AP Biology
Exercise and CO2 Lab
Names____________________________________
Per_______________
Question: How do different amounts of exercise affect the time it takes for carbon dioxide to change
the color of bromthymol blue?
Manipulated Variable__________________________________________________________________
Responding Variable___________________________________________________________________
Hypothesis:
Materials
Clock/Timer
Flasks
Dropper of Bromthymol Blue
Straws
Graduated Cylinder
Empty Droppers
Procedure
1. Place 10 ml of water into one flask.
2. Add 3 drops of bromthymol blue. Immediately after adding the drops, exhale gently into the flask
until the color changes yellow. While breathing, have a partner keep track of the number of
seconds until the color change. Record this number on your table.
3. Now exercise (run in place, jumping jacks) for 1 minute. While exercising, have your partner add 10
ml into another flask.
4. Immediately after finishing your exercise, add 3 drops of bromthymol blue to the flask. Immediately
after adding the drops, exhale gently into the flask until the color changes yellow. While breathing,
have a partner keep track of the number of seconds until the color change. Record this number on
your table.
5. Rest for 3 minutes between exercises. While resting, have your partner complete their trials.
6. Exercise, in the same manner you did for step #3, this time for 2 minutes.
7. Repeat steps 4-5.
8. Repeat steps 3-5, but this time exercise for 3 minutes.
9. Calculate the average time for the bromthymol blue to change color for each amount of exercise.
Time for Bromthymol Blue to change color (in seconds)
Partner 1
Partner 2
Partner 3
Partner 4
Before
Exercising
After 1 minutes
of exercise
After 2 minutes
of exercise
After 3 minutes
of exercise
Post-Lab
1. What were two controlled variables in this lab?
2. Cellular Respiration in humans occurs in what two organelles?
3. Connecting lung respiration with cellular respiration: Bromthymol blue changes color after
being saturated with CO2. Explain how measuring CO2 tells you how much exercise your body
went through (hint: think about when and why your body produces CO2).