Biology deals with every aspect of life in a living organism. Biology examines the structure, function, growth, origin, evolution, and distribution of living things. It classifies
and describes organisms, their functions,
how species come into existence, and the interactions they have with each other and
with the natural environment. Four unifying principles form the foundation of modern biology: cell theory, evolutionary theory, genetics and homeostasis.

The fields within biology 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;