Cell Respiration
Cellular respiration refers to the process of converting the chemical energy of organic molecules
into a form immediately usable by organisms. Glucose may be oxidized completely if sufficient
oxygen is available, by the following equation:
C6H12O6 + 6O2(g) 6 H2O + 6 CO2(g) + energy
All organisms, including plants and animals, oxidize glucose for energy. Often, this energy is
used to convert ADP and phosphate into ATP.
To measure the rate of cellular respiration, the pressure change due to the consumption of oxygen
by beans will be measured with a bio-pressure sensor. It is not possible to directly measure
pressure changes due to oxygen, since the pressure sensor measures the total pressure change.
Carbon dioxide is produced as oxygen is consumed. The pressure due to CO2 might cancel out
any change due to the consumption of oxygen. To eliminate this problem, a chemical will be
added that will selectively remove CO2. Potassium hydroxide, KOH, will chemically react with
CO2 by the following equation:
2 KOH + CO2 K2CO3H2O
This will allow you to monitor pressure changes that are exclusively due to the consumption of
oxygen.
A respirometer is the system used to measure cellular respiration. Pressure changes in the
respirometer are directly proportional to a change in the amount of gas in the respirometer,
providing the volume and the temperature of the respirometer do not change. If you wish to
compare the consumption of oxygen in two different respirometers, as we will in this experiment,
you must keep the volume and temperature of the air equal in each respirometer.
Both germinating and non-germinating beans will be tested.
OBJECTIVES
In this experiment, you will
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use a CBL and gas pressure sensors to measure pressure changes.
determine whether germinating beans respire.
determine whether non-germinating beans respire.
determine whether germinating beans respire differently than non-germinating beans.
compare the rates of cellular respiration in germinating and non-germinating beans.
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MATERIALS
CBL System
TI Graphing Calculator
2 Vernier Biology Gas Pressure Sensors
2 Vernier DIN adapter cables
15% KOH in a dropper bottle
100 germinating mung beans
100 non-germinating beans
100-mL graduated cylinder
absorbent cotton
forceps
2 utility clamps
glass beads
non-absorbent cotton
thermometer
test tube rack
timer with a second hand
28 X 150 mm test tubes
two 1-hole rubber stopper assemblies
1-L beakers
ringstand
Graphical Analysis (optional)
Figure 1
PROCEDURE
1. Obtain and wear goggles.
2. Connect the CBL and calculator with the link cable using the port on each unit. Firmly press
the cable ends into each port.
3. Prepare the Biology Gas Pressure Sensors for data collection.
Plug the gas pressure sensors into the adapter cable in Channel 1 and Channel 2 of the
CBL. A rubber-stopper assembly has already been connected to each of the gas pressure
sensors as shown in Figure 1.
 Open the gas pressure sensor valves so the rubber stopper assemblies are open to the
atmosphere. Align the blue handle with the arm that leads to the gas pressure sensor, as
shown in Figure 2. The handle of the valve will always point to the arm that is closed off.
In Figure 2, the pressure sensor is closed off from the test tube and the atmosphere. Any gas
generated in the test tube will be vented into the air.
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to pressure
sensor
Figure 2
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4. To test whether germinating beans undergo cellular respiration, you will need to
  water bath.
 prepare a respirometer for the germinating beans.
 prepare a second, control respirometer containing glass
beads.
5. Set up a water bath at about 25°C . Obtain a 1-liter beaker and place about 800 mL of water. .
6. To be sure the volumes of air in the respirometers are equal, you will need to measure the
volume of the 100 mung beans that will be in the experimental respirometer. The control
respirometer must have an equal volume of glass beads (or other non-oxygen consuming
material) to make the air volume equal to the respirometer with germinating beans. Similarly,
glass beads will be used to account for any volume difference between the germinating and
non-germinating beans.
7. Obtain three test tubes and label them “T1”, T2”, and “T3”.
8. Place a small wad of absorbent cotton in the bottom of each test tube. Using a dropper
pipette, carefully add a sufficient amount of 0 to the cotton to completely saturate it. Do not
put so much that liquid can easily run out of the tube. Note: Do not allow any of the KOH to
touch the sides of the test tube. The sides should be completely dry, or the KOH may damage
the beans. Important: Potassium hydroxide, KOH, is a strong base and should be handled
with extreme caution.
9. Prepare the test tube containing germinating beans (T1):
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Add 50 mL of water to a 100-mL graduated cylinder.
Place 100 germinating mung beans into the water. Add additional beans to bring the
volume up to about 65 mL.
Measure the volume of the beans by water displacement. Record that volume in Table 1.
Gently remove the beans from the graduated cylinder and blot them dry with a paper towel.
Add a small wad of non-absorbent dry cotton to the bottom of the test tube to prevent the
beans from touching the KOH saturated cotton.
Add these germinating beans to the respirometer labeled “T1”.
10. Prepare the test tube containing non-germinating beans (T2):
Refill the graduated cylinder with 50 mL of water.
Place 100 non-germinating beans as into the water.
Measure the volume of the beans by water displacement. Record the volume in Table 1.
Add a sufficient number of glass beads to the non-germinating beans and water until they
displace exactly the same volume of water as the germinating beans.
 Gently remove the beans and glass beads from the graduated cylinder and dry them with a
paper towel.
 Add a small wad of dry non-absorbent cotton to the bottom of the test tube to prevent the
beans from touching the KOH saturated cotton.
 Add the non-germinating beans and glass beads to the respirometer labeled “T2”.
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11. Prepare the test tube containing glass beads (T3):
Refill the graduated cylinder with 50 mL of water.
Add a sufficient number of glass beads to the water until they displace exactly the same
volume of water as the germinating beans.
 Remove the glass beads from the graduated cylinder and dry them.
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Add a small wad of dry non-absorbent cotton to the bottom of the test tube to prevent the
beans from touching the KOH saturated cotton.
 Add the glass beads to the respirometer labeled “T3”.
12. Connect the pressure sensor in Channel 1 to test tube T1. Securely fit the rubber stopper
assembly into test tube T1 to be sure there is no air leakage. Connect the pressure sensor in
Channel 2 to test tube T3, the control.
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Part I Germinating beans
13. Arrange test tubes T1 and T3 in the water bath using the apparatus shown in Figure 1. Allow
them to equilibrate with the temperature of the water bath for 8-10 minutes. Be sure the tubes
are submerged to an equal depth, just up to the rubber stoppers. Record the final resulting
temperature of the water bath in Table 2.
14. Turn on the CBL unit and the calculator. Start the CHEMBIO program and proceed to the MAIN
MENU.
15. Set up the calculator and CBL for two biology gas pressure sensors.
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Select SET UP PROBES from the MAIN MENU.
Enter “2” as the number of probes.
Select MORE PROBES from the SELECT PROBE menu.
Select BIO PRESSURE from the SELECT PROBE menu.
Enter “1” as the channel number.
Select USE STORED from the CALIBRATION menu.
Select ATM from the PRESSURE UNITS menu.
Select MORE PROBES from the SELECT PROBE menu.
Select BIO PRESSURE from the SELECT PROBE menu.
Enter “2” as the channel number.
Select USE STORED from the CALIBRATION menu.
Select ATM from the PRESSURE UNITS menu.
16. Set up the calculator and CBL for data collection.
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Select COLLECT DATA from the MAIN MENU.
Select TIME GRAPH from the DATA COLLECTION menu.
Enter “12” as the time between samples, in seconds.
Enter “99” as the number of samples
Press ENTER , then select USE TIME SETUP to continue.
Enter “0.9” as the minimum pressure (Ymin).
Enter “1.06” as the maximum pressure (Ymax).
Enter “0.01” as the pressure increment (Yscl). When the test tubes have been in the water
bath for 8-10 minutes proceed to Step 17.
17. Close the air valves on the pressure sensors. Align
the blue handle with the side stem, as shown in
Figure 3.
Figure 3
18. Start measuring the pressures by pressing ENTER on the calculator. Monitor the temperature
of the water bath. The temperature should not change by more than a few °C. To maintain
water bath temperature, add hot or cold water as needed. Be sure to remove an equal amount
of water with a turkey baster or Beral pipet before you add water to the beaker, or it may
overflow.
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19. After 20 minutes, the CBL will stop taking measurements.
20. Once data collection has stopped, “SAMPLING” will change to “DONE” on the CBL screen. A
message will be displayed on the calculator indicating the data lists in which the time and
pressure data are stored.
21. Press ENTER to display a graph of pressure vs. time on the calculator screen. As you move the
cursor right or left, the time (X) and pressure (Y) values of each data point are displayed
below the graph.
22. Press ENTER on the calculator and a message will appear asking if you want to repeat the
experiment. Select NO to return to the main menu. Select QUIT from the MAIN MENU to exit
the CHEMBIO program.
23. To account for any pressure changes due to experimental error, it is necessary to create a new
data column. This new column will consist of the experimental data subtracted from the
control data. Press 2nd L3 Π 2nd L2 STO 2nd L4, then press ENTER . The adjusted pressure
is now stored in list L4.
24. Start the CHEMBIO program and proceed to the MAIN MENU.
25. The rate of respiration can be measured by examining the slope of the adjusted pressure vs.
time plot. Perform a linear regression to calculate the slope:
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Select FIT CURVE from the MAIN MENU.
Select LINEAR L1,L4 (c1,c4 on the TI-92) from the REGRESSION MENU.
The linear-regression statistics for these two lists are displayed for the equation in the form:
Y=AX+B
 Enter the slope, A, as the rate of oxygen consumption by germinating beans in Table 3.
26. Plot a graph of the data and the regression curve.
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Select SCALE TO DATA to view a graph of the data and the regression line.
Press ENTER to return to the MAIN MENU.
Part II Non-germinating beans
27. Open the air valves on the pressure sensors as shown in Figure 2. Remove test tube T1 and
replace it with test tube T2. Be sure the stoppers are firmly in place for an airtight fit.
28. Repeat Steps 16 – 26, substituting test tube T2 for test tube T1.
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DATA
Table 1
Beans
Volume (mL)
Germinating
Non-germinating
Table 2
Water bath
Temperature (°C)
room temp
Table 3
Beans
Rate of O2 consumption (atm/s)
Germinating
Non-germinating
QUESTIONS
1. Do you have evidence that cellular respiration occurred in beans? Explain.
2. What is the effect of germination on the rate of cellular respiration in beans?
3. What was the role of the control respirometer in each series of experiments?
4. Why do germinating beans undergo cellular respiration?
5. If this experiment were run for 24 hours, what would the germinating bean graph look like?
6. If this experiment were run at 0 0 C, what difference would you see in the rate of respiration?
Why?
EXTENSIONS
1. Compare the respiration rate among various types of seeds.
2. Compare the respiration rate among seeds that have germinated for different time periods,
such as 1, 3, and 5 days.
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3. Compare the respiration rate among various types of small animals, such as insects or
earthworms.
This experiment is adapted from Experiment 11, Cell Respiration, from Biology with CBL, by Scott Holman and
David Masterman, Vernier Software Co., 1997, p 11-1 to 11-6.
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