2024 EJC Prelim Biology P4 (A)

© EJC 2024 9744/04/J2H2PRELIM/2024 EUNOIA JUNIOR COLLEGE JC2 Preliminary Examinations 2024 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME ANSWERS CIVICS GROUP 2 3 - REGISTRATION NUMBER BIOLOGY Paper 4 Practical 9744/04 22 August 2024 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration 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 an HB pencil for any diagrams or graphs. Do not use stapler, paper clips, highlighters, glue or correction fluid/tape. This document consists of 22 printed pages and 2 blank pages. For Examiner’s Use 1 2 3 Total 55 Answer all questions in the spaces provided in 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. Shift Laboratory

© EJC 2024 9744/04/J2H2PRELIM/2024 2 Answer all questions. 1 You will be investigating the effect of salt concentration on the movement of water in potatoes. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 P 5 lengths of potato none – W distilled water none 150 S 1 mol dm–3 salt solution none 150 It is recommended that you wear suitable eye protection. (a) You will need to make different concentrations of salt solution using simple dilution of the 1.00 mol dm–3 salt solution, S. You will need to prepare 40 cm3 of each concentration. Table 1.2 shows two of the concentrations you will use. Decide which other concentrations of salt solution you will use. (i) Complete Table 1.2 to show how you will prepare the other concentrations. Table 1.2 final concentration of salt solution / mol dm–3 volume of S / cm3 volume of distilled water, W / cm3 1.00 0.75 0.50 0.25 0.00 40 30 20 10 0 0 10 20 30 40 [2] 1. At least 3 more concentrations (evenly spaced) (A: 4, e.g. 0.80, 0.60, 0.40, 0.20) and 2 d.p. 2. All volumes of S and W add up to 40 NOTE: In the event that you come across the term “proportional dilution”, you can assume that it is referring to “simple dilution”. In addition, doing serial dilution will not give you a 0.00 with 5 concentrations.

© EJC 2024 9744/04/J2H2PRELIM/2024 3 [Turn over Carry out step 1 to step 11. step 1 Prepare the concentrations of salt solution, as shown in Table 1.2, in the beakers provided. step 2 Cut 10 discs of potato for each of the concentrations prepared in step 1. Each disc should be approximately 3 mm thick. step 3 Place 10 discs in a line as shown in Fig. 1.1. centimetre Fig. 1.1 step 4 Measure the total length of the 10 discs and record this value in 1(a)(ii). step 5 Put the 10 discs into the beaker containing 1 mol dm–3 salt solution. step 6 Repeat step 3 to step 5 with the other discs and the salt solutions you prepared in step 1. step 7 Start timing and leave for 30 minutes. Use this time to continue with other parts of Question 1. step 8 After 30 minutes (step 7), discard the 1 mol dm –3 salt solution from around the discs and tip the discs onto some paper towel. step 9 Place the 10 discs in a line as in Fig. 1.1 and measure their total length. Record this value in 1(a)(ii). step 10 Repeat step 8 and step 9 for the other salt concentrations. step 11 Calculate the change in length for each line of 10 discs. not to scale discs 1 2 3 4 5 6 7 8 9

© EJC 2024 9744/04/J2H2PRELIM/2024 4 (ii) Record your results in an appropriate table, including raw results and processed results. Concentration of salt / mol dm–3 Initial length of potato discs / mm Final length of potato discs / mm Change in length / mm 1.00 101 90 -11 0.75 100 92 -8 0.50 98 91 -7 0.25 100 100 0 0.00 100 107 7 1. Headings: for concentration of salt with units in mol dm-3 + initial length and final length with units in mm 2. Data: records result for each concentration prepared 3. Processed data: in the form of changes in length (R: no ‘-‘ sign if length decreases) 4. Precision: in whole number for lengths (I: concentration as it has been assessed in (i) earlier) 5. Trend: lowest concentration has greatest increase [5] (iii) Explain your results for the 0.0 mol dm–3 salt solution (distilled water). [2] 1. 0.00 mol dm-3 salt solution has higher water potential than potato cells. 2. water moves into potato cells by osmosis. (R: diffuse) (A: cell sap) (iv) Suggest why a line of 10 discs was measured instead of a single disc. [1] 1. Measuring the change in length of a single disc more inaccurate than measuring a line of 10 discs. (OWTTE) (R: average length) (R: idea of more intense / maximum results) (I: replicates without explaining how it is linked to accuracy) (R: ref. to reliability / precision) (v) Identify one significant source of error in this investigation. [1] 1. Not all the discs were exactly 3 mm in thickness. 2. Knife and ruler not precise / accurate in cutting 3mm discs. [Any one] (vi) Use your results to estimate a salt concentration where there is no net movement of water into or out of the potato. 1. Correct estimate of salt concentration where there was no net movement of water into or out of the potato based on students’ results. salt concentration 0.25 mol dm–3 [1]

© EJC 2024 9744/04/J2H2PRELIM/2024 5 [Turn over (vii) Describe two improvements to your procedure that would make the estimate in 1(a)(vi) more accurate. [2] 1. Using smaller intervals of salt concentrations around the value of the candidates’ estimate (R: stating smaller intervals between 1.00 to 0.00, i.e. the entire range) (R: use a wider range) 2. Use a more precise method of cutting discs, e.g. template cutter (R: cork borer because that was the instrument used to cut the potato cylinders that candidates were given)

© EJC 2024 9744/04/J2H2PRELIM/2024 6 (b) The salt content of unprocessed food was measured. The values are shown in Table 1.3. Table 1.3 food type salt content of unprocessed food / mg per 100 g food potatoes (P) 10.0 tuna (T) 40.0 bran (B) 25.0 chicken (C) 50.0 salmon (S) 95.0 (i) Plot a bar chart of the data shown in Table 1.3 on the grid in Fig. 1.2. Use a sharp pencil. [4] Fig. 1.2 Salt content of different unprocessed food salt content of unprocessed food / mg per 100 g food P T B C S 20 40 60 80 100 0 Food type

© EJC 2024 9744/04/J2H2PRELIM/2024 7 [Turn over 1. Scale: even width of bars and scale on y-axis: 20 units to 10 small squares, labelled at least every 2 cm 2. Axis: labels on x-axis: food type and labelled P, T, B, C, S and label on y-axis: salt content of unprocessed food / mg per 100 g food 3. Plots: correct plotting of 5 bars, evenly spaced (R: if no spacing between bars) 4. Line: separate bars drawn with vertical lines and meeting horizontal lines exactly (I: no title) The salt content of the same foods that had been processed was also measured. The values are shown in Table 1.4. Table 1.4 food type salt content of processed food / mg per 100 g food pota