Question

1. all of the following can cross through the phospholipid bilayer of the plasma membrane except

a. small molecules
b. nonpolar molecules
c. hydrophobic molecules
d. charged molecules

Explanation:

The phospholipid bilayer of the plasma membrane has a hydrophobic interior (due to the fatty acid tails of phospholipids) and a hydrophilic exterior (due to the phosphate heads). Small, nonpolar, and hydrophobic molecules can pass through the bilayer because they can interact favorably with the hydrophobic interior. However, charged molecules (ions) are polar and hydrophilic, so they cannot cross the hydrophobic region of the phospholipid bilayer without the help of transport proteins.

Answer:

d. Charged molecules