Plant cells contain enzymes which catalyse some of their metabolic reactions. Some of these enzymes catalyse the release of oxygen from hydrogen peroxide. A cylinder of potato tissue will have these enzymes on the surface. When hydrogen peroxide solution and a cylinder of potato tissue are mixed, oxygen bubbles are released. You will need to investigate the effect of surface area by: • changing the surface area • counting the number of bubbles of oxygen released in a set time (dependent variable). You are provided with the materials shown in Table 1.1 and Table 1.2. Table 1.1 labelled | contents | hazard | volume / cm³ ---|---|---|--- H | hydrogen peroxide solution | moderate | 40 W | water | none | 100 If any of H comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection and gloves. Table 1.2 labelled | contents | details | quantity ---|---|---|--- P | potato cylinders | same cross-sectional area | 4 (a) To investigate the effect of surface area, other variables need to be standardised. Each potato cylinder has been provided with the same diameter but with different lengths. Each cylinder of potato tissue must be cut to the same length. 1. Cut each of the four potato cylinders in the beaker labelled P, to a length of 20 mm. To investigate the effect of surface area, the surface area can be changed by cutting each of these four cylinders into a different number of pieces. The formula for calculating the total surface area of a cylinder is shown in [Figure 1.1]. Total surface area of a cylinder = curved surface area + surface area of all the circular ends. The curved surface area of a cylinder can be calculated by using the formula: curved surface area = 2πrl π = 3.14 r = radius of cylinder l = length of cylinder All the cylinders start with the same length (20mm) and have the same radius, so the curved surface area is standard. The total curved surface area is the same for all four cylinders, even when a cylinder is cut into several pieces, as shown in the example on page 4. To change the total surface area, each cylinder is cut into a different number of pieces. The change in surface area depends on the number of the circular ends, n. surface area of all the ends = πr² n EXAMPLE One cylinder has 2 circular ends as shown in [Figure 1.2]. • number of circular ends, n = 2 • area of one circular end = πr² = 3.14 x 2² = 12.56 = 13 mm² (to the nearest whole number) • surface area of all the circular ends = πr² n = 13 x 2 = 26 mm² [Figure 1.3] shows another cylinder with the same radius and length, which is cut into two pieces. There are then 4 circular ends. • total number of circular ends, n = 4 • area of circular end = 13 mm² to the nearest whole number • surface area of all the circular ends = πr² n = 13 x 4 = 52 mm² (to the nearest whole number)

1. (a)(i)Measure the diameter of one of the cylinders in P and calculate the radius, r. r=[1]
2. (a)(ii)Calculate the curved surface area, to the nearest whole number, using 2 x 3.14 x r x 20. curved surface area =[2]
3. (a)(iii)For the potato cylinders in P, use πr² to calculate the area of one circular end to the nearest whole number. Use π as 3.14 and use r as recorded in (a)(i). area of one circular end =[1]
4. (a)(iv)Complete Table 1.3 to calculate the total surface area when using different numbers of pieces to include: • one whole cylinder • one cylinder cut into two pieces • two other cylinders cut into two different numbers of pieces. Table 1.3 number of pieces cut from one cylinder | number of circular ends, n | area of one circular end from (a)(iii) /mm² | surface area of all the ends /mm² | curved surface area from (a)(ii) /mm² | total surface area /mm² ---|---|---|---|---|--- 1 | 2 | | | | 2 | 4 | | | | | | | | | | | | | |[2]
5. (a)(v)Describe how you will standardise the position of the delivery tube in the test-tube of water, as shown in [Figure 1.4].[1]
6. (a)(vi)Record your results for the total surface area as shown in Table 1.3 and the number of bubbles at each 30 seconds in an appropriate table.[5]
7. (a)(vii)Using the results in (a)(vi), calculate for the largest surface area: • the mean number of bubbles in 30 seconds • the rate of activity, number min⁻¹. Show all the steps in your working and use appropriate units. mean number of bubbles = rate of activity =[3]
8. (a)(viii)A significant source of error in this procedure is the different size of the bubbles which are released. An improvement to reduce this error would be to measure the volume of oxygen released. Complete Table 1.4 to suggest: • how to measure the volume of oxygen released • one other significant source of error in this procedure • how to make an improvement to reduce this other error. Table 1.4 significant source of error | how to make an improvement ---|--- different sizes of bubbles released | another significant source of error | | [3]
9. (a)(ix)Think about how you could modify this procedure to investigate the effect of concentration of substrate, starting with 6% hydrogen peroxide, on the activity of the enzyme (catalase) in the potato tissue. Describe how you could change the independent variable, concentration of substrate.[1]

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