The Cilia and flagella
Cilia (singular: cilium) and flagella (singular: flagellum) are hair-like outgrowths of the cell membrane. 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. The prokaryotic bacteria also possess flagella but these are structurally different from that of the eukaryotic flagella.
The cilium and flagellum shows that they are covered with plasma membrane. Their core called the axoneme, possesses a number of microtubules running parallel to the long axis. The axoneme usually has nine doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules.
Such an arrangement of axonemal microtubules is referred to as the 9+2 array.
Both cilium and flagellum emerge from centriole-like structure called the basal bodies.
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. Thus, there are nine radial spokes. The peripheral doublets are also interconnected by linkers.
Differences between cilia and flagella
| Basis | Cilia | Flagella |
|---|---|---|
| Size- Length | Cilia are short | Flagella are long |
| Size- Thickness | Around 0.3 to 0.5 um thick. | Around 0.02 to 0.025 um thin. |
| Density | It is present in many (hundreds) per cell. | It is present in few (less than 10) per cell. |
| Position | It is present throughout the surface of cell. | It is present at both the ends or all over the surface.. |
| Found in | Eukaryotic cell | Eukaryotic cell and eukaryotic cells. |
| Appendage | Hair-like appendages extending from the surface of a living cell. | Thread-like appendages on the surface of a living cell. |
| Motion | The motion of cilia is rotational, very fast moving. | The motion of flagella is rotary movement in prokaryotes whereas it is bending movement in eukaryotes. |
| Beating | Cilia beat in coordination or one after the other. | Flagella beat independent of each other. |
| Examples | It is present in Paramecium. | It is present in Salmonella. |
| Functions | It helps in locomotion, aeration, feeding circulation, etc. | It helps in locomotion only. |