The twentieth century has seen biology come of age as a conceptual and quantitative science. Major functional phenomena rather than catalogues of animals and plants comprise the core of MODERN BIOLOGY; such heretofore seemingly unrelated fields as cytology, biochemistry, and Introduction to Genetics: A Molecular Approach are now being unified into a common frame - work at the molecular level.The purpose of this book is to document these exciting developments and to make them accessible to the introductory student. It is our conviction that since the cell is the "e;common denominator"e; of living systems, it is extremely important that the beginner should become acquainted with the major facts and theories of cell biology. This introduction will serve a dual purpose: it will provide the student with a firm basis from which to examine the other manifold phenomena of the world of life, and it will also serve to convince him, at an early stage of his development, of the crucial importance of the physical sciences to the study of living systems.