Ecology studies the relationships between living organisms and their physical environment. Ecology considers organisms at the individual, population, community, and ecosystem levels.

You shouldn't be asked to define this, but it is worth understanding.

A habitat is the place where an organisms lives.

A population refers to all of the organisms of a particular species that live in the same habitat.

A community refers to all the populations of different species that live together in a habitat.

An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.

Competition is an interaction between two or more organisms or species in which they all try to use the same limited resources.

Interdependence is the idea that all organisms in an ecosystem depend upon one another, and there are countless complex relationships between them.

If one species is removed, it can affect the whole ecosystem.

A stable community is one where all the species and environmental factors are in balance so that population sizes remain relatively constant.