General Characteristics of Phylum Protozoa

Phylum Protozoa

Introduction

Protozoans are unicellular, eukaryotic, mostly microscopic organisms that exhibit animal-like behavior, such as mobility and heterotrophy. They are considered the simplest animals, though they belong to the kingdom Protista.

1. Kingdom: Protista Example: Amoeba, Paramecium.
2. Acellular (non-cellular): Protozoa are considered acellular as they are made up of a single mass of protoplasm, not multiple cells. Example: Trypanosoma.
3. Habitat: Mostly aquatic, living freely or as parasites or commensals. Example: Entamoeba (parasitic in humans), Giardia (parasitic in intestines).
4. Grade of Organization: Protoplasmic grade, where a single cell performs all vital functions, acting like an entire organism. Example: Euglena.
5. Body Covering: The body may be naked or covered by a pellicle, a thin protective layer. Example: Paramecium (covered by a pellicle).
6. Locomotion: Locomotory structures include pseudopodia, cilia, or the absence of such structures. Example: Pseudopodia: Amoeba. Cilia: Paramecium.
7. Nutrition: Modes of nutrition can be holophytic (plant-like), holozoic (animal-like), saprophytic, or parasitic. Example: Plasmodium (parasitic).
8. Digestion: Intracellular digestion takes place in food vacuoles. Example: Paramecium.
9. Respiration: Respiration occurs through diffusion across the body surface.
10. Osmoregulation: Contractile vacuoles regulate water and maintain osmotic balance. Example: Amoeba.
11. Reproduction: Asexual: Binary fission or budding. Sexual: Syngamy or conjugation. Example: Asexual reproduction: Amoeba (binary fission). Sexual reproduction: Paramecium (conjugation).
12. Examples of Protozoa: Amoeba, Entamoeba, Giardia, Euglena, Trypanosoma, Plasmodium, Monocystis, Paramecium, Vorticella, Balantidium.

Amoeba- Pseudopodia, binary fission, freshwater                                                                                                         

Entamoeba-Parasitic (amoebic dysentery)                                                                                                                         

Giardia-Parasitic in intestines, flagellated                                                                                                                         

Euglena-Dual nutrition (mixotrophic), flagellated                                                                                                 

Trypanosoma-Flagellated parasite (sleeping sickness)                                                                                           

Plasmodium-Malaria-causing parasite, non-motile stage                                                                                     

Paramecium-Ciliated, undergoes conjugation