---
title: "Photosystem I — AP Bio Definition & Exam Guide"
description: "Photosystem I is the protein complex in the light reactions that uses light energy to pass electrons from plastocyanin to ferredoxin, producing NADPH for the Calvin cycle."
canonical: "https://fiveable.me/ap-bio/key-terms/photosystem-i"
type: "key-term"
subject: "AP Biology"
---

# Photosystem I — AP Bio Definition & Exam Guide

## Definition

Photosystem I is a protein complex involved in photosynthesis that uses light energy to transfer electrons from plastocyanin to ferredoxin, leading to the production of NADPH.

## Related Study Guides

- [3.5 Cellular Respiration](/ap-bio/unit-3/photosynthesis/study-guide/qIyyKCxB3XJI9oRI7yjl)

## Review

### Related Terms

- Plastocyanin: A small protein involved in electron transport within the chloroplasts during photosynthesis.
- Ferredoxin: An iron-sulfur protein that mediates electron transfer in a range of metabolic reactions.
- NADPH (Nicotinamide adenine dinucleotide phosphate): A coenzyme used in anabolic reactions, such as lipid and nucleic acid synthesis, which require NADPH as a reducing agent.