Pour 1 packet of dry yeast into each bottle, leaving one without yeast as control.
Put a balloon over each jar.
Wait a few minutes for the reaction to take place. The balloons will start filling.
Science Behind It
Yeast, a fungus, feeds off of the sugars. It reacts better in warm water. The yeast metabolizes the sugar through fermentation to carbon dioxide, which is what fills the balloon. The same reaction is what causes bread to rise. This reaction also creates water, a small amount of alcohol, and energy.
Tips
This project can be done as a partnership with a cooking project.