Explain the basis for groupings into five kingdoms.

Whittaker (1959) has based his scheme of classification of living organisms into five kingdoms (namely Monera, Protista, Fungi, Plantae and Animalia) on following four bases:
1. Complexity of cell structure. There are two broad categories of cell structure: Prokaryotic and Eukaryotic. Thus, two broad groups can be formed – one having prokaryotic cell structure and the other having eukaryotic cell structure. Presence or absence of cell wall is another important characteristic.
2. Unicellular and multicellular organisms. This characteristic makes a very basic distinction in the body designs of organisms and helps in their broad categorizations.
3. Mode of nutrition. Organisms basically have two types of nutritions – autotrophic (they can manufacture their own food) and heterotrophic (they obtain their food from external environment, i.e., from other organisms). Thus, organisms can be broadly classified into different groups on the basis of their mode of
nutrition.
4. Phylogenetic relationship. Phylogeny is the evolutionary history or ancestry of an organism. It is believed that the simple organisms are primitive and complex organisms are advanced. This, primitive and advance nature of organisms also helps in their classification into broad groups. For example, the Monera are believed to have given rise to Protista, from which the remaining three kingdoms of multicellular organisms have evolved.