Plants and animals need nitrogen to make proteinsproteins: organic compounds made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair.. But they cannot get nitrogen directly from the air because, as a gas, nitrogen is fairly unreactive. Plants are able to take up nitrogen compounds [compound: A compound is a substance formed by the chemical union (involving bond formation) of two or more elements. ] such as nitrates and ammonium salts from the soil.
Making nitrogen compounds from nitrogen in the air is called nitrogen fixation.
Nitrogen fixation happens in three ways:
Nitrogen compounds in living things are returned to the soil through:
Denitrifying bacteria present in soil break down nitrogen compounds and release nitrogen gas into the air.
As a result of these processes, nitrogen is cycled continually through the air, soil and living things. This is called ‘The Nitrogen Cycle’.
This animation summarises the main features of the nitrogen cycle.
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