Summary

Biological classification of plants and animals was first proposed by Aristotle on the basis of simple morphological characters. Linnaeus later classified all living organisms into two kingdoms — Plantae and Animalia. Whittaker proposed an elaborate five kingdom classification — Monera, Protista, Fungi, Plantae and Animalia. The main criteria of the five kingdom classification were cell structure, body organisation, mode of nutrition and reproduction, and phylogenetic relationships.

In the five kingdom classification, bacteria are included in Kingdom Monera. Bacteria are cosmopolitan in distribution and show the most extensive metabolic diversity; they may be autotrophic or heterotrophic in their mode of nutrition.

Kingdom Protista includes all single-celled eukaryotes such as Chrysophytes, Dinoflagellates, Euglenoids, Slime-moulds and Protozoans. Protists have a defined nucleus and other membrane-bound organelles, and they reproduce both asexually and sexually.

Members of Kingdom Fungi show a great diversity in structures and habitat. Most fungi are saprophytic in their mode of nutrition and show asexual and sexual reproduction. Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes are the four classes under this kingdom.

The Plantae includes all eukaryotic chlorophyll-containing organisms — algae, bryophytes, pteridophytes, gymnosperms and angiosperms. The life cycle of plants exhibits alternation of generations — gametophytic and sporophytic generations.

The heterotrophic, eukaryotic, multicellular organisms lacking a cell wall are included in the Kingdom Animalia. Their mode of nutrition is holozoic, and reproduction is by copulation followed by embryological development. …