Lab: Feel the Burn
Purpose: To examine what factors affect cellular respiration.
Background Information:
Under normal circumstances your body turns glucose (sugar) into ATP (energy) using oxygen through a series of
steps called aerobic (cellular) respiration. Normally after glycolysis, if enough oxygen is present, pyruvic acid (the
chemical by-product after glucose is broken down) will be taken into mitochondria and be further broken down to
produce ATP through the Krebs cycle and electron transport chain. However, when your muscles are working
extremely hard they can’t get enough oxygen to carry out aerobic respiration. For example, walking up ten flights
of stairs, doing pushups, or other forms of intense activities. Fortunately your body can turn sugar into energy
without oxygen. This process is called anaerobic respiration. Lactic acid is produced in your muscles during rapid
exercise when the body cannot supply enough oxygen to the tissues. Your muscle cells rapidly begin to produce
ATP by lactic acid fermentation. The buildup of lactic acid causes a painful, burning sensation. This is why your
muscles feel sore after only a few seconds of intense activity. The increased lactic acid can be removed primarily by
getting more oxygen into your muscle cells. The oxygen can oxidized the lactic acid back into pyruvate and than
the pyruvate can be used to fuel the Krebs cycle.
Pre-lab Questions: Answer the following questions in complete sentences, restating the question within
your answer.
1. For aerobic respiration to occur, what molecule must be present within the cell?
2. What is the difference between aerobic and anaerobic respiration?
3. During strenuous exercise, what is the burning sensation that an individual begins to feel? In order for this
burning sensation to disappear what molecule do you need to get into the body?
4. Based on the questions above and reading the background information, what is the major factor that affects
the process of cellular respiration?
Hypothesis: If we continually use our muscles, than the lactic acid that builds up will ________________________ (not
affect or affect) our performance of opening and closing the clothespin.
Materials:
Two fingers, clothespin, clock
Procedures:
1. You will work with a partner during this activity. One will perform the experiment, while the other acts as a
time keeper.
2. Use your thumb and index finger to open and close a clothespin as fast as you can in 30 seconds. Count the
number of times you are able to close the clothespin. Write down this number.
3. Repeat step 2 for four more times. You are doing 5 trials total. DO NOT REST between the trials. Make sure
that your partner writes down the number of times that you open and close the clothespin every 30
seconds.
4. Switch roles and repeat the experiment.
5. Write the data from all the members from your group and create a line graph.
Lab: Feel the Burn
Data: (copy down and fill into your science notebook)
Time (in seconds)
Group Members
30
60
90
120
150
Graph:
Graph your group’s data using a line graph. The x-axis will be the Time (in seconds) and the y-axis will be Muscle
Performance (# of times clothespin was opened). Reference your notes to see what to include on your graph.
Analysis Questions: (You do not have to copy as long as you restate the question in your answer)
1. What trend did you notice about the amount of times you were able to open and close the pin as time
continued?
2. What is lactic acid fermentation? What other activities can cause lactic acid build up?
3. Would lactic acid fermentation be considered aerobic or anaerobic respiration? Why?
4. What are possible sources of error in today’s lab?
5. What was the purpose of today’s lab? Why did we perform this experiment and how does it tie into cellular
respiration?
Conclusion Paragraph: (copy down and fill in based on your data collected)
During this lab the data showed that lactic acid __________________ (did have/ or did not have) an effect on muscle
performance. My hypothesis that lactic acid (will have/ will not have) an effect on muscle performance was
_________________ (supported/not supported) by the data collected.. In the first trial, I was able to open and close the
clothes pin ______ times, in trial two______ times, in trial three _____ times, and in the fourth trial _____ times and in the
last trial ______ times. From examining the data collected we can see the trend that as the experiment progressed,
the number of times opening and closing the clothes pin __________ (increased/decreased). This shows that lactic
acid build up in the muscles ___________________ (does/ does not) have an effect on muscles performance.