Bread Dough Rises Due to the Cellular Respiration of Yeast

When yeast is added to bread dough, it begins to metabolize the sugars present in the dough through the process of cellular respiration. This process involves breaking down the sugars into energy in the form of ATP (adenosine triphosphate) molecules. During cellular respiration, yeast produces carbon dioxide gas (CO2) as a byproduct. As this gas accumulates within the dough, it becomes trapped within the gluten network, causing the dough to rise and expand. This process is called leavening, and it results in the light, fluffy texture that we associate with bread.

Driving Question

• What biological and chemical processes must occur in order for bread dough to rise?

Probing Questions

• What are some of the ways the bread dough must be changing as the dough rises?
• Basic bread dough is made up of mostly just water, flour, sugar, and yeast. What are some ways we could alter this recipe to see what affects the ability of the dough to rise?
• What evidence do we have that yeast must be a living organism? What inferences can we make about this organism?

Classroom Suggestions

Students could:

• Make their own bread dough, trying out different recipes to see the effects different variables have on the production of carbon dioxide, by measuring how much the dough rises. For instance, try with and without the key ingredients: flour and yeast.
• Cellular respiration requires oxygen. As such bread dough should not rise in the absence of sufficient oxygen. The teacher could set up two sections of dough and allow each to rise, but put one in a sealable container and fill it with a gas other than oxygen. Compressed canned air would work well. 

Relevant Related Resources

Cellular Respiration | Science Lessons That Rock: Miscellaneous Cellular Respiration Resources. Provides resources for various cellular respiration activities that are appropriate for junior high science students.
Cellular Respiration & Exercise | Activity: Worksheet for students to critically think about how knowledge of cellular respiration can help runners train for a race.