Yeasts such as Saccharomyces cerevisiae, commonly called baker's yeast, are widely used in the baking industry, which makes the assertion correct. During fermentation, yeast breaks down sugars present in the dough and releases carbon dioxide along with ethanol. The carbon dioxide gets trapped in the sticky dough, causing it to expand and rise, which gives bread its soft and fluffy texture. Thus, the reason is also correct and it provides the proper explanation for the assertion. Hence, both the assertion and the reason are true, and the reason correctly explains the assertion.