Which of the Following Ions is Most Likely to Cross

Question

Which of the following ions is most likely to cross the plasma membrane of a resting neuron?
A)K⁺
B)Na⁺
C)Ca²⁺
D)Cl⁻
E)H₂O

Accepted Answer

K⁺ is the most likely ion to cross the plasma membrane of a resting neuron because the membrane is more permeable to K⁺ ions than to other ions. This is due to the presence of potassium leak channels that are always open and allow K⁺ ions to move down their concentration gradient, from inside the cell (where K⁺ is more concentrated) to outside the cell (where K⁺ is less concentrated). This movement of K⁺ ions establishes the resting membrane potential, which is typically around -70 mV in neurons. The other ions listed (Na⁺, Ca²⁺, Cl⁻) are also important for neuronal function but are not as likely to cross the plasma membrane at rest.