Catalase is an enzyme that is found in many plant cells and animal cells. Catalase breaks down hydrogen peroxide, which is a waste product from cell metabolism. Fig. 1.1 shows the breakdown of hydrogen peroxide by catalase. 2 H₂O₂ hydrogen peroxide catalase 2 H₂O water + O₂ oxygen Fig. 1.1 A student decided to investigate how catalase activity varies along the length of a carrot root. Fig. 1.2 shows a photograph of some carrots. [Figure 1.2] leaves shoot carrot root Fig. 1.2 The student extracted catalase from different parts of the carrot root tissue. • Carrot root tissue was mixed with a small volume of pH7 buffer and some fine sand. • The mixture was ground with a pestle and mortar. • The mixture was placed into a centrifuge tube and spun in a variable speed centrifuge for a few minutes. • This caused the mixture to be separated into a solid pellet at the bottom of the centrifuge tube and a liquid carrot extract at the top, as shown in Fig. 1.3. • The liquid carrot extract was poured into a clean test-tube. This liquid contained catalase. Fig. 1.3 shows a centrifuge and centrifuge tube with its contents, after spinning in the centrifuge for a few minutes. [Figure 1.3] lid of centrifuge tube plastic centrifuge tube (2.0 cm³) liquid carrot extract solid pellet Fig. 1.3

1. (a)State one variable that should be standardised in the procedure to obtain the liquid carrot extract, other than the carrot tissue, fine sand and apparatus used.[1]
2. (b)State the relationship between the time taken for the filter paper disc to rise to the surface of the hydrogen peroxide solution and the catalase activity of the liquid carrot extract.[1]
3. (c)(i)Identify the independent variable in this investigation.[1]
4. (c)(ii)Describe a method that the student could use to test the prediction that: As the distance from the base of the shoot increases, the catalase activity of carrot root tissue increases. Your method should be set out in a logical order and be detailed enough to allow another person to follow it. Details of how to use the centrifuge to prepare the liquid carrot extract should not be included.[6]
5. (d)(i)Identify the dependent variable in this investigation.[1]
6. (d)(ii)Complete Table 1.1 to show how these solutions could be made by proportional dilution of the 6.0% stock solution of hydrogen peroxide.[2]
7. (d)(iii)Use the information shown in Fig. 1.7 to evaluate these conclusions.[3]

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