Biological Classification



  • Biological classification
  • Dichotomous key
  • Features of dichotomous key
  • Dichotomy of Animals


Classification and Evolution of Diversity in Living Organisms:

1) For a systematic study, we need to classify organisms.

Aristotle classified animals according to whether they lived on land, in water, or in the air. This cannot give a clear idea though as organisms in living in water have nothing common except their habitat.

So nowadays classification is based on the following characteristics -

  1. Prokaryote or eukaryote

  2. Unicellular or multicellular

  3. Autotrophs or heterotrophs

  4. Level of organization

  5. Specialized organ

2) Classification helps in understanding evolution:

Primitive/lower organisms: The group of organisms which have ancient body designs that have not changed very much.

Advanced/higher organisms: The group of organisms that have acquired their particular body designs relatively recently.


Classification of Living Things

Classification presented by Aristotle –

  • He classified animals on the basis of their habitats – land, water and air.
  • But it can be easily observed that the animals that live at a particular habitat say land are still so different from each other.
  • Therefore it was decided to classify the living organisms on the basis of a hierarchy.
  • This hierarchical classification was based on the similarities and dissimilarities in the characteristics of the living organisms.
  • Organisms having similar characteristics were placed in a similar category.

Why do we need to classify organisms?

  • If we classify organisms into several categories it will be easier for us to study them.
  • It will help us in understanding how did these organisms evolve.
  • We can also understand how different organisms are related to each other.
  • We can learn why different organisms are found at distinct geographical conditions.

What is evolution?

Over a course of time the living organisms accumulate changes. These changes could be in their body type or size or their features. These changes allow them to survive better with the change in environment. This is called Evolution. This concept was introduced by Charles Darwin.


The method of arranging organisms into groups or sets on the basis of similarities and differences is called classification.

Primitive and Advanced Organisms

Primitive Organisms are the ones that have an ancient or body design. Their bodies haven't undergone many changes with time. They are called ‘Lower’ organisms as well.

The Advanced Organisms are those who have recently acquired body changes. They are also called as ‘Higher’ organisms.

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Video Tutorials

We have provided more than 1 series of video tutorials for some topics to help you get a better understanding of the topic.

Series 1

Series 2 | Biological Classification and Need of Biological Classification

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Biological Classification and Need of Biological Classification [00:02:33]
Series: Biological Classification and Need of Biological Classification


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