Protozoa are unicellular microscopic organisms found almost everywhere, in water, in moist soil, in air, or even within the bodies of other animals and plants. In this fast-moving Age of Mammals, dominated by man, it may appear at first glance that these minute animals would have little or no economic significane. However, such is not the case, and Protozoa exert far more influence in worldly affairs than is generally thought. They are harmful as well as useful, but the harmful species are relatively smaller in number as compared with the useful species.
Useful Protozoa
1. Helpful in sanitation.
Numerous holozoic Protozoa feed on putrefying bacteria in various bodies of water and thus help indirectly in the purification of water. These Protozoa play an important part in the sanitary betterment and improvement of the modern civilized world in keeping water safe for drinking purpose.
2. Planktonic Protozoa as food.
Protozoa floating in the plankton of sea provide directly or indirectly the source of food supplies to man, fish and other animals. They form one of the first links in the numerous and complicated food chains that exist in the oceans of the world. Clams and young fish feed extensively on aquatic insect larvae, small crustaceans, worms, etc., all of which take Protozoa as food. Thus, Protozoa indirectly form the food of fish, clams and other animals, which in their turn are consumed by man.
3. Symbiotic Protozoa.
Some protozoans are found in symbiotic relationship with other organisms. This association is usually beneficial to both the partners. The two partners become so dependent on each other, that one cannot get along without the other, and their separation results in the death of both. Most outstanding examples of symbionts among the Protozoa intestinal flagellates (Trichonympha, Colonympha etc.) of termites and woodroaches. According to Cleveland, these flagellates are extremely vital for the very existence of their hosts. They digest cellulose converting it into soluble glycogen substances for their hosts as are several well as for themselves.
4. Oceanic ooze and fossil Protozoa.
Tiny skeletons of dead pelagic Foraminifera, Radiolaria and Heliozoa sink to the sea bottom forming uhe soft mud or oceanic ooze. These tiny skeletons are made of silica or calcium carbonate. Over countless millions of years these skeletons, deposited on the floor of ocean, became solid and fossilized and converted into some important sedimentary rock strata found all over the world. These have been put to various commercial uses,such as filtering agents, abrasives, chalk, building stones, etc. The white chalk cliffs of Dover, England, and the limestone beds of Paris, Cairo and North America exclusively of the fossil Foraminiferida. It is hard to believe that great city of Paris is indebted to these obscure animals. Most of the buildings of Paris are made of limestone composed almost exclusively of the shells of the foraminiferan genus, Miliolina. Similarly, the great pyramids of Egypt were carved from the limestone deposits made by tests of an early Tertian foraminiferan, Nummulites. Radiolarian fossils are abundant in the hard rocks of the nature of flint and chert. They also constitute a part of Tripoli Stone, which is used in abrasive powders of materials.
5. Protozoa in study.
Protozoa are singlecelled organisms, possessing forms and functions like those of metazoan cells. They are studied in laboratories for the comprehension and application of biological principles. Due to their minute size and quick reproduction, they are studied by geneticists for heredity and variations. Knowledge of fossil Protozoa is essential for the students of geology and palaeontology. Protozoa are the progenitors of all metazoans alive today. Their study helps in understanding the probable beginning of organic matter and the origin and evolution of life on Earth. Study of physiology of Protozoa has contributed much to our knowledge about the physiology of animal cell.
Harmful Protozoa
1. Soil Protozoa.
Several species of Protozoa, present in large numbers in soil, feed open the nitrifying bacteria, and thus decline their activity and consequently tend to decrease the amount of nitrogen given to soil by the nitrifying bacteria.
2. Water pollution.
Whereas some Protozoa are helpful in water sanitation, others become responsible for water contamination or pollution. The Protozoa of faecal origin belong to this latter category. Some free-living Protozoa (e.g., Uroglenopsis) also pollute water byproducing aromatic and oily secretions with objectionable odours, which render water unfit for human consumption. Some bioluminescent dinoflagellates, such as Noctiluca, Gymnodinium and Gonyaulax, living in sea, sometimes multiply so extensively as to turn the water red with their bodies. The phenomenon is known as blooming and is the cause of 'red tides', often experienced in the sea. Outbreaks of this red water' often gives a foul and disagreeable odour to the ocean water. Large concentrations of these flagellate protozoans may even lead to destruction of fish and poisoning of edible molluscs, such as clams, oysters and mussels, etc., making them unfit for human consumption.
3. Pathogenic Protozoa.
Some protozoa cause diseases in man as well as animals and these are termed pathogenic Protozoa. They occur Some Protozoa in all classes of Protozoa.
(a) Pathogenic sarcodines.
There are common generà of parasitic amoebae, Entamoeba and Endamoeba, which live in the intestine of man and of other animals. Only two species of Entamoeba, E. histolytiea of man and other mammals and E. invadens of reptiles are known to be seriously pathogenic. E. histolytica is responsible for amoebic dysentery or amoebiasis in man, which occurs in about 60-70% Indian population. E. invadens, occurring in the colon of reptiles, causes reptilian amoebiasis.
(b) Pathogenic flagellates.
Pathogenic species of parasitic flagellates are included in the genera Leishmania, Trichomonas and Giardia. Three pathogenic species of Leishmania have been known to cause two Trypanosoma, Histomonas, severe diseases in man. L. donovani causes Kala- azar, a disease of the spleen and liver, L. tropica causes a peculiar type of skin lesion (cutaneous leishmaniasis) and L. brasiliensis causes infection of nasopharynx and skin lesion. transmitted by sandflies of the genus Phlebotomus. Parasitic species of Trypanosoma in mammals cause worst diseases. T. gambiense, is the causative. These are agent of fatal African sleeping sickness.T. Rhodesiense, T. cruzi, T. equiperdum, T. evansi, and T. brucei are other common pathogenic species. Histomonas meleagridis is mastigamoeba. Of the parasitic species of Trichomonas, T. vaginalis is organism of vaginal trichomoniasis or vaginitis in human females. T. foetus causes trichomoniasis of cattle in U.S., and T. gallinae is pathogenic in doves, pigeons, turkeys and chickens. Of the numerous species of Giardia, G. intestinalis (= G. lamblia) of man causes enterocolitis.
(c) Pathogenic sporozoans.
Protozoan superclass Sporozoa is exclusively of parasitic forms, Though most of sporozoans are harmless, yet some genera like Plasmodium, Eimeria, Isospora species. Species of Plasmodium malaria parasites as they cause the disease of malaria. Four species of Plasmodium, namely P. vivax, P. malariae, P. ovale and P. falciparum cause malaria in man. Malaria is caused by P. cyanomolgi in monkeys, by P. verghei in tree rats and by P. gallinaceum in jungle fowl of Asia. Pathogenic species of Eimeria cause the parasitic the causative Sporozoans. Protozoan pathogenic called and Babesia include are coccidiosis in chickens and rabbits. E. tenella and E. mitis infect chickens, whereas E. mana and E. steidae infect rabbits. E. canis in dogs, E. bovis in cattle and E. felina in cats, E. intricata in sheep and goats common. Isospora, intestinal parasites of man and other animals, include one truly pathogenic species of man, hominis, I. felis, 1. bigemina and I. rivolta infect cats and dogs and occur in mucous membranes of ileum. Their transmission is by cylindrical oocysts. Species of Babesia are intra-erythrocytic parasites of various vertebrates. Babesia bigemina of cattle causes the lethal haemoglobinuric fever, red-water fever or Taxas fever. B. equi in horses, B. rohdani in rodents, B. felis in cats, B. motasi in goats, etc., cause malignant jaundice, anaemia and fever in their respective hosts.
(d) Pathogenic ciliates.
Balantidium coli is the only important ciliate pathogenic parasite. It is found in the intestine of man and often in are also frogs.
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