flagellum defined in 1951 yearflagellum - flagellum;
flagellum - Fine long thread (about a quarter of a micrometre thick, and up to several hundred micrometres long) having lashing or undulating movement, projecting from a cell. Has an internal structure, shown by electron microscopy, consisting of an outer membrane continuous with plasma membrane and enclosing a matrix in which eleven fibrils (microtubules) are arranged longitudinally, a central pair of single fibrils being surrounded by nine double fibrils near the periphery. Anchored in cytoplasm on cylindrical body similar in structure to centriole known variously as basal body, blepharoplast, kinetoplast, kinetosome. Some flagella may bear exceedingly fine lateral projections (mastigon-emes) along their length, or a delicate undulating membrane. Very widely distributed; characteristic of one group of unicellular organisms (Flagellata), present in most motile gametes, in zoo-spores, and in some metazoan cells, e.g. endodermal cells of Hydra. Usually only one or a few per cell, though occasionally, in some Protozoa, many. Motion of most flagella probably consists of waves which travel along them. Flagella are responsible for movement of those unicellular organisms and reproductive cells which bear them; and they move water through body of sponges. Flagella are also found in many bacteria, but are very much simpler in structure, consisting of a single fibril. See also: Choanocyte. Compare with: Cilium.
near flagellum in Knolik
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