'Biological diversity' means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species and of ecosystems.
Classification is the arrangement of animals and plants in taxonomic groups according to their observed similarities.
Classification system as proposed by Linnaeus use a hierarchical system in which organisms are placed into groups, at different levels, according to the features they share. These groups or levels are :
Kingdom, Phylum, Class, Order, Family, Genus and Species
Species is the smallest unit of classification. A species is defined as a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.