Need of Classification of Living Beings

Characteristics of Living:


  • All living organisms grow. The increase in mass and increase in the number of individuals are twin characteristics of growth.
  • A multicellular organism grows by cell division.
  • In plants, this growth by cell division occurs continuously throughout their life span.  In animals, this growth is seen only up to a certain age. However, cell division occurs in certain tissues to replace lost cells. Unicellular organisms also grow by cell division.
  • Non-living things grow by an accumulation of material on their surface.
  • Hence growth can not be considered as defining character of living beings.


  • In multicellular organisms, reproduction refers to the production of progeny possessing features more or less similar to those of parents. Invariably and implicitly we refer to sexual reproduction.
  • Organisms reproduce by asexual means also. Fungi multiply and spread easily due to the millions of asexual spores they produce. In lower organisms like yeast and hydra, we observe budding. In Planaria (flatworms), we observe true regeneration, i.e., a fragmented organism regenerates the lost part of its body and becomes a new organism.
  • The fungi, the filamentous algae, the protonema of mosses, all easily multiply by fragmentation. When it comes to unicellular organisms like bacteria, unicellular algae or Amoeba, reproduction is synonymous with growth, i.e., increase in the number of cells. But living organisms mules, sterile worker bees do not reproduce.
  • Hence reproduction can not be considered as defining character of living beings.


  • All living organisms are made of chemicals. These chemicals, small and big, belonging to various classes, sizes, functions, etc., are constantly being made and changed into some other biomolecules.
  • These conversions are chemical reactions or metabolic reactions. 3. There are thousands of metabolic reactions occurring simultaneously inside all living organisms, be they unicellular or multicellular.
  • No non-living object exhibits metabolism. Thus, Metabolism a Defining Character of Living
  • Metabolic reactions can be demonstrated outside the body in cell-free systems.
  • An isolated metabolic reaction(s) outside the body of an organism, performed in a test tube is neither living nor non-living.
  • Hence, metabolism and cellular organization of the body is the defining feature of life forms. Thus, living organisms are self-replicating, evolving and self-regulating interactive systems capable of responding to external stimuli.

Diversity in Living World:

  • Each different kind of plant, animal or organism that we see, represents a species.
  • The number of species that are known and described range between 5-30 million. This refers to biodiversity or the number and types of organisms present on earth.
  • We should remember here that as we explore new areas, and even old ones, new organisms are continuously being identified.
  • There are millions of plants and animals in the world; we know the plants and animals in our own area by their local names. These local names would vary from place to place, even within a country.
  • Hence, there is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature.

Historical Background:

Aristotle, Greek philosopher (384 – 322 B.C.):

  • Aristotle developed the first classification system, which divided all known organisms into two groups: plants and animals.
  • Aristotle system of classification was not full proof because many animals were there they didn’t fit in the classification.
  • Aristotle’s limited classification system was used for nearly 2000 years.

Parasara (Indian sage)(Before Christ):

  • On the basis of comparative morphology, he classified plants, whose detail is given in his compilation called Vrikshayurveda.
  • He group families of plants under name ganas. These ganas can be clearly distinguished and recognised even today.

Charaka Indian Doctor and Father of Ayurveda (first century A.D.):

  • In his book ‘Charak Sanhita’ he classified 200 kinds of animals and 340 kinds of plants.

John Ray British Botanist (1628-1705):

  • He introduced the term ‘species’,
  • He collected plant species from all over Europe and give an improved form of classification of plants.

Carlous Linnaeus Swedish Naturalist (1707 – 1778) :

  • He introduced binomial nomenclature system.
  • He listed about 5900 species of plants in his book ‘Species Plantarum’ (1753).
  • He listed about 4200 species of animals in his book ‘Systema Naturae’ (1758).

George Cavier American biologist (1769 – 1832):

  • He introduced natural classification system.
  • He took into account not only the structure but also the functions of various structures and the ancestral history of the organism.
  • He studied related fossils.

Sir Julain Huxley (1940):

He introduced the term ‘New Systematics’ for the classification of living organisms based on the theory of evolution and phylogeny.

Classification and its Need:

  • The term classification was coined by A. P. de Condole.
  • Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.
  • There are a large number of organisms found on the Earth. They show variations in their shape, size, structure, habit, habitat, nutrition, etc.
  • It is difficult to remember the characteristics of all the organisms without their proper arrangement.
  • The classification helps us to explain unity in diversity of the organisms. The classification places an organism amongst those which have common characteristics.

Systematics and Taxonomy:

  • Systematics:  Systematics is a scientific study of similarities and differences among different kinds of organisms and also includes identification, nomenclature, and classification.
  • Taxonomy: It is the branch of biology which deals with the collection, identification, nomenclature, description, and classification of plants and animals.

Objectives of Systematics and Taxonomy:

  • To know various kinds of plants on the earth with their names, affinities, geographical distribution, habit, characteristics and their economic importance.
  • To have reference system for all organisms with which scientist can work.
  • To demonstrate manifold diversities of organisms and their phylogenetic (evolutionary) relationship.
  • To ascertain nomenclature.

Taxonomic Hierarchy:

  • Taxon (Pl – taxa): Taxon is a group of living organisms which is used to represent a concrete unit of classification. It may be large or small.
  • Category: A category is a rank or level in the hierarchical classification of organisms. In the hierarchy of categories, the kingdom is the highest and species is the lowest category.

Units of Classification:

Acronym: King Philip’s’s Classmates Sing a Song Of Family Genius Specially

Classification 01


  • It is the smallest and basic unit of classification. Taxonomic studies consider a group of individual organisms with fundamental similarities as a species. Thus all the individual members belonging to particular species show all similar characters and can breed among themselves to produce a similar type of organism. We should be able to distinguish one species from the other closely related species based on the distinct morphological differences. All the china rose (Hibiscus) plants are grouped under a species rosa Sinensis. All the potato plants are grouped under species tuberosum.
  • Example 1: House crow commonly called Indian crow (Corvus splendens)  and forest crow commonly called jungle crow or raven (Corvus macrorhynchos) have the same genus but they can not breed among themselves. Hence these are two different species.

Two Species of Crow

  • Example 2: Horse (Equus cabalus) and ass (Equus asinus) are of same genera but are two different species, because they do not breed among themselves. The mule is an artificial hybrid of horse and ass is sterile i.e. it can not reproduce. Hence the mule is not a species.

Genus (Pl – genera):

  • It is a group of organisms of closely related species, which resemble one another in certain characters. A genus may be monotypic genus (having single species) or polytypic genus (having many species).
  • Example: Banyan tree (Ficus benghalensis)and fig tree (Ficus carica) differ in shape, size, leaves but have the similar reproductive organ like inflorescence. Hence they are of same genera


  • It is a group of organisms of closely related genera, which resemble one another in certain characters.
  • Example: Domestic cat (Felis domestica) and Lio (Panthera leo) belong to cat family Felidae, because both of them possess the similar structure and has retractive claws.


  • It is a group of organisms of closely related families, which resemble one another in major characters.
  • Example: Both the tiger (Panthera tigris) and the wolf (Cannis lupus) possess jaws with powerful incisors and large sharp canines. This adaptation is for flesh eating. Hence tiger and wolf have the same order Carnivora.


  • It is a group of organisms of closely related sub-classes or order, which resemble one another in certain characters.
  • Example: Chordates such as rats, dogs, bats, monkeys, camel are characterised by a hairy exoskeleton, milk glands (mammari glands)and external ears, belong to the same class Mammalia.


  • It is a group of organisms of closely related class, which resemble one another in certain characters.
  • Example: all animals which have a notochord present in embryo belong to the phylum chordata.


  • It is a group of organisms of closely related phyla, which resemble one another in major characters. It
  • Example: plant Kingdom and animal kingdom

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