2018 RVHS H2 Biology Prelims Paper 3 Answers

1 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION CANDIDATE NAME CENTRE NUMBER S CLASS INDEX NUMBER BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 14 Sep 2018 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question in the spaces provided on the Question 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 not 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 / 25 2 / 25 Section B / 25 Total / 75 _____________________________________________________________________ This document consists of 19 printed pages and 1 blank page.

2 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination Section A Answer all the questions in this section. 1 Plant tissue culture is a technique to produce an entire plant using undifferentiated meristem cells. A cluster of meristem cells can be extracted and stimulated with growth hormones to differentiate to form different types of cells that give rise to an entire plant. (a) Suggest why meristem cells from any part of a plant can be used to produce the entire plant in plant tissue culture. [2] 1. The meristem cell contains all the DNA/genes/genetic material of the plant. 2. The meristem cell is totipotent.

3 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination In plant tissue culture, plant hormones are added to the meristem cells to regulate growth and differentiation to form roots and shoots. These hormones include auxin and cytokinin. The experiment set up is shown in Fig. 1.1 Fig. 1.1 The effects of various compositions of auxin and cytokinin on the cluster of meristem cells are summarised in Table 1.1. Table 1.1 Concentration of auxin / mg L -1 Concentration of cytokinin / mg L-1 Observation 0 0 10 0 8 4 6 6 4 8 0 10

4 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination (b) With reference to Table 1.1, state three conclusions on the effect of auxin and cytokinin on plant growth and differentiation. [3] 1. Both auxin and cytokinin are required for cell division / plant formation. 2. Equal concentration of auxin and cytokinin leads to growth/cell division but no differentiation. 3. High auxin concentration and low cytokinin concentration leads to cells differentiating to root. 4. Low auxin concentration and high cytokinin concentration leads to cell differentiating to shoot. The plant hormone auxin plays a key role in growth and differentiation in plants by altering the expression of selected genes. Genes that are activated or repressed by the presence of auxin are known as auxin-responsive genes (ARGs). ARG expression is controlled by two transcription factors, auxin response factor and auxin repressor. Binding of auxin response factor to ARE recruits the auxin repressor. Fig. 1.2 shows how auxin controls the expression of an ARG. Fig. 1.2

5 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination (c) Explain why auxin repressor interacts specifically with auxin response factor. [2] 1. Auxin repressor and auxin response factor interact at binding sites, 2. that are complementary shape, 3. and contains amino acid residues, 4. that can form (compatible) R group interactions . (d) With reference to Fig. 1.2, state the level at which the gene expression of the following proteins are controlled. [2] (i) Protein product of ARG Transcriptional control (ii) Auxin repressor Post-translational control (e) Describe the role of an enzyme involved in each level of control stated in (d). [4] 1. RNA polymerase, 2. binds to promoter of auxin response gene 3. to initiate transcription. 4. Proteasome, 5. recognise ubiquitin-tagged auxin repressor, 6. hydrolyses auxin repressor or 7. Enzyme transferring ubiquitin to auxin repressor, 8. tag auxin repressor for degradation 9. by proteasome.

6 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination For many years, bacteria have been genetically manipulated to produce therapeutic proteins for human diseases. In recent years, plant molecular farming, the practice of using plants to produce human therapeutic proteins, has gained the attention of many pharmaceutical companies. Plants are modified by introducing human gene sequenc es into their genomes, which serve as templates for protein synthesis. (f) Describe how protein synthesis in bacteria cells differ from plant cells. [3] Feature Bacteria Plant cell Order of transcription and translation Transcription and translation occur simultaneously Translation begins only after transcription is completed Post transcriptional modification No post transcriptional modification Modified by adding 5’ capping, RNA splicing, 3’ polyadenylation Post- translational modification No post translational modification Modified by glycosylation, phosphorylation, cleavage etc. Ribosomes involved 70S ribosomes 80S ribosomes Location Transcription and translation in cytoplasm Transcription in nucleus, Translation in cytoplasm/rough endoplasmic reticulum Plant molecular farming produces therapeutic proteins such as clotting factor XIII. Individuals suffering from haemophilia A cannot produce functional clotting factor XIII due to a point mutation. They suffer from severe bleeding and need injections of clotting factor XIII throughout their life.

7 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination (g) Describe how a point mutation can lead to the production of clotting factor XIII with reduced function. [3] 1. Base-pair substitution in clotting factor XIII gene 2. resulting to missense mutation, 3. change in corresponding mRNA codon, 4. change in corresponding amino acid, 5. with different (R group) properties. 6. Resulting polypeptide chain will not fold properly, 7. changing its three-dimensional structure/shape. Or 8. Base-pair insertion/deletion at the end of the clotting factor XIII gene 9. resulting in frameshift, 10. change in small number of terminal mRNA sequence, 11. change in corresponding amino acid at the end of the polypeptide chain, 12. with different (R group) properties. 13. Resulting polypeptide chain will not fold properly, 14. hanging its three-dimensional structure/shape.

8 River Valley High School Year 6 H2 Biology 9744 Paper 3 2018 Preliminary Examination A study investigates the presence of plant-derived blood clotting factor XIII after injection into a patient suffering from haemophilia A. Blood plasma is extracted from the patient and the proteins in the sample are separated by a technique known as sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE). In SDS-PAGE, proteins are first treated with the chemical SDS before they are inserted into wells in a polyacrylamide gel for gel electrophoresis. The proteins are then separated on the basis of size, using the same principle