AP BIOLOGY

Detailed explanation-1: -Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly. Small polar molecules, such as water and ethanol, can also pass through membranes, but they do so more slowly.

Detailed explanation-2: -Small nonpolar molecules, such as O2 and CO2, are soluble in the lipid bilayer and therefore can readily cross cell membranes. Small uncharged polar molecules, such as H2O, also can diffuse through membranes, but larger uncharged polar molecules, such as glucose, cannot.

Detailed explanation-3: -Gases like carbon dioxide and oxygen can move across the cell membrane via diffusion. Diffusion is the movement of gas molecules from a region of higher concentration, to a region of lower concentration through a semi-permeable membrane.

Detailed explanation-4: -The cell membrane’s main trait is its selective permeability, which means that it allows some substances to cross it easily, but not others. Small molecules that are nonpolar (have no charge) can cross the membrane easily through diffusion, but ions (charged molecules) and larger molecules typically cannot.