This is true that biological classification is a dynamic and ever evolving phenomenon which keeps changing our understanding of life forms. At the beginning, living being were broadly classified into two groups, viz. animals and plants. This classification was based on apparent morphological features which were quite easy to understand. But when the scientists discovered certain flaws in this classification, they began to think about a better system of classification. The most accepted system of classification today is the Five-Kingdom Classification; proposed by Robert Whittaker. The Five-Kingdom Classification takes into account structural organization and phylogenetic relationship; while classifying the living beings. As per this system; all prokaryotes have been kept under one kingdom, i.e. Monera. Furthermore, eukaryotes have been divided into four.