Materials cycle through living things and the environment. In the carbon cycle, plants and algae remove carbon dioxide from the air by photosynthesis and turn it into carbon compounds. Animals eat plants and pass the carbon along food chains. Respiration by plants, animals and decomposers returns carbon dioxide to the air. Combustion of fossil fuels and wood also releases it.
Decomposers such as bacteria and fungi break down dead organisms and waste, returning carbon dioxide to the air and mineral ions to the soil. Decay is fastest when it is warm, moist and there is plenty of oxygen. Some carbon is locked away for millions of years in fossil fuels and limestone. The water cycle also recycles water through evaporation, transpiration, condensation and precipitation, providing fresh water for plants and animals.
Worked example
Why does a compost heap get warm?
- Decomposers in the heap respire as they break down waste.
- Respiration releases energy as heat.
Answer:The heap warms up, which speeds up decay further.
Key words
- carbon cycle
- the movement of carbon between air, living things and rocks
- combustion
- burning, which releases carbon dioxide
- decay
- breakdown of dead material by decomposers
- carbon sink
- something that stores carbon, like forests or oceans
New questions every time.
NGSS-referenced: HS-LS2-5