Discuss how classification systems have undergone several changes over a period of time ?

Explanation

Since dawn of civilisation, there have been many attempts to classify the living organisms into two large kingdom: (a) Kingdom Plantae , (b) Kingdom Animalia. This system did not distinguiesh between the eukaryotes and prokaryote, unicellular and multicelluar organisms and photosyntetic ( fungi) organisms.
(iii) Haeckel (1866) identified a Kingdom Protista.
(iv) Copland gave Four Kingdom System of classification called Monera, Protia, Metaphyta and Metazoa. (v) Five kingdom System of classification was given by K.H Whittaker (1969). The five kingdom are : Monera, Protisa , Fungi , Plantae and Animalia ( For details consult chapter -2)
Whittaker has not described viruses and lichens. Stanley discussed virus,viroids etc.