These molecular motors are powered by the phosporylation cascade responsible for generating energy within the cell. In action, the filament rotates at speeds from 200 to more than 1,000 revolutions per second, driving the rotation of the flagellum. The organization of these structures is quite different from that of eukaryotic flagella. The direction of rotation determines the movement of the cell. Anticlockwise rotation of monotrichious polar flagella thrusts the cell forward with the flagellum trailing behind.
Peritrichous cells operate in the same way.
When anticlockwise rotation is resumed, the cell moves off in a new direction. This ability is important, since it allows bacteria to change direction. Bacteria can sense nutrient molecules such as sugars or amino acids and move towards them - a process is known as chemotaxis. Additionally, they can also move away from harmful substances such as waste products and in response to temperature, light, gravity, etc. This apparently intelligent behavior is achieved by changes in the frequency of tumbles.