Explain the importance of the carbon cycle, including the processes…

The idea

The carbon cycle matters because life depends on a continuous supply of carbon, and the amount of carbon dioxide in the atmosphere affects climate. Carbon is removed from the air by producers during photosynthesis and built into organic molecules. It passes along food chains as consumers eat producers and one another. Respiration in all organisms, including microorganisms, releases carbon dioxide back to the air. When organisms die, microorganisms such as bacteria and fungi act as decomposers: they break down dead material and waste, respire and release carbon dioxide, and return mineral ions to the soil. Combustion of fossil fuels releases carbon that was locked away for millions of years, raising atmospheric carbon dioxide and contributing to global warming. Without decomposers, dead material and its carbon would accumulate and nutrients would not be recycled, so the cycle would stall.

What earns the marks

• Photosynthesis by producers removes carbon dioxide from the atmosphere and stores carbon in organic molecules.
• Respiration by all living organisms, including decomposers, releases carbon dioxide back to the atmosphere.
• Microorganisms such as bacteria and fungi decompose dead organisms and waste, releasing carbon dioxide and recycling nutrients.
• Feeding transfers carbon along food chains from producers to consumers.
• Combustion of fossil fuels releases stored carbon as carbon dioxide, increasing atmospheric levels.
• The cycle maintains a supply of carbon for living organisms and helps regulate atmospheric carbon dioxide, which affects climate.

Common mistakes and how to put them right

• Saying decomposers 'create' carbon dioxide.

  Put it right by explaining they release it through respiration as they break down dead material.

• Ignoring the role of microorganisms.

  Put it right by naming bacteria and fungi as decomposers that recycle carbon and nutrients.

• Treating the carbon cycle as one-way.

  Put it right by showing carbon repeatedly moves between the atmosphere, organisms and fossil stores.

Exam tips

• Explain why each process matters, not just what it is, to answer an 'explain' question fully.
• Name specific microorganisms (bacteria, fungi) when describing decomposition.
• Link rising carbon dioxide from combustion to consequences such as global warming to show importance.