PROTOZOOLOGY is that branch of zoology that is concerned with group of animals called as the Protozoa. It is not, as its name might appear to involve, a primitive form of zoology. As a science it is somewhat young, but, owing mainly to practical significance of some of the animals with which it handles, it had in 1921 already become one of the largest and most educated fields in biology. Protozoa are very appealing animals, from both practical and theoretical point of view. Yet, they are all small, and most of them of microscopic dimensions. To general public they are thus invisible, and as a result unknown, except by conspicuous results - like diseases - that they rarely produce. These are unscientific and unnatural groups, that comprise all microscopic creatures, both animals and plants; and as a result Protozoa are still perplexed, in popular mind, with other microbes, like Bacteria, with which they have no connection.
It will be evident that protozoology, as the independent science, should essentially have arisen as a relatively late offshoot of zoology. Its history is bound up with that of microscope, the instrument that bears much same relation to protozoology that telescope does to astronomy. Before microscopes were invented no Protozoa could have been clearly visible. With the first lenses, largest and most conspicuous of them were found; and as microscopes were enhanced, more and more minute creatures slowly became known. Out of the confusion of forms which microscope has continued to reveal, Protozoa have eventually emerged as well-defined group of animals, and, consequently, those who study these animals have slowly built up new section of zoological science.
As the individual science protozoology only became self conscious at the fairly recent period. The name itself, although already in exercise between 1870 and 1880, only became current after opening of 10th century - that is to say, within memory of several living zoologists. But science was really born - although not described - when first Protozoa were found. This far-reaching discovery was made in latter half of 17th century.
Leeuwenhoek, father of protozoology, he studied and stated many Protozoa. Though several good clarifications were made and recorded, they were always disjointed, and often distorted by fancy and speculation.
Protozoolog y lie between independence and identity loss, mainly as image and consolidation are not yet stated against closely related disciplines . Single-celled organisms as models with the capable future for general life procedures speak for former, (for the most part) missing theoretical basis with regard to the taxonomic summary for investigation of objects in protozoology against this, for latter . Superordinated discipline s of general biology, like, e.g., cell biology or evolutionary biology , additionally impede the image of protozoology that has arisen in the tradition of botany and zoology . Due to the often identical investigative methods, the difference in the attempts is hardly to be seen. The early history and the initial phase of a protozoology just arising take place in the time of a paradigm change within general biology. Cell theory and descent hypothesis cause a reorientation. No more animals and plants but the elementary unit cell and the elementary process evolution are in the center of the interest. The still young protozoology constituted itself contradictorily on the same basis a s general biology between the discipline s botany an d zoology just having been replaced. Protozoa are eukaryotic microorganisms. Though they are frequently studied in zoology courses, they are considered part of microbial world as they are unicellular and microscopic.
Protozoa are notable for their ability to move separately, a feature found in majority of species. They generally lack capability for photosynthesis, though genus Euglena is prominent for motility and photosynthesis (and is thus considered both alga and protozoan). Though most protozoa reproduce by asexual methods, sexual reproduction has been observed in numerous species. Most protozoal species are aerobic, but few anaerobic species have been found in human intestine and animal rumen.
Protozoa are situated in most moist habitats. Free-living species dwell in freshwater and marine environments, and terrestrial species dwell in decaying organic matter. Few species are parasites of plants and animals.
Protozoa play the significant role as zooplankton, free-floating aquatic organisms of oceans. Here, they are found at bases of several food chains, and they participate in several food webs.
Size and shape:
Protozoa differ considerably in size and shape. Smaller species may be size of fungal cells; larger species may be observable to unaided eye. Protozoal cells do not have cell walls and thus can suppose infinite variety of shapes. Some genera have cells enclosed by hard shells, while cells of other genera are enclosed only in the cell membrane.
Several protozoa alternate between the free-living vegetative form called as atrophozoite and resting form known as the cyst. Protozoal cyst is rather analogous to bacterial spore, as it resists harsh situations in environment. Several protozoal parasites are taken in body in cyst form.
Many protozoa contain single nucleus, but some contain both macronucleus and one or more micronuclei. Contractile vacuoles may be there in protozoa to eliminate excess water, and food vacuoles are frequently observed.
Nutrition and locomotion:
Protozoa are heterotrophic microorganisms, and many species get large food particles by phagocytosis. Food particle is swallowed in food vacuole. Lysosomal enzymes then digest nutrients in particle, and products of digestion are distributed all through cell. Some species have specialized structures known as cytostomes, by which particles pass in phagocytosis.
Several protozoal species move separately by one of 3 kinds of locomotor organelles: flagella, cilia, and pseudopodia. Flagella and cilia are structurally alike, containing 9-plus-2 system of microtubules, the similar kind of structure found in tail of animal sperm cells and certain cells of unicellular algae.
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