EIS 20: Yeast Respiration

In this lesson, we learned about two forms of cellular respiration: aerobic respiration, which produces the most ATP but requires oxygen, and anaerobic respiration, which produces significantly less ATP but requires oxygen. In aerobic respiration, glucose gets broken down completely into carbon dioxide, releasing one carbon dioxide for every carbon in glucose (for a total of 6 carbons. In anaerobic respiration, glucose gets broken down into either 2, 3-carbon molecules called lactic acid or 2, 2-carbon molecules called ethanol plus 2 carbon dioxides. If you’re having trouble keeping track of these numbers, just count the carbons in each case.

In this lab, we will observe carbon dioxide being produced by yeast during respiration.

Materials

  • 4 packages or 4 x 2¼ tsp active dry yeast (Baker’s yeast)
  • 6 tsp sugar
  • 4 cup warm water. This should be similar to the temperature you would use to prepare yeast for baking. It should be warm, not hot.
  • 4 balloons (uninflated)
  • 4 plastic or glass bottles. These should have a narrow mouth (small enough to fit the balloon over).
  • A funnel. This is useful, but you may be able to manage without one. If you don’t have a funnel and are struggling to put the ingredients into the bottle, you may find it helpful to roll a piece of paper into a cone shape and use this instead.

Procedure

This video will walk you through the procedure for this lab.
  1. Put 1 package or 2¼ tsp of active dry yeast into each of your 4 bottles.
  2. Put 3 tsp sugar in bottle 1, 2 tsp in bottle 2, and 1 tsp in bottle 3. The final bottle should have yeast but no sugar.
  3. Put 1 cup of warm water in each cup.
  4. Put the balloon over the lip of each bottle. This should be completely sealed and not allow any air to get through. You may find it helpful to tape the balloon in place after achieving an air-tight seal.
  5. Periodically observe your balloons over the next 2-3 hours. You can choose to observe them longer if you like.