Final answer:
The nitrogen cycle is an example of a biogeochemical cycle through which nitrogen is recycled through the biotic and abiotic components of ecosystems. It involves processes like nitrogen fixation, decomposition, nitrification, and denitrification, with microorganisms playing a major role throughout.
Step-by-step explanation:
The nitrogen cycle is an example of a biogeochemical cycle, which is the recycling of inorganic matter between living organisms and their nonliving environment. This cycle involves multiple processes, including nitrogen fixation, decomposition, nitrification, and denitrification. Microorganisms play a major role in all of these processes.
During nitrogen fixation, nitrogen-fixing bacteria convert nitrogen gas into forms that plants can use, such as nitrates. Decomposers, on the other hand, break down dead organisms and animal wastes, releasing nutrients, including nitrogen, back into the environment.
Therefore, the correct answer is biogeochemical as option (a).