Classification Systems of Organisms

Classification Systems of Organisms

There are three classification systems of organisms. These are following

  • Two kingdom classification system
  • Three kingdom classification system
  • Five kingdom classification system

Two kingdom classification systems

  • It is the oldest system of classification
  • It divides organisms into two kingdoms, planate, and Animalia.
  • Plants are autotrophs because they can prepare food from simple organic materials.
  • Animalia is heterotrophs because they cannot prepare their food and depend upon other organisms.
  • Bacteria, fungi, and algae were included in the kingdom Plantae.

Drawbacks of the two-kingdom classification system

  • It does not explain euglena-like organisms because it is plant-like as well as animal-like.
  • It ignores the difference between prokaryotes and eukaryotes.

 Three kingdom classification systems

  • It divides organisms into three kingdoms, Plantae,  Animalia, and Protista.
  • Kingdom Protista was proposed by Ernst Hackel in 1866.
  • Protista includes those organisms that do not fit into Plantae or Animalia i.e. Euglena

 Drawbacks of three kingdom classification system

  • It ignores the difference between prokaryotes and eukaryotes.
  • It places fungi in the kingdom Plantae, which is wrong. 

 Differences of fungi from plants and animals

  • It has cellulose in its cell wall.
  • It gets food by absorption.

   Five kingdom classification systems

  • It was introduced by Robert Whittaker in 1967.
  • It is based on levels of cellular organization and principal modes of nutrition.
  • It divides organisms into five kingdoms, Plantae,  Animalia, Protista, fungi, and Monera.
  • Kingdom monera have prokaryotic cells. Kingdom Protista, Fungi, Plantae, and Animalia have eukaryotic cell

Kingdom Monera

  • It includes organisms formed by prokaryotic cells i.e bacteria and cyanobacteria.
  • Prokaryotic cells may be unicellular or form chains, clusters, or colonies.
  • Prokaryotic cells are different from eukaryotic cells.

Kingdom Protista

  • It includes eukaryotic unicellular or multicellular organisms.
  • There are three types of protists.
  1. Algae: These are plant-like protists. These have cell walls and chlorophyll. These are unicellular, colonial, or multicellular.
  1. Protozoans: These are animal-like protists.
  2. Fungus  like protists

Importance of kingdom Protista 

Biologists believe that plants, animals, and fungi are evolved from Protista. Protists are evolved from monera.

Kingdom fungi

  • It includes eukaryotic multicellular, heterotrophic organisms which get food by absorption.
  • They live on organic matter and mostly are decomposers.
  • Its example is mushrooms.

Kingdom Plantae

  • It includes eukaryotic, multicellular, autotrophic organisms. e.g mosses, flowering plants, etc.
  • Plants can make their own food by photosynthesis.
  • These have multicellular sex organs and form embryos.

Kingdom Animalia

  • It includes eukaryotic, multicellular, consumers. e.g. cow, earthworm, etc.
  • Animals ingest food and digest it in body cavities.
  • They show movements.

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