Question

Lipid bilayers are semi-permeable. What maintains the permeability of the membrane to small, uncharged and nonpolar molecules?

Answer 1

Membranes are selectively permeable to molecules so that they can maintain the internal composition of the cell. Cell membranes are permeable to small uncharged non-polar molecules. Tese molecules can pass freely through the membrane. O2, Co2 are small non-polar gases which diffuse freely in the membrane. These get dissolved in the membrane lipids and terefore can cross the membrane freely. Water molecules though polar but they still can diffuse freely in membranes. Larger molecules like glucose etc can not pass the membrane so they need protein cannels and carriers for teir diffusion,