Diversity of organism of Class 9


The method of arranging organisms into groups or sets on the basis of similarities and differences is called classification. Similarities and differences of organisms show their relationships. In fact, for understanding the living world, there is no need of knowing each and everything about all living organisms. One can study only a few representatives from each group and that would give an idea of all members of that group.

  • Taxonomic knowledge about the organism is based on their form and structure (morphology), cell (cytology), development process (embryology), remnant of the past organisms (fossils) and ecological relationship. This knowledge gained through taxonomy is assembled for future use not only for the biologists but also for others working in the field of medicines, agriculture and forestry or industry and so on.
  • In order to understand the living world, especially its diversity, it is essential to make inventory of organisms with correct identification and names.

  • It further facilitates classification of organisms based on their similarities or evolutionary relationships (phylogeny). Moreover, the biologists considerably depend on taxonomic studies of fossils for drawing evolutionary relationships among the organisms.


Classification means the ordering of organisms into groups. The branch of science that deals with the study of principles and procedures of biological classification is called taxonomy (Gk. taxis - arrangement, nomos - law; coined by A.P. de Candolle, 1813). 

Taxonomy enfolds the following fundamental elements: 

  • Identification: Identification is determining the correct place in a system of classification and finding out the correct name of an organism. It is done with the help of keys. This is carried out for an organism by determining its similarity with an already known organism. Suppose there are three plants say a, b, c. All represent different species. Another plant, say d resembles b. The recognition of the plant das identical to the already known plant b is its identification.
  • Nomenclature (Latin, nomen : name ; calare : call) : It is the science of providing distinct and proper names to organisms as per the established universal practices and rules so that they can be easily recognized and differentiated from others.

Some examples of such characters, used in grouping and sub-grouping of organisms are as follows:

(a) Cells are prokaryotic or eukaryotic 

A eukaryotic cell has membrane bound organelles and a well-defined nucleus to carry out different cellular processes in isolation from each other. In prokaryotic cells the nuclei and other organelles are not clearly demarcated. Therefore, this is a basic characteristic of classification. 

(b) Cells occur singly or in clusters 

Unicellularity and multicellularity is yet another factor of classification. Multicellular organisms show distinct division of labour. Different groups of cells performing certain specialized functions are not identical to each other which make a very basic distinction in the body designs of organisms.

(c) Organism is autotrophic or heterotrophic

The body designs of autotrophic (plants) and heterotrophic (animals) organisms are different.

(d) Organization of different body parts

Grouping of organism can be done on the basis of body organization as well. For example plants possess leaves, roots, stems, etc. and animals possess specialized organs to perform different functions.

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