What biogeochemical cycle involves the transformations of nitrogen through fixation, nitrification, assimilation, and denitrification?

What biogeochemical cycle involves the transformations of nitrogen through fixation, nitrification, assimilation, and denitrification?

• A. Oxygen Cycle
• B. Carbon Cycle
• C. Sulfur Cycle
• D. Nitrogen Cycle

Answer: (D)

Nitrogen moves through air, water, soil, and living organisms via a set of microbial and plant processes: fixation, nitrification, assimilation, and denitrification. In fixation, specialized microbes convert inert N2 gas into forms that organisms can use, such as ammonium or nitrate. Nitrification then oxidizes ammonium first to nitrite and then to nitrate, making nitrogen available in a form that plants and algae can take up. Assimilation is the uptake of these usable nitrogen forms by plants and microorganisms to build organic molecules like amino acids and nucleotides. Finally, denitrification reduces nitrate back to gaseous N2, returning nitrogen to the atmosphere and completing the cycle. This sequence is specific to nitrogen and explains how nitrogen is made available to living things and then recycled, linking the atmosphere, oceans, and biosphere. Other cycles involve different processes and elements (for example, the oxygen cycle focuses on O2, the carbon cycle on carbon compounds, and the sulfur cycle on sulfur species), but they do not include this exact series of nitrogen transformations.

Nitrogen moves through air, water, soil, and living organisms via a set of microbial and plant processes: fixation, nitrification, assimilation, and denitrification. In fixation, specialized microbes convert inert N2 gas into forms that organisms can use, such as ammonium or nitrate. Nitrification then oxidizes ammonium first to nitrite and then to nitrate, making nitrogen available in a form that plants and algae can take up. Assimilation is the uptake of these usable nitrogen forms by plants and microorganisms to build organic molecules like amino acids and nucleotides. Finally, denitrification reduces nitrate back to gaseous N2, returning nitrogen to the atmosphere and completing the cycle. This sequence is specific to nitrogen and explains how nitrogen is made available to living things and then recycled, linking the atmosphere, oceans, and biosphere. Other cycles involve different processes and elements (for example, the oxygen cycle focuses on O2, the carbon cycle on carbon compounds, and the sulfur cycle on sulfur species), but they do not include this exact series of nitrogen transformations.