CLASSIFICATION OF LIVING ORGANISMS.

Almost one and a half million animals and over a half million plants are known.
In order to study these organisms in a systematic manner, they are categorized distinctly.
Taxonomy:simply, it is a branch of science that deals with the naming and classification of the organisms.
The modern classification system is rooted in the work of Karl von Linne (Carolus Linnaeus) (1707-1778)

The broad category in which the living organisms have been placed is called as the kingdom while the smallest category of classification consists of the group of natural population that can interbreed with one another to produce fertile offspring and they are reproductively isolated with other such groups is called as species.
In between kingdom and species lie many taxonomic categories that are directed from higher to lower level as

• phylum
  
• class
  
• order
  
• family
  
• genus

the taxonomic categories from species to kingdom forms the hierarchy.
Earlier the living organisms were recognized as two kingdoms: plants and animals but it was found unworkable due to controversy over the unicellular organism like euglena (having the characteristics of both plants and animals) and the differences between the prokaryotic and eukaryotic cells.
In 1866 Ernst Hackael proposed a third kingdom to accommodate euglena, bacteria and other such organisms, but biologists still disagreed over the placement of fungi which was plant like but not an autotroph
Robert Whittaker in 1969 proposed five-kingdom classification considering the three different levels of organization associated with three different modes of nutrition, photosynthesis, absorption and ingestion.
1: kingdom Monera: prokaryotic unicellular organism including bacteria.
2:kigdom protista: eukaryotic predominantly unicellular organisms. Including euglena amoeba paramecium etc.
3: kingdom plantae: eukaryotic multicellular autotrophs.
4: kingdom animalia: eukaryotic multicellular heterotrophs (consumers).
5: kingdom fungi: eukaryotic multicellular reducers (decomposers).eg,mushrooms

Later on, Lynn Margulis and Karlene Schwartz modified this classification in 1988 keeping in mind the cytology ,genetics and organelles of symbiotic origin all along with the cellular organization and and mode of nutrition as
1: prokaryotae (Monera)
2: Protoctista (protists)
3: Plantae
4: Animalia
5:Fungi