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Our atmosphere consists of 78% nitrogen, where it is present in the form of N2. We all need it because it is a component of proteins without which we could not survive. Nitrogen fixation is an important natural process. Certain microorganisms absorb nitrogen in the form of N2. Only very few microorganisms are able to do this because they need a very special enzyme system. This is followed by several conversion steps until the nitrogen can be absorbed by other living organisms. Animals get nitrogen from their food and plants get it from the soil.
Explanation for children:
Nitrogen is a valuable compound because it is present in amino acids and proteins that all living beings need. For example, plants need nitrogen to grow their leaves and do more photosynthesis. This is why nitrogen is also present in the fertilizer. There is also a lot of nitrogen in our atmosphere, 78%. There are very useful microorganisms that can capture nitrogen as it occurs in the air. If they are quite nice, they then convert the nitrogen into a special form for the plants and give it to the plant. The microorganisms have special enzymes for capturing and transforming, and they get sugar from the plant.