Final answer:
Ions flowing through plasmodesmata in plants or gap junctions in animals exemplify direct signaling, essential for coordinating cellular responses across adjacent cells.
Step-by-step explanation:
The ions flowing through plasmodesmata in plants or gap junctions in animals are an example of direct signaling. This is a process where adjacent cells communicate with each other through fluid-filled channels that allow the transfer of small signaling molecules and ions like calcium ions (Ca²+). These communications are essential as they help maintain cellular coordination and allow a group of cells to synchronize their responses to certain stimuli, with plasmodesmata making the entire plant into a vast communication network.