Cellular Respiration Lab
AP Biology
Name: ________________________________
Period: _________
OVERVIEW
What factors affect the rate of cellular respiration in multicellular organisms?
In this experiment, you will work with seeds that are living and either dormant or
germinating (sprouting). A seed contains a plant embryo and a food supply surrounded by
a seed coat. When the necessary conditions are met germination occurs and the rate of
cellular respiration greatly increases.
In this lab, you will determine the rate of cellular respiration of dormant and germinating
pea seeds by recording how much oxygen is consumed over a period of time.
INTRODUCTION AND BACKGROUND
Living systems require free energy and matter to maintain order, to grow, and to
reproduce. Energy deficiencies are not only detrimental to individual organisms, but they
cause disruptions at the population and ecosystem levels as well. Organisms employ
various strategies that have been conserved through evolution to capture, use, and store
free energy.
Autotrophic organisms capture free energy from the environment through photosynthesis,
whereas heterotrophic organisms harvest free energy from carbon compounds produced
by other organisms.
The process of cellular respiration occurs in both plants and animals. The energy from
carbon compounds (such as glucose) is harvested to produce ATP, which is then used to
power most vital cell processes.
Did you know that plants have mitochondria and do cellular respiration too? Just like
animals and people!
The equation below shows the complete oxidation of glucose. Oxygen is required for this
energy-releasing process to occur.
C6H12O6 + 6O2  6CO2 + 6H2O + 686 kilocalories of energy/mole of glucose oxidized
The equation above tells us that for every molecule of oxygen consumed, one molecule of
carbon dioxide is produced.
In this lab, you will be building an apparatus called a respirometer, which will be used to
measure how much oxygen is consumed through cellular respiration. As the peas consume
oxygen gas during respiration, it is normally replaced by carbon dioxide, molecule for
molecule. Therefore, you would expect that there would be no change in the total volume of
the gas in the experiment. However, you will be using a chemical called potassium
hydroxide (KOH) that removes carbon dioxide through the following reaction:
CO2 + 2KOH  K2CO3 + H2O
Thus, as oxygen is consumed, the overall gas volume in the respirometer decreases. The
change in volume of gas can be used to determine the rate of cellular respiration.
Babbey, 2015
Cellular Respiration Lab
AP Biology
Name: ________________________________
Period: _________
A number of physical laws relating to gases are important to the understanding of how the
apparatus that you will use in this exercise works. The laws are summarized in the general
gas law that states:
PV = nRT
Where P is the pressure of the gas, V is the volume of the gas, n is the number of molecules
of gas, R is the gas constant (its value is fixed), and T is the temperature of the gas (in
Kelvin).
In the respirometers you will build, if temperature and volume remain constant, the gas
will move toward the region of lower pressure. During respiration, oxygen will be
consumed. Its volume will be reduced, because the carbon dioxide produced is being
converted to a solid. The net result is a decrease in gas volume within the tube and a
related decrease in pressure in the tube. The vial with the glass beads alone will permit
detection of any changes in volume due to atmospheric pressure changes or temperature
changes.
SAFETY
KOH is caustic. It is recommended that you wear safety goggles, aprons, and gloves while
handling this chemical.
PROCEDURE
Follow the steps below to set up 3 respirometers with the following contents:
Respirometer
Temperature
Contents
1
Room
Germinating Seeds
2
Room
Dry Seeds + Beads
3
Room
Beads
Procedure
1. Respirometer 1: Obtain a 100 ml graduated cylinder and fill it with 20 mL of water.
Drop 15 germinating peas in the graduated cylinder and determine the amount of water
that was displaced (which is equivalent to the volume of the peas). Record the volume of
water that was displaced by 15 germinating peas.
Pea Volume _____________ mL
Remove the peas and place them on a paper towel. They will be used in Respirometer 1.
2. Respirometer 2: Refill the graduated cylinder with 20 mL of water. Drop 15 dried peas
(not germinating) into the graduated cylinder and then add enough glass beads to attain a
Babbey, 2015
Cellular Respiration Lab
AP Biology
Name: ________________________________
Period: _________
volume change that equals the volume change you recorded when measuring the germinating peas
(see above). Remove the peas and beads and place them on a paper towel. They will be used in
Respirometer 2.
3. Respirometer 3: Refill the graduated cylinder with 20 mL of water. Start adding glass beads
until you attain the same amount of water displaced as above. Remove the beads and place them on
a paper towel. They will be used to set up the third respirometer.
4. Now you will assemble your respirometers. Obtain 3 vials, and 3 stoppers with pipettes attached.
Place a small piece of ABSORBENT cotton in the bottom of each vial, and using a dropper, moisten
the cotton with 4 drops of 15% KOH. Do NOT get KOH on the sides of the respirometer. Place a
small wad of NON ABSORBENT cotton (see Figure 5.1) on top of the KOH soaked absorbent cotton.
It is important that you use the exact same number of drops of KOH and the same amounts of cotton
for each vial.
5. Place the germinating peas in vial 1, the dry peas and beads in vial 2, and the beads only in vial 3.
Insert the stopper fitted with the calibrated pipette.
6. Lie all 3 vials on their sides on the lab countertop. Do not touch them or disturb them for 7
minutes as they equalize (adjust to the temperature and pressure of the room).
7. After 7 minutes has elapsed, carefully add a drop of red food coloring into the tip of the pipettes
of each respirometer.
8. Allow the respirometers to sit for another 3 minutes. After 3 minutes, you will begin recording
data in the table below. Every 5 minutes for a total of 20 minutes, you will record the position of the
red food coloring as it is sucked into the pipette. (Remember, as the peas go through cell respiration
they consume oxygen and release carbon dioxide. The carbon dioxide is removed by the KOH, so as the
food coloring is sucked into the pipette what you are actually measuring is the amount of oxygen used
by the contents of your respirometer).
Data Table
Respirometer 3
Time
(min)
Respirometer 1
Respirometer 2
Beads
only
Beads
only
Germinating
peas
Germinating
peas
Germinating
peas
Dry
peas
and
beads
Dry peas
and beads
Dry peas
and beads
Reading
Diff.
Reading
Difference
Corrected
difference
Reading
Difference
Corrected
Difference
XXX
XXX
XXX
XXX
0
5
10
15
20
Babbey, 2015
XXX