# Explain how the light-dependent reactions of photosynthesis produce the molecules required for the Calvin cycle.

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

## Mark scheme (4 marks)

1. Light energy is absorbed by photosystems (I and II) / chlorophyll and used to excite electrons to a higher energy level
2. Water is split (photolysis) at photosystem II, releasing oxygen as a by-product and supplying replacement electrons / protons (H⁺)
3. Excited electrons pass along the electron transport chain, driving ATP synthesis via chemiosmosis / ATP synthase
4. NADP⁺ is reduced to NADPH at photosystem I using electrons and protons, and NADPH / ATP are then available for the Calvin cycle to fix / reduce CO₂

## Key terms

- [light-dependent reactions](https://www.gradenine.co.uk/glossary/light-dependent-reactions)
- [Calvin cycle](https://www.gradenine.co.uk/glossary/calvin-cycle)

## Related

- [Revision notes for IB DP Biology Higher 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-light-dependent-reactions-of-4b64e123) · Published by Druglandscape Ltd.