How does yeast cause bread to rise?
Yeast can use carbohydrates as food. When they do this they produce carbon dioxide as a waste product. The carbon dioxide gas makes the bread dough rise.
Both fermentation and aerobic respiration break down carbohydrates to release energy the yeast cells use to power their activities and produce carbon dioxide as a waste product
Here is a video which shows an experiment using yeast fermenting a solution of sugar water. Yeast cells can carry out either fermentation or aerobic respiration depending on environmental conditions.
Video from: Noel Pauller
Hope this helps!