Carolus Linnaeus divided the organisms into two kingdoms, the plant Kingdom and the Animal Kingdom. This system was based on the characteristics of animals and the plants.

Shortcomings of Two Kingdom System of Classification

The cell of bacteria consists of cell wall and it is heterotrophic. They show characters of both plants and animals. The body of fungi is highly branched and cell has cell wall but they are heterotrophic and the stored food is glycogen. Hence, they show both plant and animal like characters. A kind of protozoan named Euglena contains chlorophylls and shows locomotion. It also shows both plant and animal like characters.

Five Kingdom System of Classification

To include all the organisms, Robort H Whittaker in 1969 proposed a new system of classification. In his system, the organisms are included in five kingdoms. They are Monera, Protista, Fungi, Animalia, and Plantae. This system is based on cellular complexity, body structure, and mode of nutrition.

General Characters:

Kingdom Monera: This kingdom includes all the unicellular, microscopic, and prokaryotic organisms, which do not contain a well-defined nucleus, the nuclear material is freely found in cytoplasm, they lack well- developed cell organelles, they may be auto or heterotrophic Example: Bacteria and Cyanobacteria

Kingdom Protista: This kingdom includes all the unicellular but eukaryotic organisms which are: auto or heterotrophic, the cell contain well defined nucleus and cell organelles, all the vital activities are performed by single cell, Example: Euglena, Volvox, Paramecium, Amoeba

Kingdom Fungi: This kingdom includes all the multicellular few are unicellular eukaryotic organisms, which are: Heterotrophic that grows on decaying organic matter, achlorophyllous, branched body, do not show locomotion, cell wall is made up of chitin, reserve food is glycogen. Example: Yeast, Mucor, Mushroom.

Kingdom Animalia: This kingdom includes all the multicellular eukaryotic organisms, which are: heterotrophic that feeds on autotrophic organisms through different way, show movement, no cell wall is present, reserve food is glycogen, body is compact. Example: Rat, Pigeon, Frog

Kingdom Plantae: This kingdom includes all the multicellular eukaryotic organisms which are: autotrophic due to having chlorophyll molecules for photosynthesis, cellulosic cell wall is present, reserve food is starch, do not show locomotion, body is branced. Example: mustard, mango etc.

In this system the monera are thought to have originated at first. The protista are originated from monera. From protista Fungi and animalia and plantae were evolved. This shows a evolutionary relationship among five kingdoms. This relationship is called phyllogenetic relationship. The evolutionary history of an organism is called phylogeny. The classification based on the phyllogenetic relationship is called phylogenetic system of classification.