ABSTRACT
Scientific study of biological membrane structure and function requires the complementary use of biophysical and biochemical methodologies. The commonality between biophysical and biochemical approaches is provided by thermodynamics. Thermodynamics is composed of phenomenological laws that determine the behavior of a material in terms of a specific set of functions that characterize the state of the material. Thermodynamics is based on two types of state variables: intensive and extensive. Extensive variables depend on the amount of material in the system; the intensive variables do not. Equilibrium thermodynamics characterizes processes that take place in an essentially reversible manner. In this chapter, the author's developed the isothermal mechanochemical equations of state from the work performed on a material element in the principal axes system. They derived these equations for arbitrary orientation of initial and instantaneous material coordinates. In the force-free state, a membrane surface pressure that is produced by collisions and forces between molecules in the membrane surface can still exist.
