Tejinder, Academic Content Writer at Edumarz
Classification is a process of identifying and grouping the organisms in categories, in such a way that the same characteristic organisms fall in the same group.
Aristotle was the first scientist who classified organisms into two categories: Animals and plants. He further made classification categories such as animals having blood and animals not having blood; animals living on land and animals living in the water.
He gave the concept of “ladder of life”, according to which all organisms present on earth can be classified in categories from lowest to highest based on body complexities. According to this humans occupy the highest step on the ladder i.e. the highest category.
But this classification system is very simple.
Basis of Classification– The characteristics based on which the living organisms can be classified.
There are some parameters on which the scientific basis of classification is done, such as:
Number of cells
Mode of nutrition
A number of the cells: Based on the number of cells present in an organism they are classified into two categories:
Unicellular – organisms whose body is made up of only one(uni) cell are called unicellular. Example: Amoeba, Paramecium
Multicellular – organisms whose body is made up of more than one i.e. multi number of cells are called multicellular.
Example: Tiger, Humans
Nuclear Organization: Based on the complexity of the nucleus organisms are classified in two categories:
Prokaryotes– organisms in which the nucleus is not well organized i.e. not bound by the nuclear membrane are called prokaryotes.
Example: Bacteria, Blue-green Algae
Eukaryotes– organisms in which the nucleus is well organized i.e. bound by nuclear membrane are called eukaryotes.
Example: Animals, Humans
Mode of Nutrition: Based on the nutrition mode of organisms they are classified in two categories:
Autotrophic – organisms which prepare their food and are not dependent on others are known as autotrophic. In other words they are able to produce organic matter from simple inorganic materials. The autotrophic organisms based on energy utilized for food preparation are further sub classified as:
Photoautotrophic – organisms which use the energy of the sun (photo) to produce food are known as photoautotrophic.
Example: Green plants
Chemoautotrophic – organisms which use the chemical energy (chemo) from inorganic reactions in the environment to produce food are known as chemoautotrophs.
Example: Nitrogen cycle bacteria
Heterotrophic– organisms which are dependent on others for food are known as heterotrophs. These organisms consume the organic matter from other organisms. It can be further divided in other categories:
Saprophytic – in this mode of nutrition the consumer secretes some digestive enzymes on the food while ingesting it.
Example: Decomposers, houseflies
Holozoic – in this mode of nutrition the food is ingested directly and inside the body of the consumer it is digested further.
Parasitic– in this mode of nutrition the organism derives nutrition from the host without killing it. They are further of two types:
Ectoparasite : organisms which feed on the external surface of the host and derive nutrition. Example: lice, ticks
Endoparasite : organisms which feed inside the body of the host and derive its nutrition. Example: tapeworm