| Term | Definition |
| carbon dioxide-oxygen cycle | process by which carbon and oxygen are exchanged among plants, animals, & the environment |
| respiration | the process of breathing in air to get oxygen and breathing out carbon dioxide gas |
| photosynthesis | the process of a plant making food in which oxygen gas is released as a waste product |
| nitrogen cycle | cycle in which nitrogen gas is "fixed" or changed into forms of nitrogen for plants to use |
| nitrates | nitrogen that has been "fixed" or changed and is in the soil to be used |
| nodules | bumps on some roots of plants that take in nitrates form the soil |
| water cycle | the cycle in which Earth's water moves through the environment |
| evaporation | process in which a liquid changes to a gas |
| condensation | process in which a gas changes to a liquid |
| precipitation | any form of water that falls from the sky |
| transpiration | the release of water vapor into the air from a plant's leaves as a waste product of photosynthesis |
| run-off | when water flows down Earth's surface |
| groundwater | accumulation of water that has seeped into the ground |