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Unit 15Lesson navigation

Grade 12 · Biology

The Calvin cycle

Why it matters

Fixing carbon into sugar.

Advanced20m reading

Last reviewed 2026-09-03 · accuracy standard

What is the Calvin cycle?

Short answer

The Calvin cycle is the second stage of photosynthesis, occurring in the stroma of the chloroplast and needing no light directly. It uses the ATP and NADPH made in the light-dependent reactions to fix carbon dioxide into an organic molecule, eventually building glucose. Because it does not require light itself, it is also called the light-independent reactions.

Concept preview

What you will be able to do

  1. 01State where the Calvin cycle happens and why it is called the light-independent stage.
  2. 02Explain carbon fixation, including the role of RuBisCO, RuBP and carbon dioxide.
  3. 03Describe how ATP and NADPH are used to reduce fixed carbon to G3P.
  4. 04Explain how RuBP is regenerated and how G3P is used to build glucose.

The light-dependent reactions ended with two energy-rich products, ATP and NADPH, and a waste gas, oxygen. But neither ATP nor NADPH is food; they are short-lived currencies that must be spent quickly. The spending happens in the second stage of photosynthesis, the Calvin cycle, named after the scientist Melvin Calvin who worked it out. The Calvin cycle takes place not on the thylakoid membranes but in the stroma, the fluid that surrounds them. Its job is to take carbon from the air, in the form of carbon dioxide, and use the energy in ATP and NADPH to build it into sugar. Because photosynthesis as a whole turns simple inorganic molecules into complex organic ones, the Calvin cycle is where the real construction happens.

School Plan

The Calvin cycle

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Related topics

Light-dependent reactions →

Frequently asked questions

Does the Calvin cycle need light?
Not directly, but it depends on the ATP and NADPH produced by the light-dependent reactions, so it stops without light.
What does the Calvin cycle produce?
It fixes carbon dioxide into organic molecules that are used to build glucose.