Cilia and flagella are projections from the cell. They are made up of micro-tubules, and are covered by an extension of the plasma membrane. These are the cell organelles present external to cell membrane and are absent in plant cells.
Cilia are outgrowths of plasma membrane of eukaryotic cells that contain a specialized cytoskeleton. It can be of two types: motile and non-motile. Motile cilia are present on multiciliated cells and helps in movement of fluids. Non-motile/ primary, cilia act as sensory antennae on receptor cells and participate in signaling between cells. Non-motile cilia usually occur one per cell while motile cilia can be present in large number.
Flagella are hair-like structure or lash-like appendage that protrudes from cells of many of living organisms which acts primarily as an organelle of locomotion.
Both cilia and flagella are hair-like organelles which extend from the surface of many animal cells. Structure is identical in both; however, flagella are longer and whip like while cilia are shorter. There are usually only a few flagella on a cell, while cilia may cover the entire surface of a cell i.e. Cilia are usually many (hundreds cilia per cell), Whereas, flagella are few (usually one to eight) in number. Flagella are used to propel the cell, while cilia are used to move substances across a surface.
The function of cilia and flagella include locomotion for one-celled organisms and to move substances over cell surfaces in multi-celled organisms.
Some Functions of the Cilia and Flagella includes:
- Ciliary or flagellar movement provides locomotion to the cell or organism.
- Cilia create food currents in lower aquatic animals.
- In the respiratory tract, ciliary movements help in the elimination of the solid particles from it.
- Eggs of amphibians and mammals are driven out from the oviduct by the aid of vibratile cilia of the latter.
Thus, cilia and flagella serve many physiological processes of the cell, such as locomotion, alimentation, circulation, respiration, excretion and perception of sense.