Cell: The Unit of Life - Cilia and Flagella

Cilia and flagella are hair-like outgrowths of the cell membrane used for locomotion and movement of surrounding fluids.

Cilia are small structures which work like oars, causing the movement of either the cell or the surrounding fluid.

Flagella are comparatively longer and responsible for cell movement. Prokaryotic flagella are structurally different from eukaryotic flagella.

The electron microscopic study shows that they are covered with plasma membrane. Their core is called the axoneme, which possesses a number of microtubules running parallel to the long axis.

The axoneme usually has nine pairs of doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules. This arrangement of axonemal microtubules is referred to as the $9 + 2$ array.

The central tubules are connected by bridges and are also enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublet by a radial spoke. Thus, there are nine radial spokes.

The peripheral doublets are also interconnected by linkers. Both the cilium and flagellum emerge from centriole-like structures called the basal bodies.