One of the very first organisms that evolved on earth was probably a type of bacteria called cyanobacteria. This was also one of the first photosynthetic organisms on earth and is responsible for the oxygen present in our atmosphere.

Even though most bacteria make us ill, they have a long-term mutual relationship with humans and are very much important for our survival. But before we elaborate on its uses, let us explore the structure of bacteria in detail.

Structure of a Bacteria

Structure of a Bacteria

Bacteria are known for their simple body design. They are single-celled microorganisms with the absence of the nucleus and other cell organelles, hence, they classified as prokaryotic organisms.

They are also very versatile organisms, surviving in extremely inhospitable conditions. Such organisms are called as extremophiles. Extremophiles are further categorized into various types based on the types of environments they inhabit:

  1. Thermophiles
  2. Acidophiles
  3. Alkaliphiles
  4. Osmophiles
  5. Barophiles
  6. Cryophiles

Another fascinating feature of bacteria is their protective cell wall which is made up of a special protein called peptidoglycan. This particular protein isn’t found anywhere else in the world expect in the cell walls of bacteria.

But few of them are devoid of this cell wall and others have a third protection layer called capsule. On the outer layer, one or more flagella or pili is attached and it functions as a locomotory organ as well as attaching part. They do not contain any cell organelle as in animal or plant cell except for ribosomes.

Ribosomes are the sites where synthesis of proteins takes place. Although they possess DNA, it floats within the cell and its region where DNA is present. This region is called as the nucleoid. In addition to this DNA, they have an extra circular DNA called plasmid. These plasmids make some strains of bacteria resistant to antibiotics.

Types of Bacteria

There are various types of bacteria that are grouped into several categories based on various features and characteristics.

Classification of Bacteria

Type of Classification




Bacillus (Rod-shaped)

Escherichia coli (E. coli)

Spirilla or spirochete (Spiral)

Spirillum volutans

Coccus (Sphere)

Streptococcus pneumoniae

Vibrio (Comma-shaped)

Vibrio cholerae

Composition of the cell wall

Peptidoglycan cell wall

Gram-positive bacteria

Lipopolysaccharide cell wall

Gram-negative bacteria

Mode of Nutrition

Autotrophic Bacteria


Heterotrophic Bacteria

All disease-causing bacteria

Type of Respiration

Anaerobic Bacteria


Aerobic Bacteria


Classification of Bacteria

Reproduction of Bacteria

Reproduction of Bacteria

Bacteria follow the asexual mode of reproduction called binary fission. A single bacterium divides to give two daughter cells. These are identical to the parent cell as well as to each other. Replication of DNA within parent bacterium marks the beginning of the fission. Eventually, cell elongates to form two daughter cells. The rate and timing of reproduction depend on the conditions like temperature and availability of nutrients. When there is a favourable condition, E.coli or Escherichia coli produces about 2 million bacteria every 7 hours.

Useful Bacteria

Not all bacteria are harmful to humans, in fact, some of these bacteria are quite important as they provide various functions. For instance, bacteria can:

  1. Convert milk into curd – Lactobacillales or lactic acid bacteria.
  2. Ferment food products – Streptococcus and Bacillus.
  3. Used in preparation of bread, cakes and other bakery food products.
  4. Help in digestion and improving the body’s immunity system.
  5. Production of antibiotics which is used in the treatment and prevention of bacterial infections.

Harmful Bacteria

There are bacteria that can make us seriously sick. They are responsible for many of the deadly diseases like pneumonia, tuberculosis, diphtheria, Syphilis, tooth decay, etc.

There are several methods that can sterilize or disinfect many of these harmful and disease-causing bacteria. These methods include- application of heat, disinfectants, UV radiations, pasteurization, boiling, etc.

Further Reading

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Practise This Question

Nucule and globule are structures present in