# A student investigates the effect of temperature on the rate of enzyme activity using a colorimeter to measure the breakdown of a coloured substrate. The student records absorbance readings every 30 seconds for 5 minutes at each temperature tested. Explain how the student could ensure that the colorimeter readings are valid and comparable between different temperature treatments.

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

> A colorimeter measures the absorbance of light passing through a solution. A higher absorbance value indicates a greater concentration of coloured substrate remaining. The student is testing temperatures of 20 °C, 30 °C, 40 °C, and 50 °C.

## Mark scheme (4 marks)

1. Calibrate (zero) the colorimeter using a blank solution before each set of readings
2. Use the same wavelength of light (filter) throughout the experiment
3. Use cuvettes of the same type/size and ensure they are filled to the same volume each time
4. Allow the reaction mixture to reach the target temperature before starting readings, to ensure temperature is controlled and not a confounding variable

## Key terms

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

## 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-9d1e20c5) · Published by Druglandscape Ltd.