1. Moving along the food chain and excretion
2. Excretion of urea releases nitrogenous compounds into soil
3. Bacteria in soil make an enzyme called urease which converts this urea into ammonia
4. Nitrifying bacteria convert ammonia into nitrates which plants can absorb
5. Death of animals, Decomposers break down protein in dead bodies of animals and plants, converting it into ammonia
6. Nitrifying bacteria then convert ammonia into nitrite, and then nitrates
7. Denitrifying bacteria in soil break down nitrates and return nitrogen gas to air, occurs in anaerobic conditions