The Carbon Cycle
Carbon moves between air, living things and Earth.
About this topic
Carbon moves between the atmosphere, living things, oceans and rocks. Plants take in CO₂ by photosynthesis, animals eat plants and pass carbon along, and respiration, decomposition and combustion return CO₂ to the air. Over millions of years, buried organisms become fossil fuels, a store of carbon that humans now release quickly.
Carbon is the backbone of every organic molecule, so its cycle links all life. The main stores, or sinks, are the atmosphere, oceans (dissolved CO₂ and shells), forests and soils, and rocks such as limestone and coal. Photosynthesis removes carbon from the air, while respiration by plants, animals and microbes puts it back.
Imagine a carbon atom in a leaf. A caterpillar eats the leaf, and the atom becomes part of the caterpillar's tissues. A bird eats the caterpillar and later breathes the atom out as CO₂, or when the bird dies, fungi decompose it and return the atom to air and soil. If the bird were buried for millions of years, its carbon might become oil.
The cycle matters because burning fossil fuels and clearing forests add CO₂ faster than natural sinks remove it, strengthening the greenhouse effect. Solutions include planting trees, protecting peatlands and using renewable energy. Do not confuse the carbon cycle with the carbon footprint: the first is the natural movement of carbon, the second a measure of human emissions.
Key ideas
- Photosynthesis removes CO₂
- Respiration and burning add it
- Fossil fuels are stored carbon
Quick check
Use cases: where The Carbon Cycle helps
- Homework: review the key idea behind The Carbon Cycle before you start a problem set.
- Exam revision: use the quick check to test whether you can recall The Carbon Cycle without notes.
- Visual learning: play with the interactive lab to see how The Carbon Cycle changes when you adjust its inputs.
- Teaching a friend: explain The Carbon 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 Carbon Cycle?
Carbon moves between air, living things and Earth.
What will I learn in The Carbon Cycle?
Photosynthesis removes CO₂. Respiration and burning add it. Fossil fuels are stored carbon.
Is The Carbon 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 Carbon 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 Carbon 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.