Cell signalling pathways

 Both unicellular and multicellular organisms are able to communicate using cell signlling pathways. These enable them to act upon signals from the environment and also send signals to other cells. Cell signalling is an important aspect of controlling cell behaviour. There are a vast range of signals that stimulate cell signalling. These can be physical signals which include heat, light and pressure, but are more commonly chemical signals such as hormones and neurotransmitters. 

Alberts et al, (2008) Molecular Biology of The Cell, 5th Edn, New York, Garland Science