(i) Species:
(a) Species is the principal natural taxonomic unit, ranking below a genus
(b) It is a group of organisms that can interbreed under natural condition to produce fertile offspring.
(c) It was thought to be an indivisible, stable and static unit.
(d) However, in the modem taxonomy, subdivision of species such as sub-species, varities and populations are seen and given more importance.
(ii) Genus:
(a) Genus is a taxonomic rank or category larger than species used in the biological classification of living and fossil organisms.
(b) Genus is a group of species bearing close resemblance to one another in their morphological characters but they do not interbreed.
(c) For e.g. Tiger, Leopard, Lion all three belong to same genus Panthera. They have common characters yet are different from each other because their genus is same but species is different.
(d) Another example is genus Solarium. Brinjal and potato both belong to this genus.
(iii) Family:
(a) It is one of the major hierarchial taxonomic rank.
(b) A family represents a group of closely related genera.
(c) For e.g. genera like Hibiscus, Gossypium, Sida, Bombax are included in same family Malvaceae.
(d) Although, there are many similarities between cat and dog, cat belongs to the family of leopards, tigers and lions, i.e. family Felidae and dog belongs to different family i.e. Canidae.
(iv) Cohort/Order:
(a) It is taxonomic rank used in the classification of organisms and recognised by nomenclature codes.
(b) An order is a group of closely related families showing definite affinities.
(c) Members belonging to same order but different families may show very few dissimilarities.
(d) For e.g. family Papaveraceae, Brassicaceae, Capparidaceae, etc with parietal placentation are grouped in order Parietales.
(e) Families of dogs and cats though are different, they belong to same order Carnivora.
(v) Class:
(a) The class is the distinct taxonomic rank of biological classification having its own distinctive name.
(b) Class is the assemblage of closely allied orders.
(c) For e.g. Orders Carnivora and order Primates belong to class Mammalia. Thus monkeys, gorillas, gibbons (Primates) and dogs, cats, tigers (Carnivora) belong to same class.
(vi) Division/ Phylum:
(a) The division is a category composed of related classes.
(b) For e.g. division Angiospermae includes two classes Dicotyledonae and Monocotyledonae.
(c) In animal classification, instead of division, the category Phylum is used.
(vii) Sub-kingdom:
(a) Different divisions having some similarities form sub-kingdom.
(b) The divisions Angiospermae and Gymnospermae forms the subkingdom Phanerogams or Spermatophyta (all seed producing plants).
(viii) Kingdom:
(a) It is the highest taxonomic category composed of different subkingdoms.
(b) For e.g. sub-kingdom Phanerogams and Cryptogams form the Plant kingdom or Plantae which includes all the plants, while all animals are included in kingdom Animalia.
