Microorganisms (microbes) are those life forms too small to be seen by the naked eye; that is, those that require a microscope or other form of magnification in order to be observed. The term microorganism is thus a functional description rather than a taxonomic one, and the grouping includes a wide variety of organisms. The article focuses on the functional role of microbes in the biosphere and in different types of habitats - especially in terms of flow of energy and matter.