Which set of substances requires either channel or transport proteins in order to cross the cell membrane?
A. H20, NaCl, C6H1206
B. NaCl, NH2CONH2, 02
C. N2, H20, C6H1206
D. N2, H20, NH3

"d.) carbon dioxide and hydrogen sulfide"

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.