Two kingdoms classification: The living organisms from the beginning have been grouped into plants and animals. This is known as two kingdom classification. Carolus Linnaeus (1758) named these kingdoms as Plantae and Animalia.
Kingdom Plantae : Kingdom Plantae includes l bacteria (prokaryotes), photosynthetic plants and j non-photosynthetic fungi.
They are characterised by:
(i) Presence of cell wall.
(ii) Occurence of inorganic crystals and central vacuole in the cell.
(iii) Absorptive mode of nutrition.
(iv) Well defined growing points with unlimited growth.
(V) Ability to manufacture food due to presence of chlorophyll.
(vi) Reserve food is stored as starch.
(b) Kingdom Animalia : Kingdom Animalia includes unicellular protozoans and multicellular animals or metazoans.
(i) Absence of cell wall.
(ii) Holozoic (ingestive) mode of nutrition.
(iii) Presence of sense organs, nervous system and excretory organs.
(iv) Reserve food is stored as glycogon.
(v) Presence of locomotion.
Limitations of the two kingdom system:
(i) Certain organisms share the characters with the animals as well as plants. For example, Euglena, a protozoan shows locomotory movement like animals, but it contains chlorophyll like plants.
(ii) Fungi have certain features of their own. They resemble plants as well as animals.
(iii) Lichens is a group of dual organisms which are formed by an association between an alga and fungus. They have no plant character, neither any animal character.
(iv) Viruses and prokaryotes became well defined. Protagonists of two kingdom classification placed all prokaryotes in kingdom Plantae.