Variety Of Life – Over one and a half million species of animals and over a half million species of plants are known. To deal with such a large collection of dissimilar forms, certainly we need some system by which species can be classified in a reasonable way. Many types of classifications are possible. We could, for example, classify flowering plants according to their colour, height, or any other character. This type of classification is not meaningful since it does not provide any information about the basic differences and similarities among different individuals.
All organisms are related to one another at some point in their evolutionary histories. however, some organisms are more closely related than others. Sparrows are more closely related to pigeons than either to the insects. Classification is based on relationship amongst individuals, that is, similarity in form or structure. Biologists have classified all living things into groups showing similarities, based upon homologies, comparative biochemistry, cytology and genetics. Large groups are divided into smaller groups up to species level. “A species is a group of natural population which can interbreed freely among themselves and produce fertile offsprings, but are reproductively isolated from all other such groups in nature”.
however “interbreeding” cannot be used as a criterion for species recognition among predominantly asexually reproducing organisms. Each species possesses its own distinct structural, ecological and behavioral characteristics, hence species are independent evolutionary units. Different species do not exchange genes between them. Since long the living things are divided in two kingdoms: plants and animals. Next each kingdom is divided into smaller groups called phyla (also divisions fro plants, algae and fungi). A phylum, in turn, is divided into classes, classes into orders, and an order into families. A family contains related genera, and a genus is composed of one or more species. Species is the basic unit of classification. Conversely speaking, the organisms are grouped into larger, more inclusive categories (taxa), each category is more general than the one below it and has emergent properties. The taxonomic categories from species to kingdom from a hierarchy as described in the classification of corn.
Biological classification of corn, zea mays
Kingdom…………………………………………….Plantea
Division (phylum)……………………………….Anthophyta (Tracheophyta)
Class…………………………………………………..Angiospermae
Order …………………………………………………Poales
Family ………………………………………………..Poaceae
Genus …………………………………………………Zea
Species ……………………………………………….mays
Members of a lower category resemble one another more than do the members of a higher taxon.
