Plant tissues contain the enzyme catalase which catalyses the breakdown of hydrogen peroxide into oxygen gas and water. Ascorbic acid acts as an inhibitor of catalase. You will investigate the effect of changing ascorbic acid concentration on catalase inhibition. 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 50 W distilled water none 50 A 1 mol dm-3 ascorbic acid solution irritant 10 If H or A comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection. You are also provided with five cylinders of potato tissue, labelled P.

1. (a)You will need to carry out a serial dilution of the 1moldm-³ ascorbic acid, A, to reduce the concentration by a factor of ten between each successive dilution. You will need to prepare four concentrations of ascorbic acid in addition to the 1moldm-3 ascorbic acid solution, A. After the serial dilution is completed, you will need to have 9cm³ of each concentration available to use.
2. (a)(i)Complete Fig. 1.1 to show how you will prepare your serial dilution. Fig. 1.1 shows the first two beakers you will use to make your serial dilution. You will need to draw three additional beakers. For each beaker, add labelled arrows to show: • the volume of ascorbic acid solution transferred • the volume of distilled water, W, added. Under each beaker, state the concentration of ascorbic acid solution.[3]
3. (a)(ii)Record your results in an appropriate table, including raw results and processed results.[6]
4. (a)(iii)Use your results in (a)(ii) to identify the greatest volume of gas produced in the reaction. greatest volume of gas produced = ................................................................. Use your answer to calculate the rate of gas production. Show your working. rate of gas production = .............................................. cm³ min-1[2]
5. (a)(iv)Describe two improvements to the procedure that would make the measurements more accurate. 1 2[2]
6. (b)(i)State the temperature of H before adding potato discs (step 16). ......................................................................................................................................................... °C State the temperature of H 2 minutes after adding potato discs (step 18). ......................................................................................................................................................... °C Calculate the change in temperature after 2 minutes. ......................................................................................................................................................... °C[2]
7. (b)(ii)State whether temperature is a significant source of error in this investigation. Explain your answer.[1]
8. (c)A study was carried out in which volunteers were given different daily doses of ascorbic acid (vitamin C) in addition to their normal diet. The maximum ascorbic acid concentration in the blood plasma of each volunteer was measured. The results are shown in Table 1.2. Table 1.2 ascorbic acid daily dose /mg maximum ascorbic acid concentration in blood plasma / µmol dm-3 0 6 50 25 200 68 500 75 1000 75
9. (c)(i)Plot a graph of the data in Table 1.2 on the grid in Fig. 1.3. Use a sharp pencil.[4]
10. (c)(ii)Suggest an explanation for the results for a daily dose of 0mg and the results for daily doses of between 500–1000 mg. 0 mg ................................................................................................................................................. ......................................................................................................................................................... 500-1000 mg .................................................................................................................................. .........................................................................................................................................................[2]

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