Flagella and Cilia



Flagella are necessary for the active movement of bacterial cells and protozoa. Flagella are single, whip-like structures that propel an organism through an aquatic environment. They use undulatory motions, where the waves of motion start at the base of the flagellum. The size, the volume of the medium, the length, position and width of the flagella on the organism determine the direction and speed propulsion of the cell. There are three different types of flagella movement. They are either planar, oarlike beating, or three dimensional waves.

In the three dimensional wave movement, the flagella whips back and forth. As a result, the organism moves forward in the direction of the flagellum.

The planar waves are mostly asymmetrical, and are on a single plane. The planar waves make the protozoan rotate on it?s longitudinal axis. The direction of movement is opposite of the direction of the wave.

The oarlike flagellar movement is the same as planer, but the waves are often very asymmetrical, and have more side to side swing. Also, the protozoan usually rotates and moves with the flagellum from the front end.


Cilia are tiny hairlike appendices that swim or beat individually or in large fields. They work like flexible oars. The movement of each cilia must be closely coordinated with all of the other cilia. This is called metachronal rhythm, which is a wave of simultaneously beating groups of cilia moving from the anterior to posterior end of the organism and is responsible for the transport of objects and materials.

Cilia play an important role in nearly all life functions in most species in the animal kingdom, including humans. Some of which are, feeding, reproduction, sensing, swimming, and transportation. Since they are so important, there has been a great deal of research done on them. Hancock made the first theoretical breakthrough in the mid-50?s, although cilia have been known about for 250 years.

Both flagella and cilia move because of a set of microtubles which contain an inner cylindrical body known as the axoneme and an outer membrane. The membrane of the flagellum or cilia contain mastigonemes, tiny scales or hairs on the surface, which increase propulsive force.

Flagella and cilia both are important in our everyday lives. They are in many living organisms. They are similar in structure, with only a few minor differences.