“Why So Tired?”
Objectives:
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Analyze the storage and release of energy through the process of cellular respiration.
Examine the relationship between exercise and fatigue as it relates to energy production in the presence
or absence of oxygen.
Define the processes that occur when oxygen is not present in the cell and aerobic respiration converts to
lactic acid fermentation.
Background:
Your body’s cells are not designed to store large amounts of oxygen for cellular respiration. During
normal activities, the amount of oxygen that is provided by breathing is sufficient, such as while you are
talking to friends or walking from class to class. However, when you are doing high levels of activity,
such as sprinting downfield for a ball, or running to pick up a drop shot, your body cannot bring oxygen
in fast enough for your cells, even though you breathe faster. So what happens in your cells?
Muscle cells prefer to use aerobic respiration as much as possible, but when they are short of oxygen
supplies, some anaerobic respiration inevitably occurs. During a sprint, human muscles can respire
anaerobically. Anaerobic respiration in humans is less efficient than aerobic respiration at releasing
energy, but releases energy faster. This explains why humans can run faster in a sprint than over longer
distances. Unfortunately, lactic acid is produced and accumulates until the muscles cannot continue
working.
Materials:
Stopwatch
1000 mL bromothymol blue
250 mL erylenmeyer flask
straw
Procedure for Student 1:
1. Student one will do as many calf raises as possible within a 20 second period. A calf raise is an exercise
where the student stands straight, feet hip width apart. The student will raise his/her heels until he is on
his tiptoes. Lower and repeat. The other student will record this information in the data table. Student
one will repeat this process ten times over a period of two minutes for ten seconds each, each time
recording the number of raises within the ten seconds.
2. Create a graph of the number of calf raises performed per trial on your data sheet and answer questions 1
and 2.
Procedure for Student 2:
Students need to use extreme caution when exhaling into the BTB. An Erlenmeyer flask is best utilized
to minimize splashing. Students must remove their mouth from the straw while inhaling and use care
to ONLY exhale through the straw.
Bromthymol Blue: Potential Acute Health Effects:
Very hazardous in case of ingestion. Hazardous in case of skin contact (irritant), of eye contact (irritant), of
inhalation. Slightly hazardous in case of skin contact (permeator).
Eye Contact:
Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for
at least 15 minutes. Cold water may be used. Get medical attention.
Skin Contact:
In case of contact, immediately flush skin with plenty of water. Cover the irritated skin with an emollient.
Remove contaminated clothing and shoes. Cold water may be used. Wash clothing before reuse. Thoroughly
clean shoes before reuse. Get medical attention.
Ingestion:
Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an
unconscious person. If large quantities of this material are swallowed, call a physician immediately. Loosen
tight clothing such as a collar, tie, belt or waistband.
http://www.sciencelab.com/msds.php?msdsId=9927468
3. Fill an Erlenmeyer flask with 100mL of bromthymol blue (btb) solution. Using a drinking straw exhale
through the straw using normal breaths. (Exercise caution not to swallow any of the liquid!) Continue to
count your breaths through the straw until the liquid in the beaker changes from blue to yellow. Record
the number of breathes required for this color change in the chart below.
4. Refill your flask with a fresh 100 mL of btb solution. Complete as many jumping jacks as possible in a
10 second period. Using the straw, exhale until the solution has turned yellow. Record your number of
breathes. Try to breathe normally. Continue to repeat this process for a total of 10 trials in a 2 minute
period.
5. Create a graph of the number of breathes required per trial on your data table. Answer questions 3 and 4.
Name ____________________________
Data Sheet: Why so tired?
Part 1
Student 1 Data: Calf Raises
Trial #
# of calf raises
1
2
3
4
5
6
7
8
9
10
1. What has happened to the number of raises per trial over the 10 trial period?
2. Write out a hypothesis in the space below for why this may be so:
3. Did you or your partner complain of feeling a burn in his or her muscles? What do you think is
happening?
Part 2
Student Data: Number of Breaths
Trial #
# of breaths to turn yellow
1
2
3
4
5
6
7
8
9
10
4. What has happened to the number of breathes per trial over the 10 trial period?
5. Write a hypothesis for why this may be so in the space below.