Cilia and Flagella – Protozoans

Cilia and flagella basically have a similar structure and distinction between the two on structural basis does not exist. There is a filament or the axoneme which has an outer membranous covering continuous with the plasma membrane of the cell surface. This axoneme encloses a matrix in which there are eleven sets of microtubules made up of protein, primarily globular tubulin.

                                 Figure: Diagrammatic representation of the ultra structure of cilia or flagella

The arrangement of microtubules is characteristically the same by and large in all cilia and flagella of eukaryotes - nine doublets of microtubules arranged in a circle around the two single central ones. The central minerotubules terminate at a basal plate at the cell surface and the peripheral ones continue internally into the cell body. At about this point another microtubule joins each of the nine pairs so that these form a short tube extending into the cell consisting of a triplet of microtubules. This contributes to the formation of the basal body or the kinetosome.