Introduction to Microbiology

Definition of Microbiology

It is a branch of science that deals with the study of microscopic forms of life these micro-organisms are less than 1 mm in size.

Characteristics of Micro-organisms 

  • These micro-organisms are very small in size generally less than 1 mm.
  • They are not visible through our naked eyes.
  • These organisms are either unicellular or multicellular.
  • Prokaryotic or eukaryotic in nature.
  • They may be motile or non motile.
  • Micro-organisms are present everywhere in our surrounding like air, water,soil, dust and bodies of plants, animals and human beings.

Taxonomic Differentiation of Micro-organisms


Taxonomic Differentiation of Microbes
Taxonomic Differentiation of Microbes


1. Protozoa

  •  Protozoa are unicellular, eukaryotic in nature.
  •  They are parasitic or saprophytic.
  •  The size range of protozoa is generally 10 – 50 micrometer.
  •  These organisms generally exist in aqueous environment and soil.
  •  They show motility by flagella, cilia, or pseudopodia.
  • Protozoa can absorbs their food material by cell membrane or by engulfing the food by phagocytosis.
  • Some parasites are pathogenic in nature .They can reproduce sexually or asexually.

  • Examples of protozoa: Amoeba, Paramecium, Euglena.

2. Algae

Algae (Wikipedia Creative Commons)
  • Algae are eukaryotic, autotrophic, unicellular or multicellular organisms.
  • Their size ranges from 1 micrometer to several feet.
  • Algae are autotrophic in nature as it contain chlorophyll pigment for photosynthesis.
  • It may be motile or non-motile in nature.
  • Algal cells can produce sexually or asexually in nature.
  • They are generally found in moist soil and aquatic environment.
  • Examples of algae-Chlorophyta, Rhodophyta, Phaeophyta, Cyanophyta.

3. Fungus

  • Fungus are eukaryotic,autotrophic or heterotrophic.
  • They are non-motile,unicellular or multicellular in nature.
  • If fungus are unicellular in nature it is called as yeast and if it is multicellular it is differentiated into molds.
  • Fungal cells may be saprophytic or parasitic.
  • It contain septate or non-septate hyphae called as mycellium with a rigid cell-wall.
  • Fungus and fungal spores are generally present in moist places,air,soil and dust.
  • Examples of fungus-Mucor,Aspergillus.

4. Bacteria

  • Bacteria are prokaryotic, unicellular micro-organisms. It size ranges from 1-2 micrometer.
  • It may be cocci,rod or spiral shape.
  • Bacteria reproduce by binary fission.
  • They may be motile or non-motile in nature.
  • Bacteria cointain a well defined cell wall .On the basis of cell-wall bacteria are classified into Gram-positive or Gram-negative bacteria.
  • They may be autotrophic or hetertrophic in nature.
  • Some bacteria are pathogenic in nature.
  • Examples of bacteria:  Staphylococcus aureus, E.coli, Streptococcus, Bacillus.

5. Viruses

  • Viruses are ultra-microscopic structure they are visible through electron microscope.
  • They are obligate intracellular parasites their size is less than 0.2 micrometer.
  • The genetic material is enclosed into a protien coat.
  • It lacks cellular components which are necessary for multiplication it depends on its host for its multiplication.
  • The genetic material may be RNA or DNA.
  • Viruses multiply on living host.
  • Examples of viruses– Herpus virus, HIV, TMV etc.

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