Page 30 - 新思维科学学生用书9 样章

1.3 The carbon cycle

Coal was formed from the remains of plants that grew in

huge swamps. Their remains were buried over millions
of years, slowly turning into coal. Coal is dug out of
the ground and then used as a fuel for cooking or
heating homes, but most of it is used in power

stations to generate electricity.

Fossil fuels contain carbon. This came from the
carbohydrates, fats and proteins in the dead
organisms. When we burn a fossil fuel, the
carbon in it combines with oxygen from

the air and forms carbon dioxide. This
is called combustion.

We can add the formation and
combustion of fossil fuels to the flow
diagram. The completed diagram is called

the carbon cycle.

carbon dioxide
combustion in the air

photosynthesis respiration respiration respiration

carbohydrates feeding carbohydrates
in plants in animals

very slow
formation feeding
feeding
fossil carbohydrates
fuels in decomposers

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