[Biology Class Notes] on Taxonomy Of Biological Classification Pdf for Exam

A Brief On Taxonomy

In order to understand the taxonomy of biological classification one needs to understand what is taxonomy. This word ‘taxonomy’ was coined by  AP De Candolle and it means ‘arrangement’. Taxonomy is a branch of science which deals with the identification, nomenclature, and classification of the organisms. The aim of taxonomy is to classify all the organisms in such a way that evolutionary development and relations are visible as well as provide identification and nomenclature of a particular organism. The principles of taxonomy help in the biological classification of the organisms on the basis of similarities and dissimilarities among the organisms.

History Of Classification

• Aristotle was the earliest who classified the organisms into two groups based on the presence or absence of blood in the organisms.

• Carolus Linnaeus who is also known as ‘Father of the modern taxonomy’ classified the organisms on the basis of external features into 6 groups as worms, insects, fishes, reptiles, birds, and quadruped.

• In 1969 RH Whittaker gave the 5 kingdom classification. This classification is the most relevant of all and is accepted.

• Later Carl Woese found that the archaebacteria were quite different from the eubacteria so they cannot be kept together. So he formed 3 domains above the level of kingdoms and gave the phylogenetic tree of evolution of these domains. The three domains are- Bacteria, Eukarya, and Archaea.

Importance Of Classification

Millions and millions of species of organisms are found on earth and it becomes difficult to study them due to such a vast number. Classifying them into groups eases the process and helps us to explore more about the biodiversity present on the earth.

Groups are made by the scientists based on a number of criteria and thus organisms with similar features are kept together.

Hierarchy Of Classification

This includes the sequential arrangement of different categories from lowest to the highest. Each category is called taxon.

Seven Levels of Taxonomic Classification

Each level here is the taxon.

• DOMAIN

• KINGDOM

• PHYLUM

• CLASS

• ORDER

• GENUS

• SPECIES

Let us study this taxon in detail

Kingdom

It is the highest category of classification. This is a broad taxonomic category. For example, Plantae kingdom has all types of plants in it and the Animalia kingdom has all types of animals from insects to tigers in it. It is a combination of different phyla.

Phylum/Division

The kingdom is further divided into a number of phyla/divisions. For example, Kingdom Animalia has 35 phyla and the Plant kingdom has 5 divisions.

Class

Phylum further breaks into a number of classes. Some examples of classes are Mammalia, Monocotyledonae, etc.

Order

The class then divides into different orders. A class is termed to have more than 2 orders depending on the population of organisms and similarities present in them.

Genus

A taxon that comes under the order is the genus. Two different organisms can have the same genus like early men and present-day men have genus Homo but the species is different. Organisms belonging to different genera cannot interbreed. For example, both the tiger and cat belong to the same family but different genera so they cannot interbreed. Genus name always starts with a capital letter.

Species

This is called the unit of taxonomic classification. The organisms belonging to the same species can interbreed with each other. Different organisms can have the same genus but species can never be the same. By the rules of nomenclature species of an organism is never capitalized and printed in italics; underlined when written.

Potato and Brinjal both belong to the same genus Melongena but the species of potato is Tuberosum and the species of brinjal is Melongena.

As we move from kingdom to species the number of similar characters of organisms keeps on increasing.

This can be understood with the following example- Both tiger and humans belong to same kingdom Animalia but both seem so different from each other and have very few characters similar like cells of the body, no cell wall but as the classification narrows down tiger is placed in the genus Panthera which also has leopard, lion, etc. These animals have more similar characters with the tiger as compared to the man.

Sample Example of Biological Classification of a Man

From this table, it is clear how taxonomical classification helps us to study the features of organisms in a better way.