| Term | Definition |
| parasitism | a symbiotic relationship that benefits the parasite but harms the parasite's partner |
| population | organisms of one species that live in the same place at the same time and that can produce offspring |
| population density | the number of individuals per unit of living space |
| predation | the feeding of one organism on another organism |
| symbiosis | a close relationship between two organisms that live together |
| water cycle | the continuous movement of water in the biosphere through evaporation, condensation and precipitation |