Plant cells contain enzymes that catalyse metabolic reactions. Some of these enzymes catalyse the release of oxygen from hydrogen peroxide. A plant extract solution can be produced which will contain these enzymes. When hydrogen peroxide and a plant extract solution are mixed oxygen is released. The oxygen forms bubbles that make a foam on the surface. You are required to investigate the effect of pH on the progress of the enzyme-catalysed reactions by: • changing the pH (independent variable) using buffers • measuring the height of the foam (dependent variable) produced by the release of oxygen. To follow the progress of this reaction you will need to measure the height of foam at different times for a total of 3 minutes.

1. (a)(i)Decide how often you will take these measurements including the final height of foam at 3 minutes. State the times when you will measure the height of foam.[1]
2. (a)(ii)Fig. 1.1A shows how a test-tube will be set up at the start (0 minutes). Fig. 1.1B shows the test-tube after 3 minutes. [Figure 1.1] The top of the foam may not form an even layer, so you will need to decide where to measure the layer of the foam. Draw a double-headed arrow on Fig. 1.1B to show where you will measure this layer of foam.[2]
3. (b)(i)Record your results for the height of foam (raw results) in an appropriate table.[4]
4. (b)(ii)Using your raw results for pH 5: • State the highest height of foam .............................................................. mm. • State the first time when this height was reached ...................................... seconds. Using these measurements, calculate the rate of production of oxygen, as millimetres per second (mms⁻¹). You may lose marks if you do not show your working. rate of oxygen production = ................................................................ mms⁻¹[2]
5. (b)(iii)State the temperature of the room before the start of the investigation. .......................................................................................................................... °C State the temperature of the room after all the measurements have been recorded. .......................................................................................................................... °C State the difference between this temperature and the temperature of the room at the start of the investigation. difference = .............................................. °C Explain whether temperature is a significant source of error in this investigation.[1]
6. (b)(iv)Record the maximum height of foam using U. .......................................................................................................................... mm[1]
7. (b)(v)Using the result in (b)(iv) and the results in (b)(i) estimate the pH of U. pH ..................................................[1]
8. (b)(vi)This procedure investigated the effect of pH on the activity of the enzymes in a plant extract solution. To modify this procedure for investigating a different variable, the pH should be kept the same. Think about how you could modify this procedure to investigate the effect of substrate concentration, using 6% hydrogen peroxide solution, on the activity of enzymes in the plant extract solution. Describe how the independent variable, substrate concentration, would be changed in an investigation. Describe how the dependent variable could be measured more accurately than measuring the height of foam. You may use a labelled diagram in the space provided. space for diagram[3]
9. (c)(i)A student investigated the effect of temperature on the rate of enzyme activity in a plant extract solution. All the other variables were standardised. The results are shown in Table 1.1. [Table 1.1] Use a sharp pencil for drawing graphs. Plot a graph of the data shown in Table 1.1.[4]
10. (c)(ii)Use your knowledge of enzymes and the data to explain the effect of temperature on the enzyme activity in the plant extract solution.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.