KINGDOM SYSTEM OF CLASSIFICATION

KINGDOM SYSTEM OF CLASSIFICATION

Based upon various criteria’s the organisms were divided into kingdoms. First into two then three, then four and ultimately into five kingdoms.

Two kingdom classification;- In two kingdom system of classification organisms were grouped on the basis of presence and absence of cell wall and gross morphology as proposed by C. Linnaeus (father of taxonomy) in 1735. Linneus divided living organisms into two kingdoms animalia (animals) and vegetabilis (plants).

Merits;-

• It was easy to understand.
• Organisms were divided on the basis of specific characters.
• It initiated a systematic method of classifying organisms.
• This basic classification was later on elaborated by addition of other characters’.

Demerits;-

• This system does not distinguish between prokaryotes and eukaryotes, unicellular and multicellular, photosynthetic and non photosynthetic organisms.
• Large no of organisms did not fall in any of the category.
• No position were assigned for slime moulds, euglena etc.

Three kingdom systems- Ernst Haeckel in 1866 separated unicellular animals, algae and fungi on the basis of lack of tissue differentiation and a new kingdom “Protista’ was introduced.

Four kingdom system;- Copeland in 1956 separated unicellular prokaryotes from the kingdom Protista of Haeckel on the basis of presence and absence of nuclear membrane and a new kingdom “Monera” was introduced.

Five kingdom systems:-

R. H. Whittaker 1969 divided all the organisms into five kingdoms based on cell structure, thallus organization, and mode of nutrition, reproduction and phylogenetic relationships. He separated fungi from the plant kingdom of Copeland and a new kingdom “fungi” was introduced. He divided living organisms into five kingdoms i.e Monera, Protista, fungi, plantae and animalia.

Merits of Five Kingdom Classification

• This system of classification is more scientific and natural.
• It is the most accepted system of modern classification as the different groups of animals are placed phylogenetically.
• The prokaryotes are placed in a separate kingdom as they differ from all other organisms in their organization.
• As the unicellular organisms are placed under the kingdom protista, it has solved many problem related to the position of organisms like euglena.
• The fungi totally differ from other primitive eukarytotes hence, placing the group fungi in a status of kingdom is justifiable.
• The kingdom Plantae and Animalia shows the phylogeny of different life styles, in the five kingdom classification, they are more homogeneous group than the two kingdom classification.
• This system of classification clearly indicates cellular organization and modes of nutrition, the character which have appeared very early in the evolution of life.

Demerits of Five Kingdom Classification

• This system of classification has drawbacks with reference to the lower forms of life.
• The Kingdom of Monerans and the Protists include diverse, heterogeneous forms of life. In both the kingdoms there are autotrophic and heterotrophic organisms. They also include organisms which have cells with cell wall and cells without cell wall.
• All the organisms of these three kingdoms do not originate from a single ancestor.
• Multicellular organisms have originated from protists several times.
• Organisms like the unicelluar green algae like volvox and chlamydomonas have not been included under the Kingdom Protista because of their resemblance to other green algae.
• The general organization of the slime moulds are completely different from the members of protists.
• In this system of classification viruses have not been given proper place.