Observing Respiration
Introduction: All living things undergo respiration. During this process, food
molecules are broken down to produce energy for cells. As part of this process,
animals take in oxygen and release carbon dioxide by breathing. Plants do not
“breathe” as animals do, so respiration is not as easily observable. How do we know
that plants respire?
Problem: Do plants release carbon dioxide as a product of respiration?
Materials:
bromthymol blue indicator (in beaker)
beaker (to hold test tubes)
aluminum foil
10 radish seedlings
3 test tubes with caps
tape
cotton ball
straw
Safety:
Wear safety goggles during the entire lab.
Do not swallow the indicator solution. (Use care when blowing through the straw.)
Procedures:
1. Pour equal amounts of bromthymol blue indicator solution into each of the test tubes
(about ¼ full). Label the test tubes 1, 2, & 3 using either masking tape or a pencil.
2. In test tube #1, use a straw to blow a few times into the liquid. Be sure not to inhale.
You should see a color change indicating the presence of carbon dioxide in the
solution. Throw away the straw when finished.
test tube #1
test tube #2
3. In a test tube # 2, place ½ a cotton ball and the radish seedlings as shown above.
4. In the test tube #3, simply leave the solution as is.
5. Make sure the tops are on all three test tubes and cover each test tube with aluminum
foil. Place all three in your beaker to sit for 24 hours. Make sure that your beaker is
labeled (you can use masking tape) before placing it in the class tray.
6. Be sure to clean up all materials. Your labeled beaker goes into the class tray.
Name:_______________________ Period:___
Observing Respiration Lab Answer Sheet
Answer all questions below. Each person should turn in their own answers.
Day 1:
1. What color did the bromthymol blue indicator turn when carbon dioxide was added
(test tube #1)? __________________________________________________________
2. Hypothesis: 10 radish seedlings were placed in test tube #2. What do you expect to
happen as the test tube sits for 24 hours? ____________________________________
Why? ________________________________________________________________
3. Why cover the test tubes with aluminum foil? ______________________________
_________________________________________________________________
4. What purpose does test tube #3 serve (the one left as is)? ______________________
_________________________________________________________________
Bring your answers to class tomorrow to finish the lab.
Day 2:
1. Observe your test tubes and fill in the following table:
test tube
description of contents
color of indicator
solution
1
2
3
2. Did the color of the indicator change in the test tube that contained the radish
seedlings? ____________________________________________________________
Explain the reason.______________________________________________________
3. Compare the reaction that occurred in the test tube that contained the radish
seedlings (test tube #2) with the one that occurred in the test tube into which you
exhaled (test tube #1). How are they similar? _________________________________
_________________________________________________________________
4. How might your results been affected if you had used more seedlings or fewer
seedlings? _____________________________________________________________
6. Why is the process of cellular respiration common to all forms of life? ___________
_________________________________________________________________