* Aristotle was the first scientist to classify living organisms (plants and animals) scientifically.
  * Aristotle used simple morphological characters to classify
Two Kingdom Classification
  * Proposed by C. Linnaeus
  * Hedivided organisms into two kingdoms- Plantae and Animalia.
Shortcomings of the system
  * A large number of organisms did not fall into either of the kingdoms.
Three Kingdom Classification
  * Proposed by E. Haeckel
  * He introduced a separate kingdom for all unicellular eukaryotes, Protista.
  * He included fungi, protozoans, algae, bacteria and slime moulds in Protista.
Shortcomings of the system
  * Prokaryotes and eukaryotes were placed together in Protista.
  * Heterotrophic bacteria and fungi placed along with autotrophic algae.
Four Kingdom Classification
  * Proposed by Copeland
  * He introduced a separate kingdom, Monera for all unicellular prokaryotes.
  * The term Monera was given by Daugherty and Allen.
Shortcomings of the system
  * No proper place in this system for fungi.
  * Other characteristics such as cell structure, mode of nutrition, habitat, methods of reproduction, evolutionary relationships etc. were not included.
Five Kingdom Classification
  * It is the advanced and most popular system of classification.
  * It was proposed by R. H. Whittaker (1969)
  * The five kingdoms are Monera, Protista, Plantae, Fungi and Animalia.
  * It is a phylogenetic system but mainly based on mode of nutrition.
  * Other criteria for five kingdom classification − cell structure, thallus organization, reproduction and major ecological role.

Shortcomings of the system
  * Both the kingdoms, Monera and Protista include autotrophic as well as heterotrophic organisms.
  * The three higher kingdoms (Plantae, Animalia and Fungi) do not have a single ancestor.
  * Members of algae are placed in different kingdoms.
  * No proper place in this system of classification for viruses.
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