Eukaryotes - Cilia and Flagella

Description:

Cilia and flagella are microscopic hair or thread like motile structures present extra-cellularly. They originate intra-cellularly from the basal body and help in locomotion, feeding and circulation.

Cilia are small hair like structures which causes the movement of either the cell or the surrounding fluid.

Flagella are longer than cilia and are responsible for cell movement. Prokaryotic flagella are structurally different from that of eukaryotic flagella.

Structure

A cilium or flagella is made up of two parts −

• Protoplasmic sheath − Outer thick and protective coat around a fluidy matrix.

• Axoneme or axial filament −

  • Central and contractile part.
  • Possess a number of microtubules running parallel to the long axis.
  • Has nine pairs of doublets of radially arranged peripheral microtubules and a pair of centrally situated microtubule.
  • Such arrangement is called 9+2 array.

• The central tubules are connected by bridges and is also enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublets by a radial spoke.

• There are nine radial spokes.

• The peripheral doublets are connected by linkers.

• Basal Bodies are the centriole structures from where cilium and flagellum emerge.