The aim of Biology is to explain the living world in terms of scientific principles. Life is something special and unique and can not be explained solely in terms of the laws of physics and chemistry. Aristotle, the great Greek philosopher and teacher, is known as the father of biology and the French naturalist, Jean Baptiste – de Lamark, was the first to used the word ‘biology’ in 1800.
The unifying concept of biology got its greatest stimulus from the English zoologist Thomas Henry Huxley, who insisted that the conventional segregation of zoology and botany was intellectually meaningless and that all living things should be studied in an integrated way. Today, scientists realise that many lower organisation are neither plants nor animals. The limits of science have always been difficult to determine and as the scope of Biology has shifted over the years, its subject areas have been changed and reorganised. Biology today is subdivided into numerous branches based on the molecule, the cell, the organism and the population. Biology also includes the study of humans at the molecular, cellular and organismal levels. If the focus of investigation is the application of biological knowledge to human health, the study is often termed as ‘biomedicine’.
The term ‘Life’ is used to summarize the activities and characteristic of all organisms – ranging from such primitive forms as cyano – bacteria to plants and animals. These activities fall into two major categories : reproduction and metabolism.
The mechanism of reproduction is now known to be controlled by the properties of certain large molecules called nucleic acids. Deoxyribonucleic acid (DNA) constitutes the hereditary material that can be passed one cell or organism to another, because DNA molecules can make copies of themselves by means of a process known as template replication.
The other major activity of living organisms is metabolism, – the physical and chemical processes by which energy from the outside world is used in such activities as reproduction (including growth), locomotion, and responsiveness to the environment (which constitutes the activities of the nervous system in animals). The energy source can be either the radiant energy of the sun, converted to a usable form by photosynthesis, or the chemical energy of ingested food. A living organism thus resembles a motor in that both convert one kind of energy into another. A precise definition of life is difficult, but, in a rough sense, an organism is considered alive if both metabolism and reproduction are active. Both metabolism and reproduction are carried on in cells.