Question

which system can move a nonpolar molecule directly through the phospholipid bilayer of the cell membrane with (down) its concentration gradient, without the use of a protein?

active transport

simple diffusion

facilitated diffusion

osmosis

Explanation:

• Active transport requires energy and often proteins, moves against gradients.
• Simple diffusion lets nonpolar molecules pass directly through the phospholipid bilayer down their concentration gradient, no proteins needed.
• Facilitated diffusion uses protein channels/carriers for molecules.
• Osmosis is only for water movement across a membrane.

Answer:

Simple diffusion