Determine which of these statements best summarizes the cellular regulation of concentration gradients.

A) Enzymes are used in the cell to build molecules on one side of membranes to establish concentration gradients.
B) Passive and active transport both function when vesicles transport materials across the cell membranes.
C) Membrane phospholipids and proteins regulate transport functions to establish concentration gradients or equilibria.
D) Selective permeability of the cell membranes results in equal amounts of substances inside and outside the cell.