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A flagellum (; plural: ''flagella'') is a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells. The word ''flagellum'' in Latin means whip. The primary role of the flagellum is locomotion but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. Flagella are organelles defined by function rather than structure. There are large differences between different types of flagella; the prokaryotic and eukaryotic flagella differ greatly in protein composition, structure, and mechanism of propulsion. However, both can be used for swimming. An example of a flagellate bacterium is the ulcer-causing ''Helicobacter pylori'', which uses multiple flagella to propel itself through the mucus lining to reach the stomach epithelium. An example of a eukaryotic flagellate cell is the mammalian sperm cell, which uses its flagellum to propel itself through the female reproductive tract. Eukaryotic flagella are structurally identical to eukaryotic cilia, although distinctions are sometimes made according to function and/or length. == Types == Three types of flagella have so far been distinguished; bacterial, archaeal and eukaryotic. The main differences among these three types are summarized below: * Bacterial flagella are helical filaments, each with a rotary motor at its base which can turn clockwise or counterclockwise. They provide two of several kinds of bacterial motility. * Archaeal flagella (Archaella) are superficially similar to bacterial flagella, but are different in many details and considered non-homologous. * Eukaryotic flagella—those of animal, plant, and protist cells—are complex cellular projections that lash back and forth. Eukaryotic flagella are classed along with eukaryotic ''motile'' cilia as ''undulipodia''〔 (A Dictionary of Biology ), 2004, accessed 2011-01-01.〕 to emphasize their distinctive wavy appendage role in cellular function or motility. ''Primary'' cilia are immotile, and are not undulipodia; they have a structurally different ''9+0 axoneme'' rather than the ''9+2 axoneme'' found in both flagella and motile cilia undulipodia. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Flagellum」の詳細全文を読む スポンサード リンク
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