# A student is investigating the effect of temperature on the rate of enzyme activity using a colorimeter. Explain the precautions the student should take to ensure the results obtained are valid and reproducible.

> OCR A-Level Biology A (H420) — 1.2 Practical skills assessed in the practical endorsement · Explain · 4 marks

> A student sets up an experiment to measure the rate of an enzyme-controlled reaction at five different temperatures (10°C, 20°C, 30°C, 40°C, 50°C). They use a colorimeter to measure the absorbance of a coloured product formed over time. The student carries out three repeats at each temperature.

## Mark scheme (4 marks)

1. Control of a named variable other than temperature to ensure validity
2. Pre-incubation of enzyme and substrate separately at the required temperature before mixing
3. Calibration of the colorimeter with a blank/reference cuvette to ensure accurate absorbance readings
4. Explanation of why repeats improve reproducibility, linked to identifying anomalous results or calculating a mean

## Key terms

- [colorimeter](https://www.gradenine.co.uk/glossary/colorimeter)
- [valid](https://www.gradenine.co.uk/glossary/valid)
- [reproducible](https://www.gradenine.co.uk/glossary/reproducible)

## 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-is-investigating-the-effect-1303f371) · Published by Druglandscape Ltd.