Scientific Method and Collecting Data
Name:
Biology 6.0
Date:
Period:
The Effects of Exercise on Cellular Respiration
BACKGROUND INFORMATION
Chemical indicators change colors as the pH of the solution changes. Bromothymol blue is a chemical indicator
that is yellow in acidic solutions and blue in basic and neutral solutions. When carbon dioxide (CO2) is
dissolved in water, it creates carbonic acid (H2CO3), which has a pH ~5.7. This reaction occurs in rainwater
absorbs carbon dioxide.
Cellular respiration (see chemical reaction below) is a chemical reaction that occurs in your cells to create
energy (ATP). When you are exercising your muscle cells are creating ATP to contract. Cellular respiration
requires oxygen (which is breathed in) and creates carbon dioxide (which is breathed out).
C6H12O6 + 6O2  6H2O + 6CO2 + 36 ATP
One of the products of cellular respiration is carbon dioxide. As cells produce CO2 in cellular respiration, it is
carried by our blood cells to our lungs where it is exhaled. You can measure the rate your cells carry out
cellular respiration by measuring how quickly you produce CO2. You will first determine your resting rate of
cellular respiration, and then you will determine your rate after exercise.
PRELAB:
1. Describe the purpose of the lab?
2. Develop a hypothesis – how will exercise affect the rate of cellular respiration.
3. Write an abbreviated procedure.
4. Create data tables to record the information in the procedure.
MATERIALS:
 Stopwatch
 Drinking straw
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Bromothymol blue solution
2 – 250 mL beakers
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Graduated cylinder
Safety goggles
PROCEDURE:
1. Fill the beaker with 40 mL distilled water and 10 mL bromothymol blue solution.
2. Assign one person to be the timer and one person to perform the experiment.
3. When the timer says “start”, the experimenter will exhale through the straw into the bromothymol blue
solution until the color changes from blue to green (greenish-yellow). DO NOT INHALE THE
SOLUTION! EXHALE FROM YOUR LUNGS!
4. Your partner will stop the time as soon as the color changes.
5. Record the time it took for the color change to occur.
6. Rinse out the beaker, and refill with 40 mL of distilled water and 10 mL of bromothymol blue solution.
7. Now have the experimenter do exercise (jumping jacks, running in place) for 30 seconds.
8. Using the same straw, exhale into the solution the same way as in step #3 and record how long it takes
for the solution to change color.
9. Rinse out the beaker, and refill with 40 mL of distilled water and 10 mL of bromothymol blue solution.
10. Now have the experimenter do exercise (jumping jacks, running in place) for 1 minute. You should feel
winded when you are finished!
11. Using the same straw, exhale into the solution the same way as in step #3 and record how long it takes
for the solution to change color.
12. Clean up - throw out straws, clean beakers with soap and water, wipe down lab tables, wash your hands.
No straws or paper towels should be left in the sink. Make sure clean beakers get placed back into the
lab drawers.
ANALYSIS AND CONCLUSION
Answer the questions below using background information in the lab, as well as your lab data. Answer the
questions in complete sentences in your lab notebook.
1. Make a graph of your results. Determine if the graph should be a line graph or a bar graph. Carefully
decide which variable belong on the X-axis and Y-axis. Be consistent with numbering the axes and the
number of blocks between the increments. Remember to label the axes and provide a title for your
graph.
2. Using your GRAPH, predict the time of color change if the experimenter did exercise for 2 minutes.
3. Explain why the color change occurred in the bromothymol solution.
4. Compare the time it took the bromothymol blue solution to change color before exercise and after
exercise. Explain why there was a difference including the data.
5. What can you conclude about the effect of exercise on the amount of carbon dioxide that is present in
your exhaled breath? Why is this so?
6. What can you conclude about the effect of exercise on breathing rate and heart rate? Why is this so?
7. Explain why it is so important to exhale completely when doing exercise?
8. State whether your hypothesis was correct or incorrect and why. In doing so, discuss what you think is
going on in the muscles of the body as muscle activity is increased. Address the need to get oxygen to
the muscles and get rid of carbon dioxide, as well as how the muscles cells get the energy needed to
continue contracting.
ANALYZE AND APPLY:
1. Make a graph of your results.
a. Determine if the graph should be a line graph or a bar graph.
b. Carefully decide which variables belong on the X and Y axis.
c. You must include a detailed title (not just X vs. Y).
d. Label the X and Y axes.
2. What is the pH scale? What pH is considered neutral? An acid? A base?
3. How is breathing related to cellular respiration?
4. Compare the time it took the bromothymol blue solution to change color before exercise and after
exercise. Explain why there was a difference.
5. Using your graph, predict the time of color change if the experimenter did exercise for 2 minutes.
6. How did bromothymol blue help you measure your rate of cellular respiration?
7. Explain why it is important to exhale completely when doing exercise.