explain basis of classification?
Answers
Our planet is home to millions of species, ranging from tiny bacteria, fungi, and amoeba to giant whales and seals. Classification of living organisms, therefore, is important because it allows biologists to identify, group, and properly name organisms.
Before the advent of modern genetically based evolutionary studies, European and American biologists primarily classified organisms into different categories based on their physical characteristics and presumed natural relationship.
Greek thinker, Aristotle classified all the types of creatures according to their similarities: animals with blood and animals without blood: animals that live on water and animals that live on land.
Aristotle assumed that creatures could be grouped in order from lowest to highest, with the human species being the highest. According to his,“Ladder of Nature”, different organisms showed different levels of complexity and abilities to thrive.
But this is a very simple way of classification.
Carolus Linnaeus, a Swedish physician, and Botanist grouped the species according to their reproductive parts and developed the two-part binomial taxonomy system of categorizing organisms according to genus and species.
Linnaeus’s work remains valid. It has been combined with the work of Charles Darwin in the field of evolution to form the foundation of modern taxonomy.
Darwin’s theory of evolution states that all modern species are derived from earlier species and that all organisms past and present, share a common ancestry.
Darwin’s theory of evolution is the organizing principle of modern taxonomy ie the classification.
Basis of Classification– The characteristics based on which the living organisms can be classified.
Characteristic: A distinguishing quality, trait or feature of an individual seen in all members of the same species
Division of labour: The phenomenon where all cells are not the same, but acquire different shape or size and become equipped to carry out different functions is called division of labour
Ancient Greek thinker Aristotle classified living beings on the basis of their habitat. He classified them into two groups, i.e. those living in water and those living on land. But his classification was too simple to justify inclusion of a particular organism into a particular group.
Some examples of scientific bases of classification are as follows:
Organization of nucleus: Nucleus may or may not be organized in an organism. On this basis, organisms can be divided into two groups, viz. prokaryotes and eukaryotes.
Prokaryotes: When nucleus is not organized, i.e. nuclear materials are not membrane bound; the organism is called prokaryote.
Eukaryotes: When nucleus is organized, i.e. nuclear materials are membrane bound; the organism is called eukaryote.
Number of cells: An organism can be composed of a single cell or many cells. An organism with a single cell is called unicellular organism. On the other hand, an organism with more than one cell is called multicellular organism.
Mode of Nutrition: On this basis, organisms can be divided into two broad groups, i.e. autotrophs and heterotrophs. An autotroph makes its own food, while a heterotroph depends on other organisms for food.
Level of Organisation: Even in case of multicellular organisms, there can be different levels of organization. When a cell is responsible for all the life processes, it is called cellular level or organization. When some cells group together to perform specific function, it is called tissue level of organization. When tissues group together to form some organs, it is called organ level of organization. Similarly, organ system level of organization is seen in complex organisms
Classification and evolution:
Organisms belonging to the same group will have more similarities and thus we can assume that they may have arisen from a common ancestor
The lower the number of similarities, the further they are away from each other in the evolutionary tree. E.g. bacteria and chimpanzee will have no similar features, while a human and a chimpanzee will have several common features. This shows that chimpanzees and humans have a common evolutionary link.