Cambridge A Level Biology 9700 — 2025 May/June Paper 3 · Variant 5

1 Catalase is an enzyme found in plant tissues. It catalyses the breakdown of hydrogen peroxide, releasing oxygen gas. When a mixture of catalase and hydrogen peroxide is put into a syringe, oxygen gas is produced and drops of the mixture come out of the nozzle of the syringe. You will investigate the effect of different concentrations of catalase on the breakdown of hydrogen peroxide. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 E 100.0% catalase solution irritant 50 hydrogen peroxide H irritant 30 solution W distilled water none 100 If any solution comes into contact with your skin, wash off immediately under cold water. You should wear suitable eye protection. You will need to make different concentrations of the catalase using proportional dilution of the 100.0% catalase solution, E. You will need to prepare 20 cm3 of each concentration, using E and W. Table 1.2 shows how to prepare two of the concentrations of catalase you will use. Decide which other concentrations of catalase you will use. (a) (i) Complete Table 1.2 for the other concentrations you will use. Table 1.2 percentage concentration volume of E volume of W of catalase / cm3 / cm3 100.0 20.0 0.0 0.0 0.0 20.0 [2] Carry out step 1 to step 8. step 1 In the beakers provided, prepare the concentrations of catalase as shown in Table 1.2. step 2 Label large test‑tubes with the concentrations of catalase prepared in step 1. step 3 Fill a 10 cm3 syringe to the 5 cm3 mark with hydrogen peroxide solution, H. step 4 Fill the same syringe to the 10 cm3 mark with the 100.0% catalase solution. step 5 Place the syringe in the large test‑tube labelled 100.0%, as shown in Fig. 1.1. 5 cm3 hydrogen peroxide solution and 5 cm3 catalase solution drops appear here Fig. 1.1 step 6 Start the timer. step 7 Count the number of drops produced in 60 seconds. Record your results in (a)(ii). step 8 Repeat step 3 to step 7 using the other concentrations of catalase prepared in step 1. (ii) Record your results in an appropriate table. [5] (iii) Describe the trend in your results. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iv) Use your results in (a)(ii) to explain the effect of catalase concentration on the breakdown of hydrogen peroxide. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (v) State the independent variable in this investigation. ..................................................................................................................................... [1] (vi) State one variable that was kept constant in the investigation. ........................................................................................................................................... ..................................................................................................................................... [1] (vii) Identify two sources of error in step 7. 1 ........................................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (viii) Describe how you would modify the procedure to investigate the effect of substrate concentration on catalase activity. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (b) The catalase activity of germinating hyacinth seeds was measured when the seeds were placed in different concentrations of salt solution. Table 1.3 shows the results of the investigation. Table 1.3 concentration of salt solution catalase activity / mmol dm–3 / arbitrary units 0 72 100 35 200 28 300 23 400 20 500 14 (i) Plot a graph of the data shown in Table 1.3 on the grid in Fig. 1.2. Fig. 1.2 [4] (ii) A germinating hyacinth seed was placed in a salt solution of unknown concentration. The catalase activity was found to be 54 arbitrary units. Estimate the concentration of salt solution at which the seed was germinated. Show on your graph how you obtained your estimate. concentration = ....................................... mmol dm–3 [2] [Total: 22]

Mark scheme: Question Answer Marks 1(a)(i) 1 states at least three concentrations of catalase (in addition to 100.0 and 0.0) ; 2 2 states the correct volume of catalase and water to make 20 cm3 of each concentration ; 1(a)(ii) 1 heading for independent variable: percentage concentration of catalase and to the left of dependent variable ; 5 2 heading for dependent variable: number of drops ; 3 number of drops for each of the five concentrations of catalase ; 4 expected trend (the higher the concentration of catalase the more drops) ; 5 results recorded in whole drops ; 1(a)(iii) correct description of the trend according to the candidates’ results ; e.g. the greater the concentration of catalase the more 1 drops 1(a)(iv) 1 the higher the concentration of catalase the more active sites available ; 2 2 increased number of enzyme substrate complexes ; 1(a)(v) catalase concentration ; 1 1(a)(vi) any one from: 1 1 volume of catalase ; 2 volume of hydrogen peroxide ; 3 concentration of hydrogen peroxide ; 4 time ; 1(a)(vii) any one from: 2 1 drops already started being produced before timing started ; 2 drop size varies ; 3 drops too fast to count accurately ; 1(a)(viii) 1 states five different concentrations of hydrogen peroxide ; 2 2 states using the same concentration of catalase ; 1(b)(i) 1 label on x-axis: concentration of salt / mmol dm-3 4 and label on y-axis: catalase activity / arbitrary units ; 2 scale on x-axis: 100 to 2 cm, labelled at least every 2 cm and scale on y-axis: 20 to 2 cm, labelled at least every 2 cm ; 3 correct plotting of all six points using small dots in circles or crosses ; 4 six plots joined with thin line passing through all points ; 1(b)(ii) 1 shows interpolation lines on graph at catalase activity of 54 arbitrary units ; 2 2 correct estimate of concentration of salt solution according to candidate’s graph ;

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2 N1 is a slide of a stained transverse section through a plant leaf. (a) (i) Draw a large plan diagram of the leaf section on N1 shown by the shaded region in Fig. 2.1 (midrib). Use a sharp pencil. draw this region Fig. 2.1 Use one ruled label line and label to identify the cuticle. [5] (ii) Observe the cells in the lower epidermis surrounding the midrib on the section of the leaf on N1. Select a line of four adjacent lower epidermal cells. • Make a large drawing of this line of four cells. • Use one ruled label line and label to identify the cell wall of one cell. [5] (b) Fig. 2.2 shows a photomicrograph of a stage micrometer scale that is being used to calibrate an eyepiece graticule. One division, on either the stage micrometer scale or the eyepiece graticule, is the distance between two adjacent lines. The length of one division on the stage micrometer in Fig. 2.2 is 1.0 mm. stage micrometer scale eyepiece graticule 0 10 20 30 40 50 60 70 80 90 100 Fig. 2.2 (i) Calculate the actual length of one eyepiece graticule unit shown in Fig. 2.2. Give your answer in micrometres (μm). Show your working. actual length = ................................................... μm [2]

Mark scheme: 2(a)(i) 1 uses most of the available space and shows at least three tissues ; 5 2 draws correct region of leaf section and no cells ; 3 draws correct proportions of the vascular tissue ; 4 draws correct subdivision of the vascular tissue ; 5 label line to cuticle and label to identify the cuticle ; 2(a)(ii) 1 lines are continuous, thin and sharp and no shading ; 5 2 draws a line of four cells and each cell touches at least one other cell ; 3 cell wall drawn as two lines ; 4 correct shape of cells ; 5 label line and label to identify the cell wall ; 2(b)(i) 1 states the correct number of eyepiece graticule units in 1.0 mm ; 2 2 shows division of 1000 by 45 ; 2(b)(ii) 1 states the correct number of eyepiece graticule units for the width of the leaf ; 2 2 multiplies this number of eyepiece graticule units by the answer from (b)(i) and appropriate units ; 2(b)(iii) states differences that are (only) observable features ; 4 any three from : feature N1 Fig. 2.3 palisade layer thin thick ; number of chloroplasts low high ; sizes of the vascular bundles large in proportion to width of leaf small in proportion to width of leaf ; number of vascular bundles more fewer ;

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