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 together and form a new cell. Others exchange genetic material during mating. 18. Respiration: Respiration takes place when oxygen diffuses into the cell, where the food molecules become oxidized.
The energy produced and the organic molecules are used for maintenance and building of the cell. Waste products ,carbon dioxide and water diffuse out of the cell. 19. Excretion: Waste materials in protozoans are removed from the cell by diffusion through the cell. They are transported out of the cell by food vacuoles that come in contact with the surface.
This is known as exocytosis. Most protozoan’s are solitary but colonial also.Protozoan’s mostly feed upon the organic food matters. Some are carnivorous who feed the other protozoan’s. Some feed only upon plants.
Most of them feed upon dead or decaying organic matters and parasitic forms live upon the tissues of hosts whereas other species are synthesizing their own food with the help of chlorophyll.
