What must occur for a message to be sent from the outside of the cell to

inside the cell?

A. A signaling molecule binds with a membrane protein.

B. Transport proteins form a channel for a large molecule.

C. Enzymes inside the cell catalyze a reaction.

D. A small, nonpolar molecule crosses the membrane.

correct answer is A

a signaling molecule binds with a membrane protein

A receptor is located on a cell membrane. Any neuronic transmission, hormone, etc. that cannot get inside of the cell's membrane will sit on the receptor in order to pass its message along to the cell. When the molecule sits on the receptor, it causes a series of reactions to occur inside of the cell. From the series of reactions that occur inside of the cell, the message is passed along, and the cell will perform as indicated by the molecule on the cell receptor.