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Updated on April 4, 2016


If we just revolve our eyes in our surroundings, we see many organisms around us. Some very small like bacteria while some big even as a elephant. Some transparent while some colorful. Some that which live only a few days while some lives for thousands of years. Some plants as small as an algae and while some tall as red wood trees of California.

And it is not easy to study all of them in detail. So all of them are classified on the basis of their similarities between them.

What is classification?

Grouping of organisms on the basis that how they are closely related.

What is the basis of classification?

Classification is done on the basis of three things.

  1. Mode of nutrition

  2. Complexity of cells

  3. Unicellular or multicellular

Mode of nutrition- there are two modes of nutrition. Auto-trophic and hetrotrophic.

Auto -trophictype of organisms make their own food by the process of photosynthesis in the presence of sun light. These mainly include plants.

Hetrotroph organisms are dependent on the autotrops of their foods. These are mainly animals

Complexity of cell– some are prokaryotic organisms and some eukaryotic organisms.

Prokaryotic organisms are the organisms which do not have well defined membrane bound organelles.

Eukaryotic organismsare the organisms which have well defined membrane bound organelles

Unicellular or Multicellular

some organisms have single cell which performs all the functions while some organisms have many cells and specified cells are to do specified functions. The organisms which have single cells is called unicellularorganismand the organisms which have multiple cells are known as multicellular organisms.

Importance of classification

There are quiet a few importance of classification they are

1 They make the study of organism easier

2 It summarizes all life forms.

3 It helps us to learn the relationship between different kinds of organisms.

4 It is the basic for all other biological sciences like ecology, zoology etc.

The hierarchy of classification - groups

Many biologists have tried to classify organisms into the category of kingdoms. Some of them are Ernst Haeckel, Robert Whittaker and Carl Woese

The classification proposed by Whittaker have five kingdoms that is:






The further classification is done by naming of organisms in to different sub groups. The classification scheme is

  • Kingdom
  • phylum [for animals ] / division [for plant]
  • class
  • order
  • family
  • genus
  • species

Species - it is the lower most category and the basic unit of classification. The members of these species look alike in their appearance. It has the widest range of organisms

Genus - similar kinds of species are classified into genus.

Family- similar genera are grouped into family

Order – similar families are grouped into order

Class – similar orders are grouped into classes

Phylum – similar classes are grouped into phylum

Kingdom– similar phyla are grouped into kingdom

The 5 kingdom classification proposed by Whittaker are -

Kingdom Monera

  • They are prokaryotic organisms and do not have defined nucleus or organelles.

  • They are mostly unicellular organisms , some have cell wall while some don't.

  • Their mode of nutrition may be auto-trophic or hetrotrophic.

  • They are usually non – motile animals.

  • Example – blue-green algae, bacteria, mycoplasma

Kingdom Protista

  • They are eukaryotic organisms and have well defined nucleus and organelles.

  • They are unicellular organisms .

  • Their mode of nutrition may be auto-trophic or hetrotrophic.

  • They have flagella for moving around.

  • Example – amoeba , paramecium , euglena etc.

Kingdom Fungi

  • They are eukaryotic , multicellular organisms.

  • They are mostly non-motile.

  • They are saprophytes i.e,they depend on dead and decaying organisms for their food.

  • They have cell wall made of chitin.

  • Examples – yeast, mushroom etc.

Kingdom Plantae

  • They are eukaryotic , multicellular organisms.

  • They have cell wall made of cellulose.

  • They are auto-trophic organisms.

  • They store carbohydrates in the form of starch.

  • Example – all plants

Kingdom Animalia

  • They are eukaryotic , multicellular organisms.

  • Their cells do not have cell wall instead they have cell membrane.

  • They are hetrotrophic.

  • They are motile i.e.,they have legs for locomotion.

How complicated is our diversity! That is why it is necessary to classify these organisms into different groups to learn about them and to understand them easily. classification of organisms have came out as boon for other biologists. It has made researches more easier than ever.


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