What is the most important structure of the circulatory system? a. the lungs c. the veins b. the heart d. the arteries

not sure if this is what you'r looking for nnew= nold

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.