Here's why:
* Passive transport relies on the natural movement of molecules from an area of high concentration to an area of low concentration (down the concentration gradient). This doesn't require energy. Examples include diffusion, osmosis, and facilitated diffusion.
* Active transport requires energy to move molecules against their concentration gradient, from a low concentration area to a high concentration area. This energy is usually supplied by ATP (adenosine triphosphate).
Think of it like pushing a ball uphill – it takes effort and energy. Active transport is like that for molecules.
Examples of active transport:
* Sodium-potassium pump: This important pump in cells moves sodium ions out of the cell and potassium ions into the cell, against their concentration gradients.
* Glucose uptake in the intestines: Glucose is transported from the gut lumen (where its concentration is lower) into the intestinal cells (where its concentration is higher).
Let me know if you'd like to learn more about active transport!
