# Explain how the structure of a chloroplast is related to its role in photosynthesis.

> IB DP Biology Standard Level (2023 syllabus) — C1.3 Photosynthesis · Explain · 4 marks

## Mark scheme (4 marks)

1. The thylakoid membranes provide a large surface area for the light-dependent reactions / for embedding photosystems and electron carriers.
2. The thylakoid lumen / interior of the thylakoid maintains a proton gradient used for ATP synthesis via ATP synthase during photophosphorylation.
3. The stroma provides the aqueous environment / contains the enzymes (e.g. RuBisCO) required for the Calvin cycle / light-independent reactions.
4. The double membrane / envelope of the chloroplast maintains an internal environment with high concentrations of CO₂, NADPH, and ATP needed for photosynthesis, or controls the passage of materials such as CO₂ and glucose.

## Key terms

- [chloroplast](https://www.gradenine.co.uk/glossary/chloroplast)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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/explain-how-the-structure-of-a-c9ae2964) · Published by Druglandscape Ltd.