Respiration in action

Project 2: Respiration produces O2 and CO2.

Saccharomyces cerevisiae is such a useful organism because it grows via both respiration and fermentation. During respiration, sugar is converted to ATP, or cellular energy, and CO2 is produced as a byproduct. When Saccharomyces cerevisiae is added to dough, it allows the dough to rise by creating pockets of CO2. What’s more, Saccharomyces cerevisiae is a useful tool for studying human cells because our cells use the same method to produce energy. In this project, we will observe the production of CO2 by Saccharomyces cerevisiae and test different sources of sugar for the capacity to provide cellular energy.



1 balloon

1 packet of yeast

1 water bottle

Warm water

Potential energy sources: white sugar, brown sugar, barley malt, molasses, honey, agave, stevia , sunflower oil



  1. Pour 1/4 packet of yeast to the water bottle.
  2. Add 25 mL warm water.
  3. Add your chosen energy source.
  4. Stretch out the balloon so it is easy to inflate.
  5. Place the balloon over the top of the bottle and observe.
  6. Measure the diameter of the balloon after 5 min, 10 min, and 20 min.
  7. Repeat using different energy sources.



What energy sources did you choose and why?


Make a table showing the time and the diameter of the balloon for each condition.


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