Dependence of Fermentation on Temperature

Activity 2: Pre-Assessment

1. How does temperature affect the rate of chemical reactions? Explain your answer.
2. What would likely influence the optimum temperature of cellular respiration for an organism? Do you think there is a temperature that cellular respiration would cease and what would determine this upper temperature limit for cellular respiration?
3. Discuss the answers to questions 1 and 2 with the class.

Activity 2: Dependence of Fermentation on Temperature

All cellular processes, like fermentation, consist of an interconnected series of chemical reactions. However, temperature can influence the rate of chemical reactions by affecting how quickly the reactants move, and therefore, how often they collide with each other. If the temperature gets too high, enzymes or other cellular proteins involved with cellular respiration can break apart, or denature, rendering them inactive. Therefore, it is very important for cells and organisms to regulate their internal temperature to ensure that cellular respiration and other chemical reactions can continue at the proper rate.

Safety Precautions

• Use protection when handling hot glass and materials.
• Do not mix very hot water with very cold water in glass containers.
• Clean up any spilled liquids to prevent slipping.

For this activity, you will need the following:

• Graduated cylinders
• Water
• Ice
• Thermometer
• Beakers
• Sugar substitute solution
• Yeast solution (one packet of yeast with 100 ml of water; can use from Activity 1)
• Hot plate
• Droppers or pipettes
• Medium-size, un-inflated balloons
• Cloth measuring tape or pieces of string and a ruler
• Balloons

For this activity, you will work in pairs.

Structured Inquiry

Step 1: Hypothesize/Predict: Unlike Activity 1, you will measure the volume of carbon dioxide gas by placing balloons over the graduated cylinders after the reactants are added. Use 10 ml of each reactant. As the balloons fill with gas, you can measure their circumference to find the volume. How do you think temperature will affect the rate of fermentation? How can this be tested? Write your hypotheses in your notebook.

Step 2: Student-Led Planning: In this lab, you will measure the changes in the circumference of a balloon. Decide, with your partner, how you will take this measurement using a practice balloon that you inflate with your mouth. Make sure that your measurement is repeatable regardless of the size of the balloon. Create a data table for your measurements of balloon circumference versus solution temperature. You should record the volume of the gas in the balloon every 2 minutes for 10-15 minutes per trial.

Step 3: Prepare the first beaker with 100 ml of water at room temperature, approximately 21 °C. Add cold or hot water to get the water as close to 21 °C as possible. Once the temperature is stable, place the graduated cylinder containing the yeast and sugar substitute directly into the water beaker. Be sure to record the actual temperature of your room temperature solution in your notebook.

Step 4: Repeat Step 3 for the cold and hot water beakers one at a time. For the cold water treatment, fill the beaker with cold water and then add ice. Wait until the temperature stabilizes before beginning the timer. For the hot water beaker, bring the water to a boil using a hot plate. Then, turn down the hot plate to maintain the water at a low boil. Record the stabilized temperatures for both treatments before immersing the graduated cylinders containing the yeast into the beakers.

Step 5: Critical Analysis: Does this set up seem to capture the carbon dioxide gas effectively? Should you adjust the quantities of any of the liquids and/or the time intervals? Discuss with your partner and then write your answers in your notebook.

Guided Inquiry

Step 1: Hypothesize/Predict: How do you think the more extreme temperatures, such as (~ 0–4 °C) and (55–60 °C) will affect the rate of fermentation? Are there any new safety concerns to consider with such changes to the temperature?

Step 2: Student-Led Planning: Pick two additional temperatures to test within the range (~ 0–4 °C) and (55–60 °C). Use the water, ice, hot plate, and thermometer to make these baths before adding the graduated cylinders containing the yeast and sugar substitute solutions. Then perform your trials as in the structured inquiry, measuring the volume of gas in the balloon. Create appropriate data tables before beginning your trials.

Step 3: Critical Analysis: How did temperature affect the rate of fermentation for this species of yeast? Is it likely any of the proteins involved in the reaction denatured and at what temperature did this occur? Graph the circumference of the balloon versus the temperature of the reaction. Based on your graph, what is the best estimate of the optimal temperature for fermentation in yeast? Discuss your answers with your partner and write them in your notebook.

Assessments

1. What likely caused the differences in reaction rate at the three temperatures examined in Activity 2?
2. How could this experiment better measure the effect of temperature changes in the natural habitat of the yeast?
3. What other biotic and abiotic factors would likely affect the rate of cellular respiration in yeast? Explain your answers.
4. What patterns can you identify in the data you collected between the yeast and the abiotic factor of temperature?