Long hair-like protoplasmic structures or extensions (actually organelles or rather microtubules)) composed of helically-coiled protein units that form the basal body of the cytoplasm of cells, and which enable cell locomotion (e.g., of spermatozoa) through a liquid medium by means of having a whip-like motility driven by the protein dyne in. They have the same basic structure as cilia, but are longer in proportion to the cell bearing them, as well as being present in much smaller numbers. There are three types of flagella: bacterial flagella (that rotate like screws), arc heal (prokaryote) flagella, and eukaryotic flagella of animals and plants. The only commonalities between these different forms of flagella are that they adhere to the outside of a cell, and move to produce propulsion. Other than that, their structures are quite different. Both eukaryote cells and bacteria can move by means of flagella. The eukaryote flagellum, however, is markedly different in structure from that of a bacterium, thus leading some to name them ‘aaundulipodium’. It is a bundle of nine pairs of microtubules surrounding a central pair (the so-called 9+2 structure).
See Acrosome, Cell locomotion, Cell migration, Cilia, Cytoplasm, Cytoskeleton, Eurkaryote cell (or organism), Filopodia, Lamillipodia, Microtubules, Organelles, Prokaryote cell (or organism)