Here's why:
* Active transport moves molecules across the cell membrane against their concentration gradient. This means moving molecules from an area of low concentration to an area of high concentration, which requires energy. Membrane proteins act as pumps, using energy (often from ATP) to move these molecules.
Here's a contrast with other types of transport:
* Passive transport does not require energy. It relies on the natural movement of molecules down their concentration gradient (from high to low). This includes:
* Simple diffusion: Movement of small, uncharged molecules directly across the membrane.
* Facilitated diffusion: Movement of larger or charged molecules aided by membrane proteins, but still down the concentration gradient (no energy needed).
Let me know if you'd like a more detailed explanation of any of these types of transport!
