Here's why:

* Glucose is a simple sugar. It's a readily available source of energy for cells.

* Cellular respiration breaks down glucose. This process releases energy in the form of ATP (adenosine triphosphate), the primary energy currency of cells.

* Other molecules can be used as fuel. While glucose is the primary source, fats, proteins, and even some other sugars can also be used for cellular respiration. However, glucose is the most efficient and readily utilized fuel source.