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Chapter: 11th 12th standard bio zoology Human Body higher secondary school

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Classification of bacteria based on the shape and arrangement

Classification of bacteria based on the shape and arrangement
The rigid bacterial cell wall determines the shape of a cell. Typical bacterial cells are spherical (Cocci), straight rods (Bacilli) or rods that are helically curved (spirilla), some bacterial cells are pleomorphic ie they can exhibit a variety of shapes eg. Arthrobacter

Classification of bacteria based on the shape and arrangement

 
The rigid bacterial cell wall determines the shape of a cell. Typical bacterial cells are spherical (Cocci), straight rods (Bacilli) or rods that are helically curved (spirilla), some bacterial cells are pleomorphic ie they can exhibit a variety of shapes eg. Arthrobacter
Cocci bacteria appear in several characteristic arrangements depending on their plane of division.
 
 Diplococci: Cells divide in one plane and remain attached in pairs.

Streptococci: cells divide in one plane and remain attached to form chains.

Tetracocci: : Cells divide in two planes and form group of four cells.
 
Staphylococci: cells divide in three planes, in an irregular pattern, producing bunches of cocci.
 
E. Sarcinae: cells divide in three planes, in a regular pattern, producing a cuboidal arrangement of cells.
Bacilli forms occur singly or in pairs (diplobacilli) or form chains (streptobacilli). In Corynebacterium diphtheriae which is a bacillus species, the cells are arranged side by side like match sticks (palisade arrangement).
 
 

Occurrence

 
Bacteria are omnipresent. They are found in all environments, where organic matter is present. They are found in air, water, soil and also in or on the bodies of plants and animals. Some of the bacteria live as commensals (eg. Escherichia coli in the human intestine) and some live as symbionts (eg. Rhizobium) in the root nodules of leguminous plants. Several of them cause diseases in plants, animals and human beings.
 

Size

 

Bacteria are very small, most being approximately 0.5 to 1 micron in diameter and about 3 to 5 microns in length.


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