Protozoans

Every protozoan is a heterotroph, either a predator or a parasite, and the group is considered a primitive relative of animals. NCERT describes four major groups.

Amoeboid protozoans live in fresh water, the sea or moist soil and move and catch prey with pseudopodia (false feet), as in Amoeba. Marine forms carry silica shells; some, such as Entamoeba, are parasites.

Flagellated protozoans are free-living or parasitic and move with flagella. Parasitic forms cause diseases such as sleeping sickness. Example: Trypanosoma.

Ciliated protozoans are aquatic and move actively with thousands of cilia. They have a gullet opening to the outside, and rows of cilia beating together steer food-laden water into it. Example: Paramoecium.

Sporozoans pass through an infectious, spore-like stage in the life cycle. Plasmodium, the malarial parasite, belongs here; malaria has an enormous effect on human populations.