Whittkar has based his scheme of classification of living organisms into five kingdom on four factors:
(i)Comlexity of cell structure : There are two broad categories of cell structure : Prokayotic and Eukaryotic. Thus, two broad groups can be formed- one having prokaryotic cell structure and the other having eukaryotic cell strcuture. Presence and absence of cell wall is another important charcteristics.
(ii) Unicellular and multicellular organisms: This characteristic makes a very basic distinction in the body designs of organisms and helps in their broad categorization.
(iii) Mode of nutrition : Organisms basically have type of modes of nutrition- Autotrophic (they can manufacture their own food) and Heterotrophic (i.e., obtian their food from external environment). Thus, they can be broady categorized into different gropus on the basic of the their modes of nutrition.
(iv) Phylogenetic relationship : Phylogney is the evolutionary history of an organism. It is believed that the simple organisms are primitive and complex organisms are advanced. Thus, 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 the Protista, from which the remaining three kindogms of multicellular organisms have evolved.
