1. Living World and Classification of Microbes

 Biodiversity and need of classification :

  • According to 2011 census, around 87 million species of living organisms are found on the earth- including land and sea. 
  • The process of dividing living organism into groups and subgroups is called Biological classification.
  • Carl Linnaeus in 1735 divided living world in 2 kingdoms -

  1. Vegetabilia 
  2. Animalia.

  • Haeckel in 1866 considered 3 kingdoms- 
  1. Protista
  2. Plants 
  3. Animals.

  • In 1925 - Chatton created two groups 
  1. Prokaryotes 
  2. Eukaryotes.

  • In 1938 Kopland divided living organisms into 4 kingdoms-
  1. Monera
  2. Protista
  3. Plants 
  4. Animals.
  • Robert Harding Whittaker (1920-1980) was an American Ecologist. 
  • In 1969 he dividedliving organisms into 5 groups.
  1. Kingdom : Monera 
    •  Unicellular,Prokaryotes
  2. Kingdom : Protista 
    • Multicellular,Eukaryotes
  3. Kingdom : Fungi 
    • Unicellular,Eukaryotes 
    • Cell wall present 
    • Organisms can’t perform photosynthesis
  4. Kingdom : Plantae 
    • Multicellular,Eukaryotes
    • Cell wall present 
    • Organisms can performs photosynthesis.
  5. Kingdom : Animalia : 
    • Multicellular,Eukaryotes
    • No cell wall
  • For this classification Whittaker considered following criteria
  1. Complexity of cell structure : Prokaryotic and Eukaryotic.
  2. Complexity of organisms : Unicellular or Multicellular.
  3. Mode of nutrition : Plants - Autotrophic- Photosynthetic Fungi- Saprophytic- Absorption from dead organisms. Animals- Heterotrophic and ingestive.
  4. Life style : Plants - Producers Animals - Consumers Fungi - Decomposers
  5. Phylogenetic relationship : Prokaryotic to Eukaryotic, unicellular to multicellular.
Kingdom 1 : Monera : 
  • lactobacilli bacteria present in curd or buttermilk.
  • All type of bacteria and blue green algae  are included in the kingdom Monera.
Characteristics :
  • All the organisms are unicellular.
  • Autotrophic or heterotrophic.
  • Prokaryotic cells without distinct nucleus or cell organelles
Kingdom 2. Protista :
  • Single celled organisms with well defined nucleus enclosed in a nuclear membrane.
  • They have pseudopodia or hair like cilia or whip like flagella for locomotion.
  • Autotrophs- eg. Euglena, Volvox contain chloroplast.
  • Heterotrophs- eg. Amoeba, Paramoecium
Kingdom 3. Fungi :
  • Non-green, eukaryotic, heterotrophic organisms.
  • Most of them are saprotrophs. 
  • They feed upon decaying organic matter.
  • Cell wall is made up of tough and complex sugar called ‘Chitin’.
  • Some fungi are thread like and many nuclei are present in the cytoplasm.
  • Examples- Baker’s yeast, Aspergillus (Fungus on corn), Penicillium, Mushrooms.
Institutional Work : National Institute of Virology, Pune :
  • It is involved in research on viruses. 
  • This institute has been founded in 1952 under the jurisdiction of Indian Council of Medical Research.

Whittaker's five kingdom system is widely accepted.

Classification of Microbes :
  • Among the living organisms, microorganisms are largest in number. 
  • Hence they are classified as follows :
  1. Bacteria
  2. Protozoa
  3. Fungi
  4. Algae
  5. Viruses
1. Bacteria (size – 1 mm to 10 mm) :
  • Unicellular, independent / parasitic  organisms. 
  • Sometimes many bacteria together form colonies.
  • Bacterial cell is prokaryotic with cell wall, but distinct nucleus or cell organelles are absent.
  • Reproduce by simple binary fission.
  • In favourable conditions, bacteria grow vigorously and can double their number in 20 minutes.
2. Protozoa (size - approximately 200 mm) :

  • Found in soil, fresh water and sea water. 
  • Some are found in the body of other organisms and are pathogenic.
  • Unicellular organisms with eukaryotic cell.
  • Great variation in cell structure, organs of locomotion and modes of nutrition among protozoans.
  • Reproduce by simple cell division.
  1. Eg.- Amoeba, Paramoecium - Free living in dirty water.
  2. Entamoeba histolytica - causes amoebiasis.
  3. Plasmodium vivax- causes malaria
  4. Euglena - autotrophic
3. Fungi- (size- approximately 10 mm to 100 mm) :
  • Found on decaying organic matter and dead bodies of plants and animals.
  • Eukaryotic organisms. 
  • Some are unicellular and others are visible with naked eyes.
  • Saprotrophic, absorb their food from decaying organic matter.
  • Reproduce sexually and asexually by cell division or by budding.
  • Eg. Baker's yeast, Candida, Mushroom.
4. Algae- (size- approximately 10 mm to 100 mm):
  • Aquatic.
  • Eukaryotic, unicellular, autotrophic organisms.
  • Photosynthesis is carried out with the help of chloroplast present in the cell.
  • Eg. Chlorella, Chlamydomonas
  • Very few species of algae are unicellular. 
  • Most of them are multicellular and visible with naked eyes.
5. Viruses-( size- approximately 10 nm to 100 nm) :
  • Generally, viruses are not considered as living organisms or they are said to be “Organisms at the edge of living and nonliving.” 
  • They are studied under microbiology.
  • Viruses are extremely minute i.e. they are 10 to 100 times smaller than bacteria. 
  • Can be seen only with electron microscope.
  • Found in the form of independent particles .
  • Virus is a long molecule of DNA (Deoxyribo Nucleic Acid) or RNA (Ribo Nucleic Acid) covered by a protein coat.
  • Viruses survive only in living plant or animal cells and produce their own proteins with help of host cell and create their numerous replica. 
  • Then they destroy the host cell and become free. 
  • These free viruses again infect new cells.
  • Viruses cause many diseases to plants and animals.
Ex- 
  1. Human – polio virus, Influenza virus, HIV – AIDS virus etc.
  2. Cattle- picorna virus
  3. Plants- Tomato- Wilt virus, Tobacco mosaic virus etc.
  4. Bacteria- Bacteriophage (viruses attack bacteria).
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