Cell signalling: the process where messages are sent to cells via a signalling pathway.
Cell signalling is important to allow multicellular organisms to control and coordinate cell activity, even if the required organs needed are large distances apart.
The cell signalling pathway is as follows:
a stimulus/signal is received by a receptor
the signal is converted into a ‘message‘ that is passed on via transduction
the ‘message‘ reaches its target (effector)
response is made
The pathway requires crossing barriers such as cell surface membranes. Hence, cell surface membranes are important in controlling the exchange of materials into and out of a cell.