Types of Micro-organisms

Micro Organism of Class 8

Micro-organisms are classified into four major groups:

  • Bacteria (Singular bacterium)
  • Fungi (Singular fungus)
  • Protozoans
  • Algae (Singular alga)
  • Viruses (Singular virus)


These are simple, single-celled organisms that can be found everywhere. Bacteria are found in three different shapes:

  • Rod-shaped, called bacilli
  • Spherical, called cocci
  • Spiral, called spirilla.

spiral bacteria

Spiral bacteria

rod shaped bacteria

Rod shaped bacteria


They are plant-like organisms without the green pigment (chlorophyll). Fungi may be unicellular (yeast) or multicellular (Bread mould, Penicillium, Aspergillus). They are preferably found at moist places.




They are unicellular animal-like organisms. They can move from place to place and also capture food.Amoeba, Giardia and Paramecium are examples of protozoa.




These are plant-like organisms that have cell walls and chlorophyll. Almost all algae live in water. Algae can be unicellular (eg. Chlamydomonas) or multicellular (eg. Spirogyra).


micro organism revision


Viruses are smaller than any known cell. They lack cellular structure and appear as non-living. But when a virus enters a living cell (a bacterium, plant, animal or even human being), it is able to reproduce.



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