What is Nitrogen Cycle? | Types, Definition, Structure, Function & Facts

What is Nitrogen Cycle?

The nitrogen cycle describes how nitrogen moves between plants, animals, bacteria, the atmosphere (air) and soil within the soil. Nitrogen is an essential element for all life on Earth.

Different Nitrogen States

For nitrogen to be used by different life forms on Earth, it must change into different states. Atmospheric nitrogen, or air, is N2. Other important nitrogen states include nitrate (N03), nitrite (NO2) and ammonium (NH4).

Nitrogen Cycle

This image shows the process of the nitrogen cycle. The most important part of the cycle is the bacteria. Bacteria help change nitrogen between states so it can be used. As nitrogen is absorbed by the soil, different bacteria help it change its state so it can be absorbed by plants. Then the animals get nitrogen from the plants.

Processes in the Nitrogen Cycle

Fixation – Fixation is the first step in the process of making nitrogen usable to plants. Here, bacteria convert nitrogen into ammonium.

Nitrification – This is the process by which ammonium is converted to nitrate by bacteria. Nitrates are what plants can then absorb.

Assimilation – This is how plants get nitrogen. They absorb nitrates from the soil in their roots. The nitrogen is then used in amino acids, nucleic acids and chlorophyll.

Ammonification – This is part of the decomposition process. When a plant or animal dies, decomposers such as fungi and bacteria convert nitrogen into ammonium so it can be returned to the nitrogen cycle.

Denitrification – Excess nitrogen in the soil is released into the air. There are also special bacteria that perform this task.

Why is Nitrogen Important to Life?

Plants and animals cannot live without nitrogen. It is an important part of many cells and processes such as amino acids, proteins and even our DNA. It is also needed to make chlorophyll in plants, which plants use during photosynthesis to create food and energy.

How have Humans altered the Nitrogen Cycle?

Unfortunately, human activity has changed the cycle. We do this by adding nitrogen to the soil with fertilizers as well as other activities that put more nitrogen oxides into the atmosphere. This adds more nitrogen than is needed for each normal cycle and upsets the balance of the cycle.

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