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A Handbook of Biology

Cilia and Flagella

8

They are hair-like outgrowths of the cell membrane.

Cilia: Small structures which work like oars. Causes the movement of the

cell or surrounding fluid.

Flagella: Longer. Responsible for cell movement. Flagella of prokaryotes

and eukaryotes are structurally different. Cilium and flagellum are

covered with plasma membrane. Their core (axoneme) has many

microtubules running parallel to the long axis.

The axoneme has 9 doublets of radially arranged peripheral

microtubules and a pair of central microtubules. This is called (9 + 2)

array.

The central tubules are

connected by bridges

and are enclosed by

a central sheath. It is

connected to one of

the tubules of each

peripheral doublet by a radial spoke. Thus, there are 9 radial spokes. The

peripheral doublets are also interconnected by linkers.

Cilium and flagellum emerge from centriole-like structure called the basal

bodies.

Centrosome is an organelle usually containing two non- membrane

bound cylindrical structures called centrioles.

9.

Centrosome and Centrioles

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They are surrounded by pericentriolar materials.

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The centrioles lie perpendicular to each other. They are made up of 9

evenly spaced peripheral fibrils of tubulin.

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Each of the peripheral fibril is a triplet. The adjacent triplets are also

linked.

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The central part of the proximal region of the centriole is also

proteinaceous and called the hub, which is connected with tubules of

the peripheral triplets by radial spokes made of protein.

Small, hair-like structure

responsible for locomotion

Cilia

Flagella

Long, lash-like appendage serving

as an organ of locomotion