SBI3C: Biochemistry

Teacher Demo: Respiration in Yeast

TopicsCellular Respiration

Timingpreparation: 5 minutesdemonstration: 15-20 minutes

Specific Expectations: SBI3C

IntroductionThis demonstration shows that the combination of yeast, sugar and water will produce a gas that can be collected. This provides students with an opportunity to draw on prior knowledge to identify the cellular process involved. Students also have a chance to predict the gas produced and determine a way to test their prediction.

Materialsdry baker’s yeastpop bottle (or narrow mouth flask)balloonsugarwarm water elastic band safety glasses

Safety ConsiderationsMost balloons are made of latex, so be aware of latex allergies. Consider using a non-latex material, or collect the gas produced in another container filled with water, so that the gas can displace the water. Wear safety glasses to model good practice.

Procedure1. Stretch the balloon before class starts.2. Prepare a chart on the front board or screen.

Minds-On3. Place 5 mL of yeast and 10 mL of sucrose in the soda bottle.4. Fill the bottle ¾ full of warm water.5. Quickly stretch the balloon over the opening of the bottle.6. Seal with an elastic band over the neck of the bottle.7. Gently swirl the bottle to speed up the reaction.8. Measure the diameter of the balloon every 2 minutes. 9. Record observations with this table.

Explain10. Ask students to explain what they have observed.

Table

DisposalDiscard liquid waste into the school composter, if appropriate. Otherwise, dilute and discard into the sink. Other materials can be discarded into the garbage. The container can be cleaned and reused or discarded into a recycle bin.

What happen?In this demonstration, students will observe that dry yeast can be activated in the presence of water and table sugar. The metabolic process produces a gas product.

How does it work? Yeast cells are inactive in the package. In the presence of water the yeast become active. Sugar is a food source, allowing the yeast to metabolize the sugar. When O2 is abundant, the yeast will use aerobic respiration. As the O2 is used up, and sugar is still present, yeast can metabolize sugar through fermentation, releasing both CO2 and alcohol.

Teaching Suggestions/Hints Use this demonstration to give an inquiry focus to the study of cellular respiration. Let the students guess the product gas and then use prior knowledge from previous

courses to recall the gas tests. Have limewater ready and a tube to transfer the gas collected to the limewater to

demonstrate that it is CO2.

Next StepsOutline the key procedure used to encourage new questions:Is sucrose the only sugar that can work? What other sugars can work? Is there an optimal temperature for the respiration process? How does the presence or absence of O2 affect the metabolic process? This requires some thinking about how to drive out the O2 to see the effects.

Additional ResourcesCellular Respiration Song (YouTube):http://www.youtube.com/watch?v=1TGg6KyOwc0

Time (minutes) Diameter of balloon (cm)02468101214

Specific Expectations SBI3CA1.1 formulate relevant scientific questions about observed relationships, ideas,

problems, or issues, make informed predictions, and/or formulate educated hypotheses to focus inquiries or research

A1.10 draw conclusions based on inquiry results and research findings, and justify their conclusions with reference to scientific knowledge

B3.3 explain the chemical changes and energy transformations associated with the process of cellular respiration, and compare the reactants to the products

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