# A student investigates the effect of temperature on the rate of enzyme activity using a colorimeter. They notice that their results show much greater variation at higher temperatures compared with lower temperatures. Explain why repeating measurements and calculating a mean would improve the reliability of the results at higher temperatures, and suggest one additional control variable the student should have kept constant throughout the investigation.

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

> A student is measuring the rate of an enzyme-controlled reaction by recording the change in absorbance over time using a colorimeter. The experiment is carried out at five different temperatures: 10 °C, 20 °C, 30 °C, 40 °C and 50 °C. At temperatures of 40 °C and 50 °C, repeat readings differ considerably from one another compared with repeats at lower temperatures.

## Mark scheme (4 marks)

1. Repeating measurements reduces the effect of random error on the data
2. Calculating a mean smooths out variation so the central tendency is a more reliable estimate of the true value
3. Explanation of why variation is greater at higher temperatures, e.g. enzyme denaturation is a stochastic/random process so individual enzyme molecules denature at slightly different times, causing fluctuating rates
4. A suitable control variable is identified with a valid reason, e.g. pH — changes in pH alter the ionic state of the active site, changing enzyme activity independently of temperature

## Key terms

- [colorimeter](https://www.gradenine.co.uk/glossary/colorimeter)
- [control variable](https://www.gradenine.co.uk/glossary/control-variable)
- [reliability](https://www.gradenine.co.uk/glossary/reliability)

## 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-299a7651) · Published by Druglandscape Ltd.