# A student carried out an investigation into the effect of pH on the activity of amylase. The student tested amylase at pH 2, pH 7 and pH 12. Explain why amylase works best at its optimum pH and why activity decreases at pH 2 and pH 12.

> WJEC A-Level Biology (Wales) — 1.1 Chemical elements and biological molecules · Explain · 5 marks

> Amylase is an enzyme that breaks down carbohydrates into simple sugars. It is produced in the pancreas and salivary glands and has an optimum pH of around 7.

## Mark scheme (5 marks)

1. At the optimum pH, the active site has a complementary shape to the substrate (starch/carbohydrate)
2. Enzyme-substrate complexes can form readily at the optimum pH, increasing the rate of reaction
3. At pH 2 and pH 12 the pH moves away from the optimum, causing the shape of the active site to change (denature)
4. The substrate can no longer fit into the active site because the shapes are no longer complementary
5. No enzyme-substrate complexes can form, so the rate of reaction decreases

## Key terms

- [amylase](https://www.gradenine.co.uk/glossary/amylase)
- [optimum pH](https://www.gradenine.co.uk/glossary/optimum-ph)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carried-out-an-investigation-35cc8336) · Published by Druglandscape Ltd.