Here's why:
* Active transport requires energy, usually in the form of ATP (adenosine triphosphate), to move substances against their concentration gradient. This means moving them from an area of low concentration to an area of high concentration.
* Passive transport, on the other hand, does not require energy. It relies on the natural movement of substances down their concentration gradient (from high to low).
Examples of active transport include:
* The sodium-potassium pump, which moves sodium ions out of the cell and potassium ions into the cell.
* The uptake of glucose into cells, which requires the use of a protein transporter and energy.
Let me know if you have any other questions!
