# A student places a green aquatic plant in a solution containing magnesium ions and carbon dioxide. The plant is kept in bright light. After several weeks, the student notices the leaves have turned yellow-green. Explain why the leaves changed colour, linking your answer to the role of magnesium ions in photosynthesis.

> AQA A-Level Biology (7402) — 3.5.1 Photosynthesis · Explain · 5 marks

## Mark scheme (5 marks)

1. Magnesium ions are needed to make chlorophyll
2. Without sufficient magnesium, the plant cannot produce enough chlorophyll
3. Chlorophyll is the green pigment in leaves / gives leaves their green colour
4. Less chlorophyll means the leaves appear yellow-green / paler / less green
5. Chlorophyll absorbs light energy for photosynthesis, so less chlorophyll reduces the rate of photosynthesis

## Key terms

- [magnesium ions](https://www.gradenine.co.uk/glossary/magnesium-ions)
- [photosynthesis](https://www.gradenine.co.uk/glossary/photosynthesis)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-places-a-green-aquatic-b1f9bd98) · Published by Druglandscape Ltd.