According to this system of classification, living organisms are divided into five kingdoms:
i- Kingdom Monera
ii- Kingdom Protista
iii- Kingdom Fungi
iv- Kingdom Plantae
v- Kingdom Animalia
i- Kingdom Monera: It includes all the prokaryotes i-e Bacteria and cyanobacteria.
ii- Kingdom Protista: It is the place for all the eukaryotic unicellular organisms, except yeast which some of them have the features of both plant and animal like. Most protists are aquatic. It includes protozoa and unicellular algae.
iii- Kingdom Fungi: It includes all the multicellular eukaryotic fungi. They are Achlorophyllous, absorptive heterotrophs. They have cell wall made up of mainly chitin. They have a body called Mycelium which is made up of a thread like structure called hyphae.
iv- Kingdom Plantae: It includes all the multicellular, eukaryotic, photosynthetic organisms. They have cell wall mainly made up of cellulose. It includes multicellular Algae, bryophytes, pteridophytes, gymnosperm and angiosperms.
v- Kingdom Animalia: All animals are multicellular, eukaryotic which are ingestive heterotrophs without cell wall. It includes all vertebrates and invertebrates except protozoa.
Virus is non cellular obligate endoparasite (lives inside host cell). It does not have cellular organization but do have nuclear material either DNA or RNA. It has protein coat called capsid that encloses the nucleic acid. It reproduces only inside the host cell. Due to its non-cellular nature it cannot be placed in any of the five kingdoms. It causes number of diseases in plant like tobacco Mosaic Disease etc and animals like, cold, flue, dengue, polio, hepatitis, AIDS etc.
Prions and viroids are also non-cellular particles so cannot be placed in five kingdom classification system.
