HCI 2024 Prelim H2 Bio P3 Ans

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2024 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 3 MARK SCHEME QUESTION 1 (a) Outline the advantages of having such multistep pathways. [2] 1. ref. to signal amplification 2. ref. to coordination / regulation 3. ref. to specificity of response (b)(i) Explain why IL6 cannot act directly on the DNA in the nucleus. [2] 1. IL-6 is hydrophilic 2. cannot pass through cell membrane (b(ii) Based on your knowledge on RTKs and with reference to Fig. 1.1, explain how IL6 leads to a cellular response. [5] 1. IL6-IL6R complex binds to gp130 2. gp130 dimerises 3. ref. to cross-phosphorylation 4. JAK phosphorylates STAT3 5. dimerised STAT3 activate expression of gene (b(iii) Suggest how regulation of STAT3 activation is an example of negative feedback. [3] 1. ref to. relevant stimulus 2. ref. to gp130 degraded 3. ref. to idea of negative feedback in this context (c)(i) With reference to Fig. 1.2 and Table 1.1, identify and explain which region(s) of gp130 are required for IL6 signalling pathway. [3] 1. ref. to R4, R5, R6 required 2. ref. to relevant supporting data from Fig. 1.2 3. ref. to relevant supporting data from Table 1.1 (c)(ii) Explain how the structure of the transmembrane domain of gp130 contributes to its function. [2] 1. ref. to hydrophobic nature 2. ref. to embedding of gp130 within membrane (d) With reference to Fig. 1.3, explain the significance of process Q in the formation of membrane-bound and soluble forms of IL6R. [3] 1. ref. to alternative splicing 2. ref. to relevant supporting data from Fig. 1.3 3. ref. to relevant supporting data from Fig. 1.3 (e) Suggest why early detection of PDAC is challenging. [1] ref. to any valid reason

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 2 (f)(i) Using the information in Fig. 1.1 and Table 1.2, identify which gene is the best target for effective treatments and explain your choice. [3] 1. gp130 gene 2. ref. to relevant supporting data from Fig. 1.1 3. ref. to relevant supporting data from Table 1.2 (f)(ii) Table 1.3 shows a few genes that are often found to be mutated in PDAC patients. With your knowledge and the relevant data provided, complete Table 1.3 to predict: ● the level of gene expression, using “” or “” ● if the gene is a proto-oncogene (POG) or tumour suppressor gene (TSG). Table 1.3 gene level of expression POG or TSG p53  TSG STAT3  POG SOCS3  TSG [2] (g)(i) Calculate the amount of DEN to be injected into a 14-day old mouse that weighs 10 g. You should show your working. [1] 250 µg (g)(ii) Discuss the effect of gp130 on tumour initiation and tumour progression. [3] 1. gp130 promotes tumour initiation and progression 2. ref. to relevant supporting data from Fig. 1.4 3. ref. to relevant supporting data from Fig. 1.5 [Total: 30]

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 3 QUESTION 2 (a) Explain why the gene IFNA2 must be obtained via reverse transcription of the mature mRNA instead of directly from the genome of B lymphocytes. [2] 1 mature mRNA only contains exons 2 mature mRNA is reversed transcribed to give continuous coding DNA sequence 3 E. coli does not have spliceosomes (b)(i) Explain the role of the gene lacI in the control of transcription of the IFNA2 gene between 0 hours and 4 hours. [2] 1 lacI is regulatory gene 2 repressor binds to operator and prevents transcription (b)(ii) With reference to Fig. 2.2, describe the changes in the concentration of recombinant IFN-α in the culture containing IPTG from when IPTG was added at 4 hours to the end of the experiment at 28 hours. [3] 1 concentration of IFN-α produced increases steeply after addition of IPTG 2 peak is at 8 hours / 4 hours after addition of IPTG 3 decrease is less steep 4 correct data quoted with units (b)(iii) Suggest two reasons for the difference between the concentration of recombinant IFN-α in the culture at 8 hours in the presence of lactose and the concentration of recombinant IFN- α in the culture at 8 hours in the presence of IPTG. [2] 1 lactose has to be converted to allolactose 2 lactose is broken down, hence less lactose / allolactose bind to repressor 3 IPTG will be at higher concentration than allolactose 4 IPTG has higher affinity for repressor protein than allolactose 5 more IPTG enters (c) Suggest how AMPR allows genetically engineered E. coli containing the recombinant plasmid to be identified. [1] only E. coli that have taken up the plasmid will grow in the presence of ampicillin [Total: 10]

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 4 QUESTION 3 (a) Assuming that the Hardy-Weinberg principle applies to this population, calculate the number of plants in the field that are heterozygous. [3] Show your working and give your answer to the nearest whole number. 1 use formula + 2 + = 1 and total number of plants to calculate genotypic frequency 2 calculate allelic frequency of dominant and recessive alleles 3 use allelic frequencies to calculate number of heterozygous plants in the field (b) A student concluded that flower colour in I. nil shows continuous variation. Explain why the student made this conclusion. [2] 1 colours not discrete / range / include intermediates 2 more than one genes 3 environment affects colour (c)(i) Explain how the stomatal response shown in Fig. 3.1 would allow I. pes-caprae to survive the effects of climate change. [3] 1 increase in CO2 concentration causes mean width of stomatal aperture to decrease 2 less water lost through stomata 3 compensates for low water availability (c)(ii) It has been hypothesised that an increase in atmospheric CO2 concentrations might result in an increase in the rate of photosynthesis and consequently, an increase in growth of plants. Suggest why there might not be significant increase in growth of I. pes-caprae plants despite increase in atmospheric CO2 concentrations. [2] 1 increased in earth surface temperature leads to an increase in the rate of enzyme- catalysed reactions 2 increase in rate of respiration, leading to loss of carbon as CO2 [Total: 10]

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 5 QUESTION 4 (a) Describe the features of DNA structure that allow DNA to stably store and accurately replicate large amount of genetic information. [15] S1 DNA being less susceptible to degradation S2 2’ carbon of deoxyribose having an attached hydrogen atom S3 DNA coiling into a tight helix S4 sugar-phosphate backbone of a DNA chain S5 phosphodiester bonds formed between 5’ phosphate and 3’ hydroxyl groups S6 phosphodiester bonds being covalent bonds S7 double helix structure S8 phosphate groups that project outside the double-helix S9 exposure to outside influences of only the sugar-phosphate backbone S10 nitrogenous bases that orientate inwards toward the central axis S11 nitrogenous bases being safely tucked inside the double-helix S12 extensive hydrogen bonds between base pairs S13 hydrophobic interactions between the stacked base pairs S14 DNA double-helix being wound around histones to form nucleosomes S15 nucleosomes being folded into higher order structures such as solenoid / chromosome A1 to complementary base-pairing A2 between A and T and between C and G A3 base sequence of one strand co