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Protists are distributed across all major groups of eukaryotes, including those that contain multicellular algae, green plants, animals, and fungi. If photosynthetic and fungal protists are distinguished from protozoa, they appear as shown in the phylogenetic tree of eukaryotic groups.
A protist (/ ˈ p r oʊ t ɪ s t /) is any eukaryotic organism (one with cells containing a nucleus) that is not an animal, plant, or fungus.The protists do not form a natural group, or clade, since they exclude certain eukaryotes with whom they share a common ancestor; [a] but, like algae or invertebrates, the grouping is used for convenience.
Protozoans are protists which feed on organic matter such as other microorganisms or organic tissues and debris. [87] [88] Historically, the protozoa were regarded as "one-celled animals", because they often possess animal-like behaviours, such as motility and predation, and lack a cell wall, as found in plants and many algae.
A protist (/ ˈ p r oʊ t ɪ s t / PROH-tist) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus.Protists do not form a natural group, or clade, but are a polyphyletic grouping of several independent clades that evolved from the last eukaryotic common ancestor.
Its field of study therefore overlaps with the more traditional disciplines of phycology, mycology, and protozoology, just as protists embrace mostly unicellular organisms described as algae, some organisms regarded previously as primitive fungi, and protozoa ("animal" motile protists lacking chloroplasts).
Some protozoa are photoautotrophic protists. These protists include strict aerobes, and use photosystems I and II in order to carry out photosynthesis which produces oxygen. [1] Diagram of Plasmodium structure. Mixotrophic protists obtain nutrients through organic and inorganic carbon compounds simultaneously. [1] All cells have a plasma membrane.
Ciliate species range in size from as little as 10 μm in some colpodeans to as much as 4 mm in length in some geleiids, and include some of the most morphologically complex protozoans. [4] [5] In most systems of taxonomy, "Ciliophora" is ranked as a phylum [6] under any of several kingdoms, including Chromista, [7] Protista [8] or Protozoa. [9]
The initial targets of Cavalier-Smith's classification, the protozoa were classified as members of the animal kingdom, [12] and many algae were regarded as part of the plant kingdom. With growing awareness that the animals and plants embraced unrelated taxa, the use of the two kingdom system was rejected by specialists.