Transcript The Nitrogen Cycle

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The movement of nitrogen, in its many
forms, between the biosphere, atmosphere,
and animals, is described by the nitrogen
cycle.
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Nitrogen gas makes up about 80 percent of
the Earth’s atmosphere.
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Nitrifying bacteria can fix nitrogen and
convert it into ammonia (NH3) or nitrates
(NO3). These bacteria are found in the soil and
in the roots of some plants.
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The family of plants that includes peas,
beans, soybeans, lentils, and alfalfa is called
the legumes. These plants have special
swellings on their roots called nodules. These
swellings house and feed bacteria, which fix
nitrogen into the soil.

Plants cannot use nitrogen gas directly. They
can only absorb it when nitrogen is found in
its converted forms, such as ammonia or
nitrates. These chemical compounds are
commonly found in products known as
fertilizers.
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Animals can gain nitrogen by eating plants.

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Bacteria and fungi that break down plant and
animal materials are called decomposers.
These bacteria return nitrogen to the soil.
Some denitrifying bacteria can
release nitrogen into the
atmosphere.
The Phosphorus cycle:
Phosphorus is a key element in cell membranes,
molecules that help release energy and in making
DNA.
Phosphorus is found in bedrock in the form of
phosphates (PO4 3-), which can dissolve in water
Once phosphates are dissolved in water algae and
plants absorb them.
Animals store phosphates in bones, teeth and
shells, which eventually end up as rock (takes
millions of years to complete)
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Sulphur is one of the components that make up
proteins and vitamins.
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Plants absorb sulphur when it is dissolved in water.
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Animals consume these plants, so that they take
up enough sulphur to maintain their health.