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: -Molecules that are hydrophobic can easily pass through the plasma membrane, if they are small enough, because they are water-hating like the interior of the membrane.

Detailed explanation-3: -Small non polar molecules (oxygen, nitrogen, carbondioxide) can easily pass through the cell membrane. Uncharged polar molecules-small (water, ammonia, glycerol) and large (glucose, sucrose) can partially pass through the cell membrane.

Detailed explanation-4: -Small lipids and steroids are hydrophobic and can readily cross the membrane. Molecules that are hydrophilic, on the other hand, cannot pass through the cell membrane-at least not without help-because they are water-loving like the exterior of the membrane, and are therefore excluded from the interior of the membrane.

Detailed explanation-5: -Answer and Explanation: The type of molecule that moves across the cell membrane most easily is small and hydrophobic.