11th Class

These are free inhabitants of mud and water, and are chemoheterotrophic unicellular bacteria. These are spiral or helicoid in shape, covered by flexible cell wall. In spirochaetes flagella are absent but the cells are able to swim over solid surface by the fibrillae. Many diseases are caused by them as Treponema pallidum causes syphilis, Leptospira causes infectious jaundice and Borrelia causes relapsing fever. Besides some spirochaetes are found in teeth.

(1) Simple staining : The coloration of bacteria by applying a single solution of stain to a fixed smear is termed simple staining. The cells usually stain uniformly. (2) Gram staining : This technique was introduced by Hans Christian Gram in 1884. It is a specific technique which is used to classify bacteria into two groups Gram +ve and Gram –ve. The bacteria are stained with weakly alkaline solution of crystal violet. The stained slide of bacteria is then treated with 0.5 percent iodine solution. This is followed by washing with water or acetone or 95% ethyl alcohol. The bacteria which retain the purple stain are called as Gram +ve. Those which become decolourised are called as Gram –ve. In general the wall of Gram +ve bacteria have simpler nature as compared to Gram –ve bacteria. E.coli is a Gram –ve bacterium. Gram negative bacterium can be seen with other more...

(1) Capsule : In a large number of bacteria, a slimy capsule is present outside the cell wall. It is composed of polysaccharides and the nitrogenous substances (amino acids) are also present in addition. This slime layer becomes thick, called capsule. The bacteria, which form a capsule, are called capsulated or virulent bacteria. The capsule is usually found in parasitic forms e.g., Bacillus anthracis, Diplococcus pneumoniae, Mycobacterium tuberculosis. It provides protection against phagocytosis and antibiotics. Capsule also protects the cell against dessication and viral attack. The capsulated bacteria are usually non-flagellated (i.e., Atrichous). Capsulated bacteria form smooth colonies and are known as S-type bacteria, which are highly virulent. Non-capsulated bacteria form rough colonies and are known as R–type bacteria. (2) Cell wall : All bacterial cells are covered by a strong, rigid cell wall. Therefore, they are classified under plants. Inner to the capsule cell wall is present. It is more...

Protista (Protistos = Primary) includes unicellular eukaryotes and show the following characters : (1) Protists include solitary unicellular or colonial unicellular eukaryotic organisms which not form tissues. (2) The unicells may be naked or covered by cell wall, pellicle, cuticle or shell. (3) Simple multinucleate organisms or stages of life cycles occur in a number of groups. (4) The organisms possess double and porous nuclear membranes, mitochondria, golgibody, plastids (in many), vacuoles, lysosomes and ribosomes is also present. Centrosome is occur in many cases. (5) In many forms, plastids, (9+2 strand) flagella and other organelles are present. (6) Some protists possess contractile vacuole for regulation of their water content. (7) Their reproductive cycles typically include both asexual divisions of haploid forms and true sexual processes with karyogamy and meiosis. (8) The organisms move by flagella or by other means or are non-motile. (9) It may be photosynthetic, holotrophic, saprotrophic, parasitic more...

Slime moulds include very interesting and peculiar organisms which share the characters of both animals and fungi. Due to this peculiarity they are commonly called fungus animals. Modern biologist include slime moulds under the kingdom-protista and called them protistan fungi. General characters (1) They do not have chlorophyll. (2) They are surrounded by the plasma membrane only (somatic parts are without cell walls). (3) At one stage of the life cycle they have amoeboid structure. (4) The slime moulds live usually amongst decaying vegetation. They are quite common on lawns and moist fields. (5) They exhibit wide range of colouration. (6) They have phagotrophic or saprotrophic nutrition. Parasitic forms are not known (7) The sporangia produce spores. Each spores possesses a cellulose cell wall. (8) The slime moulds resemble both protozoa and the true fungi. They more...

  General characters (1) This is well defined group of unicellular, golden-brown photosynthetic organisms. Majority of them are motile and flagellated but a few are non-motile and non-flagellated. Flagellated forms exhibit peculiar spinning movement. Hence, they are called whorling whips. (2) The cell wall of dinoflagellates, if present, is composed of a number of plates made up of cellulose. It is called theca or lorica. The theca contains two grooves-longitudinal sulcus and transverse girdle or annulus. (3) Usually the cells possess two flagella which are of different types (heterokont). (4) Trichocysts are rod like or spindle shaped ejective structures which occur just below the cell membrane. (5) Cells possess a relatively large and prominent nucleus known as mesokaryon. DNA is without association with histone. (6) There are numerous discoid chloroplasts without pyrenoids. They are yellow-brown to more...

It include all unicellular (or acellular) eukaryotic animals. These are most primitive organisms considered as animals because of heterotrophic nutrition and motility. About 50,000 species (30,000 present and 20,000 extinct) are so far known. Brief history : Protozoans were first studied by Leeuwenhoek (1677). The name “Protozoa” was coined by Goldfuss (1817). The branch of their study is called Protozoology. General characters (1) Protozoans are the simple and primitive organisms. (2) They are free living or parasitic. (3) All the free living forms are aquatic. (4) They are asymmetrical or radially symmetrical or bilaterally symmetrical. (5) They are unicellular (acellular). (6) They have protoplasmic grade of organization. (7) Locomotion is effected by flagella, cilia or pseudopodia. (8) Nutrition is holophytic, holozoic, saprozoic or parasitic. (9) Digestion is intracellular. (10) Excretion and respiration occurs by diffusion. (11) In fresh water protozoans osmoregulation is carried out by the contractile vacuoles. (12) Encystment more...