list the characteristics features of protozoa
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The characteristics features of protozoa are :-
- They are commonly called flagellates
- Locomotory organelles are flagella in adults
- The body is covered by a pellicle
- Binary fission is longitudinal
- They are mostly free-living though some are parasitic
- Nutrition is autotrophic or heterotrophic or both
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- There are about 50,000 known species of Phylum Protozoa.
- Protozoans exhibit mainly two forms of life; free-living (aquatic, freshwater, seawater) and parasitic (ectoparasites or endoparasites). They are also commensal in habitat.
- They are small, usually microscopic, not visualize without a microscope.
- They are the simplest and primitive of all animals.
- They have a simple body organization. i.e. with a protoplasmic grade of organization.
- The body is unicellular (without tissue and organs).
- They have one or more nuclei which are monomorphic or dimorphic.
- Body naked or bounded by a pellicle, but in some forms may be covered with shells and often provided with an internal skeleton.
- They are solitary (existing alone/single) or colonial (individuals are alike and independent).
- Body shape variables may be spherical, oval, elongated or flattened.
- Body symmetry either none or bilateral or radial or spherical.
- Body form usually constant, varied in some, while changing with environment or age in many.
- Body protoplasm is differentiated into an outer ectoplasm and inner endoplasm.
- The single-cell body performs all the essential and vital activities, which characterize the animal body; hence only subcellular physiological division of labor.
- Locomotory organs are fingers like pseudopodia, whip-like flagella, hair-like cilia or none.
- Nutrition may be holozoic (animal-like), holophytic (plant-like), saprozoic or parasitic.
- Digestion occurs intracellularly which takes place inside the food vacuoles.
- Respiration occurs by diffusion through the general body surface.
- Excretion occurs through the general body surface, but in some forms through a temporary opening in the ectoplasm or through a permanent pore called cytopyge.
- Contractile vacuoles perform osmoregulation in freshwater forms and also help in removing excretory products.
- Reproduction asexual (binary or multiple fission, budding, sporulation) or sexual (conjugation (hologamy), game formation (syngamy)).
- The life cycle often complicated with alternation of asexual and sexual phases (alternation of generation).
- Encystment commonly occurs to resist unfavorable conditions of food, temperature, and moisture, and also helps in dispersal.
- The single-celled individual not differentiated into somatoplasm and germplasm; therefore, exempt from natural death which is the price paid for the body.
- Protozoans exhibit mainly two forms of life; free-living (aquatic, freshwater, seawater) and parasitic (ectoparasites or endoparasites). They are also commensal in habitat. Examples: Euglena, Amoeba, Plasmodium, Paramecium, Podophyra, etc.
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