| abiotic factor | nonliving parts of an organism's environment: air currents, temperature, moisture, light and soil are examples |
| biological community | a community made up of interacting populations in a certain area at a certain time |
| biosphere | portion of Earth that supports life; extends from high in the atmosphere to the bottom of the oceans |
| biotic factor | all the living organisms that inhabit an environment |
| commensalism | symbiotic relationship in which one species benefits and the other species is neither harmed nor benefited |
| ecology | scientific study of interactions between organisms and their environment |
| ecosystem | interactions among populations in a community: the community's physical surroundings, or abiotic factors |
| habitat | place where an organism lives out its life |
| mutualism | a symbiotic relationship in which both species benefit |
| niche | role or position a species has in its environment; includes all biotic and abiotic interactions as an animal meets its needs for survival and reproduction |
| parasitism | symbiotic relationship in which one organism benefits at the expense of another, usually another species |
| population | group of organisms all of the same species which interbreed and live in the same place at the same time |
| symbiosis | permanent, close association between two or more organisms of different species |
| autotroph | organisms that use energy from the sun or energy stored in chemical compounds to manufacture their own nutrients |
| biomass | the total mass or weight of all living matter in a given area |
| decomposer | organisms, such as fungi and bacteria, that break down and absorb nutrients from dead organisms |
| food chain | simple model that shows how matter and energy move through an eccosystem |
| food web | model that shows all the possible feeding relationships at each trophic level in a community |
| heterotroph | organisms that cannot make their own food and must feed on other organisms for energy and nutrients |
| trophic level | organism that represents a feeding step in the movement of energy and materials through an ecosystem |