SAT Subject Biology Practice Question 116: Answer and Explanation
6. What prevents ions from crossing the plasma membrane via simple diffusion?
A. Ions are too large.
B. Ions carry a charge.
C. Ions are hydrophobic.
D. Ions do not produce a concentration difference.
E. Ions cannot interact with membrane-bound proteins.
Correct Answer: B
Because ions carry a charge, they cannot cross the hydrophobic cell membrane and so must be transported by facilitated diffusion via ion channels.