Question

the resting membrane potential depends on two factors that influence the magnitude and direction of na+ diffusion across the plasma membrane. identify these two factors.
the presence of a resting membrane potential and leak channels
the presence of concentration gradients and leak channels
the presence of concentration gradients and voltage - gated channels
the presence of concentration gradients and na+ - k+ pumps

Explanation:

To determine the two factors influencing \( \text{Na}^+ \) diffusion for resting membrane potential:

1. Concentration Gradients: Ions (like \( \text{Na}^+ \)) diffuse down their concentration gradients (more \( \text{Na}^+ \) outside the cell, so it tends to enter).
2. Leak Channels: Leak channels (e.g., for \( \text{Na}^+ \) and \( \text{K}^+ \)) allow passive diffusion. The first option is incorrect (resting potential is the result, not a cause of \( \text{Na}^+ \) diffusion). The third option is wrong (voltage - gated channels are for action potentials, not resting potential). The fourth option is incorrect (\( \text{Na}^+-\text{K}^+ \) pumps maintain gradients, not directly drive resting \( \text{Na}^+ \) diffusion). Only the second option (concentration gradients + leak channels) matches.

Answer:

B. The presence of concentration gradients and leak channels