Two Kingdom Classification

The classification in which whole living organisms of the earth are classified into two groups is known as two-kingdom classification. This system of classification is the oldest system of classification. This system of classification was based on different characteristics of animals and plants. It is the oldest system of classification.

Kingdom: Plantae

This kingdom plantae includes all plants which have the following characteristics:

• They are usually immobile and fixed in a place.
• They have branching body with a spread out appearance and green leaves.
• They have a rigid cellulosic cell wall around their cell.
• They have an autotrophic type of nutrition.
• They are less sensitive and have no organized nervous system and sense organs.
• Their locomotion is not well defined.

The kingdom Plantae includes all the green plants, mosses, multicellular seaweeds, moulds, mushrooms, lichens, tiny unicellular organisms, bacteria, ferns and flowering plants.

Kingdom: Animalia

The organisms included in an animal kingdom have the following characteristics:

• The animals are mobile and had a compact body.
• They lack the rigid cellulosic cell wall around their cells.
• They have the heterotrophic type of nutrition.
• They have a well-defined nervous system and sense organs.
• They have well-defined locomotion.
• They show a quick response to external stimulus.

The animal kingdom includes all the multicellular organisms from sponges to mammalia and unicellular organisms.

Drawbacks of two-kingdom classification:

• In two-kingdom classification, first form organisms have some plant-like characters and some animal-like characters. so, the position of such organism is not cleared. Eg: Euglena, Slime mould.
• Prokaryotic and Eukaryotic organisms are not separated. Eg: Bacteria
• Unicellular and multicellular organisms are not separated.
• Fungi have distinct morphological and physiological characters than other plants, but they are placed together in the plant kingdom.
• Lichens are a symbiotic association of algae and fungi. They are neither plant like nor animal like but they are placed in the plant kingdom.
• Two kingdom classification is more heterogeneous classification.
• In two-kingdom classification phylogeny of organisms is not shown.