Biology (from Greek βιολογία - βίος, bios, "life"; -λογία, -logia, study of) is the science that studies living organisms. Prior to the nineteenth century biology came under the general study of all natural objects called natural history. The term biology was first coined by the French naturalist Jean-Baptiste Lamarck. It is now a standard subject of instruction at schools and universities around the world, and over a million papers are published annually in a wide array of biology and medicine journals.

Biology examines the structure, function, growth, origin, evolution, distribution and classification of all living things. Five unifying principles form the foundation of modern biology: cell theory, evolution, gene theory, energy, and homeostasis.

Traditionally, the specialized disciplines of biology are grouped by the type of organism being studied: botany, the study of plants; zoology, the study of animals; and microbiology, the study of microorganisms. These fields are further divided based on the scale at which organisms are studied and the methods used to study them: biochemistry examines the fundamental chemistry of life, molecular biology studies the complex interactions of systems of biological molecules, cellular biology examines the basic building block of all life, the cell; physiology examines the physical and chemical functions of the tissues and organ systems of an organism; and ecology examines how various organisms interrelate with their environment.

Foundations of modern biology

There are five unifying principles of biology :

• Cell theory. Cell Theory is the study of everything that involves respiration and tissues. All living organisms are made of at least one cell, the basic unit of function in all organisms. In addition, the core mechanisms and chemistry of all cells in all organisms are similar, and cells emerge only from preexisting cells that multiply through cell division. Cell theory studies how cells are made, how they reproduce, how they interact with their environment, what they are composed of, and how the components of a cell function and interact.
• Evolution. Through natural selection and genetic drift, a population's inherited traits change from generation to generation.
• Gene theory. A living organism's traits are encoded in DNA. Segments of DNA that, taken as a whole, specify a trait are known as genes. In addition, traits are passed on from one generation to the next by way of these genes. All information transfers from the genotype, the unobservable genetic traits, to the phenotype, the observable physical or biochemical characteristics of the organism. Although the phenotype expressed by the gene may adapt to the environment of the organism, that information is not transferred back to the genes. Only through the process of evolution do genes change in response to the environment.
• Homeostasis. The physiological processes that allow an organism to maintain its internal environment notwithstanding its external environment.
• Energy. The attribute of any living organism that is essential for its state. (e.g. required for metabolism)