Biology - Classification of Organisms



  • The technique of classifying organisms is known as Taxonomy.

  • Taxonomy is made up of two words i.e. ‘Taxis,’ which means ‘arrangement’ and ‘Nomos,’ which means ‘method.’

  • The Swedish botanist Carolus (Carl) Linneaeus has developed the modern taxonomic system.

  • Linneaeus has developed the following hierarchy of groups to explain the taxonomy −

  • In this hierarchy, Domain is the highest order and the broadest category and Species is the lowest order category.

  • Further based on the difference between eukaryotes and prokaryotes (cells) ‘Domains’ classified into three broad categories namely −

  • Archea(Archeabacteria) − It comprises the bacteria that live in extreme environments.

    • Eubacteria − It comprises the bacteria that found in everyday life.

    • Eukaryote − It comprises almost all the world's visible living things.

  • The above given three domains are further categorized into Five following Kingdoms

  • Let’s discuss each kingdom in brief −

    • Monera − It comprises the unicellular organisms, e.g. bacteria.

    • Protista − Similar to monera (unicellular), but more developed and complex. It contains nucleus.

    • Plantae − All plants from smallest (such as algae) to the largest (such as Pine, Eucalyptus trees, etc.) are studied under this kingdom.

    • Fungi − It is a group of eukaryotic organisms that comprises microorganisms such as yeasts, molds, and mushrooms. The organisms of this kingdom do not make their food, they are basically parasites.

    • Animalia − It includes all the multicellular and eukaryotic organisms (of animal group). It is also known as Metazoa.

Binomial Nomenclature

  • The naming culture (of different organisms) practiced uniformly across the world is known as binomial nomenclature.

  • Binomial Nomenclature largely consists of two words – the first word beginning with a capital letter and known as genus (of the organism) and the second word begins with lower case letter and defines the species of the organism.

  • Binomial Nomenclature must be written in italic and also known as scientific name.

  • For example, the binomial nomenclature of human is - Homo sapiens; tiger - Panthera tigris, etc.

Eukaryotes and Prokaryotes

  • Cells are fundamentally categorized by prokaryotes and eukaryotes.


  • Prokaryotes are the smallest and simplest type of cells.

  • Prokaryotes have no true nucleus and no membrane-bound organelles. E.g. Bacteria.

  • Prokaryotes’ Genome consists of single chromosome.

  • Reproduction is asexual; basically mitosis type.


  • Eukaryotes are complex in structure.

  • Eukaryotes have nuclei and membrane-bound organelles.

  • Eukaryotes’ Genome consists of numerous chromosomes.

  • Reproduction is sexual; by mitosis and meiosis.