Symbiosis in translation from Greek in biology means interaction of two or several organisms thanks to which all partners profit. Symbiosis, in fact, covers all forms of cohabitation of organisms, including also parasitism which is called antagonistic symbiosis. There are three types of symbiosis: it is parasitism, commensalism and a mutualizm.
In most cases symbiosis is mutualistichesky. At the same time cohabitation of two organisms is favorable to both, that is arises in the course of evolution and is one of types of adaptation to life conditions. Symbiosis is capable to be implemented at the monocelled level, and not just at the level of metaphytes. In symbiosis there live plants and plants, plants and animal, animal and animal, plants and animals with microorganisms, microorganisms and microorganisms. Initially the term "symbiosis" was heard from the German botanist A. de Bari in 1879 in application to lichens. In the nature there are multiple examples of the symbiotic relations thanks to which win both views. At circulation of nitrogen in the nature the symbiosis between some plants and soil bacteria is very important. Otherwise such bacteria are called nitrogen-fixing because they are located on roots of these plants and "fix" nitrogen, in other words split strong communications of atoms of free atmospheric nitrogen, providing thereby entry of nitrogen into available connections of a plant. In this case the mutually advantageous party is obviously visible: roots serve as the habitat of bacteria, and bacteria in turn supply this plant with nutrients. There are also such symbiotic relations at which it is favorable only to one look, and at cohabitation neither the harm, nor advantage is done to another. On the example of intestines of the person it is possible to see a set of species of bacteria which inhabit intestines and are absolutely harmless. Almost similar situation happens also on an example to plants some of which settle down on branches of trees, but nutrients receive from air. They use a tree only to lean on it, without depriving at the same time of nutrients. At parasitism there is such cohabitation which is favorable only to one look, but is very harmful to other symbiont. At mutually favorable cohabitation the symbiosis is called a mutualizm. At the relations useful to one, but indifferent for another, call commensalism. Amensalizm, it the relations which are indifferent for one and are harmful to another. And endosymbiosis is an accommodation of one partner in a cell of another. Simbiologiya is the science studying symbiosis.