The main aim of classification is to group similar organisms together. In the five-kingdom classification given by Whittaker, prokaryotes are separated from eukaryotes and fungi, which were earlier placed in the plant kingdom, were placed in a separate kingdom as they are saprophytes. However, viruses that are non-cellular have not been given any place in this classification. Also, all unicellular eukaryotes having diverse properties have been placed under the kingdom Protista. They contain autotrophic, heterotrophic and saprophytic protists. This is a demerit of this system.