# A student is investigating the effect of temperature on the rate of enzyme activity using starch and amylase. Explain why the student should use a controlled variable in this investigation and give two examples of variables that should be controlled.

> OCR GCSE Biology A: Gateway Science (J247) — B7 Practical skills · Explain · 4 marks

> A student adds amylase solution to starch solution at different temperatures and tests samples with iodine solution at regular intervals to determine how quickly the starch is broken down.

## Mark scheme (4 marks)

1. A controlled variable is a variable that remains constant throughout the experiment
2. Controlled variables are kept constant so that any change in the rate of reaction is only due to the independent variable (temperature)
3. First correct example of a controlled variable, e.g. volume / concentration of amylase solution
4. Second correct example of a controlled variable, e.g. volume / concentration of starch solution OR pH

## Key terms

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

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](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-c37746b6) · Published by Druglandscape Ltd.