Requires a protein to move

ions or large hydrophilic (polar) molecules from a higher to lower

concentration

Movement of water through a

semipermeable membrane from an area of high to low concentration

Requires energy to move

amino acids, glucose and salts against the concentration gradient (i.e., from

low to high concentrations)

Difference in the

concentration of gases, solutes, or water molecules on the two sides of the cell

membrane

Movement of molecules, ions

or gases from higher to lower concentration