Here's why:

* Glucose (a type of sugar) is too large and polar to pass directly through the cell membrane. The cell membrane is made up of a lipid bilayer, which is hydrophobic (water-repelling). Glucose, being polar, can't easily cross this barrier.

* Facilitated diffusion uses transport proteins. These proteins embedded in the cell membrane act as channels or carriers that help glucose move across the membrane.

* The process is passive. It doesn't require the cell to expend energy. Instead, it relies on the concentration gradient – glucose moves from an area of high concentration outside the cell to an area of lower concentration inside the cell.

Let me know if you'd like to learn more about facilitated diffusion or the other ways cells transport molecules!