FLAGELLA AND CILIA

A flagellum (plural, flagella) is a long, whip like projection composed of microtubules. They help propel cells and organisms in a whip like motion. The flagellum of eukaryotes usually moves with an “S” motion, and is surrounded by cell membrane.
Prokaryotes may have one or many flagella for locomotion, always outside the cell membrane and normally visible only with the aid of the electron microscope. In some bacterial species the flagella twine together helically outside the cell body to form a bundle, large enough to be visible in the light microscope. These structures are quite unrelated to the flagella of eukaryotes.
A eukaryote cell usually only has about one or two flagella. The flagella also may have hair or mastigonemes, scales, connecting membranes and internal rods to something. Flagellates have one or more flagella, they move by whipping the flagella on the flagellate side to side. A sperm cell moves by means of a single flagellum. Cilia or flagella can also extend out from the stationary cells that are held in place as part of a tail goes into layer of tissue in a multicellular organism. In Eukaryotic cells, flagella are active in movements involving feeding and sensation.
Eukaryotic flagella are not the same as flagella of bacteria. They have an internal structure comprised of nine doublets of microtubules forming

a cylinder around a central pair of microtubules. The peripheral doublets are linked to each other by proteins. These proteins include dynein, a molecular motor which can cause flagella to bend and propel the cell relative to its environment, or propel water or mucus relative to the cell.
Bacterial flagella are helical filaments that rotate like screws.
Archaeal flagella are superficially similar, but are different in many details and considered non-homologous.
Eukaryotic flagella - those of animal, plant, and protist cells - are complex cellular projections that lash back and forth.
Sometimes the last are called cilia or undulipodia to emphasize their distinctiveness

Examples of bacterial flagaella arrangement schemes. A-Monotrichous; B-Lophotrichous; C-Amphitrichous; D-Peritrichous;

COURTESY

http://en.wikipedia.org/wiki/Flagellum