CJC 2023 JC2 Bio P3 (ans)

NAME: ___________________________________________ CLASS: _________ INDEX: __________ CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Higher 2 BIOLOGY 9744/03 Paper 3 Long Structured and Free-Response Questions 13 September 2023 2 Hours Candidates answer on the Question Paper. Additional Material: Writing Booklet. READ THESE INSTRUCTIONS FIRST Write your name (as per NRIC), class, and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. [PILOT FRIXION ERASABLE PENS ARE NOT ALLOWED] You may use a soft pencil for any diagrams, graphs, or rough working. Do not use staples, paper clips, highlighters, glue, or correction fluid. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question in this section. Write your answers in the writing booklet provided. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 21 printed pages and 0 blank page. [ T u r n o v e r For Examiner’s Use Section A 50 1 2 3 Section B 25 4 or 5 Total 75 Suggested Answers

2 2023 Prelim/ 9744/ 03 Section A Answer all the questions in this section. 1 Endosymbiont is a cell which lives inside another cell with mutual benefit. The organelle in Fig. 1.1 is believed to have evolv ed from the early prokaryote that was engulfed by phagocytosis. The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell. Over generations, the engulfed prokaryotic cell lost some of its independent utility and became a supplemental organelle. Fig 1.1 (a) Explain how the organelle shown above supports the endosymbiotic theory. …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………. [2] 1. Circular DNA, which is different from nuclear linear DNA. 2. 70s ribosome as compared to 80s ribosome. 3. Double membrane structure, the outer membrane was part of the host cell. (b) Explain how the organelle is adapted to its function. …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………. [3]

3 2023 Prelim/ 9744/ 03 1. The inner membrane of mitochondria is highly folded, forming structures called cristae. These cristae provide a significantly increased surface area for various enzymes involved in the electron transport chain and ATP synthesis. 2. Mitochondria have their own DNA, many of which are involved in oxidative phosphorylation and other mitochondrial functions. 3. The double membrane structure allows for compartmentalisation of the proton gradient. Scientists use the DNA of the organelle shown in Fig. 1.1 for phylogenetic analysis. Analysis of DNA has been used extensively to st udy the evolutionary relationships across many species. (c) Explain the advantages of using the DNA of t he organelle shown in Fig. 1.1 for phylogenetic analysis as compared to using nuclear DNA. …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………. [3] 1. Mitochondrial DNA tends to mutate at a faster rate compared to nuclear DNA. for distinguishing between closely related species. 2. Mitochondrial DNA does not undergo recombination, avoids the complications of recombination and genetic shuffling that can occur with nuclear DNA / Mitochondrial genome is maternally inherited, the sequence ambiguities from heterozygous genotypes are theoretically avoided. 3. Each cell contains multiple copies of mitochondrial DNA, making it relatively easy to obtain sufficient genetic material for analysis / Higher copy number, therefore, greater abundance in sample extracts. 4. Certain regions or genes within the mitochondrial genome are relatively conserved across species. For ease of comparison. The DNA of the organelle shown in Fig. 1.1 is more susceptible to oxidation than nuclear DNA, possibly because of its proximity to the elec tron transport chain in its inner memb rane. As a result, the rate of mutation becomes much higher. (d) Suggest why the DNA of the organelle shown in Fig. 1.1 has a high mutation rate. …………………………………………………………… ………………………………………………...... …………………………………………………………… ………………………………………………. [1] 1. High concentration of oxygen in mitochondria induces the mutation. 2. AVP Part of the sequence of the template DNA strand fr om 2 gene loci that code for different transport proteins in the organelle in Fig. 1.1 were shown in Fig. 1.2 below. In addition, Fig. 1.2 shows the corresponding sequences containing the mutation, mutation A and mutation B respectively.

4 2023 Prelim/ 9744/ 03 Wild-type sequence at gene locus 1 3’ – CTT AGA CTT ACT – 5’ Sequence containing mutation A 3’ – CTT AGT ACT TAC – 5’ Wild-type sequence at gene locus 2 3’ – CTC CTA AAA CCT – 5’ Sequence containing mutation B 3’ – CTC CCA AAA CCT – 5’ Fig. 1.2 (e) With reference to Fig. 1.2, state which mutation results in a frameshift. ……………………………………………………………………………………………………………. [1] 1. Mutation A Fig. 1.3 below shows the triplet codes that code for the different amino acids. Fig. 1.3 It was found that mutation A produced a fully functional tran sport protein, while mutation B led to the production of a non-functional transport protein. (f) With reference to Fig. 1.2 and Fig. 1.3, (i) suggest how mutation A could still lead to the production of a fully functional transport protein. Explain your answer. …………………………………………………………………………………………………………

5 2023 Prelim/ 9744/ 03 …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………………… ……………………………………….. [3] 1. Ref. to only a loss of one amino acid – glutamic acid (the 3rd codon is changed from glutamic acid to STOP codon) 2. Frameshift mutation (single base insertion) occurred near the end of the coding sequence. The change not affecting the different / crucial amino acid residue (i.e. binding) 3. This led to only a small / insignificant change in primary structure of protein at the C- terminus. (ii) suggest how mutation B led to the production of a non-func tional transport protein. Explain your answer. …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………… …………………………………………………………… ……………………………………….. [3] 1. Single base substitution mutation led to change in the amino acid aspartic acid to glycine. 2. The R group changes from negatively charged to non-polar , the initial bonds / interaction is disrupted. 3. This amino acid position is crucial in maintaining the 3