In this activity, learners observe what happens when yeast cells are provided with a source of food (sugar). Red cabbage "juice" will serve as an indicator for the presence of carbon dioxide. Learners will observe how carbon dioxide gas is given off by yeast cells, as indicated by turning the mixture bright pink. This activity is broken up in three parts or sessions: making the indicator (can be done in advance), demonstration of cabbage juice indicator, and conducting the investigation.