# A student is investigating the effect of substrate concentration on the rate of enzyme activity using lipase and a lipid solution. The student wants to ensure their investigation is valid and produces reliable results. Describe how the student should control variables and improve the reliability of their results in this investigation.

> OCR A-Level Biology B — Advancing Biology (H422) — 1.2 Practical skills assessed in the practical endorsement · Describe · 5 marks

> Lipase is a biological catalyst that breaks down lipids into fatty acids and glycerol. A student measures the time taken for a lipid emulsion to clear (become transparent) as an indication of the rate of reaction, at five different concentrations of lipid solution.

## Mark scheme (5 marks)

1. Control temperature throughout the investigation (e.g. using a water bath)
2. Keep the volume (or concentration) of lipase enzyme the same in each experiment
3. Keep the pH the same / constant throughout (e.g. using a buffer solution)
4. Repeat each concentration at least three times and calculate a mean
5. Identify and exclude anomalous results / outliers when calculating the mean

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-58bc9024) · Published by Druglandscape Ltd.