Exhaling Carbon Dioxide
How do cells use the energy they obtain through food?
Background With every breath, your body takes in oxygen and releases carbon dioxide. In
this activity, you will investigate the relationship between exercise and the amount of carbon
dioxide you exhale. As part of your investigation, you will also identify the independent variable,
dependent variable, and controls.
Materials (per group)
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2 150-mL beakers
bromothymol blue (0.1% solution)
2 straws
stopwatch or watch with second hand
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graduated cylinder, 25-mL
paper towels
grease pencil
Safety
□ Note the lab safety icons that appear as warnings within certain procedure steps. For an
explanation of the meaning of each icon, go to the Lab Safety information section of this
online course. Be sure to follow all safety procedures established by your teacher and your
school.
Procedure
Part 1: Testing for Carbon Dioxide
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1. Label one beaker “Beaker 1” and the other beaker “Beaker 2.” Beaker 1 will be the
control in the experiment.
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2.
Put on safety goggles, gloves, and lab apron.
3.
Bromothymol blue can be used to test for the presence of carbon dioxide.
Measure and pour 15 mL of bromothymol solution into each beaker. CAUTION:
Bromothymol blue can stain skin and clothing. Avoid spilling or splashing it on
yourself or others.
4.
Observe and record the color of the solution in both beakers.
5.
Place a straw in Beaker 2. As your partner keeps track of the time, gently blow
through the straw into the solution until the solution changes color. CAUTION: Use the
straw to breathe out only. Do not inhale or suck the solution back through the
straw. Don’t chew gum, drink, or eat in the laboratory. Never taste a chemical in
the laboratory. Your partner should begin timing when you first blow through the straw
and stop as soon as the solution changes color. Record in the data table the time it
takes for the color to change.
6.
Empty the beakers and rinse them with water.
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Part 2: Exercise and Carbon Dioxide
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7.
In Part 1, you measured the carbon dioxide that you exhaled without exercising
beforehand. Predict how the results of Part 1 would be affected by two types of
exercise: walking for 5 minutes and jogging for 5 minutes.
8.
Adapt the procedure in Part 1 to measure the carbon dioxide that you exhale
after both moderate and strenuous exercise. CAUTION: If you have a medical
condition that limits your ability to exercise, do not take part in the exercise
portion of this activity. Use the data table to record your results.
□9.
Empty and rinse the beakers. Wash your hands with soap and warm water.
Data Table
Elapsed Time for Bromothymol Blue Solution to Turn Color
No exercise
Moderate Exercise
Strenuous Exercise
Beaker 1
Beaker 2
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Analyze and Interpret Data
1. Identify Variables In Part 2, what variables did you need to control? Explain how you
controlled those variables.
2. Develop a Model You cannot directly observe the amount of carbon dioxide that you
exhale. How did you use bromthymol blue to measure the carbon dioxide?
3. Predict Did your results agree with your prediction in Step 7? Explain.
4. Draw Conclusions What is the relationship between exercise and the amount of carbon
dioxide exhaled? Cite evidence from your results to support your answer.
5. Develop a Model Identify the process in cells that produces carbon dioxide, and describe
the purpose of this process. Use this process to develop a model to describe the
relationship between food, exercise, and the amount of carbon dioxide exhaled. (Hint: Your
model should be a diagram. Use the space provided below to draw your model.)
Cells Investigation • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
6. Relate Structure and Function The human body is a complex system composed of many
parts. Analyze the results of this investigation to describe how the removal of carbon dioxide
depends on a relationship between body parts.
Extend Your Inquiry
Plan an Experiment What kind of relationship would you expect to exist between heart rate and
carbon dioxide production? Design an experiment to test your hypothesis.
Cells Investigation • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.