Demonstrating the Carbon Dioxide Content of Gaseous Yeast Digestive Byproducts:

To demonstrate that the gas produced by yeast is carbon dioxide, the instructor can let students exhale through a straw into a test tube filled with lime juice. The lime juice will turn a milky white color, which is the test for carbon dioxide. To show that the gas produced by yeast also contains carbon dioxide, fill one test tube with lime juice and another test tube with warm water, yeast, and sugar. Then use a rubber stopper with a hole in it to seal the test tube with the yeast. Place a glass pipette through the hole in the rubber stopper (but not all the way into the yeast solution). Place the other end of the glass pipette into the lime juice in the other test tube. When the gas produced by the yeast begins to bubble into the lime juice, the lime juice will turn milky white again, exactly the way it did when the student exhaled...

Demonstrating the Catalytic Effect of Heat on the Gaseous Production from Yeast:
catalyst is something that promotes a chemical reaction indirectly, without actually taking part in the reaction. To demonstrate the catalytic effect of temperature on the carbon dioxide production, place equal amounts of yeast, dough, and water into three small jars. Place one jar in the refrigerator, another in a warm place, and the last sample in a hot place. Allow the students to measure and compare the changes in the relative expansion of the three different samples to study the importance of heat as a catalyst in the process of yeast digestion and carbon dioxide gas production (UNESCO 1962).

References

UNESCO (1962) 700 Science Experiments for Everyone.

New York: Doubleday