The Cellular Process in Which a Signal Is Conveyed to Trigger a Change in the Activity or State of a Cell. Signal Transduction Begins with Reception of a Signal (e.g. a Ligand Binding to a Receptor or Receptor Activation by a Stimulus Such As Light) or For Signal Transduction in the Absence of Ligand Signal Withdrawal or the Activity of a Constitutively Active Receptor. Signal Transduction Ends with Regulation of a Downstream Cellular Process E.g. Regulation of Transcription or Regulation of a Metabolic Process. Signal Transduction Covers Signaling From Receptors Located On the Surface of the Cell and Signaling Via Molecules Located Within the Cell. For Signaling Between Cells Signal Transduction Is Restricted to Events At and Within the Receiving Cell.
Any Process That Results in a Change in State or Activity of a Cell or an Organism (in Terms of Movement Secretion Enzyme Production Gene Expression Etc.) As a Result of a Stimulus. the Process Begins with Detection of the Stimulus and Ends with a Change in State or Activity or the Cell or Organism.