How does yeast make bread dough rise?

Yeast are living microorganisms that consume sugars present in flour and produce carbon dioxide gas and alcohol as byproducts through a process called fermentation. The carbon dioxide gets trapped within the gluten network that forms when flour and water are mixed and kneaded, creating tiny gas bubbles throughout the dough. These bubbles expand as fermentation continues, causing the dough to rise and develop a light, airy structure. When the dough is baked, the heat kills the yeast, evaporates the alcohol, and causes the gas bubbles to expand further before the gluten structure sets permanently. This is what gives bread its characteristic open, spongy texture. The fermentation process also produces flavor compounds that contribute to bread's taste and aroma.