What mechanism allows small nonpolar molecules to pass through the cell membrane?

The mechanism that allows small nonpolar molecules to pass through the cell membrane is simple diffusion. This process relies on the natural tendency of substances to move from an area of higher concentration to an area of lower concentration, thus achieving equilibrium.

Nonpolar molecules, such as oxygen and carbon dioxide, can easily dissolve in the lipid bilayer of the cell membrane due to their hydrophobic nature. This characteristic allows them to pass directly through the membrane without the need for any transport proteins or energy input, which are required in other mechanisms like facilitated diffusion or active transport. Simple diffusion is a passive process, meaning it does not require cellular energy (ATP) since the movement occurs along the concentration gradient.

Understanding this principle is essential for grasping how cells exchange gases and other small molecules with their environment, which is critical for maintaining homeostasis and supporting cellular functions.