Nitrogen Cycle Chemistry Tutorial

Key Concepts

• Nitrogen gas, N_2(g), is the major constituent of air, ~78% by volume.

• Inorganic (non-carbon) compounds of nitrogen are not commonly found as minerals because most of them are water soluble.
  In dry climate locations there are beds of nitrates.
• Nitrogen is found combined in organic (carbon) compounds in all living matter, both plant and animal.
• Nitrogen in the atmosphere is the source of all nitrogen found in living matter.
• The complex interrelationship between atmospheric nitrogen, nitrate, nitrate and ammonium ions found in soils, and organic nitrogen compounds found in living matter, is called the nitrogen cycle.
• The nitrogen cycle keeps the nitrogen content of the atmosphere constant.
• Nitrogen fixation refers to the conversion of nitrogen gas into nitrogen compounds.
• Nitrification is the process of converting one nitrogen compound to another.
• Denitrification is the process of releasing nitrogen gas back into the atmosphere.

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Nitrogen Cycle

Some plants, like legumes, can convert atmospheric N₂ gas into nitrogen compounds which can be converted by bacteria into nitrates (NO₃^-), which plants can use to make plant proteins.
Soluble nitrogen compounds in soil can be taken up by plants to make plant proteins.

Animals eat the plants and by the process of digestion convert the plant proteins to animal proteins.

Plants and animals die and their decomposing cells release N₂ gas back into the atmosphere.

The nitrogen cycle involves oxidation and reduction of nitrogen.