Paul Andersen describes how cell communication is used in both single-celled and multicellular organisms. He starts by describing the symbiotic relationship between the bobtail squid and the bacteria Vibrio fisheri. He explains how bacteria use quorum sensing to communicate between each other and respond to changes in their environment. He also explains how multicellular organisms (like humans) can coordinate activities. He explains how epinephrine release from the adrenal gland can trigger a series of signal transduction pathways that can eventually lead to the release of glucose from the liver.