R.H whittaker(1969) Proposed a Five Kingdom Classification.The Kingdoms Defined By him were named Monera,Protista,Fungi,Plante and Animalia.The main criteria for classifications used by him include cell structure ,body organisation,mode of nutrition, reproduction and phylogenetic relationships.
The Three domain system has also been proposed that divides the kingdom monera into two domains ,leaving the remaining eukaryotic kingdoms in the third domain system and hereby a six kingdom classification .you will learn about this system in details at higher classes.
Let us look at this five kingdom classifications to understand the issues and considerations that influenced the classification system .Earlier classification system included the bacteria ,blue green algae ,fungi,mosses,ferns,gymnosperms and angiosperms under plants.
The character that unified this whole kingdom was that all the organisms included had a cell wall on their cells.This Placed Together Groups which is widely different in other characteristics.It Brought Together the unicellular organisms and the multicellular organisms once ,says,for example,chlamydomonas and spirogyra were placed together under algae.The classifications Did not difference between the heterotrophic group fungi, and the autotrophic green plants through they also showed a characteristics difference in their walls compositions the fungi had chittin in their walls while the green plants had cellulose cell walls .when such characteristics were considered as the fungi were placed in a separate kingdom -kingdom Fungi.
All Prokaryotic organisms were grouped together under kingdom monera and unicellular eukaryotic organisms were placed in kingdom plantae in kingdom protista .Kingdom protista has bought together chlamydomonas ,chorella(earlier placed in algae within plants and both having cell walls)