Question

Explain the structure and organisation of flagella.

Answer 1

A flagellum is a whip-like structure that allows a cell to move. ... Other cells have different means of locomotion. Cilia are similar to flagella in structure and function, but a cilium is shorter and moves differently. A ciliated cell usually has hundreds or thousands of cilia, which move in unison like little oars.

Answer 2

Structure of Cilia and Flagella:

 These are hair like outgrowths of cell membrane.

 Cilia are small structures while flagella are comparatively longer.

 Each cilium and flagellum is covered with extended plasma membrane.

 Their core is called axoneme.

 Axoneme consists of 11 microtubules arranged in (9+2) pattern: 9 pairs of doublets of radically arranged peripheral microtubules, and a pair (2) of centrally located singlets of microtubules.

 Singlets of central microtubules are connected together by bridge and are enclosed within a central sheath.

 Central sheath is connected to one of tubules of each peripheral doublet by a radial spoke. Thus, there are 9 radial spokes.

 All peripheral doublets are joined to one-another by inter doublet linkers.

Note:

 Both cilium and flagellum emerge from centriole like structure called basal bodies.

 Structure of basal body is similar to that of structure of centriole.

 Cilia occur in:

• Protozoan of class Ciliata.

• Flame cells of flatworms.

• On epithelial lining of certain cavities like fallopian tubes, trachea, renal tubules etc.

 Flagella occur in:

• Protozoan of class Flagellata.

• Choanocytes of sponges.

• Gastro dermal cells of coelenterates.

• Spermatozoa of most animals (expect Ascaris) and lower plants.

• Unicellular algae; e.g. Chlamydomonas.

• Zoospores of algae

Functions:

 Organelles of locomotion.

 Help in capturing food in many protozoan and some animals.

 Circulate food in gastro vascular cavity of coelenterates.

 Cilia of respiratory tract remove dust particles and bacteria from it.

 Cilia of urinary and reproductive tracts drive out urine and gametes.

Important: Smoking damages ciliated epithelium thus allows dust and smoke particles to enter lung alveoli.

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