# A student is investigating the effect of substrate concentration on the rate of catalase activity using hydrogen peroxide and potato tissue. Describe how the student should carry out this investigation safely and accurately, including how they would control variables to make it a fair test.

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

> Catalase is an enzyme found in potato tissue that breaks down hydrogen peroxide into water and oxygen. A student wants to investigate how changing the concentration of hydrogen peroxide affects the rate of the reaction.

## Mark scheme (5 marks)

1. Measure a fixed/equal volume of hydrogen peroxide at each concentration using a measuring cylinder / syringe
2. Control a named variable — e.g. keep the temperature constant / use equal masses or surface areas of potato tissue / keep pH constant
3. Measure the rate of reaction — e.g. collect / measure the volume of oxygen gas produced over a set time / measure time for a set volume of oxygen to be produced
4. Repeat the experiment at each concentration and calculate a mean to improve reliability
5. Safety precaution appropriate to the investigation — e.g. wear safety goggles because hydrogen peroxide is an irritant / handle glassware carefully to avoid breakage

## Key terms

- [catalase](https://www.gradenine.co.uk/glossary/catalase)
- [substrate concentration](https://www.gradenine.co.uk/glossary/substrate-concentration)

## 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-3faea791) · Published by Druglandscape Ltd.