3. how do cells respond to contact
with other cells?

Cells use the proteins called receptors which can bind the signaling molecules and initiate a physiological response with the other cells.

Explanation:

The cell to cell interaction is also known as Cellular interaction. The cells that can communicate with each other in three ways Gap junctions, Tight Junctions, desmosomes.The signaling of cells allows communicating with adjacent cells and distant cells. Ligand binding to the receptor allows for signal transduction in the cell. To terminate the ligand will be removed from the access with the receptor.