Active transport = uphill movement
Na+: low inside → high outsideK+: low outside → high insideATP supplies energy

Binding 3 Na+ inside

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Active Transport Lab

Explore how a sodium–potassium pump powers cell homeostasis.

Watch the concentration gradient

The pump spends ATP to push each ion from the side where it is less concentrated toward the side where it is already more concentrated. This is opposite to diffusion.

Mode

ATP supply80%

Pump activity70%

Temperature37 °C

Add ouabain inhibitor

Simulation speed1×

Zoom100%

Focused objectPump protein

Stage: binding cytoplasmic sodium

ATP used0

Pump cycles0

Na+ moved out0

K+ moved in0

Net charge out0

Cycle rate0/min

Gradient historyNa in / K in

Teacher / Demo tools

Laser annotation

What is happening?

The sodium–potassium pump uses one ATP molecule to push three sodium ions from low sodium concentration inside to high sodium concentration outside. It simultaneously pushes two potassium ions from low potassium concentration outside to high potassium concentration inside. Both movements go uphill, against their concentration gradients.

Pump cycle

Three sodium ions bind inside.
ATP transfers a phosphate to the pump.
The pump changes shape and releases sodium outside.
Two potassium ions bind outside.
The phosphate leaves.
The pump returns and releases potassium inside.

Learning objectives

Distinguish active transport from diffusion.
Connect ATP use to movement against a gradient.
Explain the 3-to-2 ion ratio.
Predict effects of low ATP, inhibitors, and temperature.
Relate ion gradients to membrane potential and homeostasis.

Key concepts

Primary active transport • carrier proteins • ATP hydrolysis • concentration gradients • selective membranes • electrogenic transport • cellular homeostasis

Suggested experiments

Set ATP to zero: does the pump finish another cycle?
Add ouabain: compare ion movement before and after.
Raise temperature from 10 °C to 37 °C and compare rate.
Slow time and step through each binding stage.

Explore further

Why does the pump export more positive charge than it imports? How can its sodium gradient later power glucose uptake through secondary active transport?

Score0 / 7