yeast is a fungus! How gross ! Yeast responds to warm water which makes the little cells of yeast come to life. When we make bread or cinnamon rolls we use sugar and bread, the yeast begins to eat the sugar. The yeast then digests the sugar and gives of carbon dioxide, which makes the bread rise! It also gives off alcohol, which evaporates when the bread bakes. The little bubbles expand all of the protein in the flour (gluten).
Yeast converts the sugar that you put into the dough into alcohol (only a little bit!) and carbon dioxide. Carbon dioxide is a gas, and so creates little pockets in the bread which push our and make the dough rise.