All of these are evidence of a common evolutionary ancestry for cell signaling except both bacteria and eukaryotic cells have receptors for intercellular signaling in their cell membranes both plant and animal cells participate in cell junctioning both plant and animal cell plastids code for cell membrane receptors both unicellular bacteria and yeast have complex cell-signaling systems that use chemical messengers Yeast cells, plant cells, and mammal cells all share many similarities in cell signaling. This provides evidence that cell-signaling mechanisms are only found in organisms that use methods of sexual reproduction intercellular communication evolved as a way for multicellular organisms to coordinate cell functions eukaryotic cells use signal transduction pathways, while prokaryotic cells use a more primitive form of signaling signal transduction pathways appeared in cells before the evolution of multicellular organisms