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Nitrogen Cycle

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Sarah Woods

on 21 March 2010

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Transcript of Nitrogen Cycle

Air is 79% nitrogen, but most organisms can't use the nitrogen in this form.

Nitrogen is needed to make proteins, DNA, and amino acids.

4 Major Stages of the Nitrogen Cycle:
Nitrogen fixing bacteria living in the roots of many legumes and in the soil convert nitrogen from the atmosphere into ammonia. The energy in lightning can also break apart nitrogen, which then combines with oxygen in the air to form nitrogen oxides. These dissolve in rain, forming nitrates which are absorbed into the soil. However this process only contributes to 5%-8% of nitrogen fixation. Nitrification takes place when aerobic nitrifying bacteria convert ammonia to nitrites and then nitrates. Plants then take up the nitrates through the process called assimilation. Denitrifying bacteria use the nitrates produced in nitrification and through anaerobic respiration they convert the nitrates into nitrogen gas. Decomposers convert waste and dead tissue into ammonia and ammonium ions, which are then used in the process of nitrification. Decay is also called nitrogen mineralization. Nitrogen gas in the atmosphere cannot be used by organisms- it needs to be broken apart by fixation so other atoms can combine with it to create a product that can be used. Through assimilation, some plants
can also take up ammonia and
ammonium ions as well as the nitrate
ions. They use these ions to make
organic molecules essential to life. Denitrification completes the nitrogen cycle- it is the only part that returns forms of nitrogen back into the atmosphere. Human Influences on the Nitrogen Cycle: When we burn any fuel, nitric oxide is added into the atmosphere which eventually forms acid rain. Acid rain can damage trees, aquatic ecosystems, metals, and other building materials. When we harvest nitrogen rich crops, we are removing nitrogen from topsoil. Agricultural runoff can add
extra nitrogen compounds to
the aquatic ecosystems. An
excess of nitrogen causes
eutrophication. There is a
rapid growth of plants, which
eventually die and cause an
increase ofdecomposition which
robs the ecosystem of oxygen,
thus causing the death of
aerobic organisms. Fertilizers and the decomposition
of livestock waste add excess
nitrous oxide to the soil. When
the nitrous oxide reaches the
atmosphere, it enhances the
greenhouse effect and also
contributes to the depletion
of the ozone layer. Nitrogen Cyle Fixation Denitrification Decay Nitrification
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