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.

2. Protozoans: These are animal-like protists.
3. 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.