The Calvin Cycle
CO₂ is fixed into sugar using ATP and NADPH.
About this topic
The Calvin cycle occurs in the stroma. The enzyme rubisco fixes CO₂ onto the five-carbon sugar RuBP; the resulting compounds are reduced using ATP and NADPH from the light reactions to form G3P (a three-carbon sugar). Most G3P is recycled to regenerate RuBP, and some is used to build glucose and other organic compounds.
It is also called the light-independent stage, though it relies on products of the light reactions. Plants use the sugars for energy, starch storage, cellulose and growth.
For every three CO2 molecules fixed, the cycle makes six G3P, of which five are recycled to regenerate RuBP and one is available to build glucose; so two turns-worth of three-carbon sugars are needed for one glucose. Rubisco is probably the most abundant enzyme on Earth, though it is rather slow and sometimes grabs oxygen by mistake.
The cycle is sometimes called the dark reactions, but this is misleading, because it needs ATP and NADPH from the light reactions and so stops soon after light stops. Crops such as maize and sugar cane use special C4 pathways to avoid wasteful oxygen binding, helping them thrive in hot climates. Students should remember that the Calvin cycle does not directly use light.
Key ideas
- In the stroma
- Rubisco fixes carbon
- Makes G3P then glucose
Quick check
Use cases: where The Calvin Cycle helps
- Homework: review the key idea behind The Calvin Cycle before you start a problem set.
- Exam revision: use the quick check to test whether you can recall The Calvin Cycle without notes.
- Visual learning: play with the interactive lab to see how The Calvin Cycle changes when you adjust its inputs.
- Teaching a friend: explain The Calvin Cycle in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is The Calvin Cycle?
CO₂ is fixed into sugar using ATP and NADPH.
What will I learn in The Calvin Cycle?
In the stroma. Rubisco fixes carbon. Makes G3P then glucose.
Is The Calvin Cycle part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the The Calvin Cycle lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study The Calvin Cycle?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.