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Revision Notes»Biology»Microbes in Human Welfare

Revision Notes on Microbes in Human Welfare

Bacteria

(1) Study of bacteria is called bacteriology.

(2) Linnaeous placed them under genus vermes.

(3) Nageli classified bacteria under schizomycetes.

(4) Bacteria are unicellular, microscopic organisms.

(5) These are the smallest cell wall having prokaryotic cell.

(6) They differ from animals in having a rigid cell wall and being capable to synthesize vitamins.

Size:

(i) Bacteria are the smallest of all known cellular organisms which are visible only with the aid of microscope.

(ii) They are 3 to 5 microns (1 m = 1/1000 millimetre or about 1/25,000 inch) in length.

(iii) A few species of bacteria are approximately 15m in diameter.

Shape:

(i) The shape bacteria usually remain constant.

(ii) Some of them are able to change their shape and size with changes in environmental conditions. Such bacteria, which change their shape, are called pleomorphic.

(iii) The bacteria possess the following forms.

(a) 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.

(b) Bacilli: They are rod–shaped bacteria with or without flagella. They may occur singly (bacillus), in pairs (diplobacillus) or in chain (streptobacillus).

(c) Vibrios: These are small and ‘comma like, kidney like. They have a flagellum at one end and are motile, vibrio bacteria has curve in its cell e.g., Vibrio cholerae.

(d) Spirillum (Spira = Coil): The spirillum bacteria (plural-spirilla). 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, spirochaete, etc.

(e) Filament: The body of bacterium is filamentous like a fungal mycelia. The filaments are very small e.g. Beggiota, Thiothrix etc.

(f) Stalked: The body of bacterium posses a stalk e.g. Caulobacter.

(g) Budded: The body of bacterium is swollen at places e.g. Retrodomicrobiom.

Explanation:

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