Bacterial Flagella are single stranded quite similar to micro tubular fibre. They are 7 um in length and 0.02 um in diameter. Basal body, hook and filament constitute the bacterial flagellum. Basal body is rod like structure which has ring like swellings.
A gram negative bacterium has two pair of rings. One is present in cell wall and other is present in cell membrane. While Gram positive bacteria has one pair of rings. They are present in cell membrane. Hook is the curved part which connects filament with basal body. Filament is the long structure which causes turbulence in the water. It is made up of flagellin.
Some authors believe that bacterial flagella causes rotational movement which brings backward movement of water.
