Which term describes the movement of nitrogen through living systems and the environment?

• A. Carbon Cycle
• B. Nitrogen Fixation
• C. Nitrifying Bacteria
• D. Nitrogen Cycle

Answer: (D)

The movement of nitrogen through living systems and the environment is described by the nitrogen cycle. This cycle shows how nitrogen travels among the atmosphere, soil, water, and organisms, changing forms along the way—from N2 gas in the air to ammonia, nitrite, nitrate, and organic nitrogen, and back to gaseous N2. Key steps include nitrogen fixation, where bacteria capture atmospheric nitrogen into usable forms; nitrification, where ammonia is converted to nitrite and then nitrate by nitrifying bacteria; assimilation, where plants take up nitrates; ammonification, where decomposers return organic nitrogen to ammonium; and denitrification, where some nitrogen returns to N2 gas. The carbon cycle is a separate cycle, while nitrogen fixation is just one process within the broader nitrogen cycle, and nitrifying bacteria are organisms that drive part of the cycle.