Which characteristic makes osmosis different from diffusion? 1. Osmosis requires facilitation by an energy-carrying molecule, such as ATP. Diffusion requires no additional energy to move molecules across the concentration gradient. 2. Osmosis is used for gases, such as oxygen and carbon dioxide. Diffusion is used for water that contains salt or sugar molecules. Net movement in osmosis is from areas of higher water concentration to areas of lower water concentration. 3. Net movement in diffusion occurs from areas of higher solute concentration to areas of lower solute concentration. 4. Osmosis occurs through a permeable membrane. Diffusion must occur through a semipermeable membrane.