AP BIOLOGY

Detailed explanation-1: -Thus, gases (such as O2 and CO2), hydrophobic molecules (such as benzene), and small polar but uncharged molecules (such as H2O and ethanol) are able to diffuse across the plasma membrane. Other biological molecules, however, are unable to dissolve in the hydrophobic interior of the phospholipid bilayer.

Detailed explanation-2: -Because the cell membrane is semipermeable, only small, uncharged substances like carbon dioxide and oxygen can easily diffuse across it. Charged ions or large molecules require different kinds of transport.

Detailed explanation-3: -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-4: -Answer and Explanation: Large molecules, polar molecules, and ions, cannot easily pass through the cell membrane. Large molecules, such as glucose, amino acids, and proteins, are simply too big to fit through the phospholipid bilayer.

Detailed explanation-5: -The walls of the alveoli share a membrane with the capillaries. That’s how close they are. This lets oxygen and carbon dioxide diffuse, or move freely, between the respiratory system and the bloodstream.