What type of molecules are often passed through the cell membrane via facilitated diffusion?

Facilitated diffusion is a process that allows specific molecules to cross the cell membrane with the help of transport proteins. This process is particularly important for molecules that are unable to pass through the lipid bilayer of the membrane due to their size or polarity.

Large polar molecules, such as glucose and certain amino acids, cannot easily diffuse through the hydrophobic lipid bilayer because of their size and the polar nature of their chemical bonds. Instead, they rely on specialized proteins known as carrier proteins or channel proteins that facilitate their passage across the membrane without the use of energy. This mechanism ensures that essential nutrients and substances can enter the cell efficiently while maintaining the integrity of the cell membrane.

In contrast, small nonpolar molecules can easily diffuse through the lipid bilayer because they are hydrophobic and do not require transport proteins. Similarly, ions, which are charged particles, generally require specific channels for passage due to their charge and the surrounding aqueous environment. Gases like oxygen and carbon dioxide can easily pass through the membrane because they are small and nonpolar.

Thus, facilitated diffusion is specifically designed to assist larger polar molecules that cannot cross the membrane by simple diffusion.