Sugar serves as the food source for yeast. Here's how it works:

* Yeast is a single-celled organism: It needs energy to survive and grow.

* Sugar provides that energy: Yeast uses a process called fermentation to break down sugar molecules.

* Fermentation produces alcohol and carbon dioxide: This is the basis for things like bread rising and alcoholic beverages.

In simpler terms: Just like we eat food to get energy, yeast eats sugar to fuel its own activities.