Mutualism, Parasites and Commensalism
Cannot produce their own food
They must eat other organisms for nutrients and for energy
When two organisms live together in close proximity and both benefit from the relationship.For example, a clowfish and anemone, red cod and shirmp, leguminous plants and nitrogen.
Some organisms feed on other bodies and blood supply without providing anything in return.These parasites may cause disease or threaten a organisms nutrion by destroying other food sources or stealling the nutrients from the host organism.
A parasite can't survive without its host. As a host organism evolved, the parasites own evolution must have been closely linked so it can survive any environmental change.