Biology is a branch of natural science which deals with the study of life and living organisms. It focuses on their physical structure, molecular interactions, physiological mechanisms, chemical processes, development and evolution. It considers cells as the fundamental unit of life and genes as the basic unit of heredity. It also perceives evolution as the force that is responsible for the creation and extinction of species. There are a number of sub-disciplines within biology such as theoretical biology and experimental biology. Theoretical biology uses mathematical methods for the formulation of quantitative models. Experimental biology conducts empirical experiments for testing the validity of proposed theories and understanding the mechanisms underlying life. This textbook is a valuable compilation of topics, ranging from the basic to the most complex theories and principles in the field of biology. Some of the diverse topics covered herein address the varied branches that fall under this category. Those in search of information to further their knowledge will be greatly assisted by this book.