Paul Andersen explains how changes in the signal transduction pathway can affect organisms. He begins with a brief discussion of the tetrodotoxin produced by the California Newt. He then explains how anthrax affects adenylate cyclase and thereby shuts down the signal transduction pathway. He also explains how diabetes mellitus is caused by the blood glucose pathway. A brief discussion of zombie powder is also included.

Paul Andersen explains how signal transduction pathways are used by cells to convert chemical messages to cellular action. Epinephrine is used as a sample messenger to trigger the release of glucose from cells in the liver. The G-Protein, adenylyl cyclase, cAMP, and protein kinases are all used as illustrative examples of signal transduction. A review of the concepts is also included.

Paul Andersen discusses cell communication. He begins by explaining how he communicates with other individuals using various forms of electronic communication. He them explains how cells communicate when the distance between them is big, small, and zero. He explains how antigen presenting cells pass information on antigen structure by touching in the immune response. He explains how neurotransmitters are used to transfer and manipulate nerve signals. And he finally explains how the endocrine system sends messages throughout the body.

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.