This course develops the physical concepts that apply to the understanding of biological systems. The forces that play roles in biological systems are discussed and the role of thermal energy is especially emphasized. Topics discussed include protein structure, helix-coil transitions, double layer potentials, membrane structure and transport, Nernst-Planck equations and electrochemical potential, molecular motors, and action potentials and voltage sensitive channels. The capstone of the course is the study of the potassium channel in axons. The treatment of biophysical phenomena and methods is based on physical principles, which will be treated with appropriate mathematics when necessary.