Carbon dioxide and water readily combine to form carbonic acid. The change in pH as the acid dissociates can be demonstrated with an indicator dye that changes color at a particular pH. In your physiology lab, you perform this experiment in two beakers containing room-temperature water and indicator, labeled Resting and Exercise based upon the status of the student who exhaled through a straw into the solution. The Resting student had been sitting at the table for 30 minutes before exhaling while the Exercise student had just finished sprinting up the stairs to class late. A stopwatch was used to measure how long it took for the solutions to change color. The following data were generated by the students. Explain why the time required for the color to change was different between groups, using the word
substrate in your answer.
| Student | Time for reaction (seconds): Resting | Time for reaction (seconds): Exercising |
| 1 | 123 | 20 |
| 2 | 114 | 23 |
| 3 | 136 | 17 |
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