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Biology / Living Organisms

Classification of Living Organisms

As there exists millions of living organisms on this planet earth, it will be unimaginable for the human beings to study all of them separately. Classification of living organisms into different groups will make it easier for us to identify them and compare their characteristics. Taxonomy is the branch of science that deals with the identification, nomenclature and classification of living things.

Taxonomy of Living Things

The unit of classification of living organisms is called taxon (plural - taxa). Generally, a taxon is known by a particular name and will be given a particular ranking in the scientific classification of living things.

  • The basic taxon is Species, which is a group of organisms which can interbreed among themselves.

  • Related species are included in the next level taxon known as Genus (plural - Genera), e.g. Man is known by his scientific name Homo sapiens, where Homo is the Genus name and sapiens is the Species name.

  • Related Genera are included in the next level taxon known as Family, e.g. Man belongs to the Family, Hominidae.

  • Related Families are included in the next level taxon known as Order, e.g. Man belongs to the Order, Primate.

  • Many related Orders belong to the next level taxon known as Class, e.g. Man belongs to the Class, Mammalia.

  • All the related Classes belong to the next level taxon known as Phylum (plural - Phyla), e.g. Man belongs to the Phylum, Chordata.

  • All Phyla belong to the next level taxon, Kingdom, e.g. Man belongs to the Kingdom, Animalia.

The Scientific naming of living organisms that is followed today, is binomial nomenclature. It was first introduced by Swiss botanist, Gaspard Bauhin. But the Swedish botanist, Carolus Linnaeus also known as father of taxonomy, developed it more precisely. In scientific nomenclature, the Genus name always starts with a capital letter and the Species name always starts with a small letter. The nomenclature in which both Genus and Species are same, is known as Tautonym, e.g. Naja naja (Cobra) and Axis axis (Spotted Deer).

Kingdoms of Living Things

American ecologist, Robert Whittaker made an attempt in classifying living organisms into five kingdoms namely, Protista, Monera, Fungi, Animalia and Plantae.

  • Monera : Monera kingdom consists of unicellular organisms like cyanobacteria and bacteria, which are prokaryotes i.e. having no nucleus inside the cell. These organisms are very small in size.

  • Protista : Organisms that come under kingdom Protista are mostly unicellular except few multicellular species. Amoeba, euglena and paramecium are some of the examples that come under Protists. The Protists are eukaryotic in nature, i.e. they are having a distinctive nucleus inside the cell.

  • Fungi : Kingdom Fungi has both unicellular and multicellular organisms. Yeasts are examples of unicellular fungi. Molds and mushrooms are examples of multicellular fungi.

  • Animalia : Kingdom Animalia consists of only multicellular organisms without having any cell wall. Fish, earthworms, man, snakes, etc. are some of the examples of animals. They cannot make food on their own for their nutrition but rely on plants, fungi or other animals and hence are called heterotophs.

  • Plantae : Kingdom Plantae consists all plants and these are multicellular organisms. Plants can make their own food by a process known as photosynthesis and hence are called autotrophs. Plants are having a cell wall made of cellulose. Mosses, ferns, cashew tree, etc. are some of the examples of plants.