Cellular respiration is the procedure of changing the chemical
energy of organic molecules into a type that can be used by organisms.
Glucose may be oxidized completely if an adequate amount of oxygen is
Equation For Cellular
+ 6O2 -> 6CO2 + 6H2O + energy
Carbon dioxide is formed as
oxygen is used. The pressure due to C02 might cancel out any change due
to the consumption of oxygen. To get rid of this problem, a chemical
will be added that will selectively take out C02. Potassium hydroxide
will chemically react with carbon dioxide by the following equation:
C02 + 2 KOH ->
A respirometer is the system
used to measure cellular respiration. Pressure changes in the
respirometer are directly relative to a change in the amount of gas in
the respirometer, as long as the volume and the temperature of the
respirometer do not change. To judge the consumption of oxygen in two
different respirometers you must reach equilibrium in both
A number of physical laws
relating to gases are important to the understanding of how the
equipment that you will use in this exercise works. The laws are
summarized in general gas law that states: PV = nRT Where:
P--the pressure of the gas
V--the volume of the gas
n--the number of molecules of gas
R--the gas constant
T= the temperature of the gas
In this experiment, the rate of cellular respiration
in the germinating peas, in both water baths, will be much higher than
that of the beads and non-germinating peas. The cooler temperatures in
the other water bath should cause the rate to be much slower in all
A Water bath, thermometer, masking tape, washers, beads, germinating
peas, non-germinating peas, beakers, graduated cylinder, ice, paper, and
pencil are needed for this lab.
Begin the experiment by setting up two water baths, one at room
temperature and the other at 10 degrees Celsius. Next, find the volume of
germinating peas, non- germinating peas and bead, and beads alone.
Repeat these steps for another set of peas and beads. Assemble the six respirometers,
placing enough KOH pellets to cover
the bottoms of the respirometers. Put non-absorbent
cotton balls in each respirometer above the KOH pellets and then add the peas and beads.
Place one set of respirometers in the room temperature
water bath and the other set into the 10 degree water bath. Slightly
elevate the respirometers, supporting them with masking tape, for 5 minutes while they
equilibrate. Then lower the respirometers into the water bath and take
a reading at 5, 10, 15, 20, 25, and 30 minute time intervals. Record the
data into the table.
1. In this activity, you are investigating both the effect of
germination versus non-germination and warm temperature versus cold
temperature on respiration
rate. Germinating peas should consume more oxygen than
non-germinating peas. Peas germinating at warm temperatures should
consume more oxygen than peas germinating at cold temperatures.
2. This activity
uses a number of controls. Identify at least three of the control, and
describe the purpose of each control.
Water baths held at constant temperature
Volume of KOH is the equal in every tube
Equilibration time is identical for all respirometers
3. Graph the results from
the corrected difference column for the germinating peas and dry peas at
both room temperature and 10 degrees Celsius.
4. Describe and explain the
relationship between the amount of oxygen consumed and time. The
amount of oxygen consumed was greatest in germinating peas in warm
water. The oxygen consumption increased over time in germinating peas.
5. Complete the following table:
6. Why is it necessary to correct the readings from the peas with the
readings from the beads?
To show the actual rate at which cellular respiration occurs in the
peas. The beads were the control variable.
7. Explain the effect of germination (versus non-germination) on peas
Germination, the seeds are growing and need to respirate to grow.
8.Explain the results shown in the sample graph in your lab manual.
As the temperature increased, enzymes denatured so germination was
9. What is the purpose of KOH in this experiment?
KOH pellets absorb carbon dioxide and form an insoluble precipitate
10. Why did the vial have to be completely sealed around the stopper?
The stopper at the top of the vial had to be completely sealed so
that no gas could leak out of the vial and so that no water would be
able to enter into the vial.
11. If you used the same experimental design to compare the rates of
respiration of a 25 g reptile and a 25 g mammal, at 100 degrees Celsius,
what results would you expect? Explain your reasoning.
I would expect the respiration to be higher in the mammal since they
are warm blooded.
12. If respiration in a small mammal were studied at both room
temperature 21 degrees Celsius and 10 degrees Celsius, what results
would you predict? Explain your reasoning.
Respiration would be higher at 21 degrees because the animal would
have to keep his body temperature up.
13. Explain why water moved into the respirometer pipettes.
While the peas underwent cellular respiration, they consumed oxygen and
released carbon dioxide. The carbon dioxide reacted
with the KOH resulting in a decrease in the volume of gas in the pipette
and the vial. Because the pipette tip was exposed to the water bath,
water moved into the pipette.
13. Design an experiment to
examine the rates of cellular respiration in peas that have been
germinating for 0, 24, 48 and 72 hours. What results would you expect?
Set up four respirometers which have one of the
following-Seeds that have not begun to germinate; Seeds that have been
germinating for one day; Seeds that have been germinating for two days;
Seeds that have been germinating for three days. It is expected that
there will be no oxygen used by the seeds that have not germinated yet.
The seeds that had been germinating for three days would consume the
The seals on the respirators may not have been completely air-tight. The use
of KOH pellets, instead of liquid, may have caused errors in the carbon
dioxide absorbed. The temperature may have been slightly off in the water baths.
Oxygen consumption in the respirometers with germinating peas was
greater than that in respirometers with non-germinating peas.
Respiration rate was also affected by temperature. Respiration occurred
at a faster rate in the respirometers in the warm water bath.