Cilia and Flagella
Cilia and flagella are hair like projection on the surface of the cells. The internal structure of both cilia
and flagella is same but they may differ in size, number and pattern of movement. The flagella are
longer, few in number, exhibit undulating motion and beat independently. Whereas, cilia are numerous
and relatively short and beat perpendicularly in metachronous (cilia of a row beating one after the other)
or in synchronous rhythm (all cilia of a row beating simultaneously).
Structure of Cilia and Flagella :
Cilia and flagella share a common ultrastructure. Each consists of a longitudinal axoneme. The axoneme
enclosed is in a spiral sheath of cytoplasm and a plasma membrane. Axoneme is made up of a bundle of
eleven longitudinal microtubules. Nine peripheral doublets are arranged in a ring. In the centre of the
ring are two single microtubules. This arrangement is called "9 +2" pattern.
Cilia and flagella originate from their basal bodies embedded in the cytoplasm. Basal bodies have the
same circular arrangement of microtubule triplets as centrioles.
Mechanism of Movement of Cilia and Flagella
Movement of Cilia:
The movement of cilia is due to sliding of double fibrils in two groups one after the other. Five out of
nine double fibrils contract simultaneously. As a result cilium bends or shortens. It is called effective
stroke. Four out of nine double fibrils contract and cilium becomes straight. It is called recovery stroke.
Movement of Flagella:
A flagellum causes movement by the passage of rapid successive waves of bending from the attached to
the free end, as it can be seen in flagellar movement of human sperms, which propel them forward
within the fluid medium of the female reproductive tract.
Movement of Cilia and Flagella
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