When an apple fruit is cut open, the cut surface of apple tissue quickly becomes brown and is less likely to be eaten. This change in colour is shown in the diagram. [Figure 3.1: Diagram showing a white apple tissue immediately after being cut, and a brown apple tissue a short time after being cut]

1. (a)The change in colour of the apple tissue is due to a series of chemical reactions. An enzyme called PPO acts as a catalyst for one of these reactions.
2. (a)(i)State what is meant by the term catalyst.[2]
3. (a)(ii)The change in colour can be prevented by placing the cut surface of apple tissue in boiling water for a short time immediately after the fruit is cut. Explain this observation using the lock and key hypothesis of enzyme action.[4]
4. (b)Scientists have recently used the process of genetic engineering to develop a type of apple that does not produce the enzyme PPO in its tissues. Suggest possible advantages of this type of apple.[3]

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