1) Yeast cells communicate via mating factors that allow them to aggregate and form spore-forming structures called fruiting bodies during reproduction.
2) Animal and plant cells communicate via direct connections like gap junctions and plasmodesmata respectively or through signaling molecules that activate responses in nearby or distant target cells.
3) Cells detect extracellular signaling molecules through receptor proteins that activate intracellular signal transduction pathways involving second messengers, protein phosphorylation, and changes in gene expression to produce responses in the target cell.