What is nitrogen cycle?

What is nitrogen cycle?

• A. The series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms, including nitrogen fixation and decomposition
• B. The transfer of nitrogen from the atmosphere to the soil, to living organisms, and back to the atmosphere
• C. A cycle of nitrogen that occurs only in plants
• D. The cycle of nitrogen that exists only in water

Answer: (A)

Understanding how nitrogen moves and changes form in ecosystems is what this item tests. Nitrogen exists mainly as N2 gas in the atmosphere, which most organisms cannot use directly. The cycle involves converting nitrogen into usable forms (like ammonium and nitrate) and then back into inert forms, through processes such as nitrogen fixation, ammonification, nitrification, and denitrification, all across air, soil, water, and living organisms. This interconnected set of transformations is what drives the nitrogen cycle. The best statement captures that wide, interlinked set of changes across environments and organisms, mentioning nitrogen fixation and decomposition as examples of those transformations. The other options describe parts of the idea or inaccurately confine it (to plants only or to water only), which misses the full, ecosystem-wide nature of the cycle.

Understanding how nitrogen moves and changes form in ecosystems is what this item tests. Nitrogen exists mainly as N2 gas in the atmosphere, which most organisms cannot use directly. The cycle involves converting nitrogen into usable forms (like ammonium and nitrate) and then back into inert forms, through processes such as nitrogen fixation, ammonification, nitrification, and denitrification, all across air, soil, water, and living organisms. This interconnected set of transformations is what drives the nitrogen cycle.

The best statement captures that wide, interlinked set of changes across environments and organisms, mentioning nitrogen fixation and decomposition as examples of those transformations. The other options describe parts of the idea or inaccurately confine it (to plants only or to water only), which misses the full, ecosystem-wide nature of the cycle.