Movement is one of the most important characteristics of living organisms. At cellular level the cytoplasm exhibits streaming movement (cyclosis). At the organismic level, the plants and animals move their parts.
Although movements vary greatly, yet they involve three basic mechanisms.
1. Amoeboid Movement (=Pseudopodia movement):
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It is typical of Amoeba. It helps in food capture, and change of place. This of movement is found in leucocytes (phagocytes and macrophages of the human lymphatic system).
2. Ciliary Movement:
It is characteristic way of ciliated protozoans such as Paramecium. Cilia of feeding apparatus of Paramecium drive water and food. Cilia and water currents that pass over the gills of bivalve molluscs (e.g., Lamellidens- fresh water mussel); drive water through the water vascular system of echinoderms (e.g. Asterias- starfish). Cilia in the former is associated with feeding, while the cilia of the later help locomotion. Cilia of the upper respiratory tract of humans keep the invading microbes and dust particles out. Whereas the cilia of the Fallopian tube (=oviduct) and vasa efferentia of humans females and males transport ova and spermatozoa respectively.
An enlarged version of cilium is known as flagellum. Flagella help in swimming of protozoans like Euglena and spermatozoa (sperms) of various animals. Flagella are also helpful in maintenance of water current in the canal system of sponges.
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3. Muscular Movement:
This basic mechanism is used in the majority of vertebrates, including humans. The universal property of this mechanism is to exert of force by alternate contraction and relaxation.