The carbon cycle

Home learning focus

Learn how carbon is moved through the environment by the carbon cycle.

This lesson includes:

  • one video showing how carbon dioxide is put in and taken out of the atmosphere
  • two activities


In the carbon cycle, carbon is constantly removed from, and returned to, the environment.

One of the biggest sources of carbon on Earth is carbon dioxide. Watch this video to find out how it is constantly cycling into and out of the atmosphere.

How CO₂ goes in to and out of the atmosphere

The processes of the carbon cycle

Carbon is the major element that makes up all living things and is found in carbohydrates, fats and proteins.

There are many processes that impact on the carbon cycle. These include: photosynthesis, feeding, respiration, fossilisation, combustion, excreting, egestion and decomposition.

It is essential for these processes to remain balanced if the carbon cycle is to remain balanced. However, human action can impact on these processes, and can therefore impact the balance of the carbon cycle.

Photosynthesis removes CO₂ from the atmosphere

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Plants absorb carbon dioxide from the atmosphere and use it to create sugar, starch and other organic compounds.

This is the only process in the cycle that decreases the level of carbon dioxide in the atmosphere.


Moves carbon in the form of biological molecules along the food chain.


When living organisms (plants, animals and decomposers) respire they release carbon dioxide into the atmosphere (this is a form of excretion).


If conditions are not favourable for the process of decomposition, dead organisms decay slowly or not at all. These organisms build up and, if compressed over millions of years, can form fossil fuels (coal, oil or gas).


The burning of fossil fuels releases stored carbon dioxide into the atmosphere.


When waste is removed from the body (eg urine). This excreted material can be broken down during the process of decomposition.


The removal of carbon-containing faeces from an animal. This egested material can be broken down during the process of decomposition.


When complex, carbon compounds in dead organisms, urine and faeces are broken down into simpler carbon compounds by bacteria or fungi.


Activity 1

Carbon cycle questions

Test your knowledge of the carbon cycle with this downloadable worksheet from Teachit Science. Either print it out or write your answers on a sheet of paper.

Carbon cycle questions

Activity 2

Carbon cycle

Test your knowledge of the carbon cycle with this downloadable cut and stick worksheet from Beyond.

You will need a pair of scissors or you can just draw your answers.

Carbon cycle cut and stick

There's more to learn

Have a look at these other resources around the BBC and the web.

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