Final answer:
The nitrogen cycle is a biogeochemical cycle critical for sustaining life by recycling nitrogen through ecosystems, involving processes such as nitrogen fixation, nitrification, and denitrification, carried out by various microorganisms.
Step-by-step explanation:
The nitrogen cycle is a critical biogeochemical cycle in which nitrogen is recycled through ecosystems. This cycle encompasses several steps involving the transfer and transformation of nitrogen between its various chemical forms and the biotic and abiotic components of ecosystems. The nitrogen in the atmosphere, which is not directly usable by most organisms, is converted into a usable form through a process called nitrogen fixation, conducted by microorganisms like bacteria living in the soil or in symbiosis with the roots of legumes. This fixed nitrogen is then available for uptake by plants, which use it to synthesize essential organic molecules such as proteins and nucleic acids.
When plants and animals die or excrete waste, the nitrogen within these organic materials gets released back into the soil through the process of decay. Another group of microorganisms takes over, converting these nitrogenous wastes into nitrates in a process known as nitrification, thus making nitrogen available again for plant use. Eventually, the cycle is completed by denitrification, where different types of bacteria convert nitrates back into nitrogen gas, releasing it into the atmosphere and starting the cycle anew.
This continuous cycle of nitrogen ensures that this critical element is constantly available for the growth and reproduction of living organisms and maintains the balance of ecosystems. Thus, the nitrogen cycle is integral for sustaining life on Earth, moving nitrogen through terrestrial and aquatic systems alike.