This unit is intended to help the student gain knowledge of various functions of biological systems within the human body. It focuses on functions at molecular, cellular, tissue, organ and system levels. It highlights basic cellular processes, homeostatic mechanisms and control of body functions and physiology of the respiratory and cardiovascular systems. It presents a systemic approach to the study of functions of the cell by covering the cell structure, functions of cellular organelles, cell membrane physiology, body fluid compartments and homeostasis. Students then learn the physiology of the autonomic nervous system, respiratory system and circulatory system.