Active — Transport Via A Protein Channel [top]

Inside the office, the concentration of sodium ions is very low. The workers inside need some of those sodium ions to balance their systems, but there’s a problem: In normal diffusion, things move from crowded to less crowded. But here, the cell needs to move sodium ions against that natural flow—from the less crowded inside to the very crowded outside!

The pump is now in its “open to the outside” shape. It loves potassium ions (K⁺). It grabs two potassium ions from outside. active transport via a protein channel

Because the pump changed shape, it now swings open to the outside of the wall. The three sodium ions, no longer able to hang on, tumble out into the crowded street. They have moved from low concentration (inside) to high concentration (outside). That is active transport . Inside the office, the concentration of sodium ions

That’s like trying to push a crowd of people up an escalator going down. It requires energy . Embedded in the office wall is a special, revolving door. This isn’t just any door; it’s a protein channel called the Sodium-Potassium Pump . The pump is now in its “open to the outside” shape