Which of the following is true about the movement of ions across excitable living membranes?
A) Ions always move actively across membranes through leakage channels.
B) Some ions are prevented from moving down their concentration gradients by ATP-driven pumps.
C) Sodium gates in the membrane can open in response to electrical potential changes.
D) The bulk of the solutions inside a cell are negatively charged.
Answer: B) Some ions are prevented from moving down their concentration gradients by ATP-driven pumps.