In multicellular organisms, cells have to be able to communicate with other cells so they can work together to coordinate their activities for the benefit of the entire organism. One type of cell-cell communication involves the release of chemical signals by one cell that travel to another cell where they cause a change in the second cell (called a target cell ).

a. Describe the basic steps involved in the response of a target cell to a chemical signal produced by another cell. 

b. Organisms from bacteria to slime molds to higher plants and animals all share the ability to carry out cell-cell communication. Research has shown many common features in the signal transduction mechanisms in all of these cells. Describe the basic chemical processes for cell communication that are found throughout all of these living systems and that point to a common evolutionary origin for this process.