We found out that yeast is a fungi. When it is mixed with warm water and sugar it wakes up and starts to eat the sugar. As it eats, it makes a gas called Carbon Dioxide. Yeast mixed with warm water and sugar helps to make the bread rise in the oven. Carbon Dioxide gas makes air bubbles in the bread.
We watched the yeast, warm water and sugar fizz up and make bubbles. Then Rob put a balloon over the end of the bottle and the gas slowly filled up the balloon!