CBSE Class 9 Answered

Cilia are minute hair-like cytoplasmic outgrowths of a cell. They are motile and designed either to move the cell itself or to move substances over or around the cell. The primary purpose of cilia in mammalian cells is to move fluid, mucous, or cells over their surface.

Cilia are rare in plants. Ciliates (a class of phylum Protozoa) possess motile cilia and use them for either locomotion or to simply move liquid over their surface.

In larger eukaryotes, cilia are rarely found alone, usually present on a cell's surface in large numbers and beating in coordinated waves (ciliated epithelium). In humans, for example, cilia are found in the lining of the trachea and bronchi, where they sweep mucus and dirt out of the lungs. In female mammals, the beating of cilia in the Fallopian tubes moves the ovum from the ovary to the uterus. Cilia are also found in kidney tubules.