2013 HCI H2 Biology Prelims Paper 3 Answers

HWA CHONG INSTITUTION / 2013 JC2 H2 BIOLOGY / PRELIMINARY EXAMINATION / MARK SCHEME 1 HWA CHONG INSTITUTION 2013 JC2 H2 BIOLOGY PRELIMINARY EXAMINATION MARK SCHEME QUESTION 1 (a) Outline how the isolated viral RNA can be convert ed into a double-stranded cDNA in step 1. [2] 1. Reverse transcriptase catalyses synthesis of the single-stranded c DNA using the isolated viral RNA template 2. DNA polymerase converts the single-st randed cDNA into a double-stranded cDNA (b) (i) Explain how the recombinant Ti plasmid in step 2 can be formed. [3] 1. The same restriction enzyme is used to cleave both the viral gene coding for TMV coat protein from the cDNA formed in Step 1 and the Ti plasmid 2. to produce complementary sticky ends which fa cilitate annealing of / formation of hydrogen bonds between the viral gene and linearized Ti plasmid 3. DNA ligase is added to covalently link / form phos phodiester bonds between the viral gene and linearized Ti plasmid to produce a recombinant Ti plasmid (ii) Explain the purpose of having a leaf-specific prom oter in the recombinant Ti plasmid formed in step 2. [2] 1. The leaf-specific promoter will ens ure that the viral gene coding for TMV coat protein is only expressed in the leaves of transgenic plants 2. to ensure production of TMV coat protein (c) Suggest another important role of Agrobacterium tumefaciens in the process of creating transgenic plants which are resistant to TMV. [1] 1. Agrobacterium tumefaciens allows for in vivo amplification / production of numerous / multiple copies of the recombinant Ti plasmid (d) (i) Describe the functions of two other named ingredients in the growth media in the development of plant tissues. [4] Ingredient Use in developing tissue 1a. Carbon source, e.g. glucose / sucrose 1b. As respiratory substrate due to lack in autotrophic ability for proliferation of cells and regeneration of shoots 2a. Plant growth regulators, auxins 2b. Stimulates root growth by promoting cell growth & differentiation 3a. Plant growth regulators, cytokinins 3b. Stimulates shoot growth by promoting cell growth & differentiation 4a. Amino acids 4b. Precursors for prot ein synthesis to stimulate cell growth 5a. Vitamins 5b. As catalysts / coenzymes / enz yme activators in various metabolic processes 6a. Antibiotics 6b. Prevent growth of systemic mi crobes / effectively control systemic infection (ii) Explain the significance of the change of environment for the newly form ed plantlets in the final stage of tissue c u l t u r e . [ 2 ] 1. The change of environment represents the shift from heterotrophic / sugar-requiring to autotrophic / free- living condition 2. and the acclimatization of the plantlets to the outdoor environment before they develop into whole transgenic plants [Total: 14 marks] PAPER 3

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