Symbiosis - Lesson 53
Symbiosis refers to the living together in close association of two organisms, either for mutual benefit or not. The bacteria that normally live in the digestive tract of humans are an example of symbiosis. Parasitism is an example of symbiosis in which, one organism benefits and the other does not. The definition of symbiosis is in flux, and the term has been applied to a wide range of biological interactions. The symbiotic relationship may be categorized as being mutualistic, parasitic, or commensal in nature. Others define it more narrowly, as only those relationships from which both organisms benefit, in which case it would be synonymous with mutualism. Symbiotic relationships included those associations in which one organisms lives on another (ectosymbiosis, such as mistletoe), or where one partner lives inside the other (endosymbiosis, such as lactobacilli and other bacteria in humans or zooxanthelles in corals). Symbiotic relationships may be either obligat