Here's why:
* Active transport requires energy to move molecules against their concentration gradient. This means moving them from an area where they are less concentrated to an area where they are more concentrated.
* Passive transport, on the other hand, does not require energy and moves molecules down their concentration gradient (from high to low concentration).
Examples of active transport include:
* The sodium-potassium pump, which moves sodium ions out of cells and potassium ions into cells, both against their concentration gradients.
* The uptake of glucose by intestinal cells, which requires energy to move glucose from the gut lumen into the cells.
Let me know if you'd like more details about active transport or any specific examples!
