The term “biodiversity” has been derived from ‘bio’ and ‘diversity’. “Diversity” means variety within a species and among species. Biodiversity is a measure of the variety of organisms present in different ecosystems.

The branch of biology which deals with classification is called taxonomy and the branch which deals with classification and also traces the evolutionary history of organisms is known as systematics.

Classification is based on relationship amongst organisms and such relationship is got through similarities in characteristics.

Taxonomic Hierarchy

The groups into which organisms are classified are known as taxonomic categories or taxa (singular “taxon”). The taxa form a ladder, called taxonomic hierarchy. All organisms are divided into five kingdoms. So kingdom is the largest taxon. On the basis of similarities, each kingdom is further divided into smaller taxa in the following way:

Phylum (Division: for plants and fungi): A phylum is a group of related classes.

Class: A class is a group of related orders.

Order: An order is a group of related families.

Family: A family is a group of related genera.

Genus: A genus is a group of related species.

Species: A species consists of similar organisms.


Species is the basic unit of classification. “A species is a group of organisms which can interbreed freely among them and produce fertile offspring, but are reproductively isolated from all other such groups in nature.” Each species possesses its own distinct structural, ecological and behavioural characteristics.

Solving a Biological Problem

The scientific method in which biological problems are solved, is termed as biological method

A biological problem is a question related to living organisms that is either asked by some one or comes in biologist’s mind by himself.

Observations are made with five senses of vision, hearing, smell, taste and touch. Observations may be both qualitative and quantitative

Biologist organizes his/her and others’ observations into data form and constructs a statement that may prove to be the answer of the biological problem under study. This tentative explanation of observations is called a hypothesis

Deductions are the logical consequences of hypotheses.

Biologist performs experiments to see if hypotheses are true or not.

Biologist gathers actual, quantitative data from experiments. Data for each of the groups are then averaged and compared statistically. To draw conclusions, biologist also uses statistical analysis

Biologists publish their findings in scientific journals and books, in talks at national and international meetings and in seminars at colleges and universities. Publishing of results is an essential part of scientific method. It allows other people to verify the results or apply the knowledge to solve other problems.

Introduction to Biology

Biology is the scientific study of life. The word “biology” has been derived from two Greek words; ‘bios’ meaning ‘life’ and ‘logos’ meaning ‘thought or reasoning’.

Divisions and Branches of Biology

There are three major divisions of biology which study the different aspects of the lives of the major groups of organisms.



This division of biology deals with the study of animals.


This division of biology deals with the study of plants.


This division of biology deals with the study of microorganisms such as bacteria etc. In order to study all the aspects of life, these divisions are further divided into different branches as defined below.

Morphology: This branch deals with the study of form and structures of living organisms.

Anatomy: The study of internal structures is called anatomy.

Histology:The microscopic study of tissues is called histology.

Cell biology: The study of the structures and functions of cells and cell organelles is called cell biology. This branch also deals with the study of cell division.

Physiology: This branch deals with the study of the functions of different parts of living organisms.

Genetics:The study of genes and their roles in inheritance is called genetics. Inheritance means the transmission of characters from one generation to the other.

Embryology: It is the study of the development of an embryo to new individual.

Taxonomy: It is the study of the naming and classification of organisms into groups and subgroups.

Palaeontology: It is the study of fossils, which are the remains of extinct organisms.

Environmental biology: It deals with the study of the interactions between the organisms and their environment.

Socio-biology: This branch deals with the study of social behaviour of the animals that make societies.

Parasitology: This branch deals with the study of parasites.

Biotechnology: It deals with the practical application of living organisms to make substances for the welfare of mankind.

Immunology: It is the study of the immune system of animals, which defends the body against invading microbes.

Entomology: It is the study of insects.

Pharmacology: It is the study of drugs and their effects on the systems of human body.

Jabir Bin Hayan (721 – 815 AD): He was born in Iran and practised medicine in Iraq. He introduced experimental investigation in chemistry and also wrote a number of books on plants and animals. His famous books are “Al-Nabatat” and “Al-Haywan”.


Abdul Malik Asmai (740 – 828 AD): He is considered the first Muslim scientist who studied animals in detail. His famous writings include “Al-Abil (camel)”, “Al-Khail (horse)”, “Al-Wahoosh (animal)”, and “Kalq al-ansan”.


Bu Ali Sina (980 – 1037 AD):He is honoured as the founder of medicine and called as Avicenna in the West. He was a physician, philosopher, astronomer and poet. One of his books “Al-Qanun-fi al-Tib” is known as the canon of medicine in West.