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Last Updated : 20 Dec, 2023
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Taxonomy is derived from two Greek words taxis, meaning order, and nomos, meaning rule. The system of naming and categorizing flora, fauna, and microorganisms is known as taxonomy. Taxonomists identify and classify species using observations of their morphology, behaviour, genetics, and biochemistry. It is estimated that between 10 and 15 million species have evolved on Earth but taxonomists have only identified 1.78 million species of plants, animals, and microorganisms to date. Taxonomy is not limited to just biology but it has been developed in other practical fields also such as computing.


Classification of Organisms

Hierarchical systems of classification are those in which the largest groupings are arranged first, followed by the smallest. Organisms that are arranged into groups are simpler to examine.

The kingdom is the largest group. Each kingdom is further subdivided into phyla (singular phylum). Each phylum is subdivided into classes, orders, families, genera, and species. Various fungi, plants, animals, and microbes are referred to as distinct “species.” A species is a potentially interbreeding group of creatures that may generate viable offspring that themselves can interbreed. Thus, creatures of of two different species, such as a zebra a horse, cannot interbreed, whereas animals of the same species can.

The Linnaean system ( Naming of organisms)

The most common and the best-known taxonomies in biology is the one devised by the Swedish scientist Carl Linnaeus (1707 – 1778). He is known as the father of Taxonomy. In his Linnean system of binomial nomenclature (binomial = two names; nomenclature = naming), each organism is classified based on its genus and its species. Both the terms used are Latinized. For example, the modern humans are known as Homo sapiens.

Three Domains of Classification

All organisms are divided into three main Domains.

  1. Archaebacteria: They are thermophilic (heat-loving bacteria) that live in high temperature vents.
  2. Eubacteria: They are single celled organisms without well-developed nucleus.
  3. Eukarya: They are all other organisms with a well-formed nucleus in their cells.(Eu: true; Karyon : nucleus)

Whittaker’s Five Kingdom Classification

Within a given kingdom, all species shares many traits with respect to their growth and behaviour. There used to be just two kingdoms for plants and animals. Whittaker proposed in 1969 that protozoa belong to the animal kingdom and bacteria to the plant world. He classified the kingdoms into five. The most widely recognised taxonomy of the five kingdoms of nature is still in place today, while recent developments in genetics have prompted new suggestions for change. Such is the situation for the sixth kingdom of Carl Woese and George Fox, who categorised bacteria into two types (Archaea and Bacteria) in 1977, and the seventh kingdom of Cavalier-Smith, who added a new group to the previous six for algae known as Chromista.

The kingdoms are further classified into phyla. Every phylum is divided into several classes, classes are further divided into orders, orders into families. A family consist of many genera (singular genus). Every genus contains several species. Species are isolated from their related species of the same genus by reproductive barriers, which means that members of one species cannot interbreed with that of another species to produce a viable offspring.





Eukaryotes, multi-celled, heterotrophs, aerobic respiration, mobile and sexual reproduction.

Dog, Earthworm


Eukaryotes and multi-celled, autotrophs, immobile, sexual or asexual reproduction.

Fern and tree


Eukaryotes, aerobic, multi-celled saprotrophs, reproduce by spores.

Yeast, moulds, Mushroom


Single-celled and well-formed nucleus (Eukaryotes)



Single-celled and no well-formed nucleus (Prokaryotes). Most bacteria are aerobic and heterotrophic whereas archaea are anaerobic and chemosynthetic.

Archaea and Bacteria

Plant Taxonomy

Kingdom Plantae is divided into the following four phylum. The important characteristic features of the different phyla of Kingdom Plantae.




Nonvascular plants

They are small; lack roots, stems, and leaves. They lack a vascular system for transporting water and nutrients.; and produce spores rather than seeds.

Mosses and Hornworts

Seedless vascular plants

They have true roots, leaves, and stems, and their spore-producing structures permit wide dispersal. They also have a vascular system composed of xylem and phloem, allowing the movement of water and solutes.


Gymnosperms (nonflowering seed plants)

They do not produce a seed within a protective structure of a fruit and are wind pollinated and most (all except one species) have separate male and female reproductive structures called cones.


Angiosperms (flowering seed plants)

They have their seeds enclosed in a fruit and they are vascular plants.

Fruits and vegetables

Animal Taxonomy

Kingdom Animalia is divided into the following eleven phylum. The important characteristic features of the different phyla of Kingdom Animalia





Body with pores and canals in walls.


Coelenterata (Cnidaria)

Cnidoblasts present.



Comb plates for locomotion



Flat body, suckers.

Taenia (Tapeworm), Fasciola (Liver fluke).


Often worm-shaped, elongated.

Ascaris (Roundworm)


Body segmentation like rings.



Exoskeleton of cuticle, jointed appendages.

Butterfly, Scorpion


External skeleton of shell usually present



Water vascular system, radial symmetry.

Asterias (Star fish)


Worm-like with proboscis, collar and trunk.



Notochord, dorsal hollow nerve cord, gill slits with limbs or fins.


Levels of Taxonomy

There are three levels of taxonomy corresponding with three periods of taxonomy:

  • Alpha taxonomy: This is the level of taxonomy by which species are characterized and naming of the species is done.
  • Beta taxonomy: This is the level of taxonomy by which the arrangement of species in their natural system of categories is made.
  • Gamma taxonomy: This is the level of taxonomy which deals with the intra specific variations and evolutionary sequence and also a causal interpretation of organic diversity.


To conclude, the classification of organisms into groups reflect their evolutionary and morphological relationships: kingdom, phylum, class, order, family, genus, species. Taxonomy has significance in placing organisms in ranks, determining which category a new organism belongs to in order to identify it. Organisms that are arranged into groups are simpler to examine. Taxonomy is developed not only in biology but also in other practical fields.

FAQ’s on Taxonomy

1. Who is the Father of Taxonomy?

Swedish scientist Carl Linnaeus (1707 – 1778) is known as the father of Taxonomy.

2. Who gave 5 Kingdom Classification

Whittaker’s gave five kingdom classification in 1969.

3. Name the Three Domains into which all the Organisms of the World are Categorised.

All organisms are now divided into three main Domains i.e.Archaebacteria, Eubacteria and Eukarya.

4. Name the Five Kingdoms of Classification.

Kingdom Animalia, Plantae, Fungi, Protista and Monera are the five Kingdoms of Classification.

5. Who is credited for the Binomial Nomenclature of Organisms?

CCrl Linnaeus (1707 – 1778), the father of Taxonomy, is credited for the Binomial Nomenclature of organisms.

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