Membrane

You keep a single cell alive against physics that never stops. Sodium leaks in on its own and potassium leaks out on its own, both for free — putting either back where it belongs runs against the gradient and costs ATP, which your mitochondria make from a finite supply of glucose.

• Sodium constantly leaks inward; pumping it out costs energy.
• Potassium constantly leaks outward; pumping it in costs energy.
• Water follows the total solute concentration, moving toward whichever side has more.
• Let the inside get too concentrated and water floods in until the cell bursts.
• Let the outside get too concentrated and water leaves until the cell collapses.
• Substrate is finite, so every pump you run is drawn against a supply that does not refill.

• Desktop: hold the on-screen pump buttons or hold A / left-arrow (Na out) and D / right-arrow (K in); Start and New cell in the bar.
• Phone & tablet: press and hold the two pump buttons, fully touch-friendly.

• Watch total solute, not either ion. Osmosis does not care which salt it is — the cell bursts or shrivels on the sum, so a tidy sodium level with runaway potassium kills you just the same.
• Pump in small corrections rather than large ones. Overshooting one gradient creates the opposite emergency, and you pay ATP in both directions.
• Leaks are free and pumps are not, which means doing nothing always costs less than acting — right up until it costs everything.
• Budget the substrate as the real clock. Running the pumps perfectly still ends when the glucose does.
• Both failure modes are lethal, so there is no safe direction to drift in. Balance is the only stable state.

Membrane turns cellular homeostasis into a real-time survival game built on osmosis and ATP-driven active transport.

• Skills: cell biology, homeostasis, osmosis, active transport
• Best for: roughly grades 9–12 (ages 14+)
• For parents & teachers: cellular homeostasis in real time.

Sodium leaking in and potassium leaking out for free, with restoring either costing energy, is the membrane potential as an ongoing expense.

Making the leak continuous and unavoidable is the original honesty.

That is biologically exact. The sodium-potassium pump runs constantly against those gradients and consumes a substantial share of a cell's entire energy budget — which is why the resting state of a neuron is not rest at all but expensive, continuous work.

Membrane turns cellular homeostasis into a real-time survival game built on osmosis and ATP-driven active transport. It's an original, free browser game with daily and practice cells to keep alive.

A free, original browser game on PlayPendium. No download, no install.