The carbon cycle

Ecology and the environment · Cycles within ecosystems · note 1 of 2

Spec 4.10Download all Cycles within ecosystems notes (PDF)Download all notes (PDF)4 pages

The carbon cycleSpec 4.10

All living things are made of carbon compounds. The carbon cycle returns carbon to the atmosphere as carbon dioxide, so that it is available for plants to use in photosynthesis again. Carbon is also stored in fossil fuels, which are the remains of long-dead organisms.

Plants and algae take carbon dioxide from the air and use it in photosynthesis to make carbon compounds such as glucose, starch and proteins.
The carbon compounds pass along the food chain when animals feed.
All living organisms (plants, animals and decomposers) release carbon dioxide into the air by respiration.
When plants and animals die, and when they produce waste, decomposition by bacteria and fungi breaks down the material. The decomposers release carbon dioxide into the air by respiration.
Burning fuels such as wood, coal, oil and natural gas (combustion) releases carbon dioxide into the air.

The role of decomposers

Decomposers are bacteria and fungi. They break down dead plants, dead animals and waste, and they respire as they do so, releasing carbon dioxide. Without decomposers, dead material would pile up and the carbon in it would be locked away. The supply of carbon dioxide for photosynthesis would eventually run out.

Exam tip:

Name the process at each arrow. Photosynthesis takes carbon dioxide out of the air. Respiration, decomposition and combustion put it back.

Carbon cycle diagram: carbon dioxide in the air is taken in by plants in photosynthesis, passes to animals by feeding, goes to dead material by death and waste, is broken down by decomposers, and returns to the air by respiration of plants, animals and decomposers and by combustion of fuels. — The carbon cycle: **photosynthesis** takes carbon dioxide in; **respiration**, **decomposition** and **combustion** put it back.