Which example involves a cell membrane receiving and sending messages? a. the cell membrane prevents glucose from entering a cell. b. a transport protein allows a large molecule to enter a cell. c. cells of an organism tell each other when predators are near. d. an enzyme acts as a catalyst for a reaction on a cell membrane.

The correct option is C.
When a cell membrane is receiving and sending message, that means that information is been passed across to the cell membrane and at the same time the cell is passing the information across to the other cells, so a network of cell communication is set up. This is an example of what happen when an organism is near danger. His cells set up a communication network which tells the animal to run away.