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8th Grade Core
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Sugars are the energy loaded molecules created by plants in the process of photosynthesis. These sugars are then used by living things for energy. The process of converting sugar to mechanical energy always results in some energy being converted to heat.

In this experiment, you will use yeast. Yeast is a living organism that needs special treatment. Make sure that your yeast is fresh. The yeast that is not used should be refrigerated. Yeast cells consume sugar to obtain energy. As the yeast respires, it uses oxygen. The oxygen is converted to carbon dioxide.


Materials :

  • Yeast
  • Sugar
  • 125 ml Erlenmeyer flask
  • One 4-inch balloon, deflated
  • Luke-warm water
  • Masking tape
  • String
  • Metric ruler
Safety concerns: icon Be sure to keep all glassware, and chemical safety rules. DO NOT allow your beaker to be covered or stoppered. Make sure that you protect your body and clothing from the reactions. As with all science lab activities, the most important safety rule is to follow all teacher directions.

Procedure :

  1. Measure the following and place each into the Erlenmeyer flask:
    • 20 g of sugar
    • 120 ml of lukewarm water.
  2. Measure 5 grams of yeast and place into the balloon.
  3. Carefully stretch the balloon over the opening of the Erlenmeyer flask without dropping the yeast into the solution.
  4. Seal the location where the balloon and flask meet using the masking tape.
  5. Lift the balloon upward and shake to release the yeast into the Erlenmeyer flask.
  6. Shake the Erlenmeyer flask and allow the reaction to occur.
  7. Measure the circumference of the balloon (using the string) every minute.
  8. Record each measurement.
  9. After each measurement, shake the flask gently to further mix the contents.
  10. Continue to measure and shake the flask until you have taken 20 minutes of data.


Record your data based on the time and circumference of the balloon.
Time (minutes) Circumference
Time (minutes) Circumference

Graph your data. Create a line graph using time for the X-axis and circumference for the Y-axis.



  1. What you observe happening in this reaction.
  2. What gas do you think is being produced?
    • Where did the gas come from?
    • How could you prove the gas is what you think it is?
    • How do you think the gas was formed?
  3. What do you predict will happen to the balloon after 24 hrs?


To observe how much heat energy is given off as the yeast consumes sugar, you will need to do a similar experiment using a digital thermometer. You will need to determine how you can cover the flask with the thermometer inside it the entire time. Measurements can still be taken each minute and recorded in a similar data table. A line graph would help you compare time and temperature.

Review Science safetey rules here.

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Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

  1. The title of the activity
  2. The URL (Internet address)
  3. Your name.

Remember that no pictures can be used that show student faces or student names on it. 

Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 8th grade science core.

Updated October 24, 2008 by: Glen Westbroek

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