Plant cells produce the enzyme catalase that catalyses the hydrolysis (breakdown) of hydrogen peroxide into water and oxygen, as shown in Fig. 1.1. catalase hydrogen peroxide ---> water + oxygen [Figure 1.1] A cylinder of potato tissue will have catalase molecules on its surface. When potato tissue is put into hydrogen peroxide solution, oxygen bubbles are released and a foam forms at the surface of the hydrogen peroxide solution. You will investigate the effect of ethanol concentration on the activity of catalase by measuring the height of the foam. You are provided with the materials shown in Table 1.1. Table 1.1 labelled | contents | hazard | volume/cm³ H | hydrogen peroxide solution | harmful irritant | 40 W | water | none | 200 E | 100% ethanol | flammable | 80 P | 5 potato cylinders | none | – If any of H comes into contact with your skin, wash off immediately with cold water. It is recommended that you wear suitable eye protection.

1. (a)(i)The length of the potato cylinders may not be precisely 4 cm. Identify one other source of error in the procedure you have carried out.[1]
2. (a)(ii)You will investigate the effect of different concentrations of ethanol on catalase activity. You will need to carry out a serial dilution of the 100% ethanol, E, to reduce the concentration by half between each successive dilution. You will need to prepare three concentrations of ethanol in addition to the 100% ethanol, E. After the serial dilution is completed, you will need to have 30cm³ of each concentration available to use. Complete Fig. 1.2 to show how you will prepare your serial dilution. Each beaker should have: • a labelled arrow to show the volume of ethanol transferred • a labelled arrow to show the volume of distilled water, W, added • a label under the beaker to show the concentration of ethanol. [Figure 1.2][3]
3. (a)(iii)Carry out step 8 to step 14. step 8 Prepare the concentrations of ethanol as shown in Fig. 1.2. step 9 Put one potato cylinder into each beaker. Start timing and leave for 5 minutes. step 10 Label test-tubes with the ethanol concentrations prepared in step 8. step 11 After 5 minutes (step 9), remove the potato cylinders from the beakers and put them into the appropriately labelled test-tubes. step 12 Put 5 cm³ of hydrogen peroxide solution into the test-tube labelled 100. Immediately start timing. step 13 Measure the height of the foam after 1 minute and after 2 minutes. Record the results in (a)(iii). step 14 Repeat step 12 and step 13 with the potato cylinders in each of the other test-tubes. Record your results in an appropriate table. Include the results recorded in step 7.[5]
4. (a)(iv)Calculate the rate at which the foam was produced at 1 minute and at 2 minutes for 100% ethanol, E. Show your working. Include the unit in your answer.[1]
5. (a)(v)Use your results in (a)(iv) to describe how the rate changes with time.[1]
6. (a)(vi)With reference to the activity of catalase, explain why the results of 0 (step 7) were important in this investigation.[1]
7. (a)(vii)State the dependent variable in this investigation.[1]
8. (a)(viii)Suggest two improvements to the investigation you have carried out to increase the confidence in your results.[2]
9. (b)(i)Some fruits turn brown when they are cut into slices for eating. This browning can make the fruit less appealing to eat and difficult to sell. The enzyme polyphenol oxidase (PPO) catalyses an oxidation reaction when fruit is cut, causing the fruit tissue to turn brown. Scientists carried out an investigation to see how exposing wampee fruits to different concentrations of ethanol affected the activity of PPO in the fruit tissue. A large sample of wampee fruits was divided into five equal groups. Each group of fruit was sealed in a plastic container and treated with a different concentration of ethanol. After a short time in storage, the activity of the enzyme PPO in the wampee fruit tissue was recorded. The results are shown in Table 1.2. Table 1.2 concentration of ethanol / µdm³ dm-3 | PPO activity /arbitrary units 0 | 2.20 100 | 1.40 200 | 0.95 400 | 0.70 500 | 0.60 Plot a graph of the data in Table 1.2 on the grid in Fig. 1.3. Use a sharp pencil. [Figure 1.3][4]
10. (b)(ii)Suggest an explanation for the pattern shown in the data.[2]

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