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A prokaryote (/ p r oʊ ˈ k ær i oʊ t,-ə t /; less commonly spelled procaryote) [1] is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles. [2] The word prokaryote comes from the Ancient Greek πρό (pró), meaning 'before', and κάρυον (káruon), meaning 'nut' or 'kernel'. [3]
Many protist species can switch between asexual reproduction and sexual reproduction involving meiosis and fertilization. [6] In contrast to the cells of prokaryotes, the cells of eukaryotes are highly organised. Plants, animals and fungi are usually multi-celled and are typically macroscopic. Most protists are single-celled and microscopic.
Prokaryotes play important roles in ecosystems as decomposers recycling nutrients. Some prokaryotes are pathogenic, causing disease and even death in plants and animals. [5] Marine prokaryotes are responsible for significant levels of the photosynthesis that occurs in the ocean, as well as significant cycling of carbon and other nutrients. [6]
The cryptomonads (>100 species), also known as cryptophytes, are flagellated algae found in aquatic habitats of diverse salinity, characterized by extrusive organelles or extrusomes called ejectisomes. Their chloroplasts, of red algal origin, contain a nucleomorph, a remnant of the eukaryotic nucleus belonging to the endosymbiotic red alga. [86]
Systematists today do not treat Protista as a formal taxon, but the term "protist" is still commonly used for convenience in two ways. [22] The most popular contemporary definition is a phylogenetic one, that identifies a paraphyletic group: [23] a protist is any eukaryote that is not an animal, (land) plant, or (true) fungus; this definition [24] excludes many unicellular groups, like the ...
Prokaryotes are single-celled organisms such as bacteria, whereas eukaryotes can be either single-celled, such as amoebae, or multicellular, such as some algae, plants, animals, and fungi. Eukaryotic cells contain organelles including mitochondria, which provide energy for cell functions; chloroplasts, which create sugars by photosynthesis, in ...
[1] [2] Historically, protozoans were regarded as "one-celled animals". When first introduced by Georg Goldfuss , in 1818, the taxon Protozoa was erected as a class within the Animalia, [ 3 ] with the word 'protozoa' meaning "first animals", because they often possess animal -like behaviours, such as motility and predation , and lack a cell ...
The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. DNA-bearing organelles like mitochondria and chloroplasts are remnants of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, where at least part of the rest of the cell may have been derived from an ancestral archaean prokaryote ...