SYMBIOSIS
The term symbiosis (from the Greek: σύν syn "with"; and βίωσις biosis "living") commonly describes close and often long-term interactions between different biological species. The term was first used in 1879 by the German mycologist, Heinrich Anton de Bary, who defined it as: "the living together of unlike organisms
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 natureOthers define it more narrowly, as only those relationships from which both organisms benefit, in which case it would be synonymous with mutualismSymbiotic relationships included those associations in which one organisms lives on another (ectosymbiosis, such as mistletoe), or where one partner lives inside another (endosymbiosis, such as lactobacilli and other bacteria in humans or zooxanthelles in corals). Symbiotic relationships may be either obligate, i.e., necessary to the survival of at least one of the organisms involved, or facultative, where the relationship is beneficial but not essential to survival of the organisms
Endosymbiosis is any symbiotic relationship in which the symbiote lives within the tissues of the host; either in the intracellular space or extracellularlyExamples are nitrogen-fixing bacteria (called rhizobia) which live in root nodules on legume roots, Actinomycete nitrogen-bacteria called Frankia which live in Alder tree root nodules, single-celled algae inside reef-building corals, and bacterial endosymbionts that provide essential nutrients to about 10%–15% of insects.
Ectosymbiosis, also referred to as exosymbiosis, is any symbiotic relationship in which the symbiont lives on the body surface of the host, including the inner surface of the digestive tract or the ducts of exocrine glands Examples of this include ectoparasite such as lice, commensal ectosymbionts, such as the barnacles that attach themselves to the jaw of baleen whales, and mutualist ectosymbionts such as cleaner fish.
