2024 VJC H2 Bio P4 MS

VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2024 HIGHER 2 NAME : ……………………………………………………….………………. CT CLASS: ………………..……… BIOLOGY Paper 4 Practical 9744 / 04 29/08/2024 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. READ THESE INSTRUCTIONS FIRST Write your name and CT in all the work in hand in. Give details of the practical shift and laboratory, where appropriate, in the boxes provided. 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. Answer all questions 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 bracket [ ] at the end of each question or part question. Shift Laboratory Question Marks 1 2 Total This document consists of 18 printed pages. [Turn over]

Answer all questions. Question 1 Researchers are exploring the development of plant-based, biode gradable plastics as an alternative to petroleum-based plastics. Switchgrass is an example of a c rop that synthesises polymers n aturally and is used for biodegradable plastic production. Switchgrass which are genetical ly modified with genes from anot her organism can result in the plants synthesising more polymers. These plants are termed as transgenic plants. The ability to synthesise polymers is highly dependent on the growth rate of the plants, which in turn depends on the rate of photosynthesis. (a) (i) For the same concentration of chloroplasts, predict how the ra te of photosynthesis in the commercially-available switc hgrass chloroplast extract woul d compare to that in the transgenic plant. [1]  The chloroplast extract from the transgenic plant will have a higher rate of photosynthesis; To test for the rate of photosynthesis, the blue dye, DCPIP, wh ich acts as a substitute for NADP+ can be used. oxidised DCPIP (dark blue) photosynthesising tissues reduced DCPIP (colourless) You are required to:  investigate the rate of photosynthesis in different concentrat ions of commercially available switchgrass chloroplast extract  obtain a chloroplast extract from the transgenic plant  estimate the concentration of chloroplasts in the transgenic plant. You are provided with:  15 cm3 commercially available 10% swi tchgrass chloroplast extract, in a small vial labelled SE1  A leaf from transgenic plant labelled T  cold buffer solution, in a large vial labelled B  distilled water, in a large vial labelled W  a block of agar stained with DCPIP. The DCPIP agar may stain your skin. You are advised to wear gloves when handling the agar. The agar must be covered using alu minium foil when not in use t o prevent decolourisation. Assume that the temperature in the lab remains relatively const ant. It is not necessary to use a water bath maintained at room temperature. Proceed as follows.

1 You are required to carry out a serial dilution of SE1 to reduce the concentration of the chloroplast extract by a factor of ten between each of three successive dilutions, SE2, SE3 and SE4. You will need to make up 8.0 cm3 of each solution. Some of this will be used to make the next solution. (ii) Describe how you would carry out serial dilution to obtain SE2, SE3 and SE4. [3] 1. Correct switchgrass chloropla st extract used for each dilution; 2. Correct volumes of switchgrass chloroplast extract and disti lled water used to make up 8.0 cm3 of each solution; 3. Ref to appropriate and logical steps in description; concentration switchgrass chloroplast extract / % switchgrass chloroplast extract used for dilution volume of switchgrass chloroplast extract used for dilution / cm 3 volume of distilled water used / cm3 1.00 (SE2) SE1 0.8 7.2 0.10 (SE3) SE2 0.8 7.2 0.01 (SE4) SE3 0.8 7.2 (iii) Suggest an advantage of carrying out serial dilution. [1]  Ref. to ability to obtain small concentrations – not possible with simple dilution from stock as volumes of stock solution needed to make small concentrations are too small to be measured accurately with the apparatus provided;  Ref. to ability to test a bigger range of concentrations; 2 Label three small vials, SE2, SE3 and SE4. Use them to prepare the different concentrations of SE2, SE3 and SE4, as described in (a)(ii). 3 Place the block of DCPIP stained agar onto a white tile. Using a ruler and a knife, cut the agar block into identical cubes of about 1.5 cm × 1.5 cm × 1.5 cm, as shown in Fig. 1.1. It may be difficult to cut them to exactly the same size. You w ill use only five agar cubes for this part of the experiment. Choose five that are the most identical to one another. Set aside the rest of the agar cubes for backup. Place all the agar cubes onto the Petri dish provided and cover the Petri dish with aluminium foil. Fig. 1.1 4 Using a white tile and knife, chop up 3.0 cm by 3.0 cm of the fresh leaf T into smaller pieces and put them into the mortar.

5 Slowly add approximately 15.0 cm 3 of cold buffer solution B to the mortar. Grind the leaf pieces to obtain a chloroplast extract of T. (iv) Outline the importance of using cold buffer for chloroplast extraction. [1] Any one:  Cold – Lower activity of hydrolytic enzyme / Make hydrolytic e nzyme inactive to prevent damages to chloroplasts;  Contains pH buffer – Maintains pH to prevent denaturation of enzymes in chloroplasts; 6 Place a sieve on top of the opening of a large plastic vial. F ilter the contents of the mortar to remove the plant debris, keeping filtrate TE. 7 Use a piece of aluminium foil to cover the vial containing TE to protect it from light. 8 Label a small vial TE and put 7.0 cm3 of TE into the vial. 9 You will only need 7.0 cm 3 of SE1. Use a syringe to discard any excess SE1 from the small vial into the sink. Put a piece of agar cube into the small vial con taining SE1 and immediately start the stopwatch. Incubate for 10 minutes. 10 Repeat step 9 for SE2, SE3, SE4 and TE. You may stagger the start times for incubation of each vial. 11 Gently swirl the contents of the vials at regular intervals.Wh ile you are incubating the agar cubes, continue to read through this Question Paper up to step 15 and complete (a)(vi). 12 Fill a large vial with tap water. This will be used to rinse t he agar cubes in step 13 to stop the reaction. 13 After 10 minutes, use a pair of forceps to remove the agar cub es from each solution and rinse the cubes in the vial. 14 Put each agar cube on a white tile and cut it into half. (v) In the square below, draw the decolourised region and DCPIP stained region of the cut end of the agar cube that has been immersed in SE1. Add a ruled line to label the “ decolourised region” and a secon d ruled line to label “DCPIP stained region”. [1]

15 Measure the length of the DCPIP stained region for all the agar cubes, to the nearest mm. Record these measurements in the table prepared in (a)(vi). Ensure that these measurements are done immediately as the agar cubes will continue to decolourise when exposed to light. (vi) Use this space to record your results for step 15 in a suitable format. [3] concentration of SE / % len gth of DCPIP stained region / mm 10.00 9 1.00 10 0.10 11 0.01 13 Unknown (TE) 1 0 1. Correct trend; 2. Correct headings and units; 3. Data to nearest whole number (mm); (vii) Using the data obtained in (a)(vi), estimate the concentrat ion of chloroplasts in TE. [1]  1.00% (A: 0.10%); (vii