The Nitrogen Cycle.

The diagram depicted below is a detailed illustration of the nitrogen cycle.

A summary of the six steps of the nitrogen cycle:

1. Plants using diffusion and active transport absorb nitrate ions. Nitrogen is required for the synthesis of proteins and other compounds in plants. The nitrogen compounds are passed through the food chain as other organisms feed on the plants and each other.  Waste products such as undigested food, urine and feces and dead organisms are added to the soil, as they contain nitrogen compounds.)
2. Ammonification:  Decomposers release ammonium ions once the proteins of dead organisms and animal wastes are broken down.
3. Nitrification: Conducted by nitrifying bacteria. Oxidation of ammonia or ammonium ions yields nitrites first and then nitrates.
4. Denitrification:  Denitrifying bacteria reduce nitrates to nitrogen gas.
5. Nitrogen fixation:  The first step in the synthesis of nitrogenous compounds.  Two types:
• Atmospheric fixation:  A spontaneous process carried out via lightning. Only small amounts of nitrogenous compounds are fixed in this way.
• Industrial fixation: Also known as the Haber process; An energy inefficient process used in the production of nitrogen fertilizers.
6. Biological fixation:  Sixty percent of nitrogen gas is fixed by nitrogen fixing bacteria.  Nitrogen fixing bacteria thrive in the root nodules of legumes, while others are free living in the soil.

It is important to note that microorganisms are significant to all five of the reactions of the nitrogen cycle:  ammonification, nitrification, denitrification, nitrogen fixation, and biological fixation.  As such, it can be concluded that microorganisms play a vital role in making nitrogen available for living organisms prior to its transport into the atmosphere.