Which option correctly pairs a process with its cycle?

• A. Photosynthesis with the nitrogen cycle
• B. Respiration with the carbon cycle
• C. Nitrogen fixation with the nitrogen cycle
• D. Decomposition with the water cycle

Answer: (C)

Biogeochemical cycles describe how elements move through living things and the environment, and each cycle has processes that define it. Nitrogen fixation is the conversion of atmospheric nitrogen (N2) into ammonia or other usable forms, a key step in the nitrogen cycle that makes nitrogen available to organisms. Because of that specific role, pairing nitrogen fixation with the nitrogen cycle is the best match.

The other options lean toward the carbon cycle rather than nitrogen: photosynthesis uses light to convert CO2 into organic matter, tying to carbon flow; respiration releases CO2 as organisms metabolize, also part of carbon cycling; decomposition recycles carbon and other nutrients within ecosystems. The water cycle is driven mainly by physical processes like evaporation and precipitation rather than nitrogen-transforming biology, so linking decomposition to the water cycle isn’t fitting.