Transport — The Nernst-Planck Approach

Abstract

The living cell requires for its proper functioning materials that originate outside the cell, and as a result of its functioning produces materials that leave the cell. The passage of molecules across the cell membrane is known in many cases to be a purely diffusive process, describable in principle by the same physical laws that control the diffusion of molecules in solution or across artificial membranes, or the migration of atoms in solids. There are, however, numerous examples of so-called active transport, which involves the use of energy obtained from chemical processes to drive molecules across membranes, frequently against their concentration gradients. In this chapter we will not be concerned with these biologically more interesting processes, but rather with the (at first sight), simpler processes that can be classified under the heading of diffusion.