<P> Unicellular eukaryotes usually reproduce asexually by mitosis under favorable conditions . However, under stressful conditions such as nutrient limitations and other conditions associated with DNA damage, they tend to reproduce sexually by meiosis and syngamy . </P> <P> Of eukaryotic groups, the protists are most commonly unicellular and microscopic . This is a highly diverse group of organisms that are not easy to classify . Several algae species are multicellular protists, and slime molds have unique life cycles that involve switching between unicellular, colonial, and multicellular forms . The number of species of protists is unknown since only a small proportion has been identified . Protist diversity is high in oceans, deep sea - vents, river sediment and an acidic river, suggesting that many eukaryotic microbial communities may yet be discovered . </P> <P> The fungi have several unicellular species, such as baker's yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe). Some fungi, such as the pathogenic yeast Candida albicans, can undergo phenotypic switching and grow as single cells in some environments, and filamentous hyphae in others . </P> <P> The green algae are a large group of photosynthetic eukaryotes that include many microscopic organisms . Although some green algae are classified as protists, others such as charophyta are classified with embryophyte plants, which are the most familiar group of land plants . Algae can grow as single cells, or in long chains of cells . The green algae include unicellular and colonial flagellates, usually but not always with two flagella per cell, as well as various colonial, coccoid, and filamentous forms . In the Charales, which are the algae most closely related to higher plants, cells differentiate into several distinct tissues within the organism . There are about 6000 species of green algae . </P>

The scientific name of a microorganism is a combination of the