Here's why:
* Passive transport moves substances down their concentration gradient (from high to low concentration) without requiring energy. Examples include diffusion, osmosis, and facilitated diffusion.
* Active transport requires energy to move substances against their concentration gradient (from low to high concentration). This energy is often provided by ATP (adenosine triphosphate).
Think of it like this: Imagine a hill. Passive transport is like rolling a ball downhill, it happens naturally. Active transport is like pushing a ball uphill, it requires effort and energy.
Examples of active transport:
* The sodium-potassium pump, which moves sodium ions out of cells and potassium ions into cells, essential for nerve impulse transmission.
* The uptake of nutrients by cells, like glucose, against its concentration gradient.
* The removal of waste products from cells.
