After reading this term paper you will learn about the composition of nitrogen cycle present in the atmosphere.
Nitrogen gas makes upto 78% of our atmosphere and a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA) and certain vitamins. Nitrogen is found in biologically important compounds suck as alkaloids and urea.
Nitrogen is thus an essential nutrient for all life-forms. Nitrogen cannot be directly used from the air and thus it has to be converted into nitrate and nitrites that are easily absorbed by plants.
Nitrogen Fixing Bacteria:
‘Nitrogen-fixing’ bacteria may be free-living or be associated with some species of dicot plants. They are found in the roots of legumes (generally the plants which give us pulses) in special structures called root nodules. These bacteria convert nitrogen into nitrates or nitrites which gets dissolved in water and is easily available to plants for its use in preparing amino acids.
Physical Process of Nitrogen Fixation:
Other than the nitrogen fixing bacteria, lightening helps in converting atmospheric nitrogen. During lightning, the high temperatures and pressures created in the air convert nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain. These are then utilized by various life-forms.
Plants generally take up nitrates and nitrites and then convert them into amino acids that 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 the animals.
Once the animal or the plant dies, other bacteria in the soil convert various compounds of nitrogen back into nitrates and nitrites. This nitrogen compound is then converted (by other set of bacteria) into the elemental nitrogen form and released into the atmosphere.