How does eukaryotic and prokaryotic organisms undergo facilitated diffusion?

Answer 1

Diffusion is the ability of molecules to follow a concentration gradient, moving from regions of high to low concentration. For small, nonpolar molecules such as O2, CO2, and some narcotics, they are small enough to slip through the phospholipid bilayer of the plasma membrane. Small, polar molecules such as water, are also small enough to slip through, but because of their polar nature, this movement is impeded by a factor of 1000. What about larger molecules like glucose? These molecules are too big to slip through the phospholipid bilayer, regardless of the concentration gradient. Larger molecules require a protein channel for transport across the plasma membrane. Because the movement will be driven by the concentration gradient, this movement is called facilitated diffusion, to indicate that a protein channel is necessary. Both prokaryotic and eukaryotic cells have protein channels for this purpose.