Cellular Respiration (Ashley Min)
Title: Yeast Inflating a Balloon with CO2 (8th Grade)
Principle(s) Investigated: Release of energy from breakdown of organic compounds. Similarities and differences between aerobic & anaerobic respiration.
Biology/Life-Science
1g. Students know the role of the mitochondria in making stored chemical-bond energy available to cells by completing the breakdown of glucose to carbon dioxide.
Materials: 2 packets of active dry yeast, warm water, 2 small clear plastic bottle, 2 rubber balloons, sugar
Procedure:
- 1. Fill the bottles up with about one inch of warm water.
- ( When yeast is cold or dry the micro organisms are resting.)
- 2. Add all of the yeast packet (one per bottle) and gently swirl the bottle a few seconds.
- (As the yeast dissolves, it becomes active - it comes to life! Don't bother looking for movement, yeast is a microscopic fungus organism.)
- 3. Add the sugar to one bottle and swirl it around some more.
- 4. Blow up the balloon a few times to stretch it out then place the neck of the balloon over the neck of the bottle. (per bottle)
- 5. Let the bottles sit in a warm place for about 20 minutes
Student prior knowledge: Autotrophs vs heterotrophs. Anaerobic vs aerobic. Synthesis reactions consume energy to combine molecules to create more complex compounds . Decomposition reactions release energy by breaking down organic food molecules to simpler forms. Knowledge of chemical equations. That living cells need energy for cellular processes. That ATP is a form of energy that the cells can use.
Explanation:
Cellular Respiration is the process that cells use to transfer energy from organic food molecules to chemical bonds in ATP. The equation for cellular respiration for when oxygen is available is:
The first major step in cellular respiration is glycolysis.
The next step depends on whether or not oxygen is available. If oxygen is available, cells use the Krebs Cycle and the electron transport chain to make up to 36 ATPs.
When oxygen is not available, cells use anaerobic processes to produce ATP called fermentation.
The two types of fermentation are
lactate fermentation (muscle when working out hard) and
alcoholic fermentation (such as yeast in beer).
Fermentation has the advantage of being able to occur without the presence of oxygen however it produces much less ATP than aerobic respiration and also creates a toxic by product.
The yeast is a living, single-celled, microscopic fungus. It is dormant but when mixed with warm water it comes alive. By adding sugar we give the yeast something to eat. The yeast will convert the sucrose into glucose and then undergo glycolysis. Because it is a facultative anaerobe it can undergo either cellular respiration in the presence of oxygen or fermentation depending on whether or not oxygen is available. It will undergo cellular respiration creating CO2 and water and once out of oxygen it will ferment creating alcohol and CO2. The CO2 will inflate the balloon. The yeast in the warm water without sugar will not inflate the balloon because it has nothing to consume and turn into CO2.
Fill in the blanks:
Questions & Answers: Give three thought-provoking questions and provide detailed answers.
1. Does this demonstration represent aerobic or anaerobic respiration? This demonstration initially represents aerobic respiration because the yeast do have oxygen to consume however if we left it long enough the yeast would switch to fermentation creating a byproduct of alcohol and CO2.
2. The following is the chemical equation for when combustion of glucose.
What are the similarities an differences between the equation for burning glucose and the equation for cellular respiration in the presence of oxygen? The equations are nearly exactly the same except the form of energy. In cellular respiration the energy is released in the form of chemical bonds in ATP, while in combustion it is released in the form of light and heat.
3. Breakdown of glucose yields the synthesis of 36-38 ATPs which preserves around 40& of the energy available in glucose while a car burning oxygen is about 25% efficient. What happens with the rest of the energy that is harnessed to run the car? What is one explanation why cellular respiration might be so efficient? The energy is in the form of heat which is why our car engines get so hot and thus we need a coolant. Cellular respiration is more efficient because it involves many small steps.
Applications to Everyday Life:
1. Yeast is used to make bread today. The carbon dioxide bubbles make the bread soft and fluffy and through the process of baking the yeast dies and any alcohol is burned off. If you don't put yeast, the bread will be flat and hard.
2. Yeast is used to make alcoholic beverages such as beer and wine. In wine, the yeast ferments, consuming the sugar and the "byproduct" is the alcohol. In still wines they "degas" the beverage so it doesn't sparkle. In sparkling wines like champagne, the still wine then goes through a second fermentation in which the carbon dioxide are kept.
3. Fermentation in yeast occurs with the yeast converting the sucrose to glucose and then through glycolysis whose products are pyruvate (a 3-carbon molecule) and ATP. The first step of cellular respiration for humans is also glycolysis.
Photographs:
Videos: Yeast Balloon Video
References:
Panhandle Area Educational Consortium
Greenberg, Jon, ed. BSCS Biology. A Molecular Approach. New York: Glencoe/McGraw-Hill, 2001. Print.