BIOLOGY Volume 1 - A Guide to General Biology - 2004

2. THE DIVERSITY OF LIFE ON EARTH

2.6. Kingdom Protoctista

2.6.6. Protozoa

Like Algae, Protozoa form a large group of protoctists. These are single-celled, animal-like organisms with a heterotrophic mode of Nutrition. Over 50,000 species are known, and they can be found wherever Water is present. Most of them are free-living organisms characterized by various means of locomotion. Some, however, are parasitic. Notably, these include Plasmodium, which causes a disease estimated to have killed more people than any other. This disease—malaria—remains one of the world's most deadly killers.

In this section, we have chosen the free-living Organism the slipper animalcule (Paramecium caudatum) as a study example for protozoa, as it is typical of this level of Organization. The malaria parasite is discussed in Chapter 15.



Last update: 06/08/2026

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