Whittaker has used the following three criteria for delimiting the different kingdom:
(a) Complexity of cell structure, prokaryotic and eukaryotic.
(b) Complexity of body structure or level of structural organisation, unicellular and multicellular.
(c) Mode of nutrition is autotrophic and heterotrophic. Whittaker's five kingdom are Monera, Protista, Plantae, Fungi and Animalia.
Advantages of this classification :
(a) It exhibits phylogenetic relationship between diverse groups.
(b) It justifies the position of algae, fungi, higher plants, animals.
Euglena and bacteria etc., indicates levels of organization, nutrition and major ecological roles.
Disadvantages of this classification:
(a) Protists show great diversity.
(b) Three higher kingdoms are polyphyletic.
(c) Viruses are not prokaryotes or eukaryotes. They do not belong to any kingdom.