# A student is investigating the effect of temperature on the rate of reaction of the enzyme amylase. The student adds amylase solution and a starch solution to a test tube and places it in a water bath at 20 °C. Every 30 seconds, the student removes a drop of the mixture and adds it to a drop of iodine solution on a spotting tile. When starch is present, iodine solution turns blue-black. When starch is no longer detected, the student records the time taken. The student repeats the investigation at 40 °C and 60 °C. Explain why the rate of the amylase reaction differs between 40 °C and 60 °C.

> OCR A-Level Biology B — Advancing Biology (H422) — 1.1 Practical skills assessed in a written examination · Explain · 5 marks

> Amylase is an enzyme that breaks down starch into simple sugars. The enzyme has an active site which is complementary in shape to its substrate. At high temperatures, the shape of the active site can be permanently changed.

## Mark scheme (5 marks)

1. At 40 °C the enzyme amylase has a higher rate of reaction / breaks down starch faster than at 60 °C
2. At 60 °C the enzyme has been denatured
3. At 60 °C the active site changes shape permanently / is no longer complementary to the starch substrate
4. Because the active site is changed, the substrate (starch) can no longer bind to the active site / the enzyme–substrate complex cannot form
5. Therefore at 60 °C the starch is not broken down / the rate of reaction is greatly reduced or zero at 60 °C

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](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-is-investigating-the-effect-64fe0265) · Published by Druglandscape Ltd.