Nitrogen cycle: Difference between revisions
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The nitrogen cycle is an important process where the atmospheric [[Nitrogen|nitrogen]] is converted, through various biological and physical processes, to substances that can be used by [[Organism|organisms]].The main processes in this cycling of nitrogen are : nitrogen fixation, nitrification, [[Ammonia|ammonification]] and denitrification.<ref>Kennedy,P. &amp;amp;amp; Sochacki,F. (2008) Biology A. Heinemann of Pearson Education Limited.</ref> | |||
=== Nitrogen Fixation === | === Nitrogen Fixation === | ||
[[Nitrogen|Nitrogen]] fixation is a process where the atmospheric nitrogen is converted or 'fixed' into [[Ammonia|ammonia]] .The ‘fixing’ occurs in lightning, through industrial process or mostly is done by nitrogen fixing soil bacteria like the ''[[Cyanobacteria|Cynobacteria]]'' and also bacteria living in the root nodules of legumes called ''Rhizobium''.<ref>Wagner, S. C. (2011) Biological Nitrogen Fixation. Nature Education Knowledge 3(10):15</ref | [[Nitrogen|Nitrogen]] fixation is a process where the atmospheric nitrogen is converted or 'fixed' into [[Ammonia|ammonia]] .The ‘fixing’ occurs in lightning, through industrial process or mostly is done by nitrogen fixing soil bacteria like the ''[[Cyanobacteria|Cynobacteria]]'' and also bacteria living in the root nodules of legumes called ''Rhizobium''.<ref>Wagner, S. C. (2011) Biological Nitrogen Fixation. Nature Education Knowledge 3(10):15</ref> | ||
==== | ==== Fixation by lightning ==== | ||
The atmospheric nitrogen molecule is broken due to the energy from lightning and this enables the nitrogen [[Atoms|atoms]] to bind with oxygen in air to form Nitrogen oxide then dissolve in rain and form nitrates and ammonia which pours into the soil. These nitrates and ammonia are then assimilated by the plants.<ref>Meteorol, J. and Viemeister, P. E. (1960) Lightning and the origin of nitrates found in precipitation, 7, 681</ref> | |||
==== | ==== Industrial Fixation ==== | ||
With high pressure, temperature of 450<sup>o</sup>C and an iron catalyst, the atmospheric nitrogen can combine with [[Hydrogen|hydrogen]] to form ammonia through an industrial process called the harber process. Ammonia is further processed to form [[Urea|urea]] and [[Ammonia|ammonium nitrate]] <ref>http://www.chemguide.co.uk/physical/equilibria/haber.html</ref> | |||
==== Biological Fixation ==== | |||
Most of the nitrogen 'fixing' is done by [[Bacteria|bacteria]]. ''[[Cyanobacteria|Cynobacteria]]'' lives freely in the soil and ‘fixes’ the nitrogen by converting it into ammonium. The ''Rhizobium'' bacteria produce ammonia which is then taken up by the legume plants through their root nodules. There is a mutualistic relationship present between the bacteria and the plant since, the bacteria [[Reduction|reduces]] nitrogen to ammonia to be taken up by the plant in exchange for shelter and [[Carbohydrates|carbohydrates]] .Thus, legumes plant often increase the nitrogen content of nitrogen-deprived soils.<ref>http://aces.nmsu.edu/pubs/_a/A129/</ref> | |||
=== | === Nitrification === | ||
Nitrification is a process where ammonia is converted to nitrites [[]]and then to nitrates, before it can be taken up directly by plants. The conversion of ammonia to nitrites is done by nitrifying bacteria called the ''Nitrosomonas''. The nitrite is further converted to nitrate by another type of nitrifying bacteria called the ''Nitrobacter.'' Through the activities of these bacteria, nitrogen is made available to be taken up by plants and so, animals obtain nitrogen by eating these plants.<ref>Appleman,M.D., Fisher, T. and Fisher,E. (1952) Nitrification by Certain Heterotrophic Bacteria present in Soil. Journal of Bacteriology. 64 (4). P.596.</ref><br> | |||
=== Ammonification === | |||
<br> | When plants and animals die, they get decomposed by decomposers, which include [[Aerobic|aerobic]] and [[Anaerobic|anaerobic]] bacteria and fungi. During decomposition, bacteria convert the nitrogen nutrients back into ammonium and ammonia, which then can go through nitrification and denitrification process again.<ref>&amp;lt;a href="http://science.jrank.org/pages/4690/Nitrogen-Cycle-Ammonification-nitrification.html"&amp;gt;Nitrogen Cycle - Ammonification And Nitrification&amp;lt;/a&amp;gt;</ref><br> | ||
=== Denitrification === | |||
=== | |||
It is the process of reducing nitrates and nitrites back into the atmospheric nitrogen. This process completes the nitrogen cycle. Denitrification is done by denitrifying bacteria, like Pseudomonas, in anaerobic conditions as these bacteria live deep in soil and in aquatic sediments. These bacteria use nitrates as the final electron acceptor, rather than oxygen, during respiration and releases nitrogen gas into the atmosphere. <ref>Kennedy,P. &amp;amp;amp; Sochacki,F. (2008) Biology A. Heinemann of Pearson Education Limited.</ref> | |||
=== References === | |||
=== | |||
<references /> | |||
Revision as of 00:47, 28 November 2014
The nitrogen cycle is an important process where the atmospheric nitrogen is converted, through various biological and physical processes, to substances that can be used by organisms.The main processes in this cycling of nitrogen are : nitrogen fixation, nitrification, ammonification and denitrification.[1]
Nitrogen Fixation
Nitrogen fixation is a process where the atmospheric nitrogen is converted or 'fixed' into ammonia .The ‘fixing’ occurs in lightning, through industrial process or mostly is done by nitrogen fixing soil bacteria like the Cynobacteria and also bacteria living in the root nodules of legumes called Rhizobium.[2]
Fixation by lightning
The atmospheric nitrogen molecule is broken due to the energy from lightning and this enables the nitrogen atoms to bind with oxygen in air to form Nitrogen oxide then dissolve in rain and form nitrates and ammonia which pours into the soil. These nitrates and ammonia are then assimilated by the plants.[3]
Industrial Fixation
With high pressure, temperature of 450oC and an iron catalyst, the atmospheric nitrogen can combine with hydrogen to form ammonia through an industrial process called the harber process. Ammonia is further processed to form urea and ammonium nitrate [4]
Biological Fixation
Most of the nitrogen 'fixing' is done by bacteria. Cynobacteria lives freely in the soil and ‘fixes’ the nitrogen by converting it into ammonium. The Rhizobium bacteria produce ammonia which is then taken up by the legume plants through their root nodules. There is a mutualistic relationship present between the bacteria and the plant since, the bacteria reduces nitrogen to ammonia to be taken up by the plant in exchange for shelter and carbohydrates .Thus, legumes plant often increase the nitrogen content of nitrogen-deprived soils.[5]
Nitrification
Nitrification is a process where ammonia is converted to nitrites [[]]and then to nitrates, before it can be taken up directly by plants. The conversion of ammonia to nitrites is done by nitrifying bacteria called the Nitrosomonas. The nitrite is further converted to nitrate by another type of nitrifying bacteria called the Nitrobacter. Through the activities of these bacteria, nitrogen is made available to be taken up by plants and so, animals obtain nitrogen by eating these plants.[6]
Ammonification
When plants and animals die, they get decomposed by decomposers, which include aerobic and anaerobic bacteria and fungi. During decomposition, bacteria convert the nitrogen nutrients back into ammonium and ammonia, which then can go through nitrification and denitrification process again.[7]
Denitrification
It is the process of reducing nitrates and nitrites back into the atmospheric nitrogen. This process completes the nitrogen cycle. Denitrification is done by denitrifying bacteria, like Pseudomonas, in anaerobic conditions as these bacteria live deep in soil and in aquatic sediments. These bacteria use nitrates as the final electron acceptor, rather than oxygen, during respiration and releases nitrogen gas into the atmosphere. [8]
References
- ↑ Kennedy,P. &amp;amp; Sochacki,F. (2008) Biology A. Heinemann of Pearson Education Limited.
- ↑ Wagner, S. C. (2011) Biological Nitrogen Fixation. Nature Education Knowledge 3(10):15
- ↑ Meteorol, J. and Viemeister, P. E. (1960) Lightning and the origin of nitrates found in precipitation, 7, 681
- ↑ http://www.chemguide.co.uk/physical/equilibria/haber.html
- ↑ http://aces.nmsu.edu/pubs/_a/A129/
- ↑ Appleman,M.D., Fisher, T. and Fisher,E. (1952) Nitrification by Certain Heterotrophic Bacteria present in Soil. Journal of Bacteriology. 64 (4). P.596.
- ↑ &lt;a href="http://science.jrank.org/pages/4690/Nitrogen-Cycle-Ammonification-nitrification.html"&gt;Nitrogen Cycle - Ammonification And Nitrification&lt;/a&gt;
- ↑ Kennedy,P. &amp;amp; Sochacki,F. (2008) Biology A. Heinemann of Pearson Education Limited.