Definition: Unicellular or acellular microscopic organisms possessing typical cell structure called protozoa. These are acellular, microscopic, single celled with typical cellular structures.
PHYLUM PROTOZOA GENERAL CHARACTERS
1. Small: usually microscopic and can be seen with naked eyes. 2. Body: Acellular with one or more than one nuclei.
3. Symmetry: Non-symmetrical, bilateral, radial, spherical. 4. Body covering: A pellicle.
5. Shape: Usually constant.
6. Division: of labour no physiological division of labour hence acellular. 7. Locomotion: Pseudopodia, flagella (whip like) and cilia (hair like) or organs absent. 8. Nutrition: Holozoic, holophytic, parasitic or saprozoic. 9. Excretion: Through contractile vacuoles or generally through body surface. 10. Reproduction: Asexually and sexually.
11. Life histories: Often complicated by alternation of generation. 12. Encystment: Helps in dispersal and resist untavourable condition. 13. Habit and habitat: These are ubiquitous or cosmopolitan. Free living protozoans are usually aquatic (marine or fresh water). Several protozoan’s are commensal, symbiotic and parasitic species. Parasitic protozoan’s are internal or external. 14. Nutrition; Protozoan’s hunt, digest and store food. Most are heterotrophs. They feed on other animals to obtain the nutrients they need to live. 15. Movement: Protozoan’s move by the use of cilia, flagella, pseudopods or some have no movement (Sporozoa). 16. Defense: When too much water collects in the cell, the vacuole move to the outer surface of the cell and squeezes out the water. This stops the cell from swelling up and bursting. 17. Reproduction: Asexual reproduction of protozoans occurs when the cell divides in half by binary fission. Some which are parasites multiply within the host. Some protozoans reproduce sexually as well. This can happen when two protozoans carrying half of their regular genetic material fuse...
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