Question

the plasma membrane is much more permeable to k+ than to na+. why?
the na+-k+ pumps transport more k+ into cells than na+ out of cells.
ligand-gated cation channels favor a greater influx of na+ than k+.
there are many more k+ leak channels than na+ leak channels in the plasma membrane.
there are many more voltage-gated k+ channels than voltage-gated na+ channels.

Explanation:

1. Analyze Option 1: The \( \text{Na}^+-\text{K}^+ \) pump transports 3 \( \text{Na}^+ \) out and 2 \( \text{K}^+ \) in per cycle, so it doesn't transport more \( \text{K}^+ \) into cells than \( \text{Na}^+ \) out. Eliminate this option.
2. Analyze Option 2: Ligand - gated cation channels' preference for \( \text{Na}^+ \) influx doesn't explain the resting membrane permeability to \( \text{K}^+ \) being higher. Eliminate this option.
3. Analyze Option 3: Leak channels are responsible for the resting membrane permeability. There are many more \( \text{K}^+ \) leak channels than \( \text{Na}^+ \) leak channels, so the plasma membrane is more permeable to \( \text{K}^+ \) at rest. This option is correct.
4. Analyze Option 4: Voltage - gated channels are involved in action potentials, not the resting membrane permeability which determines the relative permeability of \( \text{K}^+ \) and \( \text{Na}^+ \) in the resting state. Eliminate this option.

Answer:

C. There are many more \( \text{K}^+ \) leak channels than \( \text{Na}^+ \) leak channels in the plasma membrane.