Final answer:
Gap junctions are specialized cell junctions in animal cells that are formed by connexin proteins. They enable the direct transfer of small molecules and ions between adjacent cells, facilitating rapid communication and response within tissues.
Step-by-step explanation:
Gap junctions are formed by c) Connexins. Gap junctions, a type of cell junction in animal cells, allow for direct communication between adjacent cells by acting as channels that permit the passage of water and small solutes. These junctions consist of two connecting rings made of connexin proteins which are embedded in the cell membranes of adjacent cells, thereby enabling materials to move directly from one cell to another without entering the extracellular fluid.
While desmosomes, also known as adherens junctions, glue cells together with cadherins to form strong tissues and sheets of cells, and tight junctions create watertight seals, gap junctions facilitate cell-to-cell communication for coordinated responses.