Membrane potential Knowledge-Based Practice

Questions

1. 1.

   Which of the following events would cause hyperpolarization of an animal cell's resting membrane potential?

   • A) An influx of sodium ions into the cytosol
   • B) A net movement of calcium ions into the intracellular fluid
   • C) A closure of resting potassium leak channels
   • D) An increase in the net outward movement of potassium ions
2. 2.

   Which of the following describes the condition at which the electrochemical equilibrium potential of an ion is reached across a plasma membrane?

   • A) The electrical force opposing ion movement exactly balances the chemical concentration force, resulting in zero net flux of that ion.
   • B) The intracellular and extracellular concentrations of that ion become equal, causing all channel-mediated transport to cease.
   • C) The membrane potential reaches zero millivolts, neutralizing the electrical field across the lipid bilayer.
   • D) ATP-driven active transport completely overcomes passive channel diffusion, preventing any movement across the membrane.
3. 3.

   Which statement best describes the physical distribution of electrical charge that creates the resting membrane potential in a living cell?

   • A) An equal concentration of all major cations and anions is maintained across both sides of the lipid bilayer.
   • B) Positively charged ions are sequestered exclusively in the extracellular fluid, while anions exist solely within the cytoplasm.
   • C) The entire intracellular fluid possesses a massive net negative charge throughout the whole volume of the cytoplasm.
   • D) A tiny excess of negative charges lines the inner membrane surface paired with an equivalent excess of positive charges on the outer surface, while bulk fluids remain neutral.
4. 4.

   Why is the resting membrane potential of an animal cell typically much closer to the equilibrium potential of potassium than to that of sodium?

   • A) Potassium ions are entirely absent from the extracellular fluid under resting physiological conditions.
   • B) Sodium ions diffuse across the hydrophobic lipid core without requiring transport proteins.
   • C) The plasma membrane completely lacks channel proteins capable of conducting sodium ions.
   • D) The plasma membrane exhibits a much higher permeability to potassium ions than to sodium ions at rest.
5. 5.

   Which of the following processes is directly responsible for maintaining the resting membrane potential in animal cells by actively moving ions against their concentration gradients?

   • A) Transporting three $\text{Na}^+$ ions out of the cell and two $\text{K}^+$ ions into the cell via $\text{Na}^+/\text{K}^+$-ATPase
   • B) Allowing equal diffusion of $\text{Na}^+$ and $\text{K}^+$ ions down their electrochemical gradients through non-gated channels
   • C) Transporting two $\text{Na}^+$ ions out of the cell and three $\text{K}^+$ ions into the cell using energy from GTP hydrolysis
   • D) Actively pumping impermeable organic anions out of the cytoplasm to increase the interior positive charge

Answers and step-by-step solutions appear after you finish the test.