Question

because ions carry a charge (positive or negative), their transport across a membrane is governed not only by concentration gradients across the membrane but also by differences in charge across the membrane (also referred to as membrane potential). together, the concentration (chemical) gradient and the charge difference (electrical gradient) across the plasma membrane make up the electrochemical gradient. consider the plasma membrane of an animal cell that contains a sodium - potassium pump as well as two non - gated (always open) ion channels: a na⁺ channel and a k⁺ channel. the effect of the sodium - potassium pump on the concentrations of na⁺ and k⁺ as well as the distribution of charge across the plasma membrane is indicated in the figure below. which of the following statements correctly describe(s) the driving forces for diffusion of na⁺ and k⁺ ions through their respective channels? select all that apply. view available hint(s) the diffusion of na⁺ ions into the cell is facilitated by the na⁺ concentration gradient across the plasma membrane. the diffusion of na⁺ ions into the cell is impeded by the electrical gradient across the plasma membrane. the diffusion of k⁺ ions out of the cell is impeded by the k⁺ concentration gradient across the plasma membrane. the diffusion of k⁺ ions out of the cell is impeded by the electrical gradient across the plasma membrane. the electrochemical gradient is larger for na⁺ than for k⁺.

Explanation:

1. For "The diffusion of Na⁺ ions into the cell is facilitated by the Na⁺ concentration gradient across the plasma membrane": The [Na⁺] is high outside and low inside, so the concentration gradient drives Na⁺ into the cell (facilitated diffusion via Na⁺ channel), so this is correct.
2. For "The diffusion of K⁺ ions out of the cell is impeded by the electrical gradient across the plasma membrane": The inside of the cell is negative, and K⁺ is positive. When K⁺ tries to diffuse out (down its concentration gradient, high inside - low outside), the negative inside attracts the positive K⁺, impeding its outward diffusion. So this is correct.
3. For "The electrochemical gradient is larger for Na⁺ than for K⁺": The Na⁺ has both a strong concentration gradient (high out - low in) and an electrical gradient (inside negative, so Na⁺ is attracted in), while K⁺'s electrical gradient (negative inside attracts K⁺) opposes its concentration gradient (high inside - low outside). So the net electrochemical gradient for Na⁺ is larger. This is correct.

The other options: "The diffusion of Na⁺ ions into the cell is impeded by the electrical gradient" is wrong (electrical gradient attracts Na⁺ in, so it facilitates, not impedes). "The diffusion of K⁺ ions out of the cell is impeded by the K⁺ concentration gradient" is wrong (K⁺ concentration gradient is high inside - low outside, which drives K⁺ out, not impede).

Answer:

• The diffusion of $\text{Na}^+$ ions into the cell is facilitated by the $\text{Na}^+$ concentration gradient across the plasma membrane.
• The diffusion of $\text{K}^+$ ions out of the cell is impeded by the electrical gradient across the plasma membrane.
• The electrochemical gradient is larger for $\text{Na}^+$ than for $\text{K}^+$.