The classification systems have undergone several changes with time. The first attempt of classification was made by Aristotle. He classified plants as herbs, shrubs, and trees. Animals, on the other hand, were classified on the basis of presence or absence of red blood cells. This system of classification failed to classify all the known organisms.Therefore, Linnaeus gave a two-kingdom system of classification. It consists of kingdom Plantae and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms and between eukaryotes and prokaryotes. Therefore, there were large numbers of organisms that could not be classified under the two kingdoms.So, Ernest Haeckel, then, separated unicellular eukaryotic organisms into separate kingdom named Protista and hence, gave three kingdom classification.After that Copeland separated all prokaryotic organisms into a separate kingdom named Monera and hence, Four-Kingdom systems of classification came into existence.And lastly, a five kingdom system of classification was proposed by R.H. Whittaker in 1969 to separate achlorophyllous, decomposer organism into a separate kingdom named Fungi. So five kingdoms now are: 1) Monera2) Protista3) Fungi4) Plantae5) Animalia