Classification of Organisms

Introduction

• 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.

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Eukaryotes and Prokaryotes

• Cells are fundamentally categorized by prokaryotes and eukaryotes.

Prokaryotes

• 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

• 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.