A1.2.2.1 Nitrogen Cycle
Atmospheric Nitrogen is converted into useful compounds by bacteria. It enters the food chain through nitrogen-fixing bacteria in the soil, which create nitrates. Nitrates can then be absorbed by plants and dissolved into the soil by water. The plants use the nitrates to create proteins.
It enters the food chain as animals eat those plants (herbivores), and in turn may be eaten by other animals (carnivores). When an animal excretes waste, nitrogen is released back into the environment. When an animal dies, it decomposes and as it breaks down, nitrogen is formed through ammonification. This may then be assimilated by plants or returned to atmospheric nitrogen by nitrifying bacteria.
Source: http://www.epa.gov/maia/html/nitrogen.html
Nitrogen Fixation:
Nitrogen Fixation is the process that takes nitrogen from its natural molecular form in the atmosphere and converts it into nitrogen compounds (including ammonia, nitrate and nitrogen dioxide).
Nitrification:
Nitrification is the inorganic production of nitrates.
Nitrogen gas is converted to nitrate. In soil, this is a two step process completed by nitrifying bacteria.
- Nitrite-producing bacteria convert ammonia to nitrite.
- Nitrate-producing bacteria convert nitrite to nitrate.