Which of the Following Cannot Readily Cross the Blood-Brain Barrier

Question

Which of the following cannot readily cross the blood-brain barrier?
A) carbon dioxide
B) potassium ions
C) oxygen
D) water

Accepted Answer

Potassium ions are charged particles and the blood-brain barrier is selectively permeable to only certain molecules, so ionized particles like potassium cannot easily pass through. Carbon dioxide, oxygen, and water are small non-polar molecules that can pass through the blood-brain barrier.