Biological Classification

Classification is the process of process of grouping organisms into different categories based on easily observable characters. The earliest classification was done by Aristotle. He used simple morphological characters to classify organisms. He grouped plants into trees, shrubs and herbs. Animals were divided into two groups, animals which have blood and do not have blood.

Linnaeus classified the living organisms into two groups – Kingdom Animalia and Kingdom Plantae. This system is known as Two – Kingdom classification. However, this system could not distinguish eukaryotes from prokaryotes, unicellular organisms from multicellular; and photosynthetic algae from non- photosynthetic algae. Hence, this classification was less accepted.

The most accepted classification system is the Five Kingdom classification proposed by R. H. Whittaker in 1969. He added three more kingdoms. Thus the five kingdoms are Monera, Protista, Fungi, Plantae and Animalia. The classification was mainly based on five different characters.

  1. Cell type: Kingdom Monera includes prokaryotes. All other kingdoms had eukaryotic organisms.
  2. Cell wall: Cell wall is absent in Animalia and in some members of Protista. Monera had non-cellulosoic cell wall. Fungi had chitinous cell wall. Plantae had cellulosic cell wall.
  3. Nuclear membrane: It is present in all kingdoms except Monera.
  4. Body organization: Monera and Protista had cellular organization. All other kingdoms had multicellular organization.
  5. Mode of Nutrition: Kingdom Monera, and Protista are autotrophic as well as heterotrophic. Plantae are completely autotrophic. Fungi and Animaliae are heterotrophic.

Other famous classification systems are – Three domain system, six kingdom system and Eight kingdom system.

Eu – bacteria

Archae -bacteria

Three domain

E U K A R Y A

System

Five kingdom

Monera

Animalia

Fungi

Plantae

Protista

Classification.

Archae -bacteria

Plantae

Protista

Animalia

Eu – bacteria

Six Kingdom

Fungi

Classification

Archae -bacteria

Eu – bacteria

Animalia

Fungi

Eight Kingdom

Plantae

Classification

Chromista

Protista

Archezoa

Five Kingdom Classification

In the Five Kingdom Classification, all prokaryotic organisms were brought together to form the Kingdom Monera.

All unicellular eukaryotic organisms were grouped into Kingdom Protista. By creating this group, Whittaker was able to bring many unicellular organisms which were earlier added in Plantae and Animalia kingdoms.

Most scientists prefer to divide Kingdom Monera into two groups: Eubacteria and Archaebacteria for the convenience in classification. Hence, a Six – Kingdom classification is more prevalent in taxonomy.

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