The term “biodiversity” is a concise form of “biological diversity” and was coined by Walter G. Rosen in 1986.
Biodiversity is the occurrence of diverse or varied forms of living beings which differ from one another in external appearance, size, color pattern, internal structure, nutrition, behaviour, habitat etc.
Note: Mega diversity is the high degree of richness of different types of forms found in an area. The area or region of mega diversity on earth is humid tropical region lying between tropic of Cancer and tropic of Capricorn.
The system of grouping of living forms on the basis of similarities and differences is called classification.
The branch of biology concerned with classification is called taxonomy. Taxonomy is a biological science which deals with identification, nomenclature and classification of organisms following certain rules.
Purpose of Classification (Importance of classification):
Classification makes the study of a wide variety of living organisms easier.
Classification helps in understanding the phylogeny of organisms.
Classification provides knowledge about the origin and genetic relationship among living beings.
Classification forms a base for the development of other biological sciences.
Classification and Evolution:
Early systems of classification were artificial i.e., they were based on a few arbitrarily chosen criteria such as size, colour and nature of the organisms.
In the 19th century, the artificial systems of classification were replaced by natural systems of classification. The important aspects of this natural basis of classification are:
It considers a number of characters.
It include internal (anatomical) as well as external (morphological) characters.
It indicated overall similarities and differences between the organisms.
It places related organisms in the same group.
The classification of life forms is closely related to their evolution. The idea of evolution was first described by Charles Darwin in his book, the Origin of species in 1859.
He explained that first formed (older) organisms were simpler, while younger organisms (modern) are more complex, i.e., complexity in design of simple forms has increased over evolutionary time and has become modern complex form.
Binomial nomenclature is a system of giving distinct and proper names to organisms with each name consisting of two words, generic and specific.
Binomial nomenclature was proposed by Carolus Linnaeus (Karl von Linnaeus).
Hierarchy of Categories or Groups:
The main aim of a taxonomic study is to assign organism an appropriate place in a systematic framework of classification. This framework is called taxonomic hierarchy by which the taxonomic groups are arranged in definite order, from higher to lower categories.
A category is called taxon (plural taxa). The taxa or categories used in the classification of animals are kingdom, phylum, class, order, family, genus and species.
The categories used in plants are kingdom, division, class, order, family, genus and species.
Note: Species is a group of individuals with similar morphological characters, which are able to breed among themselves and produce fertile offspring of their own kind.
Living organisms have been classified variously according to different criteria; however, the following two systems are most in use.
Two-Kingdom System of classification:
This system of classification was given by Carolus Linnaeus (1758). According to this system, the whole living beings are put into two kingdoms- Plant kingdom and Animal kingdom.
Later taxonomic studies indicated that certain organisms did not fit either under Plant kingdom or Animal kingdom. Accordingly, a German Zoologist, E.H. Haeckel (1866) raised a third kingdom Protista for unicellular organisms.
Five-Kingdom System of classification:
R. H. Whittaker (1959) has classified the living organisms into following five kingdom:
Kingdom Monera (Prokaryotic bacteria and Blue green algae)
Kingdom Protista (Unicellular eukaryotic organisms- protozoans, fungi and algae)
Kingdom Fungi (Multicellular fungi)
Kingdom Plantae (Multicellular green plants and advanced algae)
Kingdom Animalia (Multicellular animals)
Characteristics of Five-Kingdom:
The monerans are extremely small and structurally the simplest of all the living beings.
The organisms belonging to this group are simple, unicellular and microscopic. These organisms are prokaryotic.
Cell wall is present in some organisms and absent in others.
They do not possess a defined nucleus and lack cell organelles.
Some organisms can synthesize their food (autotrophic), while some organisms exhibit heterotrophic mode of nutrition.
This group includes Bacteria, mycoplasma and blue-green algae.
This group consists of many types of unicellular eukaryotes.
They have a defined nucleus and also membrane-bound organelles.
Some of these organisms use appendages, such as hair-like cilia or whip-like flagella for moving around.
Their mode of nutrition can be autotrophic or heterotrophic.
This group includes Diatoms, protozoans and unicellular algae.
Fungi are simple, eukaryotic non-green (lacking chlorophyll) organisms.
Cell wall is present. It is made up of a tough complex sugar called chitin.
They are non-photosynthetic. The mode of nutrition is heterophic. Most of then use dead and decaying organic matter as food and are therefore called saprophytes. Some of them are parasitic.
Some fungal species live in permanent mutually dependent relationships with blue-green algae (or cyanobacteria). Such relationships are called symbiotic. These symbiotic life forms are lichens.
Most fungi are multicellular. Yeast is a unicellular fungus.
This group includes Mucus, Penicillium, yeast etc.
This group consists of multicellular eukaryotic organisms.
They are autotrophs and use chlorophyll for photosynthesis.
They possess a cell wall made of cellulose.
Kingdom Plantae is further classified as Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.
This group includes all photosynthetic plants.
This group consists of all multicellular eukaryotes which do not possess a cell wall.
These organisms are heterotrophic.
Cell wall is absent.
Kingdom Animalia is further classified as Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata, Protochordata and Vertebrata.