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