Biological Classification Test - 2

Although all single-celled eukaryotes (except some unicellular algae e.g., Chlamydomonas, Chlorella etc., and fungi e.g., Yeasta and animals, which are placed in their respective kingdoms along with their closely related multicellular organisms) are placed in kingdom Protista, yet its boundaries are not well defined.

Protists are mostly aquatic organisms, therefore, they are found in the sea, freshwater and moist soil. Many protists are found in water bodies in the form of plankton. Some protists live in the bodies of animals as parasites

The kingdom protista has been  broadly divided into three main groups:
(i) Photosynthetic Protists (Protistan Algae) example, Dinoflagellates, Chrysophytes and Euglenoids
(ii) Consumer-Decomposer Protists(Slime Moulds)
(iii) Protozoan Protists
Euglenoids are Euglena like unicellular flagellates which possess pellicles instead of cell wall. Chrysophytes include diatoms and desmids. They belong to the division Chrysophyta/Bacillariophyta. The dinoflagellates belong to division Pyrrophyta and class Dinophyceae. Slime moulds possess the characters of both animals and fungi and, therefore they are commonly called fungus-animals.

The body of diatoms is covered by a transparent ' siliceous shell (silica deposited in cell wall) known as frustule. The frustule is made of two valves, epitheca and hypotheca. The two valves fit together like a soap box. The frustule possesses very fine markings, pits, pores and ridges.

Diatomite deposits are often accompanied by petroleum fields. Much of the petroleum of today is probably due to decayed bodies of the past diatoms. Diatomite is porous and chemically inert. It is, therefore, used in filtration of sugar, alcohols, oil, syrups and antibiotics. Diatomaceous earth is used to make sound proofrooms. Diatomite is employed as a cleaning agent in tooth pastes and metal polishes.

Diatoms are are very important photosynthesizers. About half of all the organic matter synthesized in the world is believed to be produced by them. Diatoms are probably the most numerous of all plants like protists. Because of this abundance, they are one of the most important primary producers of the sea. There are about 5,500 species of diatoms, mainly marine.The diatoms constitute an important phytoplankton component of the oceans.

The diatom shells piling up at the bottom of oceans over millions of years formed deposits called diatomaceous earth.These deposits may be thousand metres thick with as many as five million diatom shells in each cubic centimetre. This diatomaceous earth is used in many small and large scale industries.

Dinoflagellates are a group of about 1,000 species of photosynthetic protists. The dinoflagellates are important components of phytoplankton. Most of them are marine but some occur in fresh water. Some dinoflagellates such as Gymnodinium and Gonyaulax grow in large number in the sea and make the water look red and cause the so called “red tide”.

Euglenoids are unicellular flagellate protists commonly found in fresh water ponds, pools and moist mud. They lack cellulose cell wall. The body is covered bv thin and flexible pellicle (= periplast). The pellicle has oblique but parallel stripes called myonemes. The euglenolds have two flagella, usually one long and one short. Though the euglenoids are photosynthetic in the presence of light, when deprived of sunlight they behave like heterotrophs by predating on smaller organisms (holozoic) or feeding on organic remains (saprobic). Such a mode of nutrition is called mixotrophic (i.e., a mix of holophytic + saprobic or holozoic). Photosynthetic pigments of euglenoids are identical to those present in higher plants, e.g. chl a and chl b.

• The body of Euglena is covered by a plasma membrane followed by periplast or pellicle. At the place of union of the two branches the flagellum bears a swelling called paraflagellar body (photoreceptor).
• The posterior end is pointed. The anterior end of the cell is blunt and bears an eccentric cytostome (mouth).
• At one end of the reservoir, the cytoplasm contains an orange red stigma (eye spot). Pyrenoids (proteinaceous bodies) may be present in the chloroplasts. The endoplasm contains several paramylum bodies.

Dinoflagellates are basically unicellular, motile and biflagellate, golden brown, photosynthetic protists. The two flagella are different (heterokont), one transverse flagellum and other longitudinal flagellum.The longitudinal flagellum is narrow, smooth, directed posteriorly and lies in the sulcys. The transverse flagellum is ribbon-like and lies in the cingulum or annulus. The two types of flagella beat in different directions. A well defined nucleus is present, which has been named as mesokaryon.

Organism shown in the figure is Gonyaulax. It belongs to dinoflagellates group of organisms. Gonyaulax calendula is poisonous to vertebrates.

A free living thalloid body of the acellular slime moulds is called plasmodium. The plasmodium is wall-less mass of multinudeate protoplasm covered by slime. All the nuclei in the plasmodium divide simultaneously. Chlorophyll is always absent. The plasmodium often possesses a number of branched veins. The protoplasm present in the veins shows reversible streaming movement. The veins disappear and reappear as the plasmodium moves about.

Slimemoulds do not have chlorophyll. They are surrounded by the plasma membrane only (somatic parts are without cell walls). The slime moulds live usually amongst decaying vegetation. They are quite common on lawns and moist fields. They exhibit wide range of colouration. They have phagotrophic or saprotrophic nutrition. Parasitic forms are not known (Bold et all, 1987). Both asexual and sexual modes of reproduction are found. They produce spores within sporangia. A spore possesses a cell wall of cellulose.

Trypanosom a gambiense, causes Gambian sleeping sickness. The parasite is transmitted by blood sucking tse-tse fly, Glossina palpalis. Leishmania donovani cause kala-azar or dum-dum fever (= visceral leishmaniasis). The parasite is transmitted by sandfly, Phlebotomus argentipes and other species. Causal organisms of bloth diseases belong to flagellated protozoans of kingdom Protista.

Euglena is studied as plant as well as animal. It is called plant animal.
Plant characters of Euglena:
(i) Presence of chloroplasts with chlorophyll.
(ii) Holophytic (photosynthetic) nutrition in presence of light.
Animal characters of Euglena:
(i) Presence of pellicle which is made up of proteins and not of cellulose.
(ii) Presence of stigma and paraflagellar body (photosensitive structures).
(iii) Presence of contractile vacuole (not found in plants).
(iv) Presence of longitudinal binary fission.
(v) Can show holozoic nutrition when deprived of light.

The given protozoan is Trypanosoma gambiense. Trypanosoma gambiense causes sleeping sickness transmitted by Tsetse fly.

All sporozoans are endoparasites. Sexual reproduction takes place through syngamy. Asexual reproduction of through multiple fission. Under unfavourable conditions they form cysts.
Examples: Plasmodium (the malaria] parasite), Monocystis, etc.

Paramoecium is a free living ciliate which is found in fresh water. Most widely distributed species are Paramoecium caudatum and Paramoecium aurelia. The, cilia of the extreme posterior end are longer and form a bunch called caudal tuft.

Leishmania donovani is a flagellated protozoan.