Biospheres
The part of earth and it's atmosphere that can support life.
Biomes
These are large geographical areas that are classified by climate (rainfall and temperature ranges) and the plant and animal life that live there; can be aquatic (water) biomes and terrestrial (land) biomes.
Ecosystems
An ecosystem is the smallest level that has both living (biotic) and non living (abiotic) things in a defined area.
The size of an ecosystem does not matter as long as it has both the living and non living things in it. An ecosystem can be the pond in your back yard (fish, water), a forest (plants, air), or even the millions of bacteria that are growing in that last sip of coke you did not finish yesterday (coke, bacteria).
Communities
Communities are the living things that are found in a given ecosystem. All types of interactions occur between the different species in a community. For example; wolves eat deer which nourish the wolf and the wolf droppings nourish the grass that feeds the deer.
Populations
Populations are a group of the same species that live in a community.
Species
A species is one specific kind of organism. Organisms within a species can mate and successfully reproduce with each other.