General Description of Bacteria | Kingdom Monera : Class 11

BIOLOGY | BOTANY
UNIT FOUR : KINGDOM MONERA
Class : 11

Bacteria

Bacteria are discovered by Anton Van Leeuwenhoek in 1676. They are found everywhere in air, water, soil, and bodies of organisms. There is no natural death of bacteria. They are killed either using chemicals or by infecting with virus. 

Morphology 

Size of the bacteria varies from 2-5µm and 0.3-0.8µm width in rod shaped bacteria. In spherical bacteria the size varies from 0.5 – 1µm in diameter. 

Spherical bacteria: the bacteria having spherical in shape are called coccus bacteria. The coccus bacteria may be found singly and freely are called monococcus or micrococcus. When they are found in the group of two is called diploccus. Sometimes they are found in the group of four are called tetracoccus. Some of them are found in chain are called streptococcus and some are found in large group like bunch of grape called staphylococcus. 

Rod like Bacteria: the bacteria having shape of the cell is if rod like called bacillus. The bacillus bacteria are found in singly and freely are called monobacillus. Some of them are found in the group of two are called diplobacillus. They are also found in chain are called streptobacillus. 

Helical Bacteria: The bacteria having shape of the cell is coiled called helical bacteria. These are of two types: 

Vibrio: The bacteria having the shape are comma like are called Vibrio. eg. Vibrio cholera. 

Spirillum: The bacteria having shape is helically coiled are called Spirillum. 

Cell Structure 

Capsule : The capsule is the outer most covering of gelatinous substance is called capsule. It is made up of polysaccharides. The capsule may be absent in some bacteria. They are called non-capsulated bacteria and other having capsule are called capsulated bacteria. Usually the capsulated bacteria are poisonous or virulent that causes diseases and the non-capsulated bacteria are non-virulent. The function of the capsule is to protect cell, protects from desiccation and secrets poisons. 

Cell wall 

It is found under the capsule in capsulated bacteria and the outermost layer in non-capsulated bacteria. It is rigid and is composed of a kind of complex substance called peptidoglycan or Murine or Mucopeptide. The peptidoglycan is composed of complex carbohydrates called N-acetyle muramic acid and N acetyl glucosamine and aminoacid ie. L alanine, D alsnine and D glutanic acid. Polysaccharides and lipids are also present in cell wall. 

Function of cell wall

It provides rigidity to the cell, it maintains cell shape; it protects protoplasm of the cell. 

Cell membrane 

It is thin elastic and permeable membrane made up of protein and phospholipids. The main function is protection, maintains cell shape, and helps in osmosis and diffusion.