The carbon cycle
Carbon is an essential A substance made of one type of atom only. for life on Earth and most biological molecules include carbon atoms. Carbon is present in:
- carbon dioxide gas in the atmosphere
- carbon dioxide dissolved in the oceans
- The main chemical composition of limestone. in the shells of sea creatures
- calcium carbonate in the form of limestone
- A compound that contains hydrogen and carbon only. compounds in fossil fuels
- Food belonging to the food group consisting of sugars, starch and cellulose. Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess. In plants, carbohydrates are important for photosynthesis. molecules in living organisms
The carbon cycle shows how atoms of this element are cycled between different compounds within the Living elements of an ecosystem, such as plants and animals. and Non-living elements of an ecosystem, such as climate, temperature, water, and soil type. components of an A community of animals, plants and microorganisms, together with the habitat where they live. at different times.
Image caption, Stage one of the carbon cycle
Carbon enters the atmosphere as carbon dioxide from respiration and combustion.
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The The processes and events involved in recycling carbon in the environment. is easiest to understand in terms of its processes and the conversion of carbon that they undertake. The three key processes and their 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 |
Almost all living things depend on A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. in Plants that begin food chains by making energy from carbon dioxide and water. (eg green plants). This process converts carbon dioxide into carbohydrates which support other living things. Animals feed on plants, so the carbon compounds are passed along A sequence (usually shown as a diagram) of feeding relationships between organisms, showing which organisms eat what and the movement of energy through trophic levels.. Animals and plants The chemical change that takes place inside living cells, which uses glucose and oxygen to release the energy that organisms need to live. Carbon dioxide is a by-product of respiration., releasing carbon dioxide back into the atmosphere.
When dead plants and animals are decomposed by Microscopically small organism, such as a bacterium or single-celled fungus. Also called a microorganism., carbon dioxide is released to the atmosphere and mineral ions are returned to the soil.
