Q. What is mutualism?

The Mutualism is the ecological interaction in which both participants advantage and that is obligatory for their survival.

The Mutualism is a harmonious (positive) ecological interaction. The Mutualism is as well known as symbiosis. Instance of mutualism are the association between microorganisms that digest cellulose and the ruminants or insects within which they live the lichens, formed by cyanobacteria or algae that make organic material for the fungi and absorb water with their help nitrifying bacteria of the genus Rhizobium that associated to leguminous plants offer nitrogen to these plants.