# A student investigates the effect of temperature on the rate of enzyme activity using a colorimeter to measure the decolouration of a dye. Explain why it is important that the student uses a water bath to maintain the temperature of the reaction mixture, rather than placing the tubes directly in a room-temperature environment.

> OCR A-Level Biology A (H420) — 1.1 Practical skills assessed in a written examination · Explain · 4 marks

> A student is investigating how temperature affects the rate of an enzyme-controlled reaction. They use a colorimeter to record how quickly a coloured substrate is broken down at different temperatures (20°C, 30°C, 40°C, 50°C). They are deciding whether to use a water bath or simply leave the tubes on the bench.

## Mark scheme (4 marks)

1. A water bath provides a consistent/uniform temperature throughout the reaction mixture
2. Temperature affects the rate of enzyme activity / enzyme kinetics, so uncontrolled fluctuations would act as a confounding variable
3. Room temperature fluctuates / is not reliably at the target temperature, so the independent variable cannot be precisely set
4. This ensures the investigation is a fair test / results are valid and reproducible, as temperature is the only variable being changed

## Key terms

- [colorimeter](https://www.gradenine.co.uk/glossary/colorimeter)
- [water bath](https://www.gradenine.co.uk/glossary/water-bath)
- [decolouration](https://www.gradenine.co.uk/glossary/decolouration)
- [rate of enzyme activity](https://www.gradenine.co.uk/glossary/rate-of-enzyme-activity)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](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-investigates-the-effect-of-a94e9ea2) · Published by Druglandscape Ltd.