It is defined as a process of giving hierarchy of categories by scientific procedure based on features of organisms and arranging them into different groups.
Need for Biological Classification:
• To study and include each organism along with its identification and habitat.
• To establish the relationship among different organisms and to know about their evolution.
Objectives of Classification are quite similar to needs of biological classification. There are basically three types of Biological Classification which can be categorized as artificial, natural and phylogenetic.
What is Artificial Classification?
Artificial Classification uses form, shape as prominent features for grouping organisms. Animals were also classified on basis of red blood cells, habitat such as land, water or air. They were also classified on their basis to fly or not to fly. This system is relatively easy to follow.
Artificial System of Classification has many disadvantages. It relies just on form and shape of organisms and does not take into account other features. So it is difficult to understand the evolution of organism. It leads to misunderstanding of any relationship among organisms. The different types of organisms are arranged in same groups like birds, insects, bats they fly and they are grouped in same criteria. The form and shape of organism is not permanent and it changes with time. For Example, some plants keep on changing their shape in different seasons.
What is Natural System of Classification?
It takes into account multiple features such as anatomy, physiology, pathology, biochemistry, reproduction & cytology to compare the organisms and establish a relationship between them. It overshadows all the disadvantages of artificial system of classification. It helps to understand the evolution of organism by knowing the relationship between them.
The features undertaken in this classification are constant. In this bird, reptiles and mammals are placed in the different groups based on the multiple features as discussed above. For example humans have 4 chambered hearts, warm blooded nature and de nucleated erythrocytes. Fishes have 2 chambered hearts, cold blooded and respire through gills.
What is Homology?
In this a relationship is established between the structures which can be compared and originates from same source. It helps us to understand the evolution of an organ.
What is Molecular Homology?
In this a relationship is established between the molecules like proteins, RNA which originate from same source to know about differences and similarities.
A Natural System for classification was proposed by Bentham & Hooker in Genera Plantarum.
What is Phylogenetic System of Classification?
It is defined as a relationship based on the evolutionary aspect of organisms. It is based on Darwin’s Concept of Natural Selection. It tells us about the original relationship among organisms. The foremost phylogenetic system of classification was given by Engler & Prantl. They divide the plants into primitive and modern types.
Phlogenetic System relies on fossil records and is not static. It never fulfills as there is difficulty in recording fossils, tracking and keeping record of them as new fossils start appearing. Zoologists and Botanists have entirely different or conflicting view about phylogenetic system of classification. Zoologists rely on structural aspect of organism to link with evolutionary aspect. Botanists do not rely on structural aspect to link with evolutionary aspect.
What is Phenetic Classification?
It is a type of phylogenetic classification which relies on similar and dissimilar features present in today’s organism without including evolutionary and other related aspects. It depends upon other branches of taxonomy like cytotaxonomy, chemotaxonomy, numerical and cladistic taxonomy.
What is Cytotaxonomy?
It is defined as a classification which is based on cytological studies (number of chromosomes, meiosis behavior). It helps us to establish relationship between different organisms based on these features like man has 46 chromosomes and apes have 48.
What is Chemotaxonomy?
It is also known as Biochemical Systematics.It is defined as a method of classification which is based upon chemical constituents (amino acids, crystals, alkaloids etc). Chemicals are generally static and specific.
What is Numerical Taxonomy?
It is defined as a statistical method based upon number of featured derived from almost every branch of biology. A number is assigned and computer analysis is done later on. A statistician is required to obtain the results and evaluate them. Graphic displays are quite common.
What is Cladistic Taxonomy?
It is defined as a method which is based on common ancestral origin. It is further divided into ancestral and derived characters. Ancestral characters are those which are present in the entire group while derived ones are those which differ from ancestral and may or may not present in the entire group.
Derived Characters are not static they keep on changing. They lead to evolution. While ancestral characters are fixed.
What is Cladogram?
It is a phylogenetic tree in which organisms are arranged based on their characters (Derived or Ancestral).
Organisms are classified into different kingdoms based on the system of classification.
