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A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea
For much of the 20th century, prokaryotes were regarded as a single group of organisms and classified based on their biochemistry, morphology and metabolism. Microbiologists tried to classify microorganisms based on the structures of their cell walls, their shapes, and the substances they consume. [11]
Valonia ventricosa is among the largest known single-celled organisms. Its thallus consists of a thin-walled, tough, multinucleate cell with a diameter that ranges typically from 1 to 4 centimetres (0.4 to 1.6 in), although it may achieve a diameter of up to 5.1 centimetres (2.0 in) in rarer cases.
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 ]
Gromia sphaerica is a large spherical testate amoeba, a single-celled eukaryotic organism and the largest of its genus, Gromia.The genus itself contains about 13 known species, 3 of which were discovered as late as 2005. [1]
Kandler's pre-cell theory is supported by Wächtershäuser. [65] [66] In 1998, Carl Woese, based on the RNA world concept, proposed that no individual organism could be considered a LUCA, and that the genetic heritage of all modern organisms derived through horizontal gene transfer among an ancient community of organisms. [67]
Euglenids or euglenoids are one of the best-known groups of eukaryotic flagellates: single-celled organisms with flagella, or whip-like tails.They are classified in the phylum Euglenophyta, class Euglenida or Euglenoidea.
Caulerpa species support their large cell size by having the cytoplasm circulate constantly, supported by a network of microtubules. This behavior was known in 1967. [10] The cytoplasm does not leak out when the cell is cut. Regeneration is directional, with rhizoids at the bottom and fronds at the top. [11]