Question

complete the table to compare the three types of passive transport. simple diffusion facilitated diffusion osmosis molecules cross the membrane through the phospholipids molecules cross the membrane through proteins molecules move down their concentration gradient molecules move without using cellular energy

Explanation:

• Simple diffusion: Small non - polar molecules (e.g., oxygen, carbon dioxide) cross the membrane through the phospholipids. All passive transport (simple diffusion, facilitated diffusion, osmosis) involves molecules moving down their concentration gradient and without using cellular energy.
• Facilitated diffusion: Polar or large molecules (e.g., glucose) cross the membrane through proteins (channel or carrier proteins). It also has the characteristics of passive transport (down concentration gradient, no energy use).
• Osmosis: Movement of water molecules. Water can cross the membrane through the phospholipids (to a limited extent) and also through aquaporins (proteins). And it is a passive process (down concentration gradient of water, no energy use).

Answer:

	simple diffusion	facilitated diffusion	osmosis
molecules cross the membrane through proteins	No	Yes	Yes (aquaporins)
molecules move down their concentration gradient	Yes	Yes	Yes
molecules move without using cellular energy	Yes	Yes	Yes