Biology is the natural science that involves the study of life and living organisms, including their physical structure, chemical composition, function, development and evolution. Modern biology is a vast field, composed of many branches. Despite the broad scope and the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation of new species. Living organisms are open systems that survive by transforming energy and decreasing their local entropy to maintain a stable and vital condition defined as homeostasis. See glossary of biology.
Biomedicine (i.e. medical biology) is a branch of medical science that applies biological and physiological principles to clinical practice. The branch especially applies to biology and physiology. Biomedicine also can relate to many other categories in health and biological related fields. It has been the dominant health system for more than a century.
Molecular biology is a branch of biochemistry which concerns the molecular basis of biological activity between biomolecules in the various systems of a cell, including the interactions between DNA, RNA, and proteins and their biosynthesis, as well as the regulation of these interactions. Writing in Nature in 1961, William Astbury described molecular biology as:
Despite the beliefs and teachings of religion and psychology, impulses are biological and psychic directional signals to nudge the individual toward his or her greatest opportunities for expression and development privately, and also to insure the person's contribution to mass social reality.
Jane Roberts in The God of Jane: A Psychic Manifesto, p. 17
Today, nearly all biologists acknowledge that evolution is a fact.
Neil A. Campbell, Biology 2nd ed., 1990, Benjamin/Cummings, p. 434
I like to define biology as the history of the earth and all its life — past, present, and future. To understand biology is to understand that all life is linked to the earth from which it came; it is to understand that the stream of life, flowing out of the dim past into the uncertain future, is in reality a unified force, though composed of an infinite number and variety of separate lives.
Rachel Carson Preface to Humane Biology Projects (1961) by the Animal Welfare Institute