2024 NYJC Prelim Biology P3 (Q)

NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 13 September 2024 Additional Materials: Insert, Answer booklet 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. 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 on the separate Answer Paper. 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 no use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 2 3 Section B Total This document consists of 13 printed pages. [Turn over H

2 9744 / H2 Biology / 03 Section A Answer all the questions in this section. 1 Part of the information required for Question 1 is presented in the insert. Cross references to Fig. 1.1 and Fig. 1.2 are included in the questions for which Fig. 1.1 and Fig. 1.2 are relevant. Bioinformatics is the collection, processing and analysis of biological data using computer software. The application of bioinformatics allows whole sequences of homologous genes to be compared across different bacterial species. (a) Explain why bioinformatics can used to compare gene sequences and suggest a conclusion that can be made from the percentage similarity data obtained. [2] (b) Humans use antibiotics to treat bacteria infections. Different types of antibiotics work i n different ways to either kill or inhibit the reproduction of the bacteria. (i) Outline how penicillin acts on bacteria and use Fig. 1.1 to suggest why penicillin has little or no effect at treating diseases caused by Gram-negative bacteria. [3]

3 9744 / H2 Biology / 03 (ii) The use of antibiotics has resulted in the emergence of antibiotic resistant bacteria. Antibiotics such as nalidixic acid acts as an inhibitor of an enzyme involved in DNA replication. Suggest how a substitution mutation in the gene coding for this enzyme could result in antibiotic resistance. [4] (c) The outer membrane of E.coli contains transport proteins called OmpF porins. These porins allow the passive movement of water, ions and small, polar molecules across the outer membrane. Each OmpF porin is formed from three identical polypeptides. (i) Suggest and explain the features of an OmpF porin as a membrane transport protein. [4]

4 9744 / H2 Biology / 03 (ii) E. coli can regulate the number of OmpF porins in the outer membrane to adapt to changing conditions. One control mechanism used by E. coli involves the production of a small mRNA molecule known as micF. micF binds to the part of the mRNA molecule containing the START codon for the OmpF polypeptide. Explain how the presence of micF prevents production of OmpF porins. [3] (d) Fig. 1.1 shows that the outer membrane of the cell wall of E. coli contains lipopolysaccharides (LPS). These are not present in the cell surface membrane. Each LPS consists of a lipid and a polysaccharide portion. The O antigen is the outer part of the polysaccharide portion of the LPS. It faces the aqueous external environment. (i) Define the term polysaccharide. [2]

5 9744 / H2 Biology / 03 (ii) Some strains of E. coli are pathogenic. Different pathogenic strains have different O antigens. Suggest why infection with one pathogenic strain of E. coli does not provide immunity to a different pathogenic strain. [3] (e) (i) With reference to Fig. 1.2, identify two events that occur during binary fission that do not occur during mitosis in human cells. [2] (ii) Binary fission produces genetically identical daughter cells unlike meiosis in sexual reproduction. Genetic variation is key to the survival of a species. Outline briefly two possible ways in which variation can be introduced into the bacterial population. [2] [Total: 25]

6 9744 / H2 Biology / 03 2 Photosynthesis is an energy transfer process that results in the production of carbohydrate. It has two stages: the light-dependent stage and the light-independent stage. Cyclic photophosphorylation and non-cyclic photophosphorylation are essential pathways in photosynthesis that occur in the light-dependent stage. (a) (i) Describe the similarities and differences between cyclic photophosphorylation and non-cyclic photophosphorylation. [3] (ii) Explain why herbicides that prevent cyclic photophosphorylation and non-cyclic photophosphorylation stop carbohydrates from being produced in the chloroplast. [2]

7 9744 / H2 Biology / 03 (b) The rate of regeneration of RuBP in the Calvin cycle is known to limit the r ate of photosynthesis. Sedoheptulose-1,7-bisphosphatase (SBPase) is an enzyme in the Calvin cycle that controls the rate of regeneration of RuBP. SBPase is coded for by the gene SBPase. In an experiment, wheat plants were genetically modified to make more SBPase by introducing the SBPase gene from another grass species, Brachypodium distachyon. The resulting GM wheat plants were named Sox4. • Wild type plants (not GM) and Sox4 plants were grown. • A leaf from the wild type plant was placed in a sealed glass vessel. • The carbon dioxide (CO2) concentration in the vessel was increased so that the intercellular air spaces also had an increase in CO2 concentration. • The other environmental conditions were kept constant. • The rate of fixation of CO2 was measured for the leaf. • The experiment was repeated with a leaf from a Sox4 plant. Fig. 2.1 shows the rate of fixation of CO 2 by the leaves of wild type plants and Sox4 plants when the intercellular air space CO2 concentration was increased. Fig. 2.1

8 9744 / H2 Biology / 03 (i) With reference to Fig. 2.1, describe and explain the results shown by the wild type plants. [3] (ii) With reference to Fig. 2.1, explain the differences in the rate of fixation of CO 2 between wild type plants and Sox4 plants. [2]

9 9744 / H2 Biology / 03 Phytochromes are able to detect red light and far-red light, which are requi red for photosynthesis to occur in plants. Upon reception of light by the phytochrome receptor, two signal transduction pathways are elicited in a Sox4 plant cell as show in Fig. 2.2. Both pathways eventually result in the synthesis of enzymes involved in chlorophyll production. Fig. 2.2 (c) With reference to Fig. 2.2, (i) identify the second messengers involved in the signalling pathway. [1] (ii) explain one step of the signal transduction stage in the cytoplasm that illustrates signal amplification. [2]

10 9744 / H2 Biology / 03 (iii) compare the activation of calmodulin with that of the final protein kinase in a protein kinase cascade. [2] [Total: 15] 3 The Hayflick limit is the number of cell division a normal somatic, diffe rentiated human cell can undergo before cell division stops. (a) Using your knowledge on DNA replication in cells, explain how the Hayflick limit occurs. [3]