Polyphenol oxidase is an enzyme involved in the browning of fruit. Fig. 1.1 shows browning of the skin of bananas. [Figure 1.1] A student extracted polyphenol oxidase enzyme from ripened bananas. The student used this enzyme extract to investigate the factors affecting the activity of the enzyme. The student initially found that the enzyme extract was too concentrated, so the student made a 1:10 dilution of the enzyme extract.

1. (a)Describe how the student made a 1:10 dilution of the enzyme extract.[1]
2. (b)(i)Identify the independent variable in this experiment.[1]
3. (b)(ii)Identify one variable that the student has standardised.[1]
4. (c)(i)Use Fig. 1.2 to calculate the initial rate of this reaction in absorbance units per second (aus⁻¹). Show your working. initial rate of reaction = .............................................. aus⁻¹[2]
5. (c)(ii)Using the internet, the student found that pH 7.0 is the optimum pH for polyphenol oxidase. On Fig. 1.2, sketch the line you would expect to get for the rate of reaction at pH 3.0.[1]
6. (d)The student wanted to determine the effect of the concentration of the substrate, dopamine hydrochloride solution, on the rate of the enzyme-catalysed reaction. The student was provided with a stock solution of 0.2% dopamine hydrochloride solution and the diluted enzyme extract prepared in (a). Describe a method the student could use to collect the data that is needed to determine the effect of the concentration of dopamine hydrochloride solution on the rate of the enzyme-catalysed reaction. Your method should be set out in a logical order and be detailed enough to let another person follow it.[7]
7. (e)The browning of fruit such as bananas can make them more difficult to sell. One way to prevent browning of bananas is to use an anti-browning agent. The student searched the internet and found data from different scientific papers on the inhibitory effect of various anti-browning agents on polyphenol oxidase from different plants. The student processed and ranked these data, as shown in Table 1.1. [Table 1.1] The student concluded that heated onion extract was the most effective anti-browning agent and that EDTA was the least effective. Use the information to suggest why this conclusion may not be supported.[2]
8. (f)The student found that a sulfur-containing molecule in the heated onion extract acted as a non-competitive inhibitor to the enzyme polyphenol oxidase. Fig. 1.3 is a graph showing how the substrate concentration affects the rate of polyphenol oxidase activity. On Fig. 1.3 sketch the curve that shows the rate of activity for polyphenol oxidase treated with the heated onion extract. [Figure 1.3][1]

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.