference to Fig.1.1 and Fig.1.2, describe and explain the effect of β-catenin on cyclin D1 gene expression from G1 to S and mitosis of mammary gland cell. [4] [data response] [HI-2] [effect on cyclin D1 gene expression] 1. [Describe] As β-catenin activity level increases from 20% to 35% from G1 to S phase, cyclin D1 protein level increases from 29 a.u.