The five kingdoms:

In 1937, E-Chatton suggested the terms "Procariotique" to describe bacteria and "Eukariotique" to describe animal and plant cells. In 1967, Robert Whittaker introduced the five-kingdom classification system. This system is based on:

1. The levels of cellular organization i.e. prokaryotic, unicellular eukaryotic, and multicellular eukaryotic.
2. The principal modes of nutrition i.e. photosynthesis, absorption, and ingestion. On this basis, organisms are classified into five kingdoms: monera, protista, fungi, Plantae, and Animalia.

Modification in the five kingdoms classification:

In 1988, Lynn Margulis and Karlene Schwartz modified the five-kingdom classification of Whittaker by considering cellular organization, mode of nutrition, cytology, genetics, and organelles of symbiotic origin (mitochondria and chloroplast) They classified the organisms into the same five kingdoms as proposed by Whittaker.