Diversity - Biological Classification S ystems Over Time

Biological classification is the method of arranging organisms into groups on the basis of similarities and differences. This helps in the systematic study of a wide variety of life forms.

Early classification systems were based on habitat. Aristotle classified animals according to whether they lived on land, in water, or in the air.

The Two-Kingdom Classification was proposed by Carolus Linnaeus, dividing organisms into $Plantae$ and $Animalia$.

Robert Whittaker ($1969$) proposed the Five-Kingdom Classification. The criteria used for classification include cell structure ($Prokaryotic$ vs. $Eukaryotic$), mode of nutrition ($Autotrophic$ vs. $Heterotrophic$), and body organization.

The Five Kingdoms are: $Monera$, $Protista$, $Fungi$, $Plantae$, and $Animalia$.

Carl Woese ($1977$) modified Whittaker's system by dividing Kingdom $Monera$ into $Archaebacteria$ (or $Archaea$) and $Eubacteria$ (or $Bacteria$).

Taxonomic Hierarchy: To classify organisms, a hierarchy of categories is used, moving from the most general to the most specific: $\text{Kingdom} \rightarrow \text{Phylum (for animals) / Division (for plants)} \rightarrow \text{Class} \rightarrow \text{Order} \rightarrow \text{Family} \rightarrow \text{Genus} \rightarrow \text{Species}$

The basic unit of classification is the $Species$, which includes all organisms that are similar enough to breed and perpetuate.

Binomial Nomenclature: Developed by Carolus Linnaeus, it provides a unique two-part scientific name to every organism consisting of a Genus and a species name.