Cellular Respiration Inquiry
Introduction:
Respiration refers to two different but related processes: one is the active acquisition of gaseous
oxygen by an organism and the other is the release of energy from organic compounds within a cell.
The latter process, a chemical oxidation, is more commonly referred to as cellular respiration.
During this laboratory investigation you will measure the rate of cellular respiration under
different conditions. You will experimentally answer the following three questions:
• “Does cellular respiration occur in living pea seeds?”
• “Does cellular respiration occur at the same rate for germinating and dormant pea
seeds?”
• “Does cellular respiration occur at the same rate for pea seeds at 10°C and 25°C?”
You will also answer a fourth question of your own design, investigating the effect of another
variable of your choosing on the rate of cellular respiration.
The chemical equation for the complete oxidation of glucose is shown below. Note that oxygen is
required for this energy-releasing process to occur.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 686 calories of energy
The chemical formula gives some clues as to how you might study the rate of cellular respiration.
You could measure the consumption of oxygen (i.e., how many molecules of oxygen are consumed
when 1 molecule of glucose is oxidized?), the production of carbon dioxide (i.e., how many molecules
of carbon dioxide are produced when 1 molecule of glucose is oxidized?), or the consumption of oxygen
and the release of carbon dioxide (i.e., how many molecules of carbon dioxide are produced for every
molecule of oxygen consumed?).
In this laboratory exercise, you will measure the relative volume of oxygen consumed by
germinating and nongerminating pea seeds at two different temperatures over time.
In order to measure the volume of oxygen consumed over time you must eliminate all the carbon
dioxide produced by the reaction. In this experiment, the carbon dioxide will be removed by reacting
with potassium hydroxide (KOH) to form solid potassium carbonate (K2CO3).
CO2 + 2 KOH → K2CO3 + H2O
Therefore, if the temperature and volume in the experimental apparatus remain constant, any gas
volume change will be due to the amount of oxygen consumed. A control apparatus will be used to
detect any experimental results due to atmospheric pressure change or temperature change.
Materials
Plastic pan
Ice
Thermometer
100 ml graduated cylinder
Germinating peas
Dormant peas
Plastic beads
Test tubes (25 X 200 mm)
Stopper–pipette apparatus
Absorbent cotton
Pasteur pipette
KOH solution (15%)
Nonabsorbent cotton
Masking tape
Respirometer weights
Graph paper
Aprons
Black plastic
Procedure
Part A. Preparations
1. Before coming to class on the day of the experiment, propose and record hypotheses for each of
the problems being studied in this laboratory investigation. Be sure to include your rationale for
AP Biology Lab:
Cellular Respiration Inquiry
Page 2
each hypothesis. After studying the apparatus and procedures, write predictions for each
experiment.
2. Working with your group, develop a fourth experimental question to be investigated. Make sure
to write your hypothesis and rationale for your fourth question before coming to class on the
day of the experiment. Examples of student inquiries that have been conducted include (but are
NOT limited to):
• “Do sliced peas respire at a different rate than whole peas?”
• “Do boiled/frozen peas respire at a different rate than unboiled/unfrozen peas?”
• “Do peas treated with acid/base/salt solution respire at a different rate than
untreated peas?”
You are encouraged to develop your own experimental question for this investigation.
3. Both a room temperature bath and a 10°C bath should be set up immediately in plastic pans to
allow time to adjust each temperature. Add ice to attain the 10°C bath. (If your teacher assigns
different groups to only one temperature, you need only set up only one bath.) Add a piece of
black plastic to the bottom of each pan.
Part B. Determining Pea Volume
1. While the baths are equilibrating, obtain a 100 ml graduated cylinder and fill it with 50 ml of tap
water. Drop in 25 germination peas and determine their volume by measuring the amount of
water that was displaced. Record the volume of the 25 germinating peas, then remove them and
place them on a paper towel. They will be used in Respirometer 1a.
2. Refill the graduated cylinder with 50 ml of water. Drop 25 dormant peas into the graduated
cylinder and then add enough plastic beads to attain a volume equal to that of the germinating
peas. Remove the peas and beads and place them on a paper towel. They will be used in
Respirometer 2a.
3. Refill the graduated cylinder with 50 ml of water. Determine how many plastic beads alone are
required to attain a volume equal to the germinating peas. Remove the beads and place them on
a paper towel. They will be used in Respirometer 3a.
4. Finally, use the same procedure to create your 4a Respirometer mixture of peas and beads.
5. If you are investigating both temperatures, Repeat Procedures 1–4 above to prepare a second set
of germinating peas, dormant peas and beads, and beads only for use in Respirometers 1b, 2b,
and 3b respectively.
Table 1. Experimental protocol
Treatment
Apparatus 1a
Apparatus 2a
Apparatus 3a
Apparatus 4a
Room Temperature
Germinating seeds
Dry Seeds + Beads
Beads
Experimental
Peas/Beads
Treatment
Apparatus 1b
Apparatus 2b
Apparatus 3b
Apparatus 4b
10 C
Germinating seeds
Dry Seeds + Beads
Beads
Experimental
Peas/Beads
Part C. Setting up the Apparatus
1. To assemble the respirometers, obtain 8 test tubes (4 if your class is dividing experimental
treatments) and 8 (3) stoppers with attached pipette. Place a small wad of absorbent cotton in
the bottom of each test tube and, using a 1-ml pipette, saturate the cotton with 15% KOH
solution. Make sure that the respirometer tubes are dry on the inside; do not get KOH on the
sides of the respirometer. Place nonabsorbent cotton on top of the KOH-soaked absorbent
cotton.
2. Label the respirometer tubes with appropriate numbers and then place one set of germinating
peas, dormant peas and beads, and beads in Tubes 1a, 2a, and 3a respectively. (Place the
second set of germinating peas, dormant peas and beads, and beads in tubes 1b, 2b, and 3b
respectively if you are doing both temperature experiments.) Insert the stoppers fitted with
calibrated pipettes.
Adapted from a college board lab activity by Fred Brown, 2006, Modified by D Knuffke, 2011
Cellular Respiration Inquiry
AP Biology Lab:
Page 3
3. Make a sling of masking tape attached to each side of the water baths to hold the pipettes out of
water during an equilibration period of 5 minutes. Place the respirometers in the water bath.
(See Figure 1 below.) Attach weights to the respirometers according to your teacher's directions.
Respirometers 1a, 2a, 3a, & 4a should rest in the room temperature water bath and
Respirometers 1b, 2b, 3b, & 4b should rest in the 10°C water bath.
Figure 1: Respirometer Diagrams (experimental not shown)
Part D. Collecting Data
1. After an equilibration period of 5 minutes, immerse all respirometers entirely in their water
baths. Water will enter the pipettes for a short distance and then stop. (If the water continues
to move into a pipette, check for leaks in the respirometer.) Working swiftly, arrange the
pipettes so that they can be read through the water at the beginning of the experiment. They
should not be shifted during the experiment. Keep your hands out of the water bath after the
experiment has started. Make sure that a constant temperature is maintained.
Figure 2. Respirometers in the water bath (experimental not shown)
2. Allow the respirometers to equilibrate for 30 seconds and then record, to the nearest 0.01 ml,
the initial position of water in each pipette (time = 0). Check the temperature in both baths.
Record the changes in the water's position in each pipette every 5 minutes for 20 minutes.
Data can be recorded in a table similar to Table 2 below.
Table 2. Measurement of oxygen consumption by germinating and dormant pea seeds at room
temperature (~25° C) and at 10° C using volumetric methods (Note: Experimental
Data Not Shown).
Adapted from a college board lab activity by Fred Brown, 2006, Modified by D Knuffke, 2011
Cellular Respiration Inquiry
AP Biology Lab:
Tem
p.
(°C)
Time
(min.)
0
Beads Alone
Reading
(ml)
Diff.*
at time
X
Page 4
Germinating Peas
Reading
(ml)
Diff.* Corrected
at time
X
Dormant Peas
Reading
(ml)
Diff.* Corrected
at time
X
0
0
0
0
0
0
Experimental
Reading
(ml)
at time
X
Diff.*
Corr.
0
0
0
0
0
0
5
25
10
15
20
0
5
10
10
15
20
3. Share data with other class teams.
4. On the same set of axes, graph the results for germinating peas, dormant peas, at both room
temperature and 10°C, along with your experimental set up (at both temperatures if possible).
Be sure to put the independent and dependent variables on the correct axes. From the graphs,
determine the rate of oxygen consumption of germinating and dormant peas at each
temperature.
In Conclusion:
1. Restate all of your hypotheses and discuss the results of your experiments as relates to the
support or refutation of those hypotheses.
2. Do you have reason to doubt your data in any of your experiments? Provide any explanation as
to why or why not.
3. Would you expect a difference in cellular respiration rate between germinating and dormant pea
seeds? Explain your reasoning.
4. Would you expect a difference in cellular respiration rate between pea seeds at different
temperatures? Explain your reasoning.
5. Explain any differences that you see in the rate of cellular respiration in your fourth tube (the
experimental tube) as compared to tubes 2 and 3. Propose explanations as to why these
differences, or lack of differences are demonstrated.
6. Don’t forget to include discussion of modifiying the experiment, and further avenues of
investigation.
Analysis Questions (following Conclusion):
1. Why was it necessary to equalize the pea volumes in each respirometer?
2. Why were plastic beads used to equalize the dormant pea volumes instead of using more peas?
3. Why was it important not to leave potassium hydroxide (KOH) on the test tube sides?
4. Why was it necessary to absorb all of the carbon dioxide produced by the reaction?
5. What function did Respirometers 3 and 6 serve?
6. Students often get pressure changes in Respirometers 3 and 6. Would you predict such a change
for inert plastic beads? What could cause this change?
Adapted from a college board lab activity by Fred Brown, 2006, Modified by D Knuffke, 2011
AP Biology Lab:
Cellular Respiration Inquiry
Page 5
Teacher Notes:
Materials:
1. 15% KOH – 37.5 g KOH brought to 250 ml with distilled water
2. Pea Seeds – 25 germinating pea seeds / team; same for nongerminating (~ 100 peas at 30 ml mark on a 50 ml
beaker) [Order info: one pound of peas / year is more than sufficient]
3. Respirometer weights – Use water-filled specimen dishes with equilibrated water
Suggestions:
1. Must germinate peas a few days in advance (soak overnight; then roll in moist paper towels for the next night in
26°C incubator)
2. Can set up room temperature baths the night before to equilibrate
3. Get ice from the cafeteria
4. Divide class into teams of 25°C or 10°C experiment; one–half on one side of the room, the other on the other half.
5. Remind students that if they need to turn the apparatus under water to better read the pipette, only touch the pipette,
not the test tube. Touching the test tube will change the temperature of the apparatus and, thus, the pressure in the
pipette.
6. Use extra long forceps to clean cotton out of tubes
Results:
1. See APB Lab Manual
Notes:
1. Written by Fred Brown, AP Biology Teacher and APB Consultant [FredBrown3@aol.com]
2. Last revised: 6/06
Adapted from a college board lab activity by Fred Brown, 2006, Modified by D Knuffke, 2011