VJC 2023 H2 9744 P4 QP

VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2023 HIGHER 2 NAME : ………………………………………………….………………. CT CLASS : ………………..……… BIOLOGY 9744 Practical 30/08/2023 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST 1. Write your name, CT class shift number and laboratory in the spaces provided. 2. Answer all questions in the spaces provided on the Question Paper. The number of marks is given in brackets [ ] at the end of each question. 3. Write in dark blue or black pen. You may use an HB pencil for diagrams, tables and graphs. 4. You should spend the first 5 minutes carefully reading the whole paper before starting to answer any question. 5. This paper consists of 3 questions. Students with the microscope and slide must begin with question 3. You may continue with question 1 or 2 after you have completed question 3. 7. 1 hr 15 min after the start of the exam, students with microscope will need to pass the instrument to their bench partners. Shift For examiner’s use 1 /20 Laboratory 2 /17 3 /18 Total /55 This document consists of 19 printed pages and 1 blank page. [Turn over]

2 Answer all questions. 1 Yeast cells contain enzymes that catalyse metabolic reactions. Some of these reactions release carbon dioxide. You will investigate the release of carbon dioxide from a mixture of yeast and carbohydrate. The mixture is put into dialysis (Visking) tubing. The dialysis tubing acts as a partially permeable membrane, allowing the carbon dioxide to diffuse out of the dialysis tubing. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm 3 Y 1g dried yeast none - G 10.0% warm glucose solution none 20 W distilled water none 50 B bromothymol blue indicator solution harmful 10 D 20 cm length of dialysis tubing in a beaker of distilled water none – If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection. To test for the release of carbon dioxide, a sample of the water surrounding the dialysis tubing is added to drops of an indicator, B. Fig. 1.1 shows the effect of increasing concentration of carbon dioxide on the colour of B. Yellow is the end-point. BLUE blue-green GREEN green-yellow YELLOW Fig. 1.1 no carbon dioxide highest concentration of carbon dioxide

3 Carry out steps 1 to 21. 1 Using hot water provided and tap water, adjust the water in the beaker labelled water-bath to 45 °C. You will not need to maintain this temperature. 2 Put 15 cm3 of G into the boiling tube labelled Y which contains 1g dried yeast. Mix well. Between step 3 and step 4, you will be leaving the apparatus for 15 minutes. Use this time to continue with other parts of Question 1. 3 Put the boiling tube Y into the water-bath for 15 minutes. 4 After 15 minutes, remove the boiling tube Y from the water-bath. 5 Stir the mixture in the boiling tube Y and pour it into a beaker. 6 Label the spotting tile (dimple tile) with the sample times in minutes, as shown in Fig. 1.2. 7 Put 3 drops of B onto the spotting tile at each sample time, as shown in Fig. 1.2. Fig. 1.2

4 Fig. 1.3 shows the apparatus you will set up for this investigation. Fig. 1.3 8 Tie a knot in the dialysis tubing as close as possible to one end, so that the end is sealed. 9 To open the other end, rub the tubing gently between your fingers and thumb. 10 Stir the mixture in the beaker from step 5 and put 6.0 cm3 of this mixture into a syringe. 11 Wipe the outside of the syringe and put the mixture from the syringe into the dialysis tubing. 12 Rinse the outside of the dialysis tubing by dipping it into the water in the container labelled D. Look carefully at Fig. 1.3 to help you with step 13 to step 15. 13 Tie a knot just above the level of the mixture in the dialysis tubing, as shown in Fig. 1.3. 14 Put the dialysis tubing into a clean boiling tube so that it is resting on the bottom of the boiling tube, as shown in Fig. 1.3. 15 Draw a line on the boiling tube so that it is half-way between the two knots, as shown in Fig. 1.3. This is where you will take your samples from. 16 In this step, measure the volume of distilled water, W, needed to cover the section of dialysis tubing containing the mixture. (a) (i) State the volume of W that you added to the test-tube in step 16. volume of W = .................................................. cm3 [1]

5 17 Take a sample of W from the boiling tube at the point you marked in step 15, using a pipette. 18 Put 3 drops of W onto B at time 0 on the spotting tile. Put the remaining W in the pipette back into the boiling tube. 19 Start timing and put the boiling tube containing the dialysis tubing into the beaker labelled water- bath. Maintain the temperature at 40 – 45 °C. 20 Mix the sample of W and B on the spotting tile and immediately record the colour in (a)(ii), using the colours stated in Fig. 1.1. 21 Repeat steps 17, 18 and 20 for each of the sampling times until the end-point (yellow) is reached for two consecutive samples. If the end-point is not reached at 10 minutes, stop timing. (ii) Record your results in an appropriate table. [4] (iii) This investigation used colour to indicate the concentration of carbon dioxide in the sample which is subjective. Describe two improvements to this investigation that would increase the accuracy of the results other than the use of colorimeter/ colour chart. 1 ............................................................................................................................................... ................................................................................................................................................... 2 ............................................................................................................................................... ............................................................................................................................................ [2]

6 (iv) A student hypothesised that glucose diffuses into the surrounding of the dialysis tube. You are provided a vial labelled R which contains the remaining contents of the boiling tube, collected after 20 minutes of the investigation. Describe and carry out an appropriate test to determine whether the student’s hypothesis can be accepted. Suggest how this would impact your results. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ..........................................................