Flagella and Movement

Animals go from place to place using amoeboid, ciliary, flagellar or muscular mode of locomotion.

In earlier articles we have seen amoeboid and ciliary mode of locomotion. Let us now get familiar with the flagella and their use by various forms of life for going places.

Flagella, like cilia, are projections from the cell surface. They are whiplike in appearance, lesser in numbers as compared to that of the cilia but are much longer. They are made up of microtubules and show the typical 9(2) + 2 structure in electron microscopic studies. The entire shaft of the flagellum is covered by the cell membrane.

They are motile and designed to move the cell or the organism. Such flagellate organisms may have the flagella which may be permanent or may appear only at one particular stage of the life cycle. The flagellate organisms are small and have a single cell or just a few cells making their whole body.

Flagella are seen -

singly in Euglena a freshwater pond dwelling green alga,

one pair in each of the 200 to 10000 cells in a colonial green alga e.g. Volvox

in the form of a ring in male gametes or zoospores of multicellular algae like Oedogonium,

in pairs in their male gametes, in bryophytes (mosses) like Funaria, randomly distributed few numbers in protista such as Mastigamoeba,

one per cell in endodermal collar cells, the choanocytes, in animal kingdom, phylum porifera i.e. in sponges,

in the form of a tuft in male gametes of pteridophytes, like ferns and in sperms of nearly all animals (exceptional animals in whom sperms have no flagella are nematodes like, the Ascaris - the round worm. Their sperms show amoeboid movement)

A flagellum is anchored into a cell by a basal body or kinetosome. On entry of a sperm into an egg cell the basal body gives rise to a centriole necessary for cell divisions.

The sperm is also called spermatozoon (zoon = animal). It is equated with an animal as it has motility. See the animated movement of a sperm - http://www.stanford.edu/group/Urchin/spe...

The flagellum forms the tail of sperm and if the sperm head is about 4 microns then the tail is 40 microns that is 10 times longer.

The flagella move very rapidly during locomotion and execute an undulatory motion in one plane or in a helical cork-screw-like motion. The bending of the flagella is a result of sliding of microtubules in the shaft in relation to each other. Alteration in the water pressure propels the cell through its aquatic environment. All land dwelling animals including man have sperms which have to have watery medium (the semen). Fern like land plants too, have male gametes which swim through water and can not sexually reproduce if water is unavailable for the locomotion of their sperms (antherozooids).

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