A leavening agent is a substance used in baking to help dough rise and become light and airy. Common leavening agents include baking soda, baking powder, and yeast. These agents produce gas, usually carbon dioxide, which creates bubbles in the dough, causing it to expand and rise during baking. Leavening agents can be classified as chemical or biological. Chemical leavening agents, like baking soda and baking powder, react with moisture and heat to release gas. Biological leavening agents, such as yeast, ferment sugars to produce carbon dioxide. Both types are essential for achieving the desired texture in baked goods.