Which Is True About Mediated Transport of Substances Across Cell

Multiple Choice

Which is true about mediated transport of substances across cell membranes?

A) It involves a specific membrane protein that functions as a carrier molecule.
B) It always involves the movement of substances against a concentration gradient.
C) It is always directly coupled to the splitting of ATP molecules.
D) There is no limit to how fast it can occur as the concentration gradient becomes larger.
E) It is the main mechanism for transporting hydrophobic molecules across membranes.