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

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

## Mark scheme (4 marks)

1. Light energy is absorbed by photosystem II (PSII), causing photoactivation/excitation of chlorophyll and the release of high-energy electrons.
2. Water is photolysed, releasing electrons to replace those lost from PSII, with oxygen released as a by-product and protons (H⁺) produced in the thylakoid lumen.
3. Excited electrons pass along the electron transport chain (plastoquinone, cytochrome b6f complex, plastocyanin), releasing energy that is used to pump protons across the thylakoid membrane, creating a proton gradient that drives ATP synthase (chemiosmosis) to produce ATP.
4. Electrons are re-energised at photosystem I (PSI) using light energy and ultimately reduce NADP⁺ (with protons) to form NADPH via the enzyme ferredoxin/NADP⁺ reductase.

## 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 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-non-cyclic-photophosphorylation-results-in-2ce61848) · Published by Druglandscape Ltd.