Final answer:
Nitrogen fixation is the step in the nitrogen cycle where bacteria remove nitrogen from the atmosphere and convert it into ammonia, making it available for use by plants.
Step-by-step explanation:
In the nitrogen cycle, the step that involves the removal of nitrogen from the atmosphere by bacteria is called nitrogen fixation.
During this process, nitrogen-fixing bacteria convert atmospheric nitrogen gas (N₂) into ammonia (NH₃), which can then be used by plants.
This is distinct from other processes in the cycle, such as ammonification (conversion of organic nitrogen into ammonia), nitrification (oxidation of ammonia to nitrite and then to nitrate), and denitrification (reduction of nitrate back into nitrogen gas, which is then released into the atmosphere).