Which baking ingredient is primarily responsible for making dough rise?

The primary ingredient responsible for making dough rise is yeast. Yeast is a living organism that ferments sugars present in the dough, producing carbon dioxide gas and alcohol in a process known as fermentation. The carbon dioxide gas gets trapped in the dough, causing it to expand and rise, which results in the characteristic texture and volume of baked goods like bread.

While baking powder also serves to leaven dough, it works through a chemical reaction rather than biological fermentation. Sugar plays a role in feeding the yeast and enhancing flavor but does not directly cause dough to rise by itself. Flour, although essential for structure and providing the necessary proteins (gluten) for elasticity, does not make the dough rise independently. Thus, yeast is the correct choice as it is the key ingredient that initiates the rising process through its biological activity.