Plants and animals could not live without nitrogen. It is an important part of many cells and processes such as amino acids, proteins, and even our DNA. The Nitrogen Cycle describes how nitrogen moves between plants, animals, bacteria, the atmosphere (the air), and soil in the ground. In general, the nitrogen cycle has five steps: nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.
The most important part of the cycle is bacteria. Bacteria helps the nitrogen change between states so it can be used. When nitrogen is absorbed by the soil, different bacteria helps it to change states so it can be absorbed by plants. Animals then get their nitrogen from the plants.
The first step of the Nitrogen Cycle is fixation. This is the process of making nitrogen usable by plants. Here bacteria change nitrogen into ammonium. During fixation, legumes and the symbiotic bacteria are associated with their root nodules. These nodules have nitrogen-fixing bacteria. Nitrogen fixing bacteria convert nitrogen into the soil to ammonia which can be taken up by some plants. The soil is a major reservoir for ammonia and other nitrogen-containing compounds.
Second step of the Nitrogen Cycle is nitrification. This is the process by which ammonium gets changed into nitrates by bacteria. Nitrates are what the plants can then absorb. In nitrification, Ammonium converted into nitrate and nitrite (NO2-) through work of nitrifying bacteria.
Following step of the Nitrogen Cycle is assimilation, This is how plants get nitrogen. They absorb nitrates from the soil into their roots. Then the nitrogen gets used in:
The fourth step of the Nitrogen Cycle is ammonification. This is part of the decaying process. When a plant or animal dies, decomposers like fungi and bacteria turn the nitrogen back into ammonium so it can reenter the nitrogen cycle.
The final step of the Nitrogen Cycle is denitrification. During denitrification, extra nitrogen in the soil gets put back out into the air. There are special bacteria that perform this task as well.
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