wat z nitrogen cycle???

In the atmosphere, the concentration of nitrogen is about 78%. It is essential for plants. Nitrogen forms a structural component of many important molecules such as DNA, RNA, and other vitamins. Plants cannot absorb nitrogen from the atmosphere. Certain forms of bacteria are able to convert atmospheric nitrogen into usable forms such as nitrates and nitrites. Such nitrogen fixing bacteria are commonly found in the roots of legumes (plants of pulses) inside special structures called root nodules. These usable forms of nitrogen are absorbed by plants to produce many compounds such as amino acids, which in turn form proteins. When an animal feeds on plants, nitrogen enters its body.When plants and animals die, they start decomposing after some time. During this process, proteins are converted into nitrates and nitrites by the action of decomposing bacteria. Certain other forms of bacteria convert nitrates and nitrites into elemental nitrogen. Thus, nitrogen flows between the various components of the biosphere in a cyclical manner. There are basically 5 steps of nitrogen cycle that help in fixing atmospheric nitrogen:  * Nitrogen Fixation (N 2 to NO 3 - or NH 4 )  * Nitrification (NH 3 to NO 3 - )  * Assimiliation (here the NH 3 and NO 3 - are incorporated into the biological tissues)  * Ammonification (organic nitrogen compounds to NH 3 )  * Denitrification (NO 3 - to N 2 )

 

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78  percent   of  total  gases  in  the  atmosphere  is  nitrogen  but  it  cannot  be  used  by  plants  and  animals  directly.  The  nitrogen-fixing  bacteria  and  algae  present  in  the  soil  fix  nitrogen  from  the  atmosphere  and  convert  into  nitrite  and  nitrate  forms.  Once  nitrogen  is  converted  into  these  usable  forms,  it  can  be  utilised  by  plants  through  their  root  system.  This  is  the  process  of  'fixing'  of  nitrogen.  Animals  feeding  on  plants  get  proteins  and  other  nitrogenous  compounds.

When  plants  and  animals  die,  bacteria  and  fungi  present  in  the  soil  convert  various  nitrogenous  compounds  into  nitrites  and  nitrates.  Certain  specialized  bacteria  convert  nitrates  and  nitrites  into  nitrogen  gas.  As  a  result,  the  percentage  of  nitrogen  in  the  atmosphere  remains  more  or  less  constant.

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