AP Biology
AP Lab Six: Cell Respiration
Name_________________________________________
This lab will work with seeds that are living, but dormant. When the necessary conditions are met,
germination occurs in seeds and the rate of cellular respiration greatly increases. In this lab, you will
measure oxygen consumption during germination and the rates of respiration at different temperatures.
Procedure
1. Set up two baths: one, at room temperature, the other at 10°C. Add ice if necessary.
2. Obtain a 100-ml graduated cylinder and fill it with 50 mL of water. Drop 25 germinating peas in
the graduated cylinder and determine the amount of water that was displaced (this is equivalent
to the volume of peas). Record the volume of the 25 germinating peas below. Remove these
peas and place them on a paper towel. They will be used in respirometer #1.
Pea Volume____________________ mL
3. Refill the graduated cylinder with 50 ml of water. Drop 25 dried peas in the cylinder, then add
enough glass beads to attain a volume equivalent to that of the germinating peas. Remove these
peas and beads and place them on a paper towel. They will be used in respirometer #2.
4. Refill the graduated cylinder with 50 mL of water. Determine how many beads would be
required to attain a volume equivalent to that of the germinating peas. Remove these beads and
place them on a paper towel. They will be used in respirometer #3.
5. Repeat steps 2-4 to prepare a second set of germinating peas, dry peas plus beads, and beads
for use in respirometers 4, 5, and 6, respectively.
6. Assembling the respirometers:
a. Obtain six vials, each with an attached stopper and pipette.
b. Place a small piece of cotton in the bottom of each vial and, using a dropper, moisten
the cotton with 5 drops 15% potassium hydroxide (KOH). Make sure the respirometer
vials are dry on the inside. Do not get KOH on the sides of the respirometer.
c. Place a small wad of nonabsorbent cotton on top of the KOH-soaked cotton. **IT IS
IMPORTANT THAT THE AMOUNT OF COTTON AND KOH ARE THE SAME FOR EVERY
RESPIROMETER**
7. Place the sets of peas and beads in the respirometers according to the following key
a. Respirometer #1 and #4: Germinating peas
b. Respirometer #2 and #5: Dry peas and beads
c. Respirometer #3 and #6: Beads only
8. Insert the stoppers fitted with the calibrated pipettes. The pipette tips should be facing out.
Place a weighted collar on each end of the vial.
9. Make a sling of masking tape across the water bath. The masking tape will hold the pipettes out
of the water.
10. Place vials 1, 2, and 3 in the room-temperature water bath. Place vials 4, 5, and 6 in the cold
water bath. Let the pipettes sit on the masking tape bath for seven minutes.
11. During the seven minutes, using a small pipette or food coloring container, place a small amount
of food coloring on the tip of each pipette.
12. After seven minutes are up, immerse all six respirometers entirely in their water bath. Water
will enter the pipettes for a short distance, then stop. If the water continues to move in, the
respirator has a leak. As soon as you submerge the respirometers, quickly turn them so that
you can read the measurements on the pipette.
13. Wait three more minutes to allow the respirometer to equilibrate. Then begin recording in table
6.1, to the nearest .01 mL, the initial position of water in each pipette (use the food coloring as a
reference). Check the temperature in the baths and record in table 6.1.
14. Every five minutes for 20 minutes, take readings of the water positions in each pipette and
record the data in table 6.1.
Post-Lab Questions
1. This lab contains a negative control group (a test that is guaranteed to provide no data). Which
group is the negative control group?
2. What is the purpose of taking a “corrected difference” instead of just a “difference”?
3. What is the effect of germination (vs non-germination) on pea seed respiration?
4. What is the purpose of KOH in this experiment?
5. Why did water (food coloring) moving into the pipette?
Lab Book Requirements
1. Date of Lab
2. Title of Lab
3. Objective of Lab
4. Manipulated and Responding variable
5. At least three controls
6. Hypothesis
7. Table 6.1
8. Conclusion
9. What is the next experiment you could perform?
10. Answers to Post-Lab Questions
Table 6.1
Temp
(C)
Column
Time
(Min)

Beads Alone
Reading
at Time X
A
Germinating Peas
Diff*
Reading
at Time X
B
C
Dry Peas and Beads
Diff*
Corrected
Diff**
Reading
at Time X
Diff*
Corrected
Diff**
D
E
F
G
H
0
5
10
15
20
0
5
10
15
20
*Difference = {Initial reading at time 0} – {Reading at time X} (B-A), (D-C), (G-F)
**Corrected Difference = {Difference in experimental groups} – {Difference in beads alone}
(D-B) and (G-B)