28. What two nonpolar gases do we exchange when performing
aerobic respiration? What specific method of transport do these
molecules use when passing across the cell membrane? Does this
method require energy?

Oxygen and carbon dioxide are the two nonpolar gases which we exchange during aerobic respiration.

Explanation:

Both oxygen and carbon dioxide are nonpolar and smaller compared to the polar water molecules. These gases pass across the cell membrane through simple diffusion. Gaseous exchange takes place through the thin alveolar and capillary walls in the lungs. Oxygen is taken in and carbon dioxide is released out during this gaseous exchange.

Diffusion of gases is a passive process and hence no energy is actually required. Since the exchange occurs as a passive transport or diffusion across a concentration gradient that is separated by membrane barrier.

"a.) well–developed vascular system."