Biological Classification
What is classification?
Anything which is grouped into convenient category based on easily observable characters.
Arrangement of organized information on the basis of similarities.
Biological classification
It is the systematic grouping of organisms which is also called biosystematics
Biosystematics
Biosystematics deals with the identification, nomenclature & classification of organisms based
on their similarities & differences
Different systems of classification
1) Artificial classification: It is a system of classification based on one or two easily
recognizable characters.
Example: Theophrastus (370-300 BC) Classified plants into: Trees, Shrubs,
Undershrubs and Herbs
Aristotle (384-322 BC) classified animals into:
Enaima ( Animals with red blood)
Anaima (Animals without blood)
Ovipary (Egg laying)
Vivipary ( Giving birth to young ones)
2) Natural classification: It is a system of classification based on natural similarities of
vegetative & floral characters.
George Bentham & Joseph Dalton Hooker Classified plant into:
Cryptogames (non flowering plants)
Phanerogams (seed bearing plants)
3)Phylogenetic classification( Cladistics): It is a system of classification based on evolutionary
& genetic relationship of organisms in addition to natural characters.
Adolf Engler & Karl Prantle classified bacteria & all plants under 14 divisions. The 14 th
divisions is embryophyta siphanogama that includes gymnosperms & angiosperms.
Kingdom Systems of classification
Two kingdom system was proposed by Carolus Linnaeus (1758).
Kingdom Plantae: It includes Bacteria, Mycoplasma. Fungi & photosynthetic plants.
Kingdom Animalia: It includes unicellular & multicellular animals.
Three kingdom system was proposed by Earnest Haeckel (1866)
Kingdom protista: It includes unicellular & colonial eukaryotes such as Bacteria, algae, fungi &
protozoans.
Kingdom plantae: It includes multicellular photosynthetic plants.
Kingdom animalia: It includes multicellular animals.
Four kingdom system was proposed by Copeland (1956)
Kingdom monera: It includes unicellular or filamentous prokaryotes such as Bacteria,
mycoplasma &cyanobacteria.
Kingdom protista: It includes unicellular eukaryotes.
Kingdom plantae: It includes multicellular autotrophic eukaryotes.
Kingdom animalia: It includes multicellular heterotrophic eukaryotes.
.
Five kingdom system (RH Whittaker-1969)
Kingdom Prokaryote Kingdom Eukaryote
Kingdom: Monera Protista Fungi Plantae Animalia
Classification based on:
Complexity of cell structure- prokaryote or eukaryote.
Complexity of organisms body- unicellular or multicellular
Mode of nutrition- autotrophic or heterotrophic
Prokaryote Eukaryote
* Do not present well develop nucleus * Having True nucleus
* present single standed DNA * Double standed DNA and Histone protein
* May have plasmid * Plasmid absent
* Absence membrane bounded cell organelles * Presence of membrane bounded organelles
* 70S ribosomes * 70s and 80 s ribosomes
* Example: Nostoc, Bacteria
* Example: Higher plant & animals
Kingdom Monera:
* Unicellular & filamentous prokaryotes.
* Omni present ( soil, air, desert, deep sea, snow & as parasites.
* Cell wall is composed of polysaccharides and amino acid.
* Autotrophic and Heterotrophic.
* Reproduce by vegetative, asexual & sexual methods.
* Example: Archaebacteria, Eubacteria, Cyanobacteria
Kingdom Protista:
* Unicellular eukaryotes.
* Cell wall is usually absent.
* Photosynthetic or non-photosynthetic.
* Locomotory structure may be cilia, flagella, pseudopodia.
* Reproduce by sexual & asexual methods.
Kingdom Fungi:
* Unicellular or multicellular eukaryotes.
* Achlorophyllus heterotrophs.
* Some are parasites & associated in the roots of higher plants.
* The thalloid plant body is called mycelium.
* Mycelium is made up of tubular thread like hyphae.
* Cell wall has chitin.
They reproduce by the following methods like vegetative, asexual, and sexual.
The following are not mentioned in the R. H. Whittaker five kingdom system of
classification
Prions: These are intracellular, infections protein particles that cause disease in animals.
They were discovered by Stanley Prusiner (1970).
Diseases:
Scrapie in sheeps
Kuru in Malaysian tribes
Creutzfeldt-Jacob disease(CJD)
Bovine spongiform encephalopathy
Viroids: These are intracellular, infections single stranded RNA particles that cause
diseases in plants. They were discovered by T.O Diener(1971).
Diseases:
Potato spindle tuber
Citrus exocortis
Cucumber pale fruit
Tomato bunchy top
Viruses: These are intracellular, infections, poisonous nucleoproteins having DNA or
RNA as genetic material. These are obligate parasites that do not have cellular structure.
They were discovered by Ivanowski(1892).
Example: TMV, HIV, T4 bacteriophage
Diseases: Tobacco mosaic, Banana bunchy top, Rabies, Brain fever & AIDS.
Lichens: These are symbiotic association between algae & fungi. The alage component
is called phycobiont(autotrophic) & fungal component is called mycobiont
(heterotrophic). Lichens are good pollution indicators.
Example: Parmelia, Cladonia.
