What makes dough rise when baking bread?

Dough rises primarily because of yeast, a living microorganism that consumes sugars in the flour and produces carbon dioxide gas and alcohol as byproducts. The carbon dioxide gets trapped within the gluten network, a stretchy protein structure formed when flour and water are mixed and kneaded. As the yeast keeps producing gas, the gluten expands and the dough puffs up. When the dough goes into a hot oven, the heat causes the trapped gas to expand further, giving the bread its final rise called oven spring. The heat also kills the yeast, sets the gluten structure, and evaporates the alcohol, leaving behind the firm, airy crumb structure of finished bread.