Nitrogen is an essential element for all living organisms, and it moves through living systems in a process called the nitrogen cycle. In the atmosphere, nitrogen exists as diatomic nitrogen gas (N2), which is inert and cannot be used by most organisms. The first step in the nitrogen cycle is nitrogen fixation, where nitrogen gas is converted into a form that can be used by plants and other organisms. This can be done by certain bacteria, such as Rhizobium, which live in a mutualistic relationship with leguminous plants, or by lightning during thunderstorms.
Once nitrogen is fixed, it can be taken up by plants through their roots and used to make proteins and nucleic acids. These plants are then consumed by herbivores, which in turn are consumed by carnivores, creating a flow of nitrogen through the food chain. When plants and animals die, decomposers such as bacteria and fungi break down their bodies, releasing nitrogen back into the soil in the form of ammonium (NH4+). This process is called ammonification.
In the soil, some of the ammonium is converted into nitrate (NO3-) by nitrifying bacteria. This nitrate can be taken up by plants and used to make more proteins. Some of the nitrate may also be denitrified by denitrifying bacteria, which convert it back into nitrogen gas and release it back into the atmosphere. This completes the nitrogen cycle, with nitrogen moving between the atmosphere, soil, plants, animals, and decomposers in a continuous loop.
Describe how nitrogen is cycled throughout living systems and the atmosphere. Your response should include the role of decomposers, producers, and consumers.
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