# Explain how non-cyclic photophosphorylation results in the production of ATP, NADPH, and oxygen during the light-dependent reactions of photosynthesis.

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

## Mark scheme (4 marks)

1. Light energy is absorbed by photosystem II (PSII), causing photoexcitation of chlorophyll / electrons are excited to a higher energy level.
2. Excited electrons pass along the electron transport chain, releasing energy used to synthesise ATP by chemiosmosis / photophosphorylation.
3. Electrons from PSII are replaced by photolysis of water, which splits water into protons, electrons, and oxygen / oxygen is released as a by-product of photolysis.
4. Excited electrons from PSI are used to reduce NADP⁺ to NADPH (with protons from the stroma / from photolysis).

## Key terms

- [non-cyclic photophosphorylation](https://www.gradenine.co.uk/glossary/non-cyclic-photophosphorylation)
- [NADPH](https://www.gradenine.co.uk/glossary/nadph)

## 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-non-cyclic-photophosphorylation-results-in-0bc69204) · Published by Druglandscape Ltd.