Complete the blanks by matching with one of the given terms - A molecule moves down its concentration gradient by passive transport, but requires _________ transport to move up its concentration gradient. - Transporter proteins and ion channels function in membrane transport by providing a ______ pathway through the membrane for specific polar solutes or inorganic ions. - __________ are highly selective in the solutes they transport, binding the solute at a specific site and changing conformation so as to transport the solute across the membran