Name ______Date ______Period ______# ______

"The Yeast of Our Worries"

A Laboratory Lesson on Anaerobic Respiration (Cellular Respiration)

Pre-Lab Questions (Use your textbook to help you answer these questions.)

1. Are all microbes bad?

2. Name some beneficial functions of microbes.

3. Are yeasts living? If so, what kingdom do they belong to?

4. If yeast is alive, what does it need to stay alive?

5. How can carbon dioxide be measured during cellular respiration?

1. Purpose/Question: What are the effects of different types of sweeteners on the respiration rate (alcoholic fermentation rate) of yeast cells?

2. Research: See pre-lab questions and the cellular respiration concept map.

3. Hypothesis: If ______, then ______.

4. Experiment

Materials:

500 mL beaker lukewarm water, 3 packets Sweet N' Low, 1 packet table sugar, 3 packets of Equal, 3 packets of yeast, 3 empty water bottles, 3 party balloons, 1 piece of duct tape, 1 piece of string, stopwatch, and 1 ruler

Procedure:

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

2. Add a packet 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.

5. Record the data and plot the results on a graph.

Data/Observations

Sweetner Type / Balloon Circumference (cm) @ 5 minutes / Balloon Circumference (cm) @ 10 minutes / Balloon Circumference (cm) @ 15 minutes / Balloon Circumference (cm) @ 20 minutes / Balloon Circumference (cm) @ 25 minutes / Balloon Circumference (cm) @ 30 minutes
Table Sugar
Sweet ‘N Low
Equal

Title: The effects of type of sweetener on the balloon circumference (amount of CO2 made). Use a key to distinguish between the different sweeteners.

6. Conclusions- Write at least one paragraph summarizing the results of your experiment. Use data to back up your conclusions.

7. Repeat/Redesign- Write at least one paragraph discussing what sources or error you may have had and/or what you might do next time to make the experiment run more smoothly.

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

*further modification can be made using different temperature of water, using starch and other solutions, and brompthymol blue to show the change in pH.