The criteria considered for classification by Whittaker are as follows:
1. Complexity of cell structure: Whether the cells of the organisms are prokaryotic or eukaryotic.
2. Complexity of organisms Whether the organisms are unicellular or multicellular is considered.
3. Mode of nutrition Whether the organism is autotrophic and is performing photosynthesis on its own or it is heterotrophic is considered. Plants are autotrophic, fungi are saprotrophic while animals use food from plants or other animals and hence they are heterotrophic.
4. Lifestyle According to nutrition, every living organism is at certain trophic level. This is called lifestyle. Plants are producers, animals are consumers while fungi are decomposers.
5. Phylogenetic relationship When the evolution proceeded gradually, there was transition from prokaryotes to eukaryotes, unicellular to multicellular. In this order the different groups of living organisms were evolved. This is known as phylogenetic relationship.
