For most citizens, getting through the gates was easy. Small molecules like water and oxygen simply drifted through the membrane’s pores in a process called passive transport. No energy needed. But for others—large nutrients, charged ions, or molecules moving against the crowd—the gates remained firmly locked. That’s where ATP came in.
In the bustling, microscopic city of Cytoville, there lived a diligent but stubborn security guard named ATP. ATP stood watch at the gates of the Cell Membrane, a shimmer, flexible wall that separated the city from the chaotic outside world, the Extracellular Space. what are the types of active transport
“Nat!” ATP called out. “I have a deal for you. You’re going to flow inside anyway. But if you do it through this special door, you can drag Suzy along with you.” For most citizens, getting through the gates was easy