Biology · Ch 7 — Plant Growth and Mineral Nutrition
Nitrogen Fixation
Nitrogen Fixation
Nitrogen fixation : The atmosphere is the source of nitrogen, but it cannot be used directly - it combines with C, H, N and O to form compounds before being used. The conversion of the free nitrogen (N2) of the atmosphere into nitrogenous salts, making it available to plants, is called nitrogen fixation. It is of two types, physical and biological fixation.
Physical and industrial nitrogen fixation
Physical Nitrogen fixation : It occurs in several steps and starts with the combination of atmospheric nitrogen with oxygen under the influence of electric discharge and thunderstorms, producing nitric oxide:
N2 + O2 --(electric discharge / thunderstorm)--> 2NO (nitric oxide)
The nitric oxide is then oxidised to nitrogen peroxide in the presence of oxygen:
2NO + O2 --(oxidation)--> 2NO2 (nitrogen peroxide)
During rains the nitrogen peroxide combines with rain water to form nitrous acid and nitric acid, which come to the ground with the rain:
2NO2 + rain water --> HNO2 (nitrous acid) + HNO3 (nitric acid)
On the ground the alkali radicals of the soil react with nitric acid to produce nitrites and nitrates, the absorbable form:
HNO3 + Ca or K salts --> Ca or K nitrates
Industrial nitrogen fixation : It occurs by the Haber-Bosch process at high temperature and pressure:
N2 + 3H2 --(450 °C, 200 atm)--> 2NH3 (ammonia)
Ammonia is then converted to urea, as urea is less toxic.
Internet my friend
Enlist the names of symbiotic and free-living nitrogen-fixing bacteria.
Always Remember
Today nearly 80 % of the nitrogen found in human tissues originates from the Haber-Bosch process. …