BLAS notes

Classification
Grouping of living organisms according to their similarities and dissimilarities is known as classification. It is the important part of modern taxonomy. There are millions of living organisms on earth. No systematic study can be done without classifying them.
The classification is not only for identification but also to know the evolutionary trend. Different systems of classification
Artificial classification
It is the classical type of classification. Ancient people tried to classify plants and animals according to use to mankind. This type of classification is based on one or few characters. It is not based on natural characters and phylogenetic relationship. Artificial classification is put forwarded by different workers in pre Darwinian era.
Natural system of classification
Natural system is based on truly natural characters such as characters of resemblance or correlation, affinities among them etc. this system considers all aspects by which closely related plants and animals come together. The best and highly recognized natural system of natural classification was proposed by George Bentham (1800 to 1894) and Joseph Dalton Hooker (1817-19110). They made the thorough observation of the plants and presented classification.
Phylogenetic system of classification
The study of history of development of a race or simply evolutionary history is called phylogeny. It includes he knowledge of ancestor, place and time of origin. This is the most advanced type of classification. This system classifies the plants and animals according to their evolutionary sequence and genetic relationship. This system was put forwarded by A Engler(1844-1893) this system enables the taxonomists to trace out ancestor and evolutionary trend.

Hierarchic system in classification

Hierarchy is a system of arrangement where taxonomic categories are placed in major units of classification
Kingdom
This is the highest caterory. There are kingdoms like Monera, Protista, Fungi or Mycota, Plantae and Animalia etc.
Division or Phylum
The division or phylum includes classes of different organisms having common characters.
Class
It is the group of orders.
Order
Group of related Families
Family
Group of related genera
Genus
Aggregation of two or more species
Species
This is the basic unit of classification. The closely resembling individuals of same kind constitute species. They can freely interbreed and produce fertile offspring. Among the member of species, there may be presence of minor differences in color, form and size etc
Two Kingdom classification
Carolus Linnaeus (1707-1778) divided all living things into two Kingdoms for the first time.
Kingdom Plantae or Plant kingdom
Some characters
Autotrophic mode of nutrition
Immobility
Rigid cellulosic wall
Less sensitive
Includes all plants
Kingdom Animalia or Animal kingdom
Some characters
Heterotrophic mode of nutrition
Mobility
Made up of cells without rigid cellulosic wall.
More sensitive because of presence of nerve cell
Includes all animals
The two kingdom classification is appreciable effort. However it could not address a great variety of animals and plants. So, it is inadequate and unsatisfactory in modern age.

Five kingdom classification
RH Whittaker of USA (1969) gave five kingdom system of classification (Science,163:150-160)
This system focuses on
Complexities of cell structure and body organization
Mode of nutrition
Phylogenetic relationship
Features of five kingdom classification
Advancement over the two kingdom classification
Based on phylogenetic relationship
Solves many problems of two kingdom classification.
Characters of five kingdom classification
Separated prokaryotes from eukaryotes
Removed anomaly of positions of many transitional and intermediate forms
All multi cellular, photosynthetic, eukaryotic with cellulosic wall included in kingdom Plantae
All multi cellular, non photosynthetic, eukaryotic with cellulosic wall included in Animal kingdom
All multi cellular, non photosynthetic plants separated from photosynthetic plants and kept in kingdom Fungi.
Brought out phylogenetic relationship amongst the primitive forms