The carbon cycle
Carbon is an essential element for life on Earth. Every living organism has carbon compounds - such as fats and proteins - inside each of its cells. The carbon cycle shows how atoms of carbon can exist within different compounds at different times and be recycled between living organisms and the environment.
Image caption, Carbon enters the atmosphere as carbon dioxide from respiration and combustion.
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Processes in the carbon cycle
The The processes and events involved in recycling carbon in the environment. is easiest to understand in terms of its processes and how carbon is converted. The three key processes and the conversions are shown in the table below.
| Process | Carbon starts as | Carbon ends as |
| Photosynthesis | Carbon dioxide | Glucose |
| Respiration | Glucose | Carbon dioxide |
| Combustion (burning) | Fuel (eg methane or wood) | Carbon dioxide |
| Process | Photosynthesis |
|---|---|
| Carbon starts as | Carbon dioxide |
| Carbon ends as | Glucose |
| Process | Respiration |
|---|---|
| Carbon starts as | Glucose |
| Carbon ends as | Carbon dioxide |
| Process | Combustion (burning) |
|---|---|
| Carbon starts as | Fuel (eg methane or wood) |
| Carbon ends as | Carbon dioxide |
- Carbon enters the atmosphere as carbon dioxide from respiration and combustion.
- Carbon dioxide is absorbed by producers to make glucose in photosynthesis.
- Animals feed on the plant passing the carbon compounds along the food chain. Most of the carbon they consume is exhaled as carbon dioxide that was formed during aerobic respiration. The animals and plants eventually die.
- Decomposers break down the dead organisms and return the carbon in their bodies to the atmosphere as carbon dioxide by respiration. In some conditions, decomposition is blocked. The plant and animal material may then be available as fossil fuel for combustion in the future.