Question

How does nitrogen eventually return to the atmosphere?

Answer 1

Hint: Nitrogen is abundant in the atmosphere. It exists in organic and inorganic forms. Inorganic forms are made available for use through nitrogen cycle.

Complete answer: Nitrogen is an important component of the atmosphere. It compromises about 78% of Earth's atmosphere. Nitrogen is required by living organisms in building protein and other important body chemicals.
Most of the living organisms including plants, animals and fungi cannot get nitrogen from the atmosphere. They only used nitrogen which is available in compound form.
There are certain bacteria that convert the free nitrogen into nitrogen compounds. This is referred to as Nitrogen Fixation. This process is the result of bacterial activity. Some of the bacteria is found in soil, some in water and some grow in roots of plants (legumes). Plants take up nitrogen compounds through their roots leading to the formation of plant and animal proteins. These plants are consumed by secondary producers and hence enter the food web.
The nitrogen is returned back to the atmosphere by the action of decomposers. Decomposer breaks down complex nitrogen compounds found in dead organisms, plant and animal's waste and release back into the soil.

Note: The continuous transformation of nitrogen and nitrogen compounds by living and nonliving organisms forms a nitrogen cycle. It involves several stages. The first stage is nitrogen fixation, where atmosphere nitrogen is converted into ammonia by symbiotic bacteria. The next stage is the nitrification where ammonia is converted into nitrates by bacteria in the soil. This is followed by assimilation where plants through their roots take nitrogen compounds leading to the formation of plant and animal proteins. The next stage is the ammonification. In this stage, decomposers release the nitrogen compounds back into the soil by breaking down complex nitrogen compounds found in dead plants and animals. The last stage is denitrification where nitrogen is back into the atmosphere after converting from nitrates.