| Term | Definition |
| Nitrate | NO3- |
| Nitrite | NO2- |
| Ammonium | NH4+ |
| Ammonia | NH3 |
| Nitrification | Reaction which uses ammonium and produces nitrite |
| Denitrification | Reaction which uses nitrate and produces nitrogen gas |
| Ammonification | Reaction which uses organic nitrogen and produces ammonia |
| Nitrogen fixation | Reaction which uses nitrogen gas and produces ammonia |
| Nitrosomonas | Bacteria which allows this reaction to occur: NH4+ --> NO2- |
| Nitrobacter | Bacteria which allows this reaction to occur: NO2- --> NO3- |
| Rhizobium | Bacteria involved in nitrogen fixation |
| Organic Nitrogen | Proteins and nucleic acid |
| Assimilation | Process which allows animals to obtain nitrogen by consuming plants |
| Symbiosis | Relationship between a legume and the rhiziobium bacteria |