Here's why:
* Active transport involves moving molecules against their concentration gradient, meaning from an area of low concentration to an area of high concentration. This is like pushing a ball uphill – it requires energy to overcome the natural tendency of the ball to roll downhill.
* Passive transport, on the other hand, doesn't require energy. Molecules move down their concentration gradient, from high to low concentration, like a ball rolling downhill.
Some examples of active transport include:
* Sodium-potassium pump: Moves sodium ions out of the cell and potassium ions into the cell, maintaining the cell's electrochemical gradient.
* Glucose uptake: Cells can actively transport glucose into the cell, even when the concentration of glucose inside the cell is higher than outside.
* Proton pumps: Move protons across membranes, which is essential for processes like ATP production.
Let me know if you have any other questions!
