In baking, what is the role of yeast?

Yeast plays a crucial role in baking, particularly in the leavening process. When yeast is added to a dough, it begins to ferment the sugars present in the flour. During this fermentation, yeast converts sugar into alcohol and carbon dioxide gas. The production of carbon dioxide is the key aspect of leavening; as the gas gets trapped within the dough, it causes the dough to rise and develop a light, airy structure. This process not only contributes to the texture of the final product but also allows for the development of complex flavors during fermentation.

While other options may touch on aspects related to baking, yeast's primary function is to facilitate leavening through gas production, making the chosen answer the most accurate in the context of baking.