Erika Veidis
Cell Respiration Lab
I.
INTRODUCTION:
Cellular respiration breaks down high energy molecules to release energy
in the form of ATP. The chemical equation of this is C6H12O6 + 6O2  6CO2
+ 6H2O + energy. This means that a cell consumes glucose and oxygen and
releases carbon dioxide, water, and energy. Contrary to fermentation, cellular
respiration requires oxygen; while fermentation is an anaerobic process,
cellular respiration is aerobic. In cellular respiration, glucose or other
macromolecules are completely oxidized, producing about ATP (about 38
ATP per molecule of glucose). This occurs through a series of enzymecatalyzed reactions.
There are three ways to measure aerobic respiration: by oxygen
consumption, carbon dioxide production, and energy release. In this lab, it
will be measured by oxygen consumption, as it is the most accurate method.
This will be done by using a respirometer.
The equation PV = nRT is the general gas law that describes the use of
the respirometer in this lab. The volume (V) and temperature (T) remain
constant. A control (the vial filled with glass beads) accounts for the changes
in pressure (atmospheric or temperature-related pressure changes). R is the
gas constant, and n is the number of molecules of gas. The carbon dioxide is
being removed by potassium hydroxide (KOH), which leaves only the
consumption of oxygen to be measured.
The purpose of this lab was to determine the rate of cell respiration in
germinating peas by measuring the amount of oxygen consumed. In this lab
the students also compared the respiration in germinating seeds and dry
seeds.
The cotton soaked in KOH was placed on the bottom of the three vials and
covered by non-absorbent cotton removed the carbon dioxide released from
the germinating seeds as they underwent cellular respiration, forming solid
K2CO3. One vial was filled with germinating peas, another with dry peas, and
the third with glass beads. It was important that the volume of each vial was
equal so as to eliminate that variable from the PV = nRT equation. When the
vials were placed underwater, the consumption of oxygen due to cellular
respiration caused the amount of air in the pipette attached to the vial to
decrease, allowing water to rush in. The vial filled with glass beads was the
control, which accounted for changes in pressure and allowed the students to
make a corrected difference to the readings of the germinating and dry peas.
II.
III.
The germinating seed should respire more than the dry seed. The
germinating seed needs more oxygen as it is growing; it is dormant. The dry
seed doesn’t need as much or any oxygen as it is not growing. Oxygen is
necessary for cellular respiration, which would be especially important to a
growing seed. Contrastingly, it is not necessary for a seed that is not
germinating, like a dry seed.
MATERIALS:
Water
100 mL graduated cylinder
10 germinating peas
10 dried peas
Glass beads
3 vials
KOH (CO2 remover)
Absorbent cotton
Non-absorbent cotton
Pipette attached to stopper
Pyroform tape
3 weights
Large pan
Tape (to use as a sling for apparatuses)
Food dye
PROCEDURE:
1. The volume of 10 germinating seeds was found by pouring water in the
graduated cylinder, recording the initial volume, and then recording the
final volume after adding the seeds.
2. Another graduated cylinder was filled and the volume was recorded. 10
dry seeds were added, and then glass beads were added until the
difference between the final volume and the initial volume (the volume of
the added seeds/beads) equaled to the volume of the germinating seeds,
found in #1.
3. The procedure was repeated for glass beads.
4. Absorbent cotton was placed on the bottom of each of three vials.
5. The cotton was moistened by dripping KOH on it. It was vital not to hit the
sides of the vial – only the cotton – as that could have altered the results.
6. Non-absorbent cotton was placed on top of the KOH-soaked cotton.
7. The pre-measured amounts of germinating seeds, dry seeds/ glass beads,
and just glass beads were added to each of three vials.
8. A pipette that was attached to a stopper was placed on top of each vial.
Pyroform tape was used to seal each vial.
IV.
9. A weight was placed on each apparatus.
10. A pan was filled with water (room temperature).
11. A white sheet of paper was placed on the bottom of the pan to make
reading the results on the pipette easier.
12. The vial was submerged and allowed to equilibrate for 7 minutes by
submerging the vial but resting the pipette on a sling made by stretching a
piece of tape across the pan.
13. At the end of the 7 minutes, the vials were completely submerged.
14. Food dye was added into the pipette to make the water mark on the
pipette easier to determine.
15. After the vials were allowed to equilibrate for 3 minutes completely
underwater, the students began gathering the results.
RESULTS:
Pea volume: 4 mL
Time Beads alone
(min)
Reading Difference
at time
x
0
.92
------------5
.90
.02
10
.89
-.01
15
.89
0
20
.88
.01
Germinating peas
Dry peas and
beads
Reading Diff. Corrected Reading Diff Co.
difference
Diff
.92
.82
.75
.68
.60
----.10
.07
.07
.08
------------.08
.06
.07
.07
.92
.88
.88
.88
.87
---.04
0
0
.01
---.02
-.01
0
0
V.
ANALYSIS:
The 4 mL of the peas/ beads was kept constant in all three vials to
eliminate volume as a variable from the PV = nRT equation.
The oxygen consumed over a 20-minute period was much greater in the
germinating peas than the dry peas. The germinating peas (with a total of .28
mL) consumed a total of .27 mL more of oxygen than the dry peas/ glass
beads, which consumed .01 mL. In 5 minutes, the germinating peas
consumed .08 mL of oxygen, while the dry peas consumed .02 mL. In 10
minutes, it was .14 and .01 respectively. The consumption by the dry peas
decreased due to the corrected difference, which was calculated by
subtracting the difference in readings in the control group from the difference
of the peas. In 15 minutes, the germinating peas consumed .21 mL of
oxygen, significantly higher than the unchanging .01 mL of the dry peas/
beads. The final reading after 20 minutes revealed that the germinating peas
consumed .28 mL and the germinating peas still had only consumed .01 mL.
The rate of oxygen consumption was .014 mL/minute in the germinating peas;
it was .0005 mL/minute in the dry peas.
A possible source of error in this experiment could’ve been the insertion of
the stopper attached to the pipette into the vial. If this wasn’t made
completely airtight, then the results would’ve been greatly altered. Oxygen
could’ve seeped through these crevices instead of solely through the pipette,
and water could’ve rushed into the vial. It would also be problematic if the
KOH got on the sides of the tube instead of just on the cotton, as then the
peas would’ve been exposed to it, and the solid K2CO3 would’ve formed
inside the vial by the peas. This might’ve obstructed the flow of oxygen into
the peas. If the water was colder than room temperature, the rate of the
reaction would’ve decreased, as the lower kinetic energy would’ve slowed
things down.
VI.
CONCLUSION:
This experiment explored possible ways to determine the rate of cell
respiration and focused on doing so by measuring the consumption of
oxygen. The difference between the rates of oxygen consumption and cell
respiration depending on the state of the pea (germinating or dry) was
observed.
The germinating peas consumed more oxygen and had a higher rate of
oxygen consumption than the dry peas, as the dry peas were dormant and
were not undergoing cell respiration. The rate of oxygen consumption directly
relates to the rate of cellular respiration, as oxygen is consumed to perpetuate
cell respiration. Since the germinating peas had a high rate of oxygen
consumption, it meant that their rate of cell respiration was much higher than
the dry peas/ glass beads. Theoretically, the dry peas should’ve had no
oxygen consumption, as they weren’t undergoing cell respiration.
The chemical equation of cell respiration is C6H12O6 + 6O2  6CO2 +
6H2O + energy. Since oxygen is consumed during cell respiration as a
reactant in the reaction, it made sense to measure its consumption to
determine the rate of cell respiration in an organism. Measuring oxygen
consumption was much more accurate and efficient than it would have been
to measure the release of carbon dioxide or energy, which are products in the
reaction.
Though it was not a factor in this experiment, a temperature change
could’ve altered the rates of cell respiration in the peas. A higher temperature
would’ve meant more kinetic energy, which would’ve sped up the rate of the
reaction. A lower temperature would’ve decreased this rate because of the
decrease in kinetic energy. Temperature is a measure of kinetic energy. Too
high or too low of a temperature could’ve kept the reaction from occurring at
all. Too low of a temperature would’ve caused movement to almost stop,
and the reaction wouldn’t have enough energy to begin or proceed. Too high
of a temperature could’ve caused the enzymes perpetuating cell respiration to
denature, or unravel and stop functioning, so the reaction would not occur.