Category : 11th Class
Monera (Monos – single) includes prokaryotes and shows the following characters :
(1) They are typically unicellular organisms (but one group is mycelial).
(2) The genetic material is naked circular DNA, not enclose by nuclear envelope.
(3) Ribosomes and simple chromatophores are the only subcellular organelles in the cytoplasm. The ribosomes are 70 S. Mitochondria, plastids, golgi apparatus, lysosomes, endoplasmic reticulum, centrosome, etc., are lacking.
(4) Sap vacuoles do not occur. Instead, gas vacuole may be present.
(5) The predominant mode of nutrition is absorptive but some groups are photosynthetic (holophytic) and chemosynthetic.
(6) The organisms are non-motile or move by beating of simple flagella or by gliding.
(7) Flagella, if present, are composed of many intertwined chains of a protein flagellin. They are not enclosed by any membrane and grow at the tip.
(8) Moneran cells are microscopic (1 to few microns in length).
(9) Most organisms bear a rigid cell wall (Peptidoglycan).
(10) Reproduction is primarily asexual by binary fission or budding. Mitotic apparatus is not formed during cell division.
(11) The kingdom Monera includes true bacteria, mycoplasma, rickettsias, actinomycetes (ray fungi) etc. Microbiologists also include blue green algae (i.e., Cyanobacteria) under the group bacteria because of the presence of prokaryotic cell structure. Studies have established that the members of archaebacteria group are most primitive and have separated from eubacteria group very early in the process of evolution.
Study of bacteria is called bacteriology. Linnaeus placed them under genus vermes. Nageli classified bacteria under schizomycetes. Bacteria are unicellular, microscopic and cosmopoliton organisms. The branch of science, which deals with the study of microorganism and their process is called as microbiology. Antony Von Leeuwenhoek is known as father of microbiology and father of modern microbiology is Robert Koch.
These are the smallest cell wall having prokaryotic cell. The bacteria constitute a highly specialised group of one celled plants. They differ from animals in having a rigid cell wall and being capable to synthesize vitamins. Bacteria were first seen by a Dutch lens maker, Antony Von Leeuwenhoek (1683) who named them animalcules. Louis Pasteur (1822-95) made a detailed study of bacteria and proposed germ theory of disease. Ehrenberg (1829) was the first to use the term bacterium. Robert Koch (1881) found that some diseases like tuberculosis, cholera in man, and anthrax in cattle is caused by bacteria. Lister introduced antiseptic surgery. He used carbolic acid for sterilization of surgical instrument. Pasturization theory was proposed by Louis Pasteur.
(1) Size : They are 3 to 5 microns (1m = 1/1000 millimetre or about 1/25,000 inch) in length. A few species of bacteria are approximately 15m in diameter.
(2) Shape : The bacteria possess the following forms :
Cocci (Gk. Kokkos = Berry) : They are oval or spherical in shape. They are called micrococcus when occur singly as in Micrococcus, diplococcus when found in pairs as in Diplococcus pneumoniae, tetracoccus in fours, streptococcus when found in chains as in Streptococcus lactis, staphylococcus when occurring in grape like clusters as in Staphylococcus aureus and Sarcine, when found in cubical packets of 8 or 64 as in Sarcina.
Bacilli : They are rod–shaped bacteria with or without flagella. They may occur singly (bacillus), in pairs (diplobacillus) or in chain (streptobacillus).
Vibrios : These are small and ‘comma or kidney' like. They have a flagellum at one end and are motile, vibrio bacteria has curve in its cell e.g., Vibrio cholerae.
Spirillum (Spira = Coil) : They are spiral or coiled like a cork-screw. The spirillar forms are usually rigid and bear two or more flagella at one or both the ends e.g., Spirillum, Spirochaetes etc.
Filament : The body of bacterium is filamentous like a fungal mycelia. The filaments are very small e.g., Beggiota, Thiothrix etc.
Stalked : The body of bacterium possesses a stalk e.g., Caulobacter.
Budded : The body of bacterium is swollen at places e.g., Rhodomicrobium.
(3) Flagellation : Depending upon the presence or absence of flagella, the bacteria are of following types :
Atrichous : When the flagellum is absent it is called atrichous. e.g., Pasturella, Lactobacillus
Monotrichous : Only one flagellum is found at one end. e.g., Vibrio cholerae.
Lophotrichous : When a group of flagella is present at one end e.g., Spirillum volutans.
Amphitrichous : When single or group of flagella is present at both the end e.g., Nitrosomonas.
Peritrichous : A number of flagella are present all over the body. e.g., E. coli, Clostridium tetani.
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