Study of living things and their vital processes. The field deals with all the physicochemical aspects of life. As a result of the modern tendency to unify scientific knowledge and investigation, however, there has been an overlapping of the field of biology with other scientific disciplines. Modern principles of other sciences—chemistry and physics, for example—are integrated with those of biology in such areas as biochemistry and biophysics. Because biology is such a broad subject, it is subdivided into separate branches for convenience of study. Despite apparent differences, all the subdivisions are interrelated by basic principles. Thus, though it was once the custom to separate the study of plants (botany) from that of animals (zoology), and the study of the structure of organisms (morphology) from that of function (physiology), the current practice is to investigate those biological phenomena that all living things have in common.

Encyclopaedia Britannica - http://www.britannica.com