Biodiversity refers to all the diverse plants, animals and microorganisms on the earth, which differ from one another in external appearance, size, colour pattern, internal structure, nutrition, behaviour and habitat.
“Diversity is the variety of living organisms which are present in a particular area.”
They range in size from microscopic bacteria, hardly a few micrometres in size, to Blue Whale (about 30 m in length) and Redwood trees (Sequoia) of California (about 100 m in height). Similarly some pine trees (e.g. Pinus) live for thousands of years while many insects like mosquitoes have a life span of a few days. There are transparent jelly fishes and worms on one hand to brightly coloured birds and flowers on the other hand.
We cannot look at them one by one. Instead, we look for similarities among the organisms, by which we can put them into different group and then study. In order to make relevant groups to study the variety of life forms, we need to decide those characteristics which decide more fundamental differences among organisms. This would create the main broad groups of organisms. Within these groups, smaller subgroups will be decided by less important characteristics.
The term “Biodiversity” was coined by Walter G. Rosen in 1986. The warm and humid tropical regions of the earth between the tropic of Capricorn and the tropic of Cancer, are rich in diversity of plant and animal life. This is called the region of “megadiversity” (12 centres in the world).
The science dealing with identification, nomenclature and classification of organisms is called taxonomy or systematics. The term “Taxonomy” was given by A.P. de Candolle. Father of Modern Taxonomy is Carolus Linnaeus.
Classification is the arrangement of organisms into groups and subgroups on the basis of their similarities and dissimilarities.
(i) Complexity of cell or nucleus (cells are either prokaryote or eukaryote).
(ii) Complexity of body organization (body of organisms are made up of either one cell or many cells).
(iii) Mode of nutrition (organisms make their own food or depend on readymade food).
Hierarchy is a system of classification into which taxonomic categories are arranged in descending order.
Taxonomic categories are ranks or grouping of organisms on the basis of their fundamental similarities and dissimilarities Plants and animals are ranked in an arrangement of known categories. Such as Kingdom, Phylum (for animals) or Division (for plants), Class, Order, Family, Genus and Species.
Plant groups or animals groups included in categories are called taxon. e.g., Pisces, Insecta.
Family - Brassicaceae
Genus - Raphanus
Species - Raphanus sativus
Here FAMILY is a category in which Brassicaceae group is a taxon.
The bewildering variety of life around us has evolved on earth. In order to make relevant groups to study the variety of life forms, we classify organism.
(1) Classification makes the study of different type of organisms easy and systematic.
(2) It helps in identification of known and unknown organisms.
(3) Classification reveals the inter-relationship among organisms.
(4) It helps in understanding the other branches of life sciences.
(5) It is based on natural relationships, resemblances and differences and provide information about phylogeny.
The process of gradual change from simple life forms to complex life forms with time is called evolution. Classification of life forms will be closely related to their evolution.
Most life forms have arisen by an accumulation of changes in body design that allow the organism possessing them to survive better. Charles Darwin first described this idea of evolution in 1859 in his book, Origin of Species.
Aristotle classified animals according to their habitat. Aristotle is considered as father of zoology.
The concept of evolution shows that:
Some groups of organisms which have ancient body designs that have not changed very much, are frequently referred to as ‘primitive’ or ‘lower’ or older’ organisms and that which have acquired their particular body designs relatively recently are called ‘advanced’ or ‘higher’ or ‘younger’ organisms. Complexity in design will increase over evolutionary time.
(Session 2025 - 26)