The Effect of Exercise on Respiration

Safety: Put on a lab apron and goggles. Handle all glassware carefully. Always use special caution when working with laboratory chemicals as they may irritate the skin or cause staining of the skin or clothing. You will be exercising during this investigation. If at any time you feel faint or dizzy sit down and immediately call your teacher.

Introduction: Respiration is the process by which food molecules are broken down to release energy. The human body obtains energy through cellular respiration, which uses oxygen, breaks down sugars and produces waste products of carbon dioxide and water. In humans, blood carries the carbon dioxide to the lungs where it is released from our bodies through exhalation.

Carbon dioxide dissolves in water to form carbonic acid. Water will become more acidic as more carbon dioxide is added. As a result, phenolphthalein, an indicator solution, can be used to show the presence of carbon dioxide in water. An acidic solution can then be neutralized with a base such as sodium hydroxide. By knowing the amount of sodium hydroxide needed to neutralize the acid, you can determine the amount of carbon dioxide in the solution.

Pre-Lab Questions:

1  Write the general equation for respiration, which shows carbon dioxide as a waste product. Within which cellular organelle does this process occur?

2  Why would human muscle cells contain many more of this organelle than skin cells?

3  Discuss what would happen to the pH of cells if the carbon dioxide was not carried away from the cells by the circulatory system and exhaled after being passed into the lungs?

4  Name the process that allows muscle cells to continue to provide (release) small amounts of energy in the absence of sufficient oxygen. Explain this process, including its effects on the body.

Materials:

Stop watch/clock 0.6% NaOH in a dropping bottle

Soda Straws Masking tape

2 200 mL flasks Phenolphthalein solution

Rubber stopper 100 mL graduated cylinder

Procedure:

1  Fill two 200 mL flasks half full with water or measure out 100 mL in a graduated cylinder and pour it into the flask. Label one flask as a control and place a rubber stopper at the top.

2  Add five drops of phenolphthalein to each flask. If the water doesn’t turn pink, add sodium hydroxide to the water drop by drop until you obtain a light pink color. Swirl the container gently between the additions of each drop of sodium hydroxide.

3  The first trial is done to examine how much carbon dioxide is produced before exercising. Insert a straw into the other flask and blow gently into the water for 20 seconds. Try to breathe normally, but exhale slowly so that you do not splash the solution out of the flask. (You may need to take one breath during the 20 second interval.) What color change do you observe?

4  Add sodium hydroxide to the flask, drop by drop, and swirl gently to mix. Try not to touch the straw with a dropper. Count the number of drops of sodium hydroxide needed to restore the pink color, comparing the color of the solution to that in the control flask. Record the number of drops of sodium hydroxide for all trials in the table.

5  Trial 2 involves minimal exercise. Jog in place for 1 minute and repeat steps 3 & 4.

6  Trial 3 involves moderate exercise. Jog in place for 2 minutes (make this a vigorous activity) then repeat steps 3 & 4.

7  Trial 4 requires moderate exercise for a longer period of time. Jog for 3 minutes (maintain a vigorous effort); then repeat steps 3 & 4.

8  If time permits continue with trial 5 by jogging for 4 minutes repeating steps 3 & 4.

Results:

Trial 1
Resting Stage / Trial 2
1 min jog / Trial 3
2 min jog / Trial 4
3 min jog / Trial 5
4 min jog
Drops of NaOH added

Analysis Questions:

1  Graph your data. Label the horizontal and vertical axes, including approximate units. Draw a best fit line. Title your graph.

2  What does the color change in step 4 indicate?

3  What is the function of the sodium hydroxide in the lab?

4  How did the carbon dioxide production change as the level of exercise was increased?

5  Use the graph to predict the amount of carbon dioxide that would be produced at the end of six minutes of exercise. Express your answer in terms of the number of drops of sodium hydroxide added.

6  Why is carbon dioxide produced in cells during exercise? What evidence supports this?

7  Describe the relationship between exercise and carbon dioxide production.

8  How does aerobic and anaerobic respiration differ?