Here's why:

* Energy Source: Glucose is the primary energy source for most cells. It's broken down through cellular respiration to produce ATP, the molecule cells use for energy.

* Active Transport: Glucose typically enters a cell through facilitated diffusion or active transport.

* Facilitated Diffusion: This process utilizes protein channels in the cell membrane to help glucose move across the membrane, following its concentration gradient (from high to low concentration).

* Active Transport: This process requires energy to move glucose against its concentration gradient (from low to high concentration). This is important when the concentration of glucose is lower outside the cell than inside.

Note: While glucose enters cells, it can also be released from cells under certain conditions, such as when liver cells release glucose into the bloodstream to maintain blood sugar levels. However, the primary direction of glucose movement is into cells.