Final answer:
The cation that will move more frequently through a small cation channel when the membrane is depolarized to +10 mV is sodium (Na+), due to a higher outside concentration gradient and membrane potential changes. The correct options D.
Step-by-step explanation:
If a membrane is depolarized to +10 mV, the cation that would move more frequently through a small cation channel is sodium (Na+).
This is because, during depolarization, the membrane potential becomes less negative, approaching zero, and sodium channels open allowing Na+ ions to enter the cell. The concentration gradient of Na+ is very strong, with a higher concentration outside the cell, which drives Na+ into the cell.
After depolarization, other voltage-gated channels, such as those specific for potassium (K+), open as the membrane potential approaches +30 mV.
This allows K+ to leave the cell, taking positive charge with it, and leading to repolarization. However, at +10 mV, the movement of Na+ is still dominant due to the stronger electrochemical gradient in comparison to K+.
The Na+/K+ transporter is not as relevant here because it operates to maintain the resting membrane potential by actively transporting Na+ out of and K+ into the cell in an ATP-dependent fashion. The correct options D .