The Na⁺/K⁺ pump eats roughly 20 to 30% of the body’s entire ATP budget just to repeat one action: each cycle pushes 3 sodium ions out and hauls 2 potassium ions in, against the gradient. Free diffusion costs nothing and only runs downhill, while active transport climbs the slope and pays in ATP — and that 3-for-2 imbalance is what keeps the membrane potential negative. Once the ATP is gone the pump stops, ions leak and the gradient collapses. Water follows the solute, so a hypotonic bath swells the cell while a hypertonic one shrivels it.
The Na⁺/K⁺ pump eats roughly 20 to 30% of the body’s entire ATP budget just to repeat one action: each cycle pushes 3 sodium ions out and hauls 2 potassium ions in, against the gradient. Free diffusion costs nothing and only runs downhill, while active transport climbs the slope and pays in ATP — and that 3-for-2 imbalance is what keeps the membrane potential negative. Once the ATP is gone the pump stops, ions leak and the gradient collapses. Water follows the solute, so a hypotonic bath swells the cell while a hypertonic one shrivels it.
Related topics in Cell & Genetics