Biological Classification - Division

What is Biological Classification?

Biological classification is the scientific procedure that involves the arrangement of the organisms in a hierarchical series of groups and sub-groups on the basis of their similarities and dissimilarities.

Right from the archaic times, several attempts have been made to classify the living organisms. 

The first man to attempt a scientific basis of classification was Aristotle. 

He used simple morphological characters to classify plants as trees, shrubs, and herbs. He classified the animals into two groups as Enaima (with red blood), Anaima (without red blood)

However, a need for a proper system of biological classification was always felt.

Need for classification of living organisms

The study of one or two organisms is not sufficient to know the essential features of the group.

All kinds of organisms do not occur in one locality.

Classification helps in knowing the relationship between the different groups of organisms.

It helps in knowing the evolutionary relationship between organisms.

Types of Classification System

Based on the types of system of classification, organisms are classified into the following kingdoms.

A. Two Kingdom Classification System

In the year 1758m Linnaeus (the father of taxonomy system) divided all the living organisms into two kingdoms. These are Plantae and Animalia.

In the year 1866, Ernst Haeckel, classified living organisms into three kingdoms i.e. Plantae, Protista, and Animalia. The new kingdom Protista included all those organisms, which lack the capability of tissue differentiation. This group included algae, fungi, and Protozoa. Later, kingdom Protista was reserved only for the unicellular organism.

Limitations of Three Kingdom Classification System

No separation of Prokaryotes and eukaryotes.

Both unicellular and multicellular organisms are classified under Protista.

C. Four Kingdom Classification System

In addition to Protista, Plantae and Animalia, the four kingdom classification system included Monera. The studies with electron microscope made it clear that bacteria and related organisms have a different nuclear structure as compared to others. These are the prokaryotes. As a result of this, Copeland in the year 1956, introduced the kingdom-Monera. Fungi continued to remain with Plantae in this system.

D. Five Kingdom Classification System

In the year 1969, this classification came into existence. RH Whittaker proposed this system. He created a separate group for fungi. The primary criterion for classification here were:

E. Six Kingdom Classification System

Carl Woese a Professor in the Department of Microbiology, University of Illinois, came up with the Six Kingdom Classification System in the year 1990. It was also known as the three-domain system as in it organism classification was done in three domains, i.e., Archaea, Bacteria and Eukarya.

It majorly used the basic principles of the five kingdom system but divides the Monera into two domains Archaebacteria, Eubacteria and other eukaryotes in the third kingdom.

1. Archaea

Archaea domain includes prokaryotic organisms. These have a monolayer core of lipids in the cell membrane and distinct nucleotides in their 16S RNA. It contains a single kingdom called Archaebacteria. This kingdom includes early prokaryotes. These are methanogens, halophiles and thermoacidophiles.

2. Bacteria

The bacteria domain consists of typical prokaryotes that lack membrane covered cell organelles. These do not have microchambers for separating various metabolic activities. It also has a single kingdom-Eubacteria.

Kingdom-Eubacteria

The members of this kingdom have peptidoglycan cell wall, naked DNA in coiled form, glycogen food reserves. There is no sap vacuole and 70S ribosomes are present. The members of this kingdom are bacteria, mycoplasma, Actinomycetes, rickettsiae, spirochaetes, cyanobacteria, Firmicutes.

3. Eukarya

The domain eukarya contain all the eukaryotes. The four kingdoms of this domain are:

Protista

Animalia

Plantae

Fungi