what is species in biology class 11

Living world is organised and categorised by various systems. Carolous Linnaeus divided all organisms into large groups called kingdoms. Kingdoms were further classified and subdivided. The criteria of such classification was variety of factors like similarity in structure, function etc. Later systems included evolutionary relationships to establish categories. The idea was that features might be lost, gained or modified according to time. Towards this the categories were arranged in a hierarchical fashion. Kingdoms, Phyla/Divisions(in case of plantae kingdom), Classes, Orders, Families, genus and species. A species is a group of closely related individuals that can breed and produce fertile offspring. This species concept was given by Ernst Mayr. However this concept produces problems when it comes to prokaryotes who can reproduce across ‘species’. For them we produce newer concepts which identify the similarity in the nucleotide sequences to classify individuals as a species. 

The ICSP, International Committee on Systematics of Prokaryotes adopts a gold standard for species assignment for prokaryotes. It hold 70% DNA-DNA hybridization for the prokaryotes to be identified as one species. Further the melting temperature (the temperature at which the double strands separate) be within 5 degrees C and the differences between rRNA gene sequences be less than 3%