Q.4. Write short note on nutrition in Protozoa. (2016)
Ans. All types of nutrition are found in Protozoa, such as holophytic, holozoic, saprozoic, mixotrophic and parasitic, etc.
(i) Holophytic nutrition: -
All those phytoflagellates possessing chloroplasts or chromatophores synthesize their food by photosynthesis. As energy is supplied by sunlight to carry on food-making activity, this method involving self-feeding is also referred to as autotrophic phototrophy. Carbon dioxide and water, acting as raw materials, enter into a complex cycle of chemical reactions and produce dextrose sugar. From dextrose paramylum may be formed which is especially characteristic of euglenoid flagellates.
(ii) Holozoic nutrition: -
Majority of free-living Protozoa derive nourishment by ingesting other organisms, both animals and plants. Such Protozoa are called holozoic, and mode of nutrition is said to be holozoic nutrition. All Sarcodina are strictly holozoic with the exception of some parasitic species. This mode of nutrition involves development of organelles for food capture, ingestion, digestion, and egestion of indigestible residues.
Q.5. Write an esay on protozoa and its parasitism. (2009)
Ans. Parasitism in protozoa: -
1. Parasite and parasitism: -
Parasites may be defined as “the species which exist at the expense of certain other species, called hosts, and are biologically and economically closely connected with them throughout their life-span”, Parasitism is an association between the parasities and their hosts. It may be defined as “an association between two organisms of such kinds that one (parasite) lives and feeds, temporarly or permanently, either in or on the body of the other (host)”.
2. Types of parasities: -
There are four types of parasites in protozoa :
1. Ectoparasites: -
Those protozoa which inhabit the external surface of their hosts. Hydramoeba hydroxena, feeding on the ectodermal cells of Hydra and Ichthyophthirius multifilis, burying in the epidermis of freshwater fishes, are examples of ectoparasitic Protozoa.
2. Endoparasites: -
Those parasites which live inside the body of their hosts. These are divided into four categories :
(a) Parasites of digestive tract: -
Those endoparasites which dwell inside the lumen of alimentary canal of hosts. Giardia lamblia , a parasitic flagellate, entamoeba histolytica, a parasitic amoeba, Isospora hominis, a parasitic coccidian, Balantidium coli, a parasitic ciliate, are all intestinal endoparasites of man.
(b) Parasites of mouth: -
Those endoparasites which reside in mouth cavity of hosts. In man, entamoeba gingivalis and Trichomonas tenax are found in pockets between the gums and teeth.
(c) Parasites of genital tract: -
Those endoparasites which inhabit the genital tract of hosts. In human female, Trichomonas vaginalis lives in vagina.
(d) Parasites of body tissues: -
Those parasites which live within tissues of hosts and may enter through skin or from disgestive tract. Species of Trypanosoma, Leishmania, Plasmodium and Babesia are common blood parasites of vertebrates.
3. Hyperparasites: -
These are protozoa parasitizing other species of parasitic Protozoa. For instance, the opalinid (Zelleriella) which lives in the frog’s intestine, is parasitized by a certain amoeba. Nosema notabilis parasitizes Sphaerospora Polymorpha which is a parasite of urinary bladder of toad fish.
4. Pathogenic parasites: -
Most of the parasitic protozoans do not cause disease conditions in their hosts except producing minor symptoms. On the other hand, certain parasites act as disease-causing organisms in man and other animals. Such parasites are referred to as pathogenic parasites. Important pathogenic parasites of man are Leishmania donovani, Trypanosoma gambiense, Plasmodium vivax, Entamoeba histolytica, etc.
(iii) Host specificity: -
The two group are exhibited regarding the most specificity. Firstly some parasites can successfully parasitize a wide variety of hosts. Trypanosoma, Entamoeba and Eimeria belong to this group. Secondly, some parasites have become restricted to only a few specific host. Coccidia of mammals (e.g. Plasmodium) are such parasites.
(iv) Transmission: -
There are different way for transiting the parasites. Entamoeba gingivalis is transferred directly from one man to another through machanical contact, like kissing (direct transfer). Some such as Entamoeba histolytica and Eimeria tenella, are transferred by cysts in water or food (contaminative transfer). Species of Trypanosoma, Plasmodium, etc. are transmitted by certain invertebrate vectors (inoculative transfer). Transmission by invasion of ovary or egg takes place for species of Babesia. Placental transference has been reported for Plasmodium in man (congenital transfer).
(v) Life cycle: -
many parasites, such as Eimeria and Monocystis, have only a single host during their life cycle, only a part spent outside the host. These are called monogenetic parasites. Other protozoan parasites (e.g. Plasmodium, Trypanosoma) have two or more hosts, two hosts are usually desigmated as the primary host, in which the parasite’s ancestors evolved and the secondary host or vector, which acts as a transmitting agent for the parasite to the other host. These are called digenetic parasites. If the parasites undergoes part of its life cycle in vector, its transmission is called cyclical, if not it is referred to as mechanical transmission. Some other animals may be infacted by the parasites and serve as a source for infacting other animals. These animals constitue the reservoir hosts.
(vi) Effects of parasites on their hosts: -
Some parasites protozoa prove to be injurious for theirhosts, while others produce almost no effect. Entamoeba histolytica destroys host’s large intestine causing large unlcerations. Eimeria stiedae is known to cause hyperplasia of the hepatic cells of rabbits. The coccidian parasites of earthworm, Polymnia nebulosa, brings about hypertrophy of the sperm mother cells. The malarial parasites of birds, Plasmodium gallinaceum, clogs the fine blood capillaries etc.
Q.6. Describe the economic importance of protozoa.
Ans. They are harmful as well as useful, but the harmful species are relatively smaller in number as compared with the useful species.
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. Clams and young fish feed extensively on aquatic insect larvae, small crustaceans, worms, etc., all of which take protozoa as food. Thus, protozoa indirectly, which in their turn are consumed by man.
3. Symbiotic protozoa: -
Some protozoas are found in symbiotic relationship with other organism. The two partners become so dependent on each other, that one cannot get along without the other and their separation result in the death of both. Most outstanding examples of symbiotic among the Protozoa are several intestinal flagellates (Trychonympha, 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 well as for themselves.
4. Oceanic ooze and fossil protozoa: -
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 are composed almost exclusively of the fossil Foraminiferida. It is hard to believe that geart city of paris in indebted to these obscure animals. The great pyramids of Egypt were carved from the limestone deposits of made by tests of an early Tertian Forminiferan Nummulites. Radiolarian fossils are abundant in the hard rock 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 single-celled 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 geneticsts for heredity and variations. Study of physiology of Potozoa has contributed much to our knowledge about the physiology of animal cell.