"The Yeast of Our Worries"

Illinois Learning Standards addressed:

ll.B.4a, ll.B.4b, ll.B.4c, ll.B.4d, ll.B.4e, ll.B.4f, 12.A.4b

This inquiry lab can be used when studying yeasts and/or cellular respiration. It can also be used when defining what makes something "alive".

Suggested Lesson Plan:

1. Take a quick poll of the class to see how many students think that in general most microbes are "bad" (rot food, cause disease etc.). Can they name some beneficial functions of microbes?

2. Pass out ziplock bags with dry yeast. Ask students to describe what they see in the bag. Is it alive? How would they know? What are some qualities that indicate something is alive?

3. Show the students two kinds of bread (a regular loaf and tortillas). What is the difference between the two breads? Why did one bread rise? Explain what yeast are and what they do. Explain the difference between the two breads.

4. If yeast is alive, what does it need to stay alive? Explain how the yeast use the sugar as food and give off carbon dioxide.

5. Ask students how carbon dioxide could be measured during cellular respiration. At this point, depending on the class, show some of the materials and ask for suggestions.

6. The teacher can lead the students to suggest the experimental design at this point. For best results:

• See the supply list for recommended amounts of materials

• The group should decide how they will measure the amount of carbon dioxide given off using the various sweeteners.

• Depending on the class period at least 30 minutes of readings should be recorded

7. The following page contains a possible lab report guide for students. This can be given to students or they can write their own.

The Yeast of Our Worries

Cellular Respiration

Lab Report guide

Purpose/Question: Will yeast breakdown various sweeteners? (As measured by the release of carbon dioxide during cellular respiration).

Hypothesis: (What do you think will happen?)

Materials: (you may add information and supplies to this list)

250 mL beaker lukewarm water 3 packets Sweet N' Low 3 packets sugar 3 packets of Equal 3 ziplock bags of yeast 3 empty water bottles 3 party balloons 1 piece of string 1 ruler

Procedure: (rewrite in your lab book, remember to be specific and use past tense)

1. Mix 200 mL of warm water and three packets of sugar in a water bottle.

2. Add a bag of yeast to each mixture and gently swirl.

3. Cap each bottle with a balloon.

4. Use a piece of string and the ruler to measure each balloon's

circumference every 5 minutes (or devise your own method to measure

the balloons).

5. Create a data table and record all data. After you have measured the

balloon for the allotted time, plot the results on a graph.

Observations:

Data table and graph

Include any qualitative observations

Conclusion

Possible sources of error

Teacher notes: Supplies:

Water bottle (3 per lab group) 7" party balloons (3 per lab group) yeast (three ziplock bags per group, use 1 t/2 teaspoon per bag) sugar packets (3 per lab group) Sweet N' Low (3 packets per lab group) Equal (3 packets per lab group) Lukewarm water (use 1 cup or 200 mL per bottle) String Scissors Rulers

The following is a suggested time line for this lab:

Day one: Introduction, pick lab groups, students write their purpose and

hypotheses

Day two: Lab groups record, gather and label materials. The group creates a data table and assigns roles for the lab. Everything should be ready so the students start the procedure on day three.

Day three: Run the lab, record data.

Day four: Write up lab report.

Student Notes:

Purpose: Relate your purpose to:

• Is yeast living?

• Cellular respiration

• Requirements for cellular respiration

• Products of cellular respiration

• How will cellular respiration be measured or quantified?

Hypothesis: Your hypothesis should reflect your purpose. What do you think will happen and why? Be specific.

Decide on the equipment you will need. Gather and label (where needed) and clearly identify your materials.

Create a data table (everyone in the group) Decide on roles during the lab: timers, recorders, equipment etc.

For best results use:

3 packets of each sugar type

1 packet or bag of yeast

200mL warm (not hot) water