Highlight the criteria used for the five kingdom system of classification.

Explanation

The criteria used for five kingdom system of classification :
Whittaker has based his scheme of classification on four factors : (i) complexity of cell structure, (ii) complexity of organism's body (iii) mode of nutrition, and (iv) phylogenetic relationships.
1. Structure of Cells. Two main types of cells are recognized : simple, primitive prokaryotic and complex, advanced eukaryotic.
2. Unicellular and Multicellular Organization. The principle of organic evolution has revealed that the earliest organisms were unicellular, they were first simple prokaryotic and later became complex eukaryotic. Some of the latter, in due course of time, evolved into simple multicelllar organisms, many of which finally became complex.
3. Modes of Nutrition. Two main modes of nutrition are recognized in organisms : autotrophic and heterotrophic. Autrotrophic nutrition is further of two types : chemosynthesis and photosynthesis. Photosynthesis may be oxygenic (oxygen-producing) as in plants or anoxygenic (nonoxygen-releasing) as in bacteria. Heterotrophic nutrition is also of two kinds : ingestive or holozoic and absorptive or saprotrophic. Autotrophic, holozoic and saprotrophic modes of nutrition correspond to the three life styles of the organisms recognized by ecologists, namely, producers, consumers and decomposers (reducers) respectively.
4. Phylogenetic Relationships. Phylogeny is the evolutionary history of an organisms. Therefore, phylogenetic relationships of organisms alone are index of their true kinship. Such relationships are not clear in all cases. Only fossil record can provide such relationships but this record is incomplete and is likely to remain so. Therefore, the phylogenetic relationships are ascertained from morphology, cytology, genetics, biochemistry and physiology for the correct classification of the organisms.