AP Biology- Cellular Respiration Pre-Lab
Purpose:

To determine the how the rate of respiration differs in germinating and nongerminating seeds.
Background: Answer the following questions. They are to be included in your lab
report in paragraph form. Do not forget to include your “Works Cited.”
What is cellular respiration? Where does it occur in aerobic organisms (what organelle)?
What are the reactants and products of aerobic cellular respiration?
Also include:
There are three ways cellular respiration could be measured. The consumption of O2
(how many moles of O2 are consumed in cellular respiration). Production of CO2 (how
many moles of CO2 are produced in cellular respiration?) and the release of energy
during cellular respiration. In this lab, the volume of O2 consumed by germinating and
non-germinating peas will be measured.
PV=nRT is the inert gas law. 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. T is the temperature of the gas in
degrees K. This law tells us several important things about gases. If temperature and
pressure are kept constant then the volume of the gas is directly proportional to the
number of molecules of the gas. If the temperature and volume remain constant, then the
pressure of the gas changes in direct proportion to the number of molecules of gas. If the
number of gas molecules and the temperature remain constant, then the pressure is
inversely proportional to the volume. 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.
In this lab, CO2 , made during cellular respiration will be removed by potassium
hydroxide (KOH) and will make potassium carbonate (K2CO3). Carbon dioxide is
removed so the change in the volume of gas in the respirometer will be directly
proportional to the amount of oxygen that is consumed. In the experiment, water will
move toward the region of lower pressure. During respiration, oxygen will be consumed
and its volume will be reduced to a solid. The result is a decrease in gas volume within
the tube, and a related decrease in pressure in the tube. The respirometer with just the
non-germinating peas will allow changes in volume due to changes in atmospheric
pressure or temperature changes.
Hypothesis:
Comparison of the rate of respiration in the germinating peas verses the non-germinating
peas.
Materials:
The materials used in the lab are as follows: water bath, tap water, masking tape,
germinating peas, non-germinating peas, cooked peas (or beads), 100 mL graduated
cylinder, 3 vials, 3 rubber stoppers, absorbent and non absorbent cotton, KOH, 5 mL
syringe, 3 pipettes, and 3 washers.
Procedure:
First, set up a room temperature 25oC water bath. Next, obtain a 100 mL graduated
cylinder and fill it with 50 mL of water. Drop in 25 germinating peas and determine the
amount of water that is displaced. Record the volume of the 25 germinating peas. Then
remove these peas and place them on a paper towel. They will be used in respirometer 1.
Next, refill the graduated cylinder with 50 mL of water and drop 25 non-germinating
peas into it. Then drop the cooked seeds into the graduated cylinder until the volume is
equivalent to that of the expanded germinating peas. Remove the peas. They will be used
in respirometer 2. Next, refill the graduated cylinder with 50 mL of water. Determine
how many cooked peas would be required to attain a volume that is equivalent to that of
the germinating peas. Remove the peas. They will be used in respirometer 3.
Assemble the three respirometers by obtaining 3 vials, each with an attached stopper and
pipette. Then put a small wad of absorbent cotton in the bottom of each vial, and using
the syringe, saturate the cotton with 15 % KOH making sure not to get the KOH on the
sides of the respirometer. Then place a small wad of nonabsorbent cotton on top of the
KOH-soaked absorbent cotton. Repeat these steps to make the other two respirometers.
Make sure to use about the same amount of cotton in each vial.
Next, place the sets of germinating peas, dry peas + cooked peas and cooked peas in vials
1, 2, and 3 and attach the stopper with the pipette. Place a washer on each of the pipettes
to be used as a weight.
Make a sling using the masking tape and attach it to each side of the water baths to hold
the pipettes out of the water during the equilibration period of 10 minutes. After the
equilibration period completely immerse all three respirometers in the water completely.
Water will enter the pipette for a short distance and stop. If it does not stop, there is a
leak. Make sure the pipettes are facing so you can read them. The vials should not be
shifted during the experiment and your hands should not be placed in the water during the
experiment.
Allow the respirometers to equilibrate for three more minutes and then record the initial
water in each pipette time 0. Check the temperature in both baths and record. Every five
minutes for 20 minutes, take readings of the water’s position in each pipette, and record
the data.
In your analysis section, in addition to graphing your results you will also need to
determine the rate of oxygen consumed of the germinating and non-germinating
peas during the experiments at room temperature. Use the formula: (y2-y1)/(x2-x1).