Here's why:
* Passive transport (like diffusion) moves molecules from a region of high concentration to a region of low concentration, following the concentration gradient. This happens naturally and doesn't require energy.
* Active transport requires energy, often provided by ATP, to move molecules against the concentration gradient. This is essential for maintaining concentration gradients within cells and organisms, which are crucial for various biological functions.
Examples of active transport:
* Sodium-potassium pump: This pumps sodium ions out of the cell and potassium ions into the cell, against their concentration gradients.
* Glucose uptake: In some cells, glucose is transported into the cell even when its concentration inside the cell is higher than outside.
Key takeaway: To move molecules from low concentration to high concentration, you need active transport that requires energy.
