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© Boardworks Ltd 20111 of 20
The Carbon Cycle
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What is carbon?
Carbon is a non-metallic element that is a vital building block
in many biological molecules. Without carbon, life would be
very different or may even be impossible.
What things can you think of that contain carbon compounds?
Carbon is also present in the atmosphere as carbon dioxide.
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What is the carbon cycle?
Carbon is constantly recycled in the environment. There are
four main processes that are involved:
photosynthesis
respiration
decomposition
combustion.
Can you think of any examples of how carbon might be
recycled in these processes?
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What is the carbon cycle?
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Recap
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Plants and algae
Plants take in carbon dioxide from the atmosphere and use it
to make glucose during the process of photosynthesis.
During the day, plants are a carbon sink. This means that
they absorb more carbon dioxide than they give out.
Plants are a carbon source during the night.
They also release a small amount of
carbon dioxide as they respire.
During the day this is normally used
up by photosynthesis but at night,
when they cannot photosynthesize,
it gets released into the atmosphere.
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The role of animals
Animals are unable to make their own food and must feed on
plants, or on animals that have eaten plants.
Some of this carbon is used to
provide glucose. During respiration,
glucose reacts with oxygen to
release carbon dioxide, water
and energy.
This food contains carbon.
Carbon also provides the building blocks for fats, proteins and
carbohydrates that make up the bodies of the animals.
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Recap
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The role of animals
Animals release carbon back into the atmosphere in three
main ways:
Carbon may also be
locked up in the shells
of animals, such as
mussels or oysters.
through respiration, when carbon is released as
carbon dioxide
when their bodies or faeces decompose
when they are eaten by other animals.
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Dead plants and animals, and their
waste, have carbon still locked up
in the carbohydrates, proteins and
fats that they were formed from.
This dead matter provides food
for detritivores, such as
earthworms, and decomposers,
such as bacteria and fungi.
Decomposition
These break down the compounds in the dead matter and
release carbon dioxide through respiration. When the matter
is fully decomposed, all the energy that was originally locked
up during photosynthesis is returned to the environment.
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Over the course of millions of years, some plant and animal
matter can become fossilized. This can happen when organic
matter is buried underneath the ground.
Peat is sometimes used as a fuel as well. This is plant matter
that has been buried and compacted for many years, though
not necessarily for as long as fossil fuels.
Fossil fuels
Over time, pressure can cause the
organic matter to form into coal,
gas or oil. These fossil fuels can
then be extracted and burned (also
known as combusted).
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Combustion
Humans burn fossil fuels and wood in power stations,
vehicles, aeroplane engines and in fires.
Carbon that has been locked up in
fossil fuels for millions of years is
released back into the atmosphere.
oxygencarbon
dioxidecarbon + + water + heat
This releases carbon dioxide, water and heat through the
process of combustion:
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Where is carbon stored?
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How is carbon recycled?
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Glossary
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Multiple-choice quiz