Flagella help cellular bodies, such as sperm and bacteria, move through liquid. Flagella, like cilia, are composed of microtubules that are connected to the plasma membrane.
The microtubules in a flagellum are grouped into nine pairs surrounding a pair of microtubules. The motion of flagella is a result of the microtubules sliding against each other. The filament, located at the end of the flagellum, is attached to the hook and is composed of flagellin. The movement of the filament depends on the movement of the motor that is connected to the hook. The basal body or motor, which is produced by centrioles, can move as fast as 300 revolutions per second.
In bacteria, the flagellum allows the bacterial body to move up or down in a straight line and change direction. The basal body that attaches to the cellular body affects the arrangement of the structure of the filament. The filament is helical-shaped, but the flagellin proteins rearrange themselves if torque from the motor is applied or removed. Some cellular bodies with flagella are able to move through tissue, creating problems for the lymph or circulatory system. Flagella are often found singly or in small numbers, whereas many cilia are found together.