Explain the life cycle of Nitrogen ?
Nitrogen cycle: Along with carbon, hydrogen, and oxygen, nitrogen is one of the most common elements that form biological molecules. Nitrogen is a major component of amino acids, which are the building block molecules of proteins and enzymes. It is also a primary constituent of nucleic acids (DNA and RNA). Although most of the nitrogen supply exists in the form of N2, or molecular nitrogen, in the atmosphere, the majority of living organisms are not able to use it directly in that form. In fact, 78% of the earth's atmosphere is composed of nitrogen gas. Since molecular nitrogen contains a triple bond between the atoms, it is a very stable molecule and therefore, biologically inert.
A large amount of energy is required to break the triple bond, and lightning is responsible for converting some of the atmospheric nitrogen into forms that organisms can use. The process of converting atmospheric nitrogen into forms that organisms can use is called nitrogen fixation. Although most organisms are not able to convert nitrogen, there are a few that are able to "fix" atmospheric nitrogen. Some free-living soil bacteria as well as some blue-green bacteria have the ability to convert nitrogen into ammonia. Other bacteria convert ammonia to nitrates through nitrification. Most plants use nitrogen in the form of nitrates.
Nitrogen is also fixed by symbiotic bacteria that live in and among the root cells of several types of plants, most notably, the legume plants such as beans, peanuts, and peas. Other plants such as alfalfa, locust, and alders also have root nodules. They contribute to the nitrogen-fixing process as well. Once nitrogen is absorbed by plants and built into the plant molecules, the nitrogen can be passed to consumers and to decomposer organisms through the food chain. Nitrogen can be mineralized and converted to organic compounds that enter the soil or water upon their death, or enter as waste through their digestive tracts. These decomposed nitrogen compounds - ammonia, nitrite, and nitrates, then become available for other plants to absorb and recycle. This process is called ammonification.
Alternatively, other bacteria, known as "denitrifiers," convert nitrites and nitrates in the soil to N2O and N2, which returns to the reservoir in the atmosphere. This process, which completes the nitrogen cycle, is called denitrification.