Biolab Chapter 12 - BSCS Biology

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Does temperature affect the metabolic activity of yeast?
Does temperature affect the rate of carbon dioxide production by yeast? Look at the experimental setup pictured at the right. As yeast metabolizes in the stoppered container, the carbon dioxide that is produced is forced out through the bent tube into the open tube, which	contains a solution of bromothymol blue (BTB). Carbon dioxide causes chemical reactions that result in a color change in the BTB. Differences in the time required for this color change to occur indicate the relative rates of carbon dioxide production by yeasts.

Problem How can you determine the affect of temperature on the metabolism of yeast? Brainstorm ideas among the members of your group. Hypothesis Decide on one hypothesis that you wil test. Your hypothesis might be that low temperature slows down the metabolic activity of yeast, or that a high temperature speeds up the metabolic activity of yeast. Objectives In this BioLab, you will: Measure the rate of yeast metabolism using a BTB color change as a rate indicator. Compare the rates of yeast metabolism at several temperatures. Use the Internet to collect and compare data from other students. Possible Materials Bromothymol blue solution (BTB) Straw Small test tubes (4)	Large test tubes (3) One-hole stoppers with glass tube inserts for large test tubes (3) Yeast/white corn syrup mixture Water/white corn syrup mixture Test-tube rack 250 mL beakers (3) Ice cubes Celsius thermometer Hot plate 50 mL graduated cylinder Glass-marking pencil 10 cm rubber tubing (3) Aluminum foil Data Sources Activity Links View Student Data Safety Precautions Always wear goggles in the lab. Be careful in attaching rubber tubing to the glass tube inserts in the stoppers. Avoid touching the top of the hot plate. Wash your hands thoroughly after cleaning out test tubes at the end of your experiements. Skill Handbook Use the Skill Handbook if you need additional help with this lab.

1. Decide on ways to test your group's hypothesis.

2. Record your procedure, and list the materials and amounts of solutions that you will use.

3. Design a data table for recording your observations.

4. Pour 5 mL of BTB solution into a test tube. Use a straw to blow gently into the tube until you observe a series of color changes. Cover this tube with aluminum foil, and set aside in a test-tube rack. Record your observations of the color changes caused by carbon dioxide in your breath.

1. What data on color change and time will you collect? How will you record your data?

2. What variables will you control?

3. What control will you use?

4. Assign tasks for each member of your group.

5. Make sure your teacher has approved your experimental plan before you proceed further.

6. Carry out your experiment.

7. Post your data in the table below.


Experimental Design - describe briefly

Water Temp. (°C)	Control tube color change?	Experimental tube color change?	Amount of time to change color (sec.)

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1. Check Your Hypotheses
Explain whether your data support your hypothesis. Use your experimental data to support or reject your hypothesis concerning temperature effects on the rate of yeast metabolism.

2. Using the Internet
How did the data you collected compare with that of other students? Compare experimental designs. Did differences in experimental design account for any differences in data collected?

3. Making Inferences
What must be the role of white corn syrup in this experiment?

4. Identifying Variables
Describe some variables that your group had to control in this experiment. Explain how you controlled each variable.

5. Drawing Conclusions
Did your experiment clearly show that differences in rates of yeast metabolism were due to temperature differences?

Prologue
Chapter 4
Chapter 10
Chapter 11
Chapter 12
Chapter 13A
Chapter 13B
Chapter 18
Chapter 23
Chapter 25