Nitrogen Cycle

THE NITROGEN-CYCLE-----
Nitrogen gas makes up 78% of our
atmosphere and nitrogen is also a part ofmany molecules essential to life like proteins,nucleic acids (DNA and RNA) and somevitamins. Nitrogen is found in otherbiologically important compounds such asalkaloids and urea too. Nitrogen is thus anessential nutrient for all life-forms and lifewould be simple if all these life-forms coulduse the atmospheric nitrogen directly.However, other than a few forms of bacteria,life-forms are not able to convert thecomparatively inert nitrogen molecule intoforms like nitrates and nitrites which can betaken up and used to make the requiredmolecules. These ‘nitrogen-fixing’ bacteriamay be free-living or be associated with some
species of dicot plants. Most commonly, thenitrogen-fixing bacteria are found in the rootsof legumes (generally the plants which giveus pulses) in special structures called root-nodules. Other than these bacteria, the onlyother manner in which the nitrogen molecule is converted to nitrates and nitrites is by aphysical process. During lightning, the hightemperatures and pressures created in theair convert nitrogen into oxides of nitrogen.These oxides dissolve in water to give nitricand nitrous acids and fall on land along withrain. These are then utilised by various life-forms.

     Plants generally take up nitrates
and nitrites and convert them into amino
acids which are used to make proteins. Some other biochemical pathways are used to make the other complex compounds containing
nitrogen. These proteins and other complex compounds are subsequently consumed by animals. Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites. A different type of bacteria convertsthe nitrates and nitrites into elementalnitrogen. Thus, there is a nitrogen-cycle innature in which nitrogen passes from itselemental form in the atmosphere into simplemolecules in the soil and water, which getconverted to more complex molecules in livingbeings and back again to the simple nitrogenmolecule in the atmosphere.

Q. What happens to the nitrogen once it isconverted into forms that can be taken upand used to make nitrogen-containing
molecules?
And: Plants generally take up nitrates
and nitrites and convert them into amino
acids which are used to make proteins. Some other biochemical pathways are used to make the other complex compounds containing
nitrogen. These proteins and other complex compounds are subsequently consumed by animals. Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites. A different type of bacteria convertsthe nitrates and nitrites into elementalnitrogen. Thus, there is a nitrogen-cycle innature in which nitrogen passes from itselemental form in the atmosphere into simplemolecules in the soil and water, which getconverted to more complex molecules in livingbeings and back again to the simple nitrogenmolecule in the atmosphere.