# A student investigates the effect of temperature on the rate of enzyme activity using a colorimeter to measure the breakdown of a coloured substrate. Explain why the student should use a control cuvette containing only buffer solution when taking colorimeter readings.

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

> A student is measuring enzyme activity at five different temperatures (10 °C, 20 °C, 30 °C, 40 °C, 50 °C). At each temperature, the student uses a colorimeter set to an appropriate wavelength to record the change in absorbance of the substrate solution over two minutes. The student notices that the buffer solution used has a very faint yellow tint.

## Mark scheme (4 marks)

1. The control cuvette is used to zero/calibrate the colorimeter
2. This removes/accounts for any absorbance due to the buffer solution itself (or the cuvette)
3. Without zeroing, the absorbance values recorded would include the background absorbance of the buffer, making results inaccurate/unreliable
4. The colorimeter must be re-zeroed with the control cuvette at each new temperature because temperature may alter the absorbance properties of the buffer/cuvette

## Key terms

- [colorimeter](https://www.gradenine.co.uk/glossary/colorimeter)
- [control cuvette](https://www.gradenine.co.uk/glossary/control-cuvette)
- [buffer solution](https://www.gradenine.co.uk/glossary/buffer-solution)

## 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-56575214) · Published by Druglandscape Ltd.