The term “biodiversity” has been derived from ‘bio’ and ‘diversity’. “Diversity” means variety within a species and among species. Biodiversity is a measure of the variety of organisms present in different ecosystems.
The branch of biology which deals with classification is called taxonomy and the branch which deals with classification and also traces the evolutionary history of organisms is known as systematics.
Classification is based on relationship amongst organisms and such relationship is got through similarities in characteristics.
The groups into which organisms are classified are known as taxonomic categories or taxa (singular “taxon”). The taxa form a ladder, called taxonomic hierarchy. All organisms are divided into five kingdoms. So kingdom is the largest taxon. On the basis of similarities, each kingdom is further divided into smaller taxa in the following way:
Phylum (Division: for plants and fungi): A phylum is a group of related classes.
Class: A class is a group of related orders.
Order: An order is a group of related families.
Family: A family is a group of related genera.
Genus: A genus is a group of related species.
Species: A species consists of similar organisms.
Species is the basic unit of classification. “A species is a group of organisms which can interbreed freely among them and produce fertile offspring, but are reproductively isolated from all other such groups in nature.” Each species possesses its own distinct structural, ecological and behavioural characteristics.