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Kingdom Classification of Living Organisms

Biology | 7-14 yrs | Reading Pod, Interactive

What is classification of kingdoms of living organisms?

In biology, classification of kingdoms is very important as living organisms need to be classified to study and to understand them better.

Who created the classification of living things?

Classification of living things was first formalised by Carolus Linnaeus (also known as Carl Linnaeus), a Swedish botanist, and zoologist, in 1735. He classified all living things as Plants and Animals on the basis of nutrition and locomotion (mobility).

The two classification system however did not indicate an evolutionary relationship between plants and animals and grouped unicellular and multicellular organisms together and some organisms were not classifiable based on the limiting parameters, including viruses.

The classification of living organisms took on a new journey with the discovery of the microscope. New organism were discovered, and new classification became necessary. Today the classification of living organism consists of six kingdoms.

How did the six kingdom of classification come to be?

The German biologist Earnst Haeckel in 1866, in his book Generelle Morphologie der Organismen, had classified the living world into three kingdoms : Protista, Plants and Animals. The group Protista included all single celled organisms that are intermediate in many respects between plants and animals.

R H Whittaker, an American Taxonomist, classified all living things in a five kingdom classification in 1969. They were Monera, Protista, Fungi, Plants and Animals.

They were classified on the basis of:

  • Complexity of cell structure
  • Complexity of body organisation
  • The mode of nutrition
  • Life style (ecological role)
  • Phylogenetic (evolutionary) relationships

The six kingdoms of classification which is the current standard of classification of all living things was defined around 1980. It was defined by Carl Richard Woese, an American microbiologist.

He based this classification on his studies of ribosomal RNA. His studies made it possible to divide the prokaryotes into two kingdoms, called Eubacteria and Archaebacteria.

What are the six kingdoms of living organisms?

1. Archeabacteria –

  • They are very primitive single celled organisms that live in harsh and severe environments.
  • Prokaryote
  • No true nucleus
  • Unicellular
  • Autotrophic or Heterotrophic
  • Live in extreme conditions and are chemically different from Eubacteria

2. Eubacteria –

  • They are classified as true bacteria and have rigid cell walls.
  • Prokaryote
  • No true nucleus
  • Unicellular
  • Autotrophic or Heterotrophic
  • Live everywhere – “true bacteria”

3. Protist –

  • They are classified as neither plants, animals or fungi. They are generally unicellular.
  • Eukaryote
  • True nucleus
  • Most are unicellular
  • Autotrophic or Heterotrophic
  • Can be protozoa, algae, funguslike, autotrophic, heterotrophic, unicellular or multicellular

4. Fungi –

  • They are classified separately from plants because of the absence of cellulose in their cell walls and the presence of chitin, a hard substance uncommon in plant cells.
  • Eukaryote
  • True nucleus
  • Multicellular (except for yeast)
  • Heterotrophic
  • Digest their food outside of their bodies

5. Plant –

  • They are classified based on the fact that they are multicellular, have chlorophyll and can manufacture their own food.
  • Eukaryote
  • True Nucleus
  • Multicellular
  • Autotrophic
  • All multicellular autotrophs
  • Start food chains, no life on Earth without plants

6. Animal –

  • They are classified based on the fact that they are multi – cellular, have mostly internal digestive systems and do not have rigid cellular walls.
  • Eukaryote
  • True Nucleus
  • Multicellular
  • Heterotrophic
  • All multicellular heterotrophs
  • Largest known kingdom with over 1 million species
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