This unit explains the general principles of signal transduction and specifically, how even the simplest organisms can detect and respond to events in their ever-changing environment. This study unit is just one of many that can be found on LearningSpace, part of OpenLearn, a collection of open educational resources from The Open University. Published in ePub 2.0.1 format, some feature such as audio, video and linked PDF are not supported by all ePub readers.