42. (a): In order to develop phylogenetic classification, R.H. Whittaker (1969), an American taxonomist, divided all the organisms into five kingdoms. Whittaker has used five criteria for delimiting the different kingdoms. (i) Complexity of cell structure, prokaryotic and eukaryotic. (ii) Complexity of body structure or structural organization, unicellular and multicellular. (iii) Mode of nutrition which is divergent in multicellular kingdoms. (iv) Ecological life style like producers (plantae), decomposers (fungi) and consumers (animalia), (v) Phylogenetic relationship. When such characteristics were considered, the fungi were placed in a separate kingdom - Kingdom Fungi. All prokaryotic organisms were grouped together under Kingdom Monera and the unicellular eukaryotic organisms were placed in Kingdom Protista. Kingdom Protista has brought together Chlamydomonas, Chlorella (earlier placed in Algae within Plants and both having cell walls) with Paramoecium and Amoeba (which were earlier placed in the animal kingdom which lack cell wall). It has put together organisms which, in earlier classifications, were placed in different kingdoms. This happened because the criteria for classification changed.