2025 YIJC [H2] Biology JC2 PE P4 ANS with Examiner Report

YISHUN INNOVA JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO. H2 BIOLOGY 9744/04 22 Aug 2025 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name and class in the spaces at the top of this page. Write in dark blue or black pen only. You may use a soft pencil for any diagrams or graphs. Do not use paper clips, highlighters, 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. The number of marks is given in brackets [ ] at the end of each question or part question. Shift Laboratory For Examiner’s Use 1 21 2 16 3 18 Total 55 This document consists of 18 printed pages and 2 blank pages.

2 @YIJC 9744/04/PE/2025 1 Plant extracts contain molecules which have many uses in industry and as medicines. It is important for scientists to be able to estimate the concentration of these molecules in plant extracts. You will estimate the concentration of molecule R in a sample of plant extract U. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 10R 10% solution of molecule R None 100 W Distilled water None 100 U Unknown concentration of molecular R in a plant extract None 40 A Sulfuric acid solution Harmful irritant 20 K Potassium manganate (VII) solution Irritant 20 If any of the solutions come in contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection and wear gloves to protect your hands when using A and K.

3 @YIJC 9744/04/PE/2025 [Turn over (a) You will need to carry out a serial dilution of the 10% molecule R solution, 10R, to reduce the concentration by half between each successive dilution. You will need to prepare four concentrations of molecule R solution in addition to the 10% molecule R solution, 10R. After the serial dilution is completed, you will need to have 10 cm3 of each concentration available for use. (i) Complete Table 1.2 to show how you will prepare your serial dilution. Table 1.2 shows the first two beakers you will use to make your serial dilution. You will need to complete the table for three additional beakers. For each beaker, state: • the concentration of molecule R solution. • the concentration of molecule R solution transferred. • the volume of molecule R solution transferred. • the volume of distilled water, W, added. Table 1.2 Concentration of molecule R solution / % Concentration of molecule R solution transferred / % volume of molecule R solution transferred / cm3 volume of distilled water, W, added / cm3 10 - 0.0 0.0 5 10 10.0 10.0 2.5 5 10.0 10.0 1.25 2.5 10.0 10.0 0.625 1.25 10.0 10.0 [3] EITHER 1. each concentration of molecule R solution filled in correctly; 1 mark each; OR 2. correct concentrations (2.5, 1.25, 0.625) and correct concentration transferred (5, 2.5, 0.625); 3. shows transfer of 10 .0 (cm3) to each beaker from the previous beaker; 4. shows 10.0 (cm3) of water added to each beaker; 1 mark each Precision to be penalised at most once for MP3 and MP4 AWARD using the higher credit criteria

4 @YIJC 9744/04/PE/2025 Molecule R will decolourise the purple acidified potassium manganate(VII) solution, K. The lower the concentration of molecule R, the greater the volume of R is needed to cause a colour change in potassium manganate(VII). Carry out step 1 to step 12. Step 1 Prepare the concentrations of molecule R solution, as decided in (a)(i), in the beakers provided. Step 2 Label 5 test-tubes with the concentrations of R you prepared in step 1. Step 3 Put 1 cm3 of A into the test-tube labelled 10%. Step 4 Put 1 cm3 of K into the same test-tube and mix well. Step 5 Put the nozzle of a clean 10 cm3 syringe into the beaker containing 10% R. Step 6 Pull the plunger out to the 5 cm3 mark so that 5 cm3 of 10% R enters the syringe. Step 7 Put the syringe containing 10% R into the test-tube from step 4 as shown in Fig. 1.2. You will be counting the number of drops needed for the first instance of colour change in K. Step 8 Gently press the plunger to add one drop of solution containing molecule R. Step 9 Mix well. Step 10 If the mixture stays purple repeat step 8 and step 9. Count the number of drops released to reach the first instance of colour change . If the number of drops needed to reach the first instance of colour change is more than 100, record as ‘more than 100’.

5 @YIJC 9744/04/PE/2025 [Turn over Step 11 Record the results in (a)(ii). Step 12 Repeat step 3 to step 11 for each of the concentrations of molecule R prepared in step 1. (ii) Record your results in an appropriate table. 1. heading for independent variable: percentage concentration of molecule R (before heading for dependent variable) and no units in body of table AND heading dependent variable: number of drops ; 2. results recorded for all concentrations ; 3. number of drops recorded for the highest concentration of R is fewer than for the lowest concentration of R ; 4. results recorded as whole drops ; percentage concentration of molecule R number of drops 10 Increasing trend 5 2.5 1.25 0.625 [4] (iii) State two significant sources of error when measuring the dependent variable in this investigation. drop size varies ; difficult to judge endpoint ; Any valid point [2] ER: Poor practices (e.g. contamination, plunger hard to control) are not significant sources of error.

6 @YIJC 9744/04/PE/2025 (iv) Suggest how you could improve the procedure to reduce one of the errors stated in (a)(iii). any one improvement and must be linked to an error in 1(a)(iii), e.g.: 1. (drop size varies) measure the volume used instead of the number of drops ; 2. (difficult to judge endpoint) use a colorimeter / spectrometer ; [1] ER: When colour change is hard to determine, a colour chart does not resolve the problem. Mention of light intensity instead of colorimeter /spectrometer is not accepted, it is the spectrum /wavelength of the specific colour that should be quantified. Bure tte is used to measure volume not number of drops. There is no error carried forward, i.e. students who were awarded the mark was based on (iv) answer. It may not be accurate. Step 13 Repeat step 3 to step 10 with U, the unknown concentration of molecule R. Step 14 Record your result in (a)(v). (v) State the number of drops of U needed to reach the end-point ...................... [1] records a number for U that is less than that recorded for 10 and more than that recorded for the lowest concentration ; (vi) Complete Fig. 1.3 to show the positions of each of the percentage concentrations of molecule R solution recorded in (a)(ii). Fig. 1.3 1. correctly labels scale bar with different concentrations of molecule R ; 2. concentrations must match to those listed in 1(a)(ii) [1] (vii) Use your results in (a)(ii) and (a)(v) to estimate the concentration of molecule R in solution U. Show this estimate of the concentration of U on Fig. 1.3, by placing the letter U on the line in the correct position. estimates the correct concentration of R in U by placing U in the correct position on the scale bar ; [1] ER: U should identified properly, not necessarily mid point between two known concentration.

7 @YIJC 9744/04/PE/2025 [Turn over (b) A student investigated the concentration of molecule R in extracts from