According to nasa scientist bruce jakosky, the ability to utilize energy from some source to drive chemical reactions is one of the three important characteristics of life. in the students' experiment, what served as an energy source for the yeast?

Yeasts are unicellular microorganisms that use sugar as food releasing carbon dioxide. With the released gas increases the pressure when oxygen is present inside the bottle, yeasts grow by the breathing process are consuming oxygen and producing carbon dioxide. And when the oxygen is finished the yeasts change to anaerobic metabolism and the degradation of sugar occurs by fermentation that produces greater amounts of alcohol and gaseous carbon dioxide.