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

> IB DP Biology Standard Level (2023 syllabus) — A2.2 Cell structure · Explain · 4 marks

## Mark scheme (4 marks)

1. The thylakoid membranes provide a large surface area for the light-dependent reactions (housing photosystems/chlorophyll/photosynthetic pigments).
2. Thylakoids are stacked into grana, increasing the surface area available for light absorption within a compact space.
3. The stroma is the fluid-filled matrix where the light-independent reactions (Calvin cycle / carbon fixation) occur, as it contains the necessary enzymes such as RuBisCO.
4. The double membrane (envelope) of the chloroplast maintains an internal environment suitable for photosynthesis by controlling the entry and exit of molecules 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-850e3b28) · Published by Druglandscape Ltd.