What is the primary role of the nitrogen cycle in ecosystems?

The primary role of the nitrogen cycle in ecosystems is to convert nitrogen from the atmosphere and other sources into forms that are usable by living organisms. Nitrogen is an essential element for all life, as it is a critical component of amino acids, proteins, and nucleic acids (DNA and RNA). However, most organisms cannot use atmospheric nitrogen (N₂) directly. The nitrogen cycle involves several key processes, including nitrogen fixation (by certain bacteria), nitrification, assimilation, ammonification, and denitrification, which work together to convert nitrogen into various chemical forms.

Through these processes, nitrogen is transformed from an inert gas into compounds like ammonia and nitrates that plants can absorb and utilize to synthesize proteins and nucleic acids. This conversion is crucial because it enables the flow of nitrogen through the food web, supporting plant growth and, in turn, the entire ecosystem, including herbivores, carnivores, and decomposers. Therefore, option B accurately describes the essence of the nitrogen cycle's role in ecosystems as it highlights the transformation of nitrogen into biologically accessible forms.