Protists are single-celledeukaryotes (which areorganisms with anucleus). The termProtista was first used byErnst Haeckel in 1866.[1] The protists are not a natural group, orclade, since they have no common origin. Likealgae orinvertebrates, they are often grouped together for convenience.
Most protists are very small. They are made up ofone or a fewcells at most – they aremicroscopic and usually invisible to thenaked eye. Somealgae are protists, if they are single-celled. Many protists are part of theplankton and are very important for theecosystem. The cells found in protists may be extremely complex, and are often little understood. It is now possible to doDNA sequencing, and a number of protists have been analysed. The results show that the Protista is not amonophyletic group. It isparaphyletic, and not a singleclade. The taxonomy of the Protista is therefore rather confused.
An example of a single celled organism in the protist kingdom is theParamecium or "slipper animalcule." TheParamecium moves using its small, hair-likefibers calledcilia, and eats using the cilia to sweep the food into its foodvacuole. Other protists can beamoebas, which move by extendingpseudopods and flowing into them, or flowing around food particles and engulfing them.
Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes
Protists are not amonophyleticclade. The term is a convenient holdall for about 20 different kinds of single-celledeukaryotes.[2] They differ in their cellorganelles, specialised units which carry out well-defined functions, likemitochondria andplastids. This proves they have made the transition fromprokaryotes in different ways. It is fairly clear now that all or most of these organelles have their origin in once-independent prokaryotes (bacteria orarchaea), and that the eukaryote cell is a 'community of micro-organisms' working together in 'a marriage of convenience'.[3][4][5][6] Admittedly, the Protista is a collection of disparate single-celled forms, but while a more sophisticated taxonomy is in flux (changing), Protista is still a useful term.
↑Haeckel, E. Das Protistenreich. Leipzig, 1878.[1]
↑Schaechter M. 2012.Eukaryotic microbes. Amsterdam, Academic Press.
↑Margulis L. and McMenamin 1990. Marriage of convenience.The Sciences30, 31-36.
↑Margulis L & Dolan M.F. 2002.Early life: evolution on the Precambrian Earth. 2nd ed, Jones & Bartlett, Boston. p89
↑Margulis L. Schwartz K.V. & Dolan M. 1999.Diversity of life: the illustrated guide to the five kingdoms. Jones & Bartlett, Boston, p94. In this work the authors propose 19 phyla for the Protista, and call this 'Kingdom' the 'Protoctista', a term which is unfortunately almost unpronounceable.
↑Dyer B.D. and Obar R.A. 1994.Tracing the history of eukaryotic cells. Columbia N.Y.
