Procedure:
1. Using a graduated cylinder, measure out 100 mL of bromothymol blue solution for each of the 4 beakers.
2. Insert one end of a drinking straw into the bromothymol blue in one of the flasks. Blow until there is a change in the appearance of the bromothymol blue solution. Repeat this procedure with the other flasks.
3. Place a sprig of Elodea into 2 flasks. Stopper all 4 flasks with the parafilm. The flasks must be completely sealed.
4. Place one flask with the Elodea and 1 flask without Elodea in the dark for 24 hours. Place the other flasks (1 with Elodea and 1 without) on a sunny windowsill for the same amount of time.
5. After 24 hours, examine each flask. Note changes of appearance
What is the control group?
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