Here's why:
* Facilitated diffusion is a type of passive transport. This means it does not require the cell to expend energy (ATP) to move substances across the cell membrane.
* Passive transport relies on the concentration gradient of the substance. The substance moves from an area of high concentration to an area of low concentration.
* Facilitated diffusion uses transport proteins embedded in the cell membrane. These proteins help the substance move across the membrane more efficiently, but they don't actively pump the substance against its concentration gradient.
In contrast:
* Active transport requires energy (ATP) to move substances against their concentration gradient. This means moving a substance from an area of low concentration to an area of high concentration.
