Final answer:
Carbon dioxide is produced during fermentation by yeast cells and is responsible for causing dough to rise by creating gas bubbles that expand the dough.
Step-by-step explanation:
During fermentation, carbon dioxide (CO₂) is produced by yeast cells causing the dough to rise. The gas forms bubbles in the dough, which cause it to expand. These same bubbles are what leave small holes in the bread once it is baked, providing the bread with its characteristic light and fluffy texture. The yeast species responsible for this process is Saccharomyces cerevisiae, commonly known as brewer's or baker's yeast. This yeast performs alcoholic fermentation where sugars such as glucose are converted into ethanol and carbon dioxide, enabling the dough to rise due to the gas produced.