Answer:
When yeast cells are used in making bread rise, they get energy from the sugar mixed within the bread dough. When oxygen is present, these single celled fungi perform cellular respiration. When there is no oxygen they perform fermentation. By performing fermentation they produce carbon dioxide gas (which causes the bread to rise) and energy storing molecules called ATP. By fermentation they produce more and more ATP. More and more energy.
Step-by-step explanation: