You will learn about "Nitrogen Cycle" in this video. Nitrogen constitutes around 78% of the air. However, atmospheric nitrogen cannot be used directly by plants and animals. Nitrogen needs to be converted to nitrogenous compounds in order to be used by plants. This process of converting nitrogen into nitrogenous compounds is called nitrogen fixation.
It takes place by a certain kind of bacteria called rhizobium bacteria which live in the root nodules of leguminous plants. They convert atmospheric nitrogen to ammonia. Nitrifying bacteria then convert ammonia to nitrites and then nitrates. Some nitrogen fixation also occurs by lightning strikes.
The plants then take these nitrates from the soil. Plants use these nitrates for the synthesis of plant proteins and other compounds. Animals then eat these plants and get the proteins. Dead plants and animal excreta contain nitrogenous wastes. Overtime, these wastes decay and ammonia is released. Nitrifying bacteria once again convert the ammonia to nitrates. Some nitrates are again used by the plants and the cycle continues. Some nitrates are converted by denitrifying bacteria into atmospheric nitrogen. Thus, Nitrogen gas goes back to the atmosphere. As a result, the percentage of nitrogen in the air remains more or less constant. This cycle is known as Nitrogen Cycle
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