The cell surface is the barrier between the cell and its environment which regulates the flow of both simple and complex molecules into and out of the cell; it is also the organelle responsible for communication between the cell and its environment. Each cell expresses receptors for a wide variety of hormones, growth factors, growth substrates and other cells. In multicellular organisms communication between cells is required for controlling development, cellular differentiation, morphogenesis and, in a more general sense, integration of myriad cell types into a single organism. The series...