Скачать или смотреть Nitrogen Cycle

The nitrogen cycle is a crucial natural process that occurs in the environment, involving the transformation of nitrogen and nitrogen-containing compounds. Nitrogen is an essential element for all living organisms because it is a key component of proteins, nucleic acids, and other biological molecules. The nitrogen cycle ensures that nitrogen is made available to living organisms in various forms.

The nitrogen cycle consists of several steps:

Nitrogen Fixation: Nitrogen gas (N2) in the atmosphere cannot be directly used by most organisms. Certain bacteria, called nitrogen-fixing bacteria, can convert atmospheric nitrogen into ammonia (NH3) or related compounds. There are two types of nitrogen fixation: biological nitrogen fixation, carried out by symbiotic and free-living bacteria, and industrial nitrogen fixation, performed through the Haber-Bosch process for the production of fertilizers.

Nitrification: Ammonia (NH3) produced by nitrogen-fixing bacteria can be further converted into nitrite (NO2-) and then nitrate (NO3-) by nitrifying bacteria. This process is known as nitrification and occurs in two stages. Ammonia-oxidizing bacteria (such as Nitrosomonas) oxidize ammonia to nitrite, and then nitrite-oxidizing bacteria (such as Nitrobacter) oxidize nitrite to nitrate.

Assimilation: Plants and other organisms take up nitrate and ammonia from the soil and use them to build organic molecules, such as proteins and nucleic acids. Animals obtain nitrogen by consuming plants or other animals.

Ammonification: Decomposers like bacteria and fungi break down organic matter (such as dead plants and animals) and animal waste, releasing ammonia back into the soil. This process is called ammonification.

Denitrification: Certain bacteria can convert nitrates and nitrites back into nitrogen gas or nitrous oxide gas (N2O), releasing it back into the atmosphere. This step completes the nitrogen cycle.
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