Membrane potential is the difference in electrical charge across a cell membrane, with the inside typically more negative than the outside. The Na⁺/K⁺ pump uses ATP to move ions against their gradients, establishing and maintaining this potential (AP Bio EK 2.8.A.1).
Membrane potential is the voltage difference across a cell's membrane. The inside of a resting cell is usually negative compared to the outside, around -70 mV in a neuron. That charge difference exists because ions like sodium (Na⁺) and potassium (K⁺) are unevenly distributed across the membrane.
Keeping that imbalance going costs energy. The Na⁺/K⁺ pump (a membrane protein that's also an ATPase) burns ATP to push 3 Na⁺ out and 2 K⁺ in per cycle, both against their concentration gradients (EK 2.8.A.1). That's active transport, not diffusion. The pump moves more positive charge out than it brings in, which helps make the inside negative. So membrane potential is really stored electrical energy, set up and maintained by active transport.
This term lives in Unit 2: Cells, specifically Topic 2.8 Mechanisms of Transport, and it's the payoff of learning objective AP Bio 2.8.A. EK 2.8.A.1 spells it out directly: metabolic energy from ATP is required for active transport and to establish and maintain electrochemical gradients, and the Na⁺/K⁺ pump and ATPase maintain the membrane potential. Membrane potential is the proof that active transport does real work. Cells spend ATP to build a gradient that stores energy, and that stored energy gets used later for everything from nerve signaling to nutrient uptake. It connects the energy theme (cells must expend energy to stay organized) to the cell-communication concepts you'll see in Unit 4.
Keep studying AP® Biology Unit 2
Na⁺/K⁺ ATPase (Unit 2)
This is the pump that builds the membrane potential. It uses ATP to move 3 Na⁺ out and 2 K⁺ in, and because it ships out more positive charge than it brings in, the inside ends up negative. No pump, no potential.
Concentration Gradient (Unit 2)
Membrane potential is half of an electrochemical gradient. The other half is the concentration gradient of ions. Together the chemical pull (concentration) and the electrical pull (charge) decide which way an ion 'wants' to move.
Sodium Channel (Unit 2)
The pump stores the potential, but channels release it. When Na⁺ channels open, sodium rushes in down its gradient and flips the voltage. That's how a stored membrane potential becomes a signal like an action potential.
Osmoregulation (Unit 2)
Both processes show why cells spend ATP to fight equilibrium. Pumping ions to hold a membrane potential and balancing water/solutes are two sides of the same idea: living cells stay alive by staying out of equilibrium.
On multiple choice, you'll see stems that describe a cell with more K⁺ inside, more Na⁺ outside, and a negative interior, then ask which term that describes. The answer is membrane potential (or electrochemical gradient). One released-style question even asks for the approximate resting value, around -70 mV. For FRQs, the term shows up in nerve-signaling contexts, like the 2019 Short FRQ Q4 on acetylcholine activating an action potential in a postsynaptic neuron. You should be able to explain that ATP-powered active transport by the Na⁺/K⁺ pump establishes the potential, and that opening ion channels lets ions flow down their gradients to change it. Tie the cause (active transport) to the effect (a charge difference the cell can use).
Membrane potential is the steady resting charge difference a cell maintains, around -70 mV. An action potential is a fast, temporary spike in that voltage when Na⁺ rushes in and the membrane briefly flips positive. Think of membrane potential as a charged battery sitting at rest, and the action potential as the moment you flip the switch and the current fires.
Membrane potential is the difference in electrical charge across a cell membrane, with the inside usually more negative than the outside.
The Na⁺/K⁺ pump uses ATP to actively transport ions against their gradients, which establishes and maintains the membrane potential (EK 2.8.A.1).
Because the pump moves 3 Na⁺ out for every 2 K⁺ in, it pushes out more positive charge and helps keep the inside negative.
A resting neuron's membrane potential is approximately -70 mV.
Membrane potential plus the concentration gradient together make the full electrochemical gradient that decides ion movement.
The stored potential is released when channels open, which is the basis for nerve signaling and action potentials.
It's the electrical charge difference across a cell membrane, with the inside typically negative relative to the outside. The Na⁺/K⁺ pump uses ATP to actively transport ions and maintain this potential, which is exactly the active-transport idea in EK 2.8.A.1.
No. Membrane potential is the resting charge difference a cell holds steady, around -70 mV. An action potential is a brief spike that happens when ion channels open and the voltage rapidly changes, then resets.
No, not on its own. The potential is established and maintained by active transport, because the Na⁺/K⁺ pump spends ATP to move ions against their gradients. Diffusion through open channels can change the potential, but the pump is what sets it up.
It pumps 3 Na⁺ out of the cell and 2 K⁺ in per cycle using ATP. Since it ejects more positive charge than it brings in, the inside becomes more negative, producing the membrane potential.
Neurons rely on a maintained resting membrane potential so they can fire signals. When something like acetylcholine triggers ion channels to open, the stored potential changes and an action potential fires, which is the setup in the 2019 Short FRQ on neurotoxins and synapses.
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