How does yeast make bread dough rise when baking?

Yeast are living microorganisms that feed on sugars present in flour. As they consume these sugars, they produce carbon dioxide gas and ethanol through a process called fermentation. The carbon dioxide gets trapped within the gluten network of the dough, forming tiny bubbles that cause the dough to expand and rise. The gluten, developed by mixing flour and water, acts like an elastic web that stretches to hold the gas without letting it escape. When the dough goes into the oven, the heat causes the gas bubbles to expand further, giving bread its light, airy texture. The heat also kills the yeast and evaporates the ethanol, while setting the gluten structure permanently into the final baked shape.