In: Biology
discuss in great details nitrogen cycle
microbiology
Answer:
The nitrogen cycle
Nitrogen is a part of vital organic
compounds in microrganisms, such as amino acids, proteins and DNA.
The gaseous form of nitrogen (N2), makes up 78% of the
troposphere. Nitrogen in the gaseous form cannot be absorbed and
used as a nutrient by plants and animals; it must first be
converted into nitrate compound in the soil by nitrogen-fixing
bacteria in soil, root nodules or lightning, so that it can enter
food chains as a part of the nitrogen cycle. The problem is,
however, that plants are unable to use nitrogen in its elemental
form—as dinitrogen. Any process by which elemental dinitrogen is
converted to a compound is known as nitrogen
fixation. It is a cycle within the biosphere which
involves the atmosphere, hydrosphere, and lithosphere.
During the conversion of nitrogen, cyanobacteria will first convert
nitrogen into ammonia and ammonium, during the nitrogen
fixation process. Plants can use ammonia as a nitrogen
source. Nitrogen fixation is carried out according to the following
reaction:
After ammonium fixation, the ammonia and ammonium that is formed
will be transferred further, during the
nitrification process. Aerobic bacteria use oxygen
to convert these compounds. Nitrosomonas bacteria first convert
nitrogen gas to nitrite (NO2-), whereas
nitrobacter convert nitrite to nitrate
(NO3-), a plant nutrient.
Plants absorb ammonium and nitrate during the assimilation process,
after which they are converted into nitrogen-containing organic
molecules, such as amino acids and DNA.
Animals cannot absorb nitrates directly. They receive their
nutrient supplies by consuming plants or plant-consuming animals.
When nitrogen nutrients have served their purpose in plants and
animals, specialized decomposing bacteria will start a process
called ammonification, to convert them back into
ammonia and water-soluble ammonium salts. After the nutrients are
converted back into ammonia, anaerobic bacteria will convert them
back into nitrogen gas, during a process called
denitrification.
Plants absorb ammonium and nitrate
during the assimilation process, after which they are converted
into nitrogen-containing organic molecules, such as amino acids and
DNA.
Animals cannot absorb nitrates directly. They receive their
nutrient supplies by consuming plants or plant-consuming animals.
When nitrogen nutrients have served their purpose in plants and
animals, specialized decomposing bacteria will start a process
called ammonification, to convert them back into
ammonia and water-soluble ammonium salts. After the nutrients are
converted back into ammonia, anaerobic bacteria will convert them
back into nitrogen gas, during a process called
denitrification.
Finally, nitrogen is released into the atmosphere again.
Dinitrogen is converted from an element to a compound by a number of naturally occurring processes. When lightning passes through the atmosphere, it prompts a reaction between nitrogen and oxygen; oxides of nitrogen—primarily nitric oxide (NO) and nitrogen dioxide (NO2)—are formed. Both oxides then combine with water vapor in the atmosphere to form nitric acid (HNO3). Nitric acid is carried to the ground in rain and snow, where it is converted to nitrites and nitrates. Nitrites and nitrates are both compounds of nitrogen and oxygen, the latter containing more oxygen than the former. Naturally occurring minerals such as saltpeter (potassium nitrate; KNO3) and chile saltpeter (sodium nitrate; NaNO3) are the most common nitrates found in Earth's crust.
Finally, dinitrogen is now converted to nitrates on very large scales by human processes. In the Haber process, for example, nitrogen and hydrogen are combined to form ammonia, which is then used in the manufacture of synthetic fertilizers, most of which contain nitrates.
Words to know:
Ammonification: The conversion of nitrogen compounds from plants and animals to ammonia and ammonium; this conversion occurs in soil or water and is carried out by bacteria.
Denitrification: The conversion of nitrates to dinitrogen (or nitrous oxide) by bacteria.
Dinitrogen fixation (nitrogen fixation): The conversion of elemental dinitrogen (N2) in the atmosphere to a compound of nitrogen deposited on Earth's surface.
Nitrification: The process by which bacteria oxidize ammonia and ammonium compounds to nitrites and nitrates.