Signal transduction is the transfer of information about the compositional state of the extracellular environment to the intracellular cytoplasm that elicits a morphological or genetic response. In more general terms, this can also be the communication of the state of supramolecular structures, such as the plasma membrane or chromatin, in the cell. This information is relayed through space by the cytoplasm and is mediated by transitions between the steady states of the cytoplasm's reaction networks. To uncover the principles that underlie the generation of spatiotemporal patterns of activity which guide cellular behaviour, functional imaging techniques that report on the activity of molecules must be combined with imaging techniques that report on the mobility of molecules.