When bananas ripen, they turn brown in colour. This is due to the formation of a brown product called melanin. The enzyme catechol oxidase acts on its substrate, catechol, leading to the formation of a brown product, melanin, as shown in Fig. 1.1. catechol oxidase catechol (pale pink substrate) melanin (brown product) [Figure 1.1] As melanin is produced, the colour of the reaction mixture changes to brown. The intensity of the brown colour produced is proportional to the concentration of melanin. The more active the enzyme, the more intense the brown colour. A colorimeter is used to measure the absorbance of the reaction mixture. Absorbance is a measure of the light absorbed by a coloured solution. With the reaction shown in Fig. 1.1, the more intense the brown colour, the higher the absorbance. Catechol oxidase can be extracted from bananas.

1. (a)Some students were asked to extract catechol oxidase by grinding a slice of banana with sand and water, using a mortar and pestle. The resulting mixture was then filtered through a piece of cloth. Suggest a reason for: grinding with sand filtering through cloth.[2]
2. (b)(i)Suggest why the students used a colorimeter to measure the absorbance rather than judging the intensity of the colour by eye.[1]
3. (b)(ii)Identify the independent variable and the dependent variable in this investigation. independent variable dependent variable[2]
4. (c)(i)Describe a method the students could use to collect the data needed to test the effect of inhibitor Y in reaction mixtures containing different concentrations of catechol solution. The description of your method should be set out in a logical way and be detailed enough for another person to follow. You should not repeat the details from (a) describing how the extract of catechol oxidase is prepared.[8]
5. (c)(ii)On [Figure 1.3], sketch the curve expected if inhibitor Y was acting as a non-competitive inhibitor.[2]
6. (c)(iii)Draw on [Figure 1.3] the positions of Vmax and Km of the enzyme when no inhibitor Y is present.[2]
7. (c)(iv)Use your graph to describe the effect of the addition of inhibitor Y on the Km of this enzyme.[1]
8. (d)Hypertension is a condition where people have long-term high blood pressure. Two main types of drug are used to lower blood pressure in people with hypertension: • ACE inhibitors • diuretics. Scientists investigated the effectiveness of the drugs when used separately and in combination. 505 people with hypertension were split into four groups as shown in [Table 1.1]. The results are shown in [Figure 1.4]. The scientists analysed the data and concluded that a combination of an ACE inhibitor and a diuretic should be used to lower blood pressure in the treatment of hypertension. With reference to the data in Table 1.1 and Fig. 1.4, discuss the conclusion that a combination of an ACE inhibitor and a diuretic should be used to lower blood pressure in the treatment of hypertension.[3]

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