Roisin A. Macdonald
Objective: Students will observe the production of CO2 gas as yeast feeds on sugar in water to produce ethanol (an alcohol) and carbon dioxide.
Initiation: Using a fresh loaf of yeast leavened bread ask students how they think the baker can possibly make the bread so light and fluffy. Facilitate the discussion towards the use of yeast. The use of yeast dates back to the Egyptians when bread and beer and wine were main sources of nutrition. As yeast feast on sugar a chemical reaction occurs that produces both carbon dioxide gas and ethyl alcohol as waste products as well as energy needed for cell reproduction. The students will see the production of CO2 as evident by the inflation of the balloon. The chemical reaction is as follows:
Yeast + C6H12O6 2CH3CH2OH + 2 CO2 + energy
Glucose Ethyl alcohol carbon dioxide energy needed to reproduce
Materials: 1 packet of dry yeast (baker's yeast); 1 cup of water; 250 milliliter beaker; thermometer; hot plate; 2 tablespoons of sugar; large rubber balloon; empty water bottle
Procedure:
1.
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Have students get into groups of two or three
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2.
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Have each group gather materials listed
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3.
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Place the cup of water into the beaker on the hot plate and heat to 110° F
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4.
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Stretch the large balloon then blow it up and let the air out, repeat a couple of times
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5.
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Once the water is heated, add the two teaspoons of sugar mix thoroughly (so all the sugar is dissolved)
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6.
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Next, add the dry yeast to the sugar water and stir to mix. Transfer the yeast/sugar water mixture quickly to the water bottle and attach the balloon on top of the bottle.
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7.
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The generation of CO2 will begin within 10 minutes, have students record their observations in their lab notebooks
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Closure: Ask students "Why do you think there are holes in a loaf of fresh bread in which the bakers has used yeast in the dough?"