Cilia and flagella are one of the most important parts of the cell. They are fine, hair-like protoplasmic processes of the cells which are similar to each other in structure. They are present in some motile cells. Both of them are the organs of locomotion in the cell. Flagella are longer than cilia and cilia are found more in number than flagella in a cell.
A flagellum is about 100 to 200 µm long. Only one to four flagella occur per cell. Many members of kingdom protista, motile algae, sperms of animals, bryophytes, pteridophytes, zoospore and motile gametes of algae etc. contain flagella in them.
Cilia are smaller parts of cells which are about 5 to 20 µm long and are present in high number. Ciliata of protozoa, flame cells of flatworms, larval bodies of many invertebrates, epithelium of respiratory tract, renal tubules, oviductal funnel etc. contain cilia.
Both cilia and flagella are made up of microtubules running longitudinally along its length which are covered by membrane extensions of plasma membrane.