Linked from
The 14 pages that link to Bacterial flagellum, each with the reason it gives.
FlagellumBroader topic: Its rotating filament propels bacteria through liquid.
BacteriaBroader topic: It enables movement toward favorable conditions and away from harmful ones.
ChemiosmosisRelated: Some bacterial flagella use proton motive force directly to power rotation.
VibrioRelated: Many vibrios use a polar flagellum to swim through aquatic habitats.