question_answer 6)

Describe briefly the four major groups of Protozoa?

Answer:

Protozoans are divided into four phyla on the basis of locomotory organelles—Zooflagellata, Sarcodina, Sporozoa and Cilliates. (i) Zooflagellates These protozoans possess one to several flagella for locomotion. Zooflagellates are generally uninucleate, occasionally multinucleate. The body is covered by a firm pellicle. There is also present cyst formation. Examples Giardia, Trypanosoma, Leishmania and Trichonympha, etc. (ii)  Sarcodines These   protozoans   possess   pseudopodia   for locomotion. Pseudopodia are of four types, i.e., lobopodia, filopodia, axopodia and reticulopodia. Pseudopodia are also used for engulfing food particles. Sarcodines are mostly free living, found in freshwater, sea water and on damp soil only a few are parasitic. Nutrition is commonly holozoic. Sarcodines are generally uninucleates. Sarcodines are of four types — Amoebids (i.e., Amoeba, etc.), radiolarians (i.e., Acanthometra, etc.), foraminiferans (i.e., Elphidium, etc.) and heliozoans (i.e., Actinophrys, etc.). (iii) Sporozoans All of them are endoparasites. Locomotory organelles (cilia, flagella, pseudopodia, etc.) are absent. Nutrition is parasitic (absorptive). Phagotrophy is rare. The body is covered with an elastic pellicle or cuticle. Nucleus is single. Contractile vacuoles are absent. Life cycle consists of two distinct asexual and sexual phases. They may be passed in one (monogenetic) or two different hosts (digenefic), e.g., Plasmodium, Monocystis, etc.   (iv) Ciliates These are aquatic, actively moving organisms because of the presence of thousands of cilia. They have a cavity (gullet) that opens to the outside of the cell surface. The coordinated movements of rows of cilia causes the water laden with food to enter into the gullet, e.g., Paramecium.