The Nitrogen Cycle
Why is Nitrogen Important?
• Nitrogen is important to both plants and
animals. Nitrogen is used in making proteins,
DNA, and chlorophyll.
How does nitrogen become part of
living organisms?
• The atmosphere is made up of approximately
78% nitrogen. This atmospheric nitrogen (N2)
is not in a form that can be used by plants and
animals.
• Nitrogen Fixation or Nitrification: is the
process where atmospheric nitrogen is
converted into a useable form of nitrogen.
Nitrogen Fixation
• Nitrogen fixation by lightning accounts for only 1% of
fixation. The energy from lightning causes nitrogen in the air
to combine with oxygen forming nitrates (NO3)
• Nitrogen fixation by bacteria . Some bacteria (nitrogen-fixing
bacteria) convert atmospheric nitrogen (N2) into
ammonium(NH4+). Some decomposing bacteria will break
down plant and animal wastes to release ammonium as well.
• Nitrifying bacteria convert ammonium into a usable form for
plants. These bacteria convert ammonium(NH4 ) into nitrates
(NO3).
Denitrification
• Denitrifying bacteria convert nitrates (NO )
back into atmospheric nitrogen (N ).
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• This completes the nitrogen cycle
Human Impacts on Nitrogen Cycle
• The use of nitrogen-rich fertilizers can cause
nitrogen to leach into nearby waterways. The
increased nitrate levels cause plants to grow
rapidly until they use up the nitrate supply
and then die. The number of herbivores will
increase when the plant supply increases and
then the herbivores are left without a food
source when the plants die. This can affect
the entire food chain.
Human Impacts of Nitrogen Cycle
• Farming also affects the nitrogen cycle. The
waste from livestock farming releases a large
amount of nitrogen into soil and water. In the
same way, sewage waste adds nitrogen to
soils and water.