Two types of transport of molecules across a cell membrane are: transport 1: solute molecules move across the cell membrane along their concentration gradient; requires no energy expenditure. transport 2: solute molecules move across the cell membrane against their concentration gradient; requires expenditure of energy. which statement is correct? a) transport 1 describes passive transport by diffusion. b) transport 2 describes passive transport by the na+/k+ pump. c) transport 2 describes passive transport by a carrier protein. d) transport 1 describes facilitated transport of substances through the membrane.