Cell Respiration Pre-Lab
These questions must be answered BEFORE you will be allowed to conduct this lab!
PREDICTIONS:
What do you predict will happen in this experiment regarding
A. The relative volume of oxygen consumed by germinating and nongerminating seeds
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B. The effect of different temperatures on seed germination
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HYPOTHESES:
You are therefore, testing two different hypotheses in this experiment. What are they?
Hypothesis 1:
Null__________________________________________________________________
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Alternative____________________________________________________________
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Hypothesis 2:
Null_________________________________________________________________
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Alternative____________________________________________________________
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1. What is the equation for the ideal gas law?
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Define each variable in the equation.
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2. In this experiment, what are we going to measure?
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3. What parts of the ideal gas law should be held constant in order for us to measure the variable we
intend to study in this experiment?
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4. What is the purpose of KOH in this experiment?
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AP Biology
5. How are you going to measure the variable you identified in question 2?
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6. What exactly is the vial containing glass beads used for?
(Yes- I know it is a control--explain what it is controlling for !)
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7. How are you going to calculate ml of oxygen consumed for each vial?
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8. This activity uses a number of controls. Identify at least 3 of the controls and describe the purpose of
each control.
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AP Biology
Cell Respiration
OVERVIEW
In this lab you will work with seeds that are dormant and seeds that have been stimulated to germinate
because they have been soaked in water. A seed contains an embryo plant and a food supply surrounded
by a seed coat. When the necessary conditions (moisture etc…) are met, germination occurs and the rate
of cellular respiration greatly increases. A dormant seed still has a plant embryo, but the embryo is not
undergoing mitosis and is therefore not needing to produce large quantities of ATP. In this experiment you
will measure oxygen consumption during germination. You will measure the change in gas volume in
respirometers containing either germinating or nongerminating grass seeds. In addition, you will measure
the rate of respiration of these seed at two different temperatures.
OBJECTIVES
Before doing this lab you should understand:
 how a respirometer works in terms of the gas laws
 the general processes of metabolism in living organisms
After doing this lab you should be able to:
 calculate the rate of cell respiration from experimental data relate gas production to respiration rate
 test the effect of temperature on the rate of cell respiration in nongerminated vs. germinate seeds in
a controlled experiment.
INTRODUCTION
Cellular respiration is the release of energy from organic compounds by metabolic chemical oxidation in
the mitochondria within each cell. Cellular respiration involves a series of enzyme mediated reactions.
The equation below shows the complete oxidation of glucose. Oxygen is required for this energy releasing
process to occur.
C6H12O6 + 6O2 → 6CO2 + 6 H2O + 686 kcal of energy/mole of glucose oxidized
By studying the equation above you will notice there are three ways cellular respiration could be measured.
One could measure the:
1. Consumption of oxygen --how many moles of oxygen are consumed in cellular respiration?
2. Production of carbon dioxide--how many moles of carbon dioxide are produced by cellular respiration?
3. Release of energy during cellular respiration.
In this experiment, the relative volume of oxygen consumed by germinating and nongerminating (dry) peas
at two different temperatures will be measured.
BACKGROUND INFORMATION
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
P
V
n
R
T
= pressure of gas
= volume of gas
= number of molecules of gas
= gas constant (its value is fixed)
= temperature of gas (Kelvin)
This law implies the following important concepts about gases:
A. If temperature and pressure are kept constant,
then the volume of gas is directly proportional to the number of molecules of gas.
B. If the temperature and volume remain constant, then the pressure of the gas changes in direct
proportion to the number of molecules of gas present.
C. If the number of gas molecules and the temperature remain constant, then the pressure is inversely
proportional to the volume.
D. If the temperature changes and the number of gas molecules is kept constant, then either pressure
or volume (or both) will change in direct proportion to the temperature.
It is also important to remember that gases and fluids flow from regions of high pressure to regions of
low pressure.
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In this experiment, the CO2 produced during cellular respiration will be removed by KOH and will form
solid K2CO3 according to the following reaction.
CO2 + 2KOH → K2CO3 + H2O
Since the carbon dioxide is being removed, the change in the volume of gas in the respirometer will be
directly related to the amount of oxygen consumed. In the experimental apparatus if water
temperature and volume remain constant, the water 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 decease in gas volume within the tube and
a related decrease in pressure in the tube. The vial with glass beads alone will permit detection of any
changes in volume due to atmospheric pressure changes or temperature changes. The amount of
oxygen consumed will be measured over a period of time.
Each group will set up 3 microrespirometers. Each group will have a DIFFERENT temperature
of water (warm, room, cold).
RESPIROMETER
TEMPERATURE
CONTENTS
A
…
Germinating Seeds
B
…
Nongerminating (Dry) seeds
C
…
Beads
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PROCEDURE:
1. Prepare a water bath at the assigned temperature: ________________
2. Assemble 3 respirometers:
a. Label 3 vials A, B and C
b. Place circle of absorbent cotton (approximately the size of a nickel) into bottom of each vial.
c. Carefully soak with 1-2 ml of 15% KOH solution
Do not allow any KOH to touch side walls of vials
d. Place circle of non absorbent cotton into vial directly on top of KOH/cotton circle. This will
keep KOH solution from touching peas during experiment
3. Find the volume of 25 germinating peas.
 Fill a 100 ml graduated cylinder to 50 ml with water
 Place the peas in the cylinder and measure the increase in water volume_____________
 Place peas on paper towel
 These are germinating peas to be used in respirometer A
4. Determine volume of 25 non-germinating peas
 Fill 100 ml graduated cylinder with 50 ml water
 add 25 non-germinating peas
 Add glass beads to raise volume to equal that obtained with swollen germinating peas
 Remove peas and beads. Place them on paper towel
 Nongerminating peas and beads will be used in respirometer B
5. Determine the volume of glass beads
 fill the 100 ml graduated cylinder with 50 ml water
 add glass beads to raise volume so it equals volume of germinating peas as determined
previously
 place glass beads on paper towel
 Glass beads to be used in respirometer C
6. Place non germinated seeds + glass beads into vial B. Insert Cork/pipet assembly into vial
7. Wrap parafilm tightly around seams (cork and tube) to seal any potential leak
8. Make sure ice water bath has equilibrated to the correct temperature
9. Place piece of masking tape over water bath to suspend pipet tips out of water during equilibration
phase
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AP Biology
10. Place each respirometer into water bath with calibrated side of pipet facing up so that
measurements can be taken.
11. Allow respirometers to equilibrate in water bath for 5 minutes.
12. After equilibration phase, immediately submerge each respirometer (put them all the way into the
water). Pipettes will take on some water. Make sure vial does not fill up with water. If it does,
there is a leak which must be corrected.
13. Arrange vials so you can read volume markings on each pipet. Weight vials to keep them
submerged.
14. Record starting point (time 0) volume of each pipet.
15. Take readings of volume of water in each pipet every 5 min. for 20 min. Record these values in
your data table.
16. Collect Vial A, B and C class data for the other temperature. Record in data table.
17. Correct volumes measured for changes in environmental variables:

Vial C measures volume changes due to environmental variables. For vial C, the environmental
effects are calculated by subtracting the volume at a given time (T x) from staring volume at starting
time (T0)
apparent ml of oxygen consumed = Vial C volume at Tx - Vial C volume at T0

Environmental effects must be applied to data collected for vial A as shown below:
ml of O2 consumed vial A =
[vial A vol. at Tx - Vial A vol. at T0] - [vial C vol. at Tx - Vial C vol. at T0]

Environmental effects must be applied to data collected for vial B as shown below:
ml of O2 consumed vial B =
[vial B vol. at Tx - Vial B vol. at T0] - [vial C vol. at Tx - Vial C vol. at T0]
Data Tables:
Room Temperature
Time
(T)
min.
Volume Readings
vial A
Vial B
Vial C
apparent ml of oxygen
consumed in vial C
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AP Biology
ml oxygen
consumed vial A
ml oxygen
consumed vial B
Ice Water Bath:
Volume Readings
Time
(T) min.
vial A
Vial B
Vial C
apparent ml of oxygen
consumed in vial C
ml oxygen
consumed vial A
ml oxygen
consumed vial B
apparent ml of oxygen
consumed in vial C
ml oxygen
consumed vial A
ml oxygen
consumed vial B
Warm Water Bath:
Volume Readings
Time
(T) min.
vial A
Vial B
Vial C
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EVALUATION:
1. Graph your corrected data for vials A & B for all three temperatures (you will have more than one line!)
 What is the independent variable?__________________________________
 What is the dependent variable?___________________________________
 Data from all temperatures should be plotted on the same graph.
 Draw the best fit straight line through the data points.
2. What accounts for the difference in oxygen consumption seen between germinating and
Non-germinating seeds?
3. Why do the glass beads seem to be using oxygen?
4. Why are the readings corrected using the glass bead values?
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AP Biology
5. From the slope of the four lines on the graph, determine the rate of oxygen consumption of germinating
and dry peas during the experiments at room temperature and 10ºC . Show your work!!!!!
Recall that rate = Δy/Δx
CONDITION
CALCULATIONS
RATE: ml O2/minute
Germinating seeds
at cold temp.
Germinating seeds
at room temp.
Germinating seeds
at warm
temperature
Dry seeds at cold
temperature
Dry seeds at room
temperature
Dry seeds at cold
temperature
6. Compare the rate of oxygen consumption at cold and room temperature. Why are they different?
7. Compare the rate of oxygen consumption at warm and room temperature. Why are they different?
8. Compare the rate of oxygen consumption at cold and warm temperatures. Why are they different?
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AP Biology
9. What basic cellular process is responsible for the oxygen consumption?
10. Explain why water moved into the respirometer pipettes.
11. What is the effect of germination (vs. Nongermination) on seed respiration?
12. Discuss whether these results support your original hypotheses.
13. Summarize your conclusions from this lab.
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14. If you used the same experimental design to compare the rates of respiration of a 25g reptile and a 25g
mammal, at 10ºC what results would you expect? Explain your reasoning.
15. If respiration in a small mammal were studied at both room temperature and 10ºC, what results would
you predict? Explain your reasoning.
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AP Biology
Part II: Developing and Implementing Your Research Plan
Reviewing the Variables
Below is a table of variables that provides a starting point for developing research questions on cellular
respiration. A number of variables that you may wish to investigate are listed in the table.
Environmental Variables
1. Temperature
2. Light (possible confusion with
Seed Variables
1. Stage of germination
2. Age of seeds
Organism Variables
1. Type of seed
2. Mixed seeds
3. Condition of seeds
4. Seed size
5. Surface area of seed
6. Others
3. other tissues
4. Other organisms
photosynthesis)
3.
4.
5.
6.
7.
Conditions for germination
Pressure
Oxygen availability
Time of the day
Others
Suggested Topics
In the previous section, you examined variables to investigate for independent research. However, you may still be
having some difficulty trying to get started with your research. Listed below are a few ideas that you might want to
investigate. Notice that the questions are limited and provide a suggestion for developing an answer.
1. Do seeds just starting to germinate consume oxygen at a greater rate than seeds that have been germinating for
several days?
2. Does the temperature of germinating seeds affect the rate of cellular respiration?
3. Do insects respire faster or slower at higher temperatures?
4. Do monocot plants respire at different rates than dicot plants?
5. Do boiled peas respire? If so, how does the respiration rate compare with that of unboiled peas?
Decide on the question you want investigate for independent research and write it below:
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Developing and Implementing Your Plan
Complete the following chart in your lab notebook and get your teacher’s approval. Materials needed must be those
already found in the lab or those that your group can bring with you on the day you run your experiment. You MUST
request materials needed from the prep room at least 24 hours prior to running your experiment.
Null Hypothesis:
Alternative Hypothesis:
Materials:
Independent Variable
Dependent Variable(s)
Controlled Variable(s)/Constants
How will data be recorded?
What kind of data analysis will you perform? How will it be
done?
Student Presentation
Research biologists keep a record of their work in their laboratory or field notebook. They communicate the final results
of their work to others a number of ways. They may publish an article or make a presentation at a meeting. To keep
others informed about work that is just getting started, biologists often use a form of presentation known as a poster.
You will be producing and presenting a poster of your research.
Use the information from the enzyme catalysis lab to prepare a mini-poster to present your findings.
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AP Biology