Baking powder is made of sodium hydrogen carbonate. It is a chemical leavening agent that, like yeast, produces carbon dioxide and is a powdered food additive (E500). There is no fermentation with baking powder whereas yeast ferments and generate volatile aromatic compounds and other positive metabolites.
Yeast is a microscopic living organism, formed of just a single cell, belonging to the taxonomic class of the “fungi”. It comes in many forms including block (compressed yeast), crumbled, liquid or dry. Yeast not only forms carbon dioxide to leaven dough, but also forms the greatest part of characteristic aromas of bread as well as influences properties of crust, crumb and freshness of bread.