It begins with nitrogen fixation, where atmospheric nitrogen (N₂) is converted into ammonia (NH₃) by bacteria or through industrial processes. This ammonia is then transformed into nitrates (NO₃⁻) via nitrification by soil bacteria, making it accessible to plants, which absorb and incorporate it into organic molecules. Animals then obtain nitrogen by consuming plants. When plants and animals die or excrete waste, decomposition (ammonification) converts organic nitrogen back into ammonia. Finally, denitrifying bacteria convert nitrates back to nitrogen gas (N₂), releasing it into the atmosphere and completing the cycle.