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Bacterial Cell

The cell is the structural and functional unit of life. All living organisms on earth are made up of single or many cells.

Bacteria are single cellular microscopic organisms. The study of bacteria is known as bacteriology and it is a branch of microbiology. The singular world of bacteria is bacterium.Bacteria have been grouped into prokaryotic, which means absence of nucleus.

Structure of Bacteria


Structure of a Bacteria

 

Characteristics of Bacteria

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$\rightarrow$ There are 3 types of bacteria based on their shapes such as: Bacteria grow in number not in size, but they make copies of themselves by dividing into half. There are three basic shapes of bacteria:

  • Rod shaped bacteria called as bacilli.
  • Spherical shaped bacteria called as cocci.
  • Curved shaped bacteria called as spirilla.

Some of the bacteria exist as single cells, others exist as cluster together.

 Respiration in bacteria: 

Anaerobic bacteria: does not require oxygen for respiration.
Aerobic bacteria: require oxygen for respiration.

Gram staining bacteria are a method of differentiating bacterial species into two large groups, which are based on their chemical and physical properties of their cell wall.

Gram positive bacteria: Those bacteria when they are stained in gram stain results in purple colour.
Gram negative bacteria: Those bacteria when they are stained in gram stain results in pink colour.
Locomotion of bacteria:
They move around by using their locomotion organs such as cilia and flagella.

Nutrition of bacteria:
They exhibits different modes of nutrition level such as-

  • Autotrophic bacteria: These bacteria are able to synthesize their own food. For e.g.: Phototropic bacteria and chemosynthetic bacteria
  • Heterotrophic bacteria: These bacteria are unable to synthesize their own food, hence they depends on other organic materials. For e.g.: saprophytic bacteria-these bacteria feeds on dead and decaying matter.
  • Symbiotic bacteria: These bacteria have a mutual benefit from other organisms. For e.g.: nitrogen fixing bacteria (or) rhizobium. 
  • Parasitic bacteria: These bacteria are present in plants, animals and human beings. These bacteria feeds on host cells and causes harm to the host. 

Reproduction in Bacteria:
The reproduction in bacteria is mainly by cell division and binary fission. In some cases few bacteria also reproduce by budding.

Bacterial Cell Structures

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Bacterial Cell Structure

Cell Wall:
  • Cell walls of bacteria are made up of glycoprotein murein.
  • The main function of cell wall is it helps in providing support, mechanical strength and rigidity to cell.
  • It protects cell from bursting in a hypotonic medium.
Plasma Membrane:
  • It is also known as cytoplasmic membrane (or) cell membrane.
  • It is composed of phospholipids, proteins and carbohydrates, forming a fluid-mosaic.
  • It helps in transportation of substances including removal of wastes from the body.
  • It helps in providing a mechanical barrier to the cell.
  • Plasma membrane acts as a semi permeable membrane, which allows only selected material to move inside and outside of the cell. 
Cytoplasm:
  • Helps in cellular growth, metabolism and replication.
  • Cytoplasm is the store houses of all the chemicals and components that are used to sustain the life of a bacterium.
Ribosome:
  • A tiny granule made up of RNA and proteins.
  • They are the site of protein synthesis.
  • They are freely floating structures that helps in transferring the genetic code.
Plasmid:
  • Plasmids are small circle of DNA.
  • Bacterial cells have many plasmids.
  • Plasmids are used to exchange DNA between the bacterial cells.
Flagella:
  • This is a rigid rotating tail.
  • It helps the cell to move in clockwise and anticlockwise, forward and also helps the cell to spin.
  • The rotation is powered by H+ gradient across the cell membrane.  
Pilli:
  • Short protein appendages.
  • Smaller than flagella.
  • Fixes bacteria to surfaces.
  • It also helps in reproduction during conjugation.
Capsule:
  • Capsule is a kind of slime layer, which covers the outside of the cell wall.
  • They are composed of a thick polysaccharide.
  • It is used to stick cells together and works as a food reserve.  
  • It protects the cell from dryness and from chemicals.
Bacterial Cell
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