Question

Whittaker’s five-kingdom classification was a more logical method of classification as compared to the two-kingdom classification. Justify the statement.

Answer 1

1. The two-kingdom classification was proposed by Carolus Linnaeus. He classified all organisms into two kingdoms based on nutrition and locomotion.
2. The two kingdoms were ‘Animalia’ (for animals) and ‘Plantae’ (for plants).
3. This system did not distinguish between: eukaryotes and prokaryotes, unicellular and multicellular organisms, and photosynthetic and non-photosynthetic organisms.
4. A large number of organisms did not fall into any category, for example, Euglena (unicellular).
5. These demerits were rectified in the five-kingdom classification, which was proposed by R. H Whittaker. The main criteria for classification were as follows:
   • Cell type: prokaryote or eukaryote.
   • Body organization: unicellular or multicellular.
   • Cell wall: whether cell wall is present or not.
   • Nuclear membrane: whether a well-defined nucleus surrounded by a nuclear membrane is present or not.
   • Mode of nutrition: autotrophs or heterotrophs.
6. Organisms that are prokaryotes and unicellular were placed under the kingdom ‘Monera’.
7. Eukaryotic unicellular organisms were placed under the kingdom ‘Protista’.
8. Eukaryotic heterotrophic organisms that included both unicellular and multicellular organisms were placed under the kingdom ‘Fungi’.
9. Multicellular organisms that can perform photosynthesis were placed under the kingdom ‘Plantae’.
10. Eukaryotic organisms that are multicellular and heterotrophic were placed under the kingdom ‘Animalia’. They lack a cell wall.
11. Thus, a more accurate classification method was possible through five-kingdom classification.