Cilia vs. Flagella

Cilia and flagella are both structures on the outside of a cell that contribute either to the movement of the cell or to the movement of fluids outside the cell. Cilia has a short, hair-like appearance and is numerous in number on the cell. Flagella is long and looks like a whip. It is generally few in number on the outside of the cell. Despite their different appearances, they have a common ultrastructure.

The ultrastructure of cilia and flagella can only be seen through a high-powered electron microscope. The structure is composed of microtubules and dynein (a motor protein). There are tunnel-like structures running through the shaft of the cilia or flagella called doublets. Each cilia or flagella has nine doublets in a ring formation on the outside of the flagella, and a pair in the middle. The doublets are connected by dynein, which move and cause the cilia or flagella to bend or flex, which in turn causes the movement of the whole structure. A basal body anchors the cilia or flagella to the cell or structure. A third outer doublet functions to hold the pieces together.