The cell membrane

A. is the site of most cellular chemical reactions.

B. alters and packages proteins and lipids.

C. controls which substances enter and exit the cell.

D. converts glucose to other energy molecules.

C. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. The basic function of the cell membrane is to protect the cell from its surroundings. It consists of the lipid bilayer with embedded proteins.