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. This process is essential for cells to maintain the necessary concentration of molecules inside them, even when the external environment has a different concentration.
* Passive transport, on the other hand, does not require energy and relies on the concentration gradient to drive the movement of molecules. Molecules move from high concentration to low concentration.
Examples of active transport include:
* Sodium-potassium pump: This pump moves sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients.
* Glucose uptake in the small intestine: Glucose is transported from the small intestine into the bloodstream against its concentration gradient.
Let me know if you have any other questions!
