Show them how it looks before liquids are added. Liquid and sugar provide the right conditions for the yeast to grow. As the yeast cells grow, they give off carbon dioxide. The carbon dioxide causes the dough to bubble. Yeast, a living thing belonging to the fungi kingdom, has been used to make bread for centuries.
Yeast is a living, microscopic fungus.
It is not a plant. It belongs to the fungi kingdom. When yeast grows and starts to digest sugars and starch in bread dough, it releases carbon dioxide. This gas becomes trapped by the dough mixture, and the bread rises. Today, scientists use other living things, such as bacteria and plants, to make new products, too.