Five kingdoms-three-domain system-classification
THREE KINGDOM SYSTEM OF CLASSIFICATION
♣ Ernst Haeckel (1866), a German zoologist suggested that a third kingdom, Protista be created to include those unicellular microorganisms that are typically neither plants nor animals. He included bacteria, algae, fungi and protozoa under Protista.
♣ Three kingdoms according to Haeckel are Protista, Plantae and Animalia.
♣ This solves the problem of assigning suitable kingdom to the organisms which have similarities with both plants and animals. However, certain drawbacks of two kingdoms system, persist in this system also.
♦Acellular and multicellular organisms are kept together in Protista.
♦ Bacteria and fungi have been grouped with unrelated organisms.
FOUR KINGDOM SYSTEM OF CLASSIFICATION
♣ Copeland (1956), an American taxonomist, suggested that all prokaryotes. i.e., bacteria. cyanobacteria, etc., be placed under kingdom Monera (= Mychota). According to Copeland, four kingdoms are Monera (= Mychota), Protista, Plantae and Animalia.
♣ Protista is single-celled eukaryotic organisms. Fungi continued to remain with plants.
♣ The main drawback of this system is that fungi are not properly placed.
FIVE KINGDOME SYSTEM OF CLASSIFICATION
♣ According to Robert H. Whittaker (1969), an American ecologist, non-chlorophyllous heterotrophic plants to be classified under kingdom Fungi. Five kingdoms in which the living world is divided are Monera, Protista, Fungi, Plantae / Metaphyta (Plants) and Animalia / Metazoa (Animals).
♣ Five Kingdom: classification is based mainly on following three main criteria:♦ Complexity of cell structure: prokaryotic or eukaryotic
♦ Complexity of cellular organisation: cellular or multicellular
♦ Mode of nutrition: autotrophic or heterotrophic.
♣ Other criteria include ecological lifestyles like producers, consumers and decomposers, and the phylogenetic relationships.
♣ The organisms, according to the Five Kingdom System, are re-distributed into additional three kingdoms while retaining the two kingdoms-Plantae and Animalia. All multicellular, mobile and heterotrophic organisms were assigned the kingdom Animalia. The photosynthetic multicellular organisms were included in the kingdom Plantae. Some of the unicellular algae and protozoans were taken out from the plant and animal kingdoms and were included in a separate kingdom. Protista. Heterotrophic plants were placed into kingdom Fungi. All bacteria and multicellular blue-green algae with prokaryotic cell were transferred from kingdom Plantae to a new kingdom Monera.
♣ In the five-kingdom classification, it is thought that the Monera has given rise to the Protista, which gave rise to the remaining three kingdoms of a multicellular organism, viz, Fungi, Plantae, and Animalia.
