2015 RI H2 Biology Prelims Paper 2 Questions

© RI 2015 Preliminary Examination 9648/02 [Turn over RAFFLES INSTITUTION 2015 Year 6 Preliminary Examination Higher 2 BIOLOGY 9648/02 Paper 2 Core paper 16th SEPTEMBER 2015 2 hours Additional materials: Answer Sheet READ THESE INSTRUCTIONS FIRST Write your index number, CT group & name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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. Section B Answer either ONE question. At the end of the examination, hand in your essay SEPARATELY. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 24 printed pages. CIVICS GROUP CANDIDATE NAME INDEX NUMBER 5 S 0 3 1 Raffles Institution Internal Examination For Examiner’s Use Section A 1 / 9 2 /10 3 /12 4 /10 5 /10 6 / 9 7 / 9 8 /11 Section B 9 or 10 /20 Total /100

2 © RI 2015 Preliminary Examination 9648/02 For Examiner’s Use Section A Answer all the questions in this section. 1 Meristematic root tissue from a barley seedling wa s prepared and its chromosomes we re observed under a microscope. Fig. 1.1 shows a cell from the root tissue at the metaphase stage of mitosis. Fig. 1.1 Fig. 1.2 shows the changes in amount of DNA at different stages of the barley life cycle. Fig. 1.2 (a) Mark out clearly with an arrow, , on Fig 1.2, the part of the graph which corresponds to the stage shown in Fig. 1.1. [1] (b) With reference to Fig. 1.2, state which of the stages, from A to D, (i) has/have the same number of chromosomes as shown in Fig. 1.1; [1]

3 © RI 2015 Preliminary Examination 9648/02 [Turn over For Examiner’s Use (ii) has/have a different number of chromosomes as shown in Fig. 1.1. [1] (c) Explain how stages in Y lead to variation. [4] (d) Explain the significance of the event occurring at X. [2] [Total : 9]

4 © RI 2015 Preliminary Examination 9648/02 For Examiner’s Use 2 Fig. 2.1 shows DNA replication. (a) (i) Use an arrow to show the direction of replication of the leading strand in the box provided in Fig. 2.1. [1] (ii) What do 5’ and 3’ on the DNA molecule represent? [2] (iii) Name the following molecules. [1] V: W: (iv) Describe the role of two named enzymes that are required for DNA replication. [2] (a) (i) V W Fig. 2.1

5 © RI 2015 Preliminary Examination 9648/02 [Turn over For Examiner’s Use Fig. 2.2 shows transcription. (b) Describe how the structure of molecule Z is adapted to its role in transcription. [2] (c) Describe how a silent mutation can result in no change in protein structure. [2] [Total : 10] Z Fig. 2.2

6 © RI 2015 Preliminary Examination 9648/02 For Examiner’s Use 3 The Jacob-Monod hypothesis describes lactose metabolism in the bacterium Escherichia coli. An investigation of this reaction in E. coli, at 25°C, was carried out as described below (refer to Fig. 3.1). • 100 cm3 of gel beads coated with E. coli were placed into each of seven identical funnels fitted with outlet taps. • 100 cm3 of solution containing 2 grams of lactose was poured into each funnel at 0 min. • At each time shown in the table, the solution from the respective funnel was released and collected. • The mass of lactose in each solution was measured. The results are shown in Table 3.1 below. Table 3.1 With reference to Table 3.1, Funnel Time (min) Mass of lactose collected in the solution (g) 1 0 2.00 2 10 2.00 3 20 1.48 4 30 0.92 5 40 0.40 6 50 0.12 7 60 0.04 (a) (i) calculate the average mass of lactose broken down per minute in funnel 5. [1] g per minute Fig. 3.1

7 © RI 2015 Preliminary Examination 9648/02 [Turn over For Examiner’s Use (ii) explain the results from funnels 3 to 7. [4] Fig. 3.2 below shows an operon that controls a catabolic reaction in E. coli. Some information on how this operon functions is also provided. (b) (i) In the presence of inducer, protein Y cannot bind to structure W. Name W. [1] mRNA mRNA Structure W Chromosome Protein Y Translation Translation Gene 1 Enzyme breaks down compound H Gene P Gene Q Gene R Fig. 3.2 Operon

8 © RI 2015 Preliminary Examination 9648/02 For Examiner’s Use (ii) A mutation occurred in gene P. This resulted in the production of a truncated protein. Assuming that the inducer is present, explain if the proteins encoded by Gene Q and Gene R are produced. [2] (c) An E. coli cell can be infected by a bacteriophage. How does the bacteriophage differ from HIV (human immunodeficiency virus) in the way its genome enters the host cell? [1] (d) Bacteriophage lambda in an E. coli cell can replicate as a prophage or lytically. These two phases are controlled by the gene regulatory proteins cI and Cro, which are encoded by the virus (refer to Fig. 3.3). When bacteria containing a lambda prophage are irradiated with ultraviolet light, the cI protein is degraded. With reference to Fig. 3.3, (i) state which phase the bacteriophage enters upon UV irradiation, [1] B) Replicate lytically Fig. 3.3 A) Replicate as a prophage

9 © RI 2015 Preliminary Examination 9648/02 [Turn over For Examiner’s Use (ii) describe the events following the degradation of the cI protein. [2] [Total : 12] 4 Glucocorticoids ( S), are a class of steroid hormones that bind to the glucocorticoid receptor (GR), and are crucial in regulation of many genes. S binds to GR, activating GR. Activated GR binds to glucocorticoid response elements (GREs) within the promoter regions of target genes. This results in the recruitment of the chromatin remodelling complex, BRG1 complex. Fig. 4.1 shows the effect of GR-mediated gene expression. Fig. 4.2 shows the effect of BRG1 complex binding to the promoter region of the target gene. Fig. 4.1 Cytoplasm BRG1 Transcription Initiation Complex RNA Nucleus GRE RNA Polymerase

10 © RI 2015 Preliminary Examination 9648/02 For Examiner’s Use Fig. 4.2 (a) Explain how the steroid hormone is able to enter the cell. [1] (b) GRs are known to have highly conserved regions which are structurally important for its function. Describe 2 structural features of GR which allows it to carry out its role. [4] (c) (i) With reference to the information provided, describe the effect of the presence of S on gene expression. [3]