HIERARCHY OF CATEGORIES USED IN TAXONOMY

Linnaeus 's scheme of arranging organisms into an ascending series of groups of ever increasing inclusiveness is the hierarchial system of classification.

INCREASING SIMILARITY AS WE COME DOWN.

A category is known as taxon. The framework of taxonomic hierarchy is as shown . All the members of a taxon show similar characteristics which are different from that of the other taxa. As we go from species to kingdom, the number of similarities decrease.

SPECIES: It is the group of individuals with similar morphological characters, able to breed among themselves and produce fertile offspring. The members of species are structurally and functionally similar.

GENUS: It includes group of related species. They have identical reproductive organs, Eg Banyan and Fig have same kind of inflorescence, flower, fruit and seed and hence belong to a genus Ficus

FAMILY:it includes group of related genus. Eg: cats and lions belong to the same family Felidae as they have structure and claws.

ORDER: It is a group of families that resemble one another in few characters. Eg Tiger and wolf have jaws with powerful incisors and large sharp canines and are thereby placed in the order Carnivora.

CLASS: It includes organisms of related orders. Eg/; cats, dogs, bats, dolphins, kangaroos , monkey , camel are  in th class mammals due to hairy exoskeleton, milk glands etc.

PHYLUM: It includes organisms belonging to different classes having a few common characters. Eg : all animals which have a notochord present in the embryo are called chordates.

KINGDOM: It includes all organisms that share distinct common charaters. eg: Plantae.

System of classification ( diversity -2)

Artificial system of classification:
These system of classification were based on size, color or nature of the organism. It is helpful in quick identification of the organism.Aristotle classified the organisms on the basis of nature of their habitat ie terrestrial, aquatic or arboreal.Theophrastus classified known plants on the basis of their form, life span and habitat into four categories- trees, herbs and shrubs.The drawback of these system were that closely related organisms got separated into different groups while unrelated organisms got grouped together.

ARISTOTLE

THEOPHRASTUS

E.H.HAECKEL

WHITTAKER

Natural system of classification: These systems were based on natural relationship between different organisms and indicated similarities and differences between the organisms. 

Two kingdom classification: Traditionally all organisms were divided into two kingdoms: animalia and plantae. Shortcomings: Fungi are non motile but non photosynthetic. Some algae on the other hand were motile .Euglena and chlamydomonas has features of both plants and animals.

Three kingdom classification: E.H. Haeckel suggested a third kingdom protista to include unicellular eukaryotic microorganisms.

Four kingdom classification: Copeland introduced the kingdom Monera for all prokaryotic organisms.

Five kingdom classification: Robert H. Whittaker divided the organisms into five kingdoms namely: monera, protista, fungi, plantae and animalia.

Six kingdom classification: Woese further divided bacteria into Archaebacteria and Eubacteria on the basis of cell wall composition.

Diversity in living organisms (class 9 definitions )

Biodiversity , a concise form of biological diversity coined by Walter .G. Rosen refers to occurrence of diverse forms of living beings which differ from each other in external appearance, size, color pattern ,nutrition, behavior and habitat.

There is 1.7 - 1.8 million organisms on earth.

Taxonomy is a biological science which deals with identification, nomenclature and classification of organism following certain rules.

The vernacular names for one organism are different in different countries and not understood. So it is important to have a distinct, specific and universal scientific name.

Binomial nomenclature is the system of giving two names to one organism. The first is the name of the genus to which the organism belongs. It’s like our surname which we share with our family members.

The second name is species name that is possessed by only one kind of organism and it does not share it with any other organism in the genus.

The convention is that the genus name is written first with its initial letter in capital and species name is written after the genus name and its initial letter is always small.

Both are printed in Italics, and if handwritten both are underlined. Eg Rana tigrina

Both names are Latin names or have Latin endings.

This system of giving two names to an organism is known as binomial nomenclature and was developed by Linnaeus in his book Species Plantarium. So Linnaeus is also called Father of Taxonomy.

Classification is the method of arranging organisms into a hierarchy of closely related groups on the basis of similarities and differences.

Importance of classification:

1.       It makes the study of organism easy.

2.       It helps us to identify the organism.

3.       It gives relationship between two groups of organisms.

4.       It helps in finding complexity and evolution of various organisms.