The five-kingdom system of classification for living organisms, including the prokaryotic Monera and the eukaryotic Protista, Fungi, Plantae and Animalia is complicated by the discovery of archaebacteria. Protista, Fungi, Plantae, Animalia, and Monera are divided on the basis of their characteristics such as cell structure, mode of nutrition, mode of reproduction and body organization.
According to the ‘Two-Kingdom Classification’, proposed by Carolus Linnaeus in 1758, living organisms were classified into two broad kingdoms, Plants and Animals. The drawbacks in classifying organisms under the old two kingdom classification are:
1. Bacteria were kept in Kingdom Plantae. These organisms have no chlorophyll and do not carry out photosynthesis. Bacteria do not have a definite nucleus nor a nuclear membrane nor chromosomes.
2. Fungi were kept in Kingdom Plantae. Bread mould is a multicellular fungi. However, it does not possess roots, stem and leaves, lacks chlorophyll and does bear any flowers, fruits and seeds like plants.