What are Protists?
Protists is a catch-all term used to describe all eukaryotic (cells with nuclei) organisms besides animals, plants, and fungi. Examples include the slime molds, water molds, the unicellular animal-like protozoa and amoeba and the plant-like protophyta. The term was abandoned as an official classification in 1990, being merged in with the fungi, plants, and animals to create the Eukarya “domain” of life, but it is still used frequently among biologists. The purpose of lumping in protists with the Eukarya domain is to emphasize that the differences between plants, animals, fungi, and protists is much less than the difference between the eukaryotes and the bacteria and archaebacteria. The term “protist” derives from the Greek protiston, meaning the “first of all ones.” Individual protists tend to be quite small, either unicellular or an undifferentiated multicellular mass. At one point, “Protista” encompassed everything that wasn’t an animal or plant, until the advent of cellular biology
Protists are microscopical, unicellular eukaryotes. They generally live in water. In some cases, protists form colonies of individuals, though the individuals are generally autonomous. Historically, researchers referred these minuscule living beings to the kingdoms of larger organisms. Then, according to the characteristics that a given protist showed, they tried to refer it to the plant kingdom (in the protophyta or algae), the animal kingdom (in the protozoa) or to the fungal kingdom. This led to a great deal of doubtful classification, for example “algae” deprived of chloroplasts and which fed on other microorganisms, “moulds” endowed with amoeboid movements like animals, or “protozoans” anchored to the substratum by a foot like they were a plant. Intuitively, it is possible to understand why protists often possess characteristics common to animals, plants and fungi: the larger organisms derive from protists. In order to avoid confusion in the classification of these microorganisms,
Most of the research in our laboratory focuses on the biology and ecology of Protists. This term refers to eukaryotic organisms that are capable of existence as single cells, and therefore are structurally more complex than bacteria and archaea. Although they have much in common with the cells of multicellular species, protists are separated functionally (although not necessarily evolutionarily) from large organisms by their ability to exist as single cells. The older terms microalgae and protozoa are often still used to refer to these species.
• They are eukaryotes because they all have a nucleus. • Most have mitochondria although some have later lost theirs (Link). Mitochondria were derived from aerobic alpha-proteobacteria that once lived within their cells. • Many have chloroplasts with which they carry on photosynthesis. Chloroplasts were derived from photosynthetic cyanobacteria living within their cells. Link to a discussion of the “endosymbiosis” theory of the origin of eukaryotes. • Many are unicellular and all groups (with one exception) contain some unicellular members. • The name Protista means “the very first”, and some of the 80-odd groups of organisms that we classify as protists may well have had long, independent evolutionary histories stretching as far back as 2 billion years. But genome analysis added to other criteria show that others are derived from more complex ancestors; that is, are not “primitive” at all. • Genome analysis also shows that many of the groups placed in the Protista are not at all close
