section 1.9. Here, it is pertinent to consider the general requirements for input and output (Conrad 1984, 1990). In biological chapters 3 and 4 of this volume). The whole medium, not just the controlling macromolecules, can then contribute to the input-output transform. But the controlling macromolecular components are critical, because the recognition-action events would otherwise be slow and difficult to mold for different functionalities. The addition of new signal substances and macromolecular species to the medium need not and in general does not yield an additive response. This nonlinear component interaction is where the potential for performing powerful context-sensitive transforms resides.