Group Activity: Two-Factor Cross

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)

2 150-mL beakers
bromothymol blue(0.1% solution)
2 straws
stopwatch or watchwith second hand
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

□1.Label one beaker “Beaker 1” and the other beaker “Beaker 2.” Beaker 1 will be the control in the experiment.

□2.Put on safety goggles, gloves, and lab apron.

□3.Bromothymol blue can be used to test for thepresence of carbon dioxide. Measure and pour 15 mLof bromothymol solution into each beaker. CAUTION:Bromothymol blue can stain skin and clothing. Avoidspilling or splashing it on yourself or others.

□4.Observe and record the color of the solution inboth beakers.

□5.Place a straw in Beaker 2. As your partner keeps track ofthe time, gently blow through the straw into the solutionuntil the solution changes color. CAUTION: Use the strawto breathe out only. Do not inhale or suck the solutionback through the straw.Don’t chew gum, drink, or eat in the laboratory. Never taste a chemical in the laboratory. Your partner should begin timingwhen you first blow through the straw and stop as soonas the solution changes color. Record in the data table thetime it takes for the color to change.

□6.Empty the beakers and rinse them with water.

Part 2: Exercise and Carbon Dioxide

□7.In Part 1, you measured the carbon dioxide that you exhaled withoutexercising 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 toexercise, 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 andwarm water.

Data Table

Elapsed Time for Bromothymol Blue Solution to Turn Color
No exercise / Moderate Exercise / Strenuous Exercise
Beaker 1
Beaker 2

Analyze and Interpret Data

Identify Variables In Part 2, what variables did you need to control? Explain how you controlled those variables.

Develop a ModelYou cannot directly observe the amount of carbon dioxide that you exhale. How did you use bromthymol blue to measure the carbon dioxide?

Predict Did your results agree with your prediction in Step 7? Explain.

Draw Conclusions What is the relationship between exercise and theamount of carbon dioxide exhaled? Cite evidence from your results to support your answer.

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.)

Relate Structure and FunctionThe 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 expectto exist between heart rate and carbon dioxide production? Design anexperiment to test your hypothesis.