| 1. | Aerobic nitrate oxidation, and nitrite reduction |
| 2. | Decomposition of organic nitrogen, and conversion of dinitrogen to ammonium compounds |
| 3. | Enteric fermentation in cattle, and nitrogen fixation by Rhizobium in root nodules of legumes |
| 4. | Anaerobic ammonium oxidation, and denitrification |
| 1. | 4 ATP for each NH3 produced |
| 2. | 8 ATP for each NH3 produced |
| 3. | 12 ATP for each NH3 produced |
| 4. | 16 ATP for each NH3 produced |