2.3.18 (HL)—Bacterial roles in nitrogen cycle

Fixation makes ammonia from N₂; nitrification makes nitrate from ammonia; denitrification returns N₂ from nitrate; ammonification makes ammonium from organic nitrogen.

Name the starting and ending chemical forms before choosing the process. Microbes control access to nitrogen by changing form, not by creating atoms.

Nitrate in water becomes atmospheric N₂ under anoxic denitrification; dead protein becoming ammonium is ammonification.

Nitrification; it is oxidation through nitrite to nitrate.

Do not use ‘fixation’ for every nitrogen change; fixation specifically starts with atmospheric N₂.