| Term | Definition |
| Biosphere | Consists of all the environments on Earth that are inhabited by life. |
| Ecosystem | Consists of all the living things in a particular area, along with all the nonliving components of the environment with which life interacts. |
| Community | The entire array of organisms inhabiting a particular ecosystem. |
| Population | Consists of all the individuals of a species living within the bounds of a specified area. |
| Organism | Individual living things. |
| Organ and Organ System | A body part consisting of two or more tissue. |
| Tissue | A group of similar cells. |
| Cell | Life's fundamental unit of structure and function. |
| Organelle | The various functional components that make up cells. |
| Molecule | A chemical structure consisting of two or more small chemical units called atoms. |