Active and passive transport of solutes across a membrane typically differ in which of the following ways? a] active transport is usually against the concentration gradient of the solute, whereas passive transport is always down the concentration gradient of the solute.
b] active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.
c] active transport always requires the use of transport proteins, but passive transport can sometimes be accomplished without a protein.
d] the first and second choices are correct.
e] the first, second, and third choices are all correct.