Classification of living organisms

CLASSIFICATION OF LIVING ORGANISMS

Classification is defined as the systematic arrangement of living organisms into groups and sub-groups on the basis of their similarities and dissimilarities.
Organisms having similar characteristic features are placed in same group and those having dissimilar features are placed in different group. Also when dissimilarities appear in same group they are further sub-divided.
The branch of science that deals with the classification of organisms is known as taxonomy.

Importance of Classification:

Classification helps in determining the similar and dissimilar characters of different types of organisms. Thus it helps in organizing the diverse living forms of life.
It makes the understanding of millions of diverse living forms systematic and easy.
It helps in identification of a variety of organisms.
It projects a good and summarized picture of all life forms at a glance.
It helps us to understand the interrelationship among different groups of organisms and environment.
It helps in predicting the line of evolution.
It also helps in nomenclature (assigning scientific name) of the particular organism.
It serves as a base for the development of other biological sciences such as biogeography etc.
Various fields of applied biology such as agriculture, public health and environmental biology depend on classification of pests, disease vectors, pathogens and components of an ecosystem.
It establishes an international communication between scientists dealing with the taxonomy.

Basis of classification:

Different criteria are used to classify the living organisms into different groups and subgroups.

Type of Cell:

All living organisms are made up of cells. They are classified on the basis of the type of cell they are made up of, i.e., prokaryotic or eukaryotic.
Prokaryotic cells are those in which a well developed nucleus is absent but genetic material is present. The region where nuclear material is present is known as nucleoid. Also membrane bound organelles are absent. Hence such organisms are the primitive and the simplest ones.
Eukaryotic cells are those in which a well developed nucleus and membrane bound organelles are present.

Cellular level:

Organisms can be made up of single cell or many cells.
All prokaryotes/ monerans are unicellular but eukaryotes can be unicellular or multicellular.
All unicellular eukaryotic organisms are placed in one group known as protista.
Multicellular organisms are further classified on the basis of their body organization.

Examples:

Body Organization:

Multicellular organisms show division of labor, i.e., the work/ function is distributed in different group of cells within the colony or body.
Some live in colony while the other show complex body organization where cells form tissue, tissues form organ; organs form organ system and all organ system function in coordination to form a living organism.
Different organisms show different levels of complexity in their body design and thus placed in different groups accordingly.

Mode of Nutrition:

Organisms are classified on the basis of its ability to synthesize food.
Those organisms that can synthesize food for themselves are known as autotrophs while those that depend on other organisms for their food are known as heterotrophs.
Multicellular autotrophs are placed in plant kingdom while multicellular heterotrophs are placed in animal kingdom.
Within these kingdoms they are sub-classified on the basis of their structural and functional complexity.