SAJC Prelims H2 Bio P4 Ans

1 St Andrew’s Junior College 2024 9744/04/Preliminary Examinations Civics Group Index Number Name (use BLOCK LETTERS) ST. ANDREW’S JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION H2 BIOLOGY 9744/04 Paper 4: Practical Exam Tuesday 20th August 2024 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name, civics group and index number on all the work you 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 a HB pencil for any diagram, graph or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in 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. The number of marks is given in brackets [ ] at the end of each question or part question. IMPORTANT INFORMATION TO CANDIDATES: Candidates with access to microscope at the start of the paper are given the first 1h 15 min to use them. Please answer QUESTION 3 within this time frame. Once you have finished working with the microscope, you can move on to QUESTION 1 or 2. Candidates with no access to microscope at the start of the paper should proceed with QUESTION 1 or 2 first. You will be given access to the microscope at 1h 15 min after the start of the paper. Shift Laboratory For Examiner’s Use 1 / 23 2 / 12 3 / 20 Total / 55 This document consists of 21 printed pages. [Turn over Marker’s comments: Please remember to write down your shift and lab no. in the provided box when asked to do so. H2

2 St Andrew’s Junior College 2024 9744/04/Preliminary Examinations Question 1 Agar stained with universal indicator can be used to investigate diffusion. When hydrochloric acid diffuses into the agar it changes the colour from green to pink. You will investigate the diffusion of different concentrations of hydrochloric acid in agar. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume/ cm3 H 2.0 mol dm-3 hydrochloric acid irritant 20.0 W distilled water none 40.0 2 Petri dishes containing agar none - sheet T sheet T - - If H comes into contact with your skin, wash off immediately with cold water. It is recommended that you wear suitable eye protection. You will need to: ● prepare different concentrations of hydrochloric acid, H ● measure the diffusion distance for each concentration of hydrochloric acid. You will need to carry out a serial dilution of the 2.0 mol dm –3 hydrochloric acid, H, to reduce the concentration by half between each successive dilution. You will need to prepare four concentrations of hydrochloric acid in addition to 2.0 mol dm –3 hydrochloric acid, H. After the serial dilution is completed, you will need to have 5.0 cm3 of each concentration available to use. (a) (i) Complete Fig. 1.1 to show how you will prepare your serial dilution. Fig. 1.1 shows the beakers you will use. For each beaker, add labelled arrows to show: ● the volume of hydrochloric acid transferred, ● the volume of distilled water, W, added.

3 St Andrew’s Junior College 2024 9744/04/Preliminary Examinations Fig. 1.1 1 states five concentrations: 2.0, 1.0, 0.5, 0.25, 0.125 mol dm−3 ; 2 states four transfers of 5.0 cm3 to each beaker from the previous beaker + arrow drawn ; 3 shows four additions of 5.0 cm3 of W to each beaker + arrow drawn; [3]

4 St Andrew’s Junior College 2024 9744/04/Preliminary Examinations Proceed as follows. 1 Prepare the concentrations of hydrochloric acid, as decided in (a)(i), in the beakers provided. The different concentrations of hydrochloric acid will be put into wells cut into the agar. The position of one well is shown in Fig. 1.2. You need to decide where to put four more wells in the agar in each Petri dish so that the wells are positioned away from each other and away from the edge of the Petri dish . Hydrochloric acid will diffuse into the agar around each well. (ii) Complete Fig. 1.2 by: ● drawing four small circles to show where you have decided the wells should be positioned in the agar ● labelling the five small circles in Fig. 1.2 with the concentrations of hydrochloric acid you prepared in step 1. Fig. 1.2 1 draws four circles with one in each quadrant and labels each with the concentration of acid ; [1] 1.0moldm-3 0.5 moldm-3 0.25moldm-3 0.125moldm-3 0.5 moldm-3 2.0 moldm-3

5 St Andrew’s Junior College 2024 9744/04/Preliminary Examinations Carry out steps 2 - 14. 2 Draw a mark on the outside edge of one of the Petri dishes containing agar. 3 Put the Petri dish on Fig. 1.2 so that the mark on the edge of the Petri dish lines up with the arrow in Fig. 1.2. Keep the Petri dish in this position over Fig. 1.2 for the whole of Step 4. 4 Use a straw to cut wells in the agar at the positions of the small circles on Fig. 1.2: ● put the end of a straw on the surface of the agar over the centre small circle. ● carefully push the straw into the agar. ● lift up the straw to leave a well in the agar. ● hold the straw over the container labelled For waste. ● blow gently through the straw to remove the agar from the end of the straw. ● if the small circle of agar is not lifted by the straw, use a scalpel or mounted needle. ● to carefully remove the agar and put it in the container labelled For waste. 5 Remove the Petri dish from Fig. 1.2 and leave it for use in step 7. 6 Repeat step 2 to step 4 with the other Petri dish containing agar. You are provided with sheet T for use in step 7 and step 8. 7 Put one of the Petri dishes on circle A on sheet T so that the mark on the edge of the Petri dish lines up with the arrow. 8 Put the other Petri dish on circle B on sheet T so that the mark on the edge of the Petri dish lines up with the arrow. 9 For each Petri dish, A and B, use a Pasteur pipette to carefully put 2.0 mol dm –3 hydrochloric acid, H, into the appropriate well in the agar, as labelled in Fig. 1.2. 10 Repeat step 9 for the other concentrations of hydrochloric acid labelled in Fig. 1.2. Do not move the Petri dishes after the wells have been filled with the hydrochloric acid. 11 Start timing. Between step 11 and step 12, you will be leaving the Petri dishes on sheet T for 20 minutes. Use this time to continue with other parts of Question 1. 12 After leaving the Petri dishes for 20 minutes, use a Pasteur pipette to remove the hydrochloric acid from the wells in both Petri dishes. Put this hydrochloric acid into the beaker labelled For waste.

6 St Andrew’s Junior College 2024 9744/04/Preliminary Examinations 13 Measure the diffusion distance, as shown in Fig. 1.3, for each concentration of hydrochloric acid in both Petri dishes. Fig. 1.3 14 Record your results in (a)(iii). (iii) Record your results in an appropriate table. Table showing diffusion distance at various concentration of hydrochloric acid Title 1 heading for independent variable: concentration of hydrochloric acid / mol dm -3 + heading for dependent variables: diffusion distance / mm 2 records a distance for stated concentrations in (a)(i) and for both Petri dishes ; 3 Average calculated and correct trend + ≤ 15 mm; 4 records distance in millimeters; (accept whole mm or 1 d.p.) [4] Concentration of hydrochloric acid / mol dm-3 diffusion distance / mm Petri dish A Petri dish B Average 2.000 9.0 9.0 9.0 1.000 8.0 7.0 7.5 0.500 8.0 7.0 7.5 0.250 7.0 5.0 6.0 0.125 5.0 4.0 4.5

7 St Andrew’s Junior College 2024 9744/04/Preliminary Examinations (iv) Calculate the rate of diffusion for 2.