Nitrogen fixation is the process by which molecular nitrogen ($N_2$) in the atmosphere is converted into ammonia ($NH_3$) or related nitrogenous compounds in soil. This process is essential for making nitrogen available to living organisms.
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Nitrogen fixation can occur abiotically through industrial processes like the Haber-Bosch process, or biologically via microorganisms such as Rhizobium bacteria.
Biological nitrogen fixation typically involves the enzyme nitrogenase, which catalyzes the conversion of $N_2$ to ammonia ($NH_3$).
Plants cannot directly use atmospheric $N_2$, so nitrogen fixation is crucial for converting it into forms they can assimilate, such as nitrates and ammonium ions.
Leguminous plants have symbiotic relationships with nitrogen-fixing bacteria in root nodules, facilitating nutrient uptake.
Fixed nitrogen compounds are vital components of amino acids, nucleic acids, and chlorophyll.
Review Questions
What role does the enzyme nitrogenase play in biological nitrogen fixation?
How do leguminous plants benefit from their relationship with Rhizobium bacteria?
Explain why nitrogen fixation is essential for plant growth.