How to Make Yeast Cells Thrive

This lesson requires the same materials as were needed for the previous activity, Yeast Cells Respire, Too (But Not Like Me and You):

• large test tubes, about 15 cm long and 20 mm in diameter; one per student
• small test tubes, about 10 cm long and 8 mm in diameter; one per student
• squares cut from plastic wrap, about 8 cm on a side; one per student
• several rubber or cork stoppers, size 2
• test tube racks to hold large test tubes
• several dropping pipettes
• five 300-ml beakers
• 1-liter flask
• 1-liter graduated cylinder
• lab thermometer
• package dry baking yeast (available in grocery stores)
• 12-ounce bottle molasses (unsulphured)
• Depending on what experiments students elect to do, you may need several extra flasks (100-300 ml), graduated cylinders (10 and 100 ml), and test tube racks. You may also need a refrigerator and an incubator or other warm location, such as a sunny window sill.
• If students decide to test the effects of pH, you will need litmus paper, lemon juice or vinegar as a safe means of lowering pH, and sodium carbonate ("washing soda") as a safe means of raising pH. If using any of these chemicals, students will also need eye protection.
• You will probably also need a few more large and small test tubes for controls, and in order to have adequate sample sizes for the student experiments.