Bacteria and their types — lesson. Science State Board, Class 9.

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எங்கள் ஆசிரியர்களுடன் 1-ஆன்-1 ஆலோசனை நேரத்தைப் பெறுங்கள். டாப்பர் ஆவதற்கு நாங்கள் பயிற்சி அளிப்போம்

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Bacteria are single-celled, microscopic organisms that live in a variety of environments. These are the simplest unicellular organisms with rigid cell walls that resemble plant cells. These species occur in soil, the ocean, and even the human intestine. There are numerous beneficial bacteria that aid in the digestion of both humans and animals. The diseases typhoid and tuberculosis are caused by bacteria.

Bacterial morphology

Introduction:

The study of bacteria is called Bacteriology.

Bacteria are classified under the kingdom called Monera.

Bacteria are present in nearly every habitat on earth, including humans. Some species can live under extreme conditions of temperature and pressure.

Bacteria are microscopic, single-celled, prokaryotic organisms because they do not have a true nucleus and other membrane-bound cell organelles.

Bacteria play an essential role in human survival—they break down nutrients in the digestive system into simpler forms.

The majority of bacterial species exist as single-celled forms. Some types of bacteria appear to be filaments of loosely joined cells, e.g. Actinomycetes.

The size ranges from less than \(1\) to \(10\)μm in length and \(0.2\) to \(1\)μm in width.

Different types of bacteria's and their size

Bacteria may be motile (able to migrate independently) or non-motile (unable to move on their own). For motility, they have unique structures called flagella that facilitate locomotion found on the cell surfaces.
Flagella are long, helical shaped structures, composed of subunits of proteins named flagellin. The base of the flagellum looks slightly broader, which is called as a hook. Hook joins filament to the motor portion of the flagellum called a basal body. The basal body is attached to the cytoplasmic membrane and cell wall. The location of flagella varies with bacterial species.

Classifications of bacteria:

1. Based on the arrangement of flagella:

Depending on the flagellum, bacteria are classified into four types.

The types bacteria's based on the flagellum

Monotrichous: Having a single flagellum at one pole.

E.g. Vibrio cholerae, Pseudomonas aeruginosa

Lophotrichous: A cluster of flagella located at one end only.

E.g. Pseudomonas fluorescens, Spirillum

Amphitrichous: Either a single or cluster of flagellum present at both cell poles.

E.g. Aquaspirillum serpens, Alcaligenes faecalis

Peritrichous: Flagella arranged along the sides of the bacteria.

E.g. Salmonella typhi, Escherichia coli

2. Shape of the bacteria:

Depending on the shapes, bacteria are classified into three types.

Type of bacteria	Shape	Example
Cocci - Spherical shaped (Cocci - Plural; Coccus - Singular)	These are unicellular, spherical or elliptical shaped.	Streptococcus pneumoniae
Bacilli -Rod-shaped (Bacilli - Plural; Bacillus - Singular)	Rod-shaped or cylindrical bacteria that either remain single or in pairs.	Mycobacterium tuberculosis
Spirillum -Spiral shaped (Spirilla - Plural; Spirillum - Singular)	These are spiral or spring-like with multiple curvature and terminal flagella.	Treponema pallidum
Vibrio -Comma shaped (Vibrios - Plural; Vibrio - Singular)	These are curved and have the appearance of a comma.	Vibrio cholerae