October 2026 - Photosynthesis Study Guide

Core ideas to know

Learn the relationships, not a string of isolated definitions. These are the facts that let you reason through unfamiliar wording.

• The overall process uses carbon dioxide and water, with light energy, to build carbohydrate and release oxygen.
• Light-dependent reactions occur in thylakoid membranes, split water, release oxygen and produce ATP and NADPH.
• Chlorophyll absorbs light and supplies energised electrons to an electron transport chain.
• The Calvin cycle occurs in the stroma and uses ATP and NADPH to fix carbon dioxide into three-carbon sugar precursors.
• Stomata allow gas exchange: carbon dioxide enters while oxygen and water vapour can leave.

A reliable way to answer

Use the same short process every time so the wording of the question does not decide your method for you.

1. Decide whether the stem follows light energy, water, oxygen, carbon dioxide or sugar.
2. Place light reactions at thylakoids and carbon fixation in the stroma.
3. Track ATP and NADPH from the light reactions into the Calvin cycle.
4. Check atom sources: released oxygen comes from water, while carbohydrate carbon comes from carbon dioxide.

Distinctions that earn marks

Terms to know

Carbon fixation

Incorporation of inorganic carbon dioxide into organic molecules.

Chloroplast

Plant-cell organelle in which photosynthesis occurs.

NADPH

Electron carrier supplying reducing power to the Calvin cycle.

Key points

• Water is split during light reactions, and its oxygen is released.
• The Calvin cycle does not directly capture light but depends on ATP and NADPH made by light reactions.
• Carbon dioxide supplies the carbon incorporated into carbohydrate.