# A student is investigating the effect of light intensity on the rate of photosynthesis in a aquatic plant. Explain how the student could ensure the light intensity is the only variable being changed during the investigation.

> OCR A-Level Biology A (H420) — 1 Development of practical skills in biology · Explain · 4 marks

> The student has access to a laboratory with a range of light sources and measuring equipment.

## Mark scheme (4 marks)

1. The student controls for temperature by using a thermostat or a water bath
2. The student controls for carbon dioxide levels by using a sealed system or a CO2 scrubber
3. The student uses multiple light sources or a variable light source to achieve different light intensities
4. The student measures light intensity using a suitable device such as a light meter

## 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-is-investigating-the-effect-b05db376) · Published by Druglandscape Ltd.