Cellular Respiration Lab Notes- Biology II
OBJECTIVES:
- Measuring O2 consumption by respiring peas (germinating and nongerminating)
- Compare rates of respiration at different temperatures
EQUATION:
C6H12O6 + 6 O2  6 CO2 + 6 H2O + energy
** See lab bench on Campbell website for pictures of respirometer and good
explanation of how respirometer works
BACKGROUND:
- In the respirometer, the peas will use oxygen and produce carbon dioxide in a
ratio of 1 mole of O2 : 1 mole of CO2
- This would cause no change in the volume of gas in the respirometer, since 1
mole of gas is produced for every mole that is taken in
- To compensate for this, we will use KOH (potassium hydroxide) to remove the
CO2. When KOH comes into contact with CO2, it produces the solid potassium
carbonate:
CO2 + 2 KOH  K2CO3 + H2O
- The removal of the CO2 will allow water to enter the tips of the pipettes as
oxygen is used (the pipettes were submerged at the beginning of the experiment
to control the initial amount of oxygen in each respirometer)
- The amount of water that enters the pipette is equal to the amount of oxygen
consumed by the peas
- We will measure the rate of respiration of germinating versus dry peas at both
room temperature and 10 degrees Celsius
PROCEDURE (quick start- see lab for more detail when writing report):
YOU MUST SET UP YOUR RESPIROMETERS AS SOON AS POSSIBLE
AFTER COMING TO CLASS!
1. Use your plastic tube to measure 25 mL of water, and add 25 germinating
peas. Write down your new volume. Dump out the water, but save the peas and
set aside on a paper towel.
2. Repeat the above procedure, except add 25 dry peas. Now add enough glass
beads to bring your volume up to what it was above. Dump out the water and
save the peas and beads on a paper towel.
3. Repeat the above procedure, except add only glass beads to equal the above
volume. Dump out the water and save the beads on a paper towel.
4. In each of your 3 respirometers, place a small piece of absorbant cotton at the
bottom and moisten with KOH (about 2 mL should be enough). Cover this cotton
with a piece of nonabsorbent cotton that is about the same size.
5. Add your germinating peas to respirometer 1, your dry peas and beads to
respirometer 2, and your beads to respirometer 3. Put the stoppers in place.
6. Put all 3 respirometers in your water bath ALLOWING THE TIPS OF THE
PIPETTES TO REST ON THE MASKING TAPE SLING. Allow to sit undisturbed
for 5 minutes. This will give the peas time to adjust to the water.
7. After 5 minutes, submerge all 3 respirometers at the same time, and quickly
turn them so that you can read the pipettes (lower numbers toward the tips).
After turning them, you should keep your hands out of the water. Allow to sit
undisturbed for another 5 minutes.
- Water should enter your pipettes initially and then stop. If water continues to
quickly enter your pipette, this means that you have a leak and will have to start
over.
8. Take your initial volume reading in each of the 3 pipettes. Record to the
nearest 0.01 mL. Repeat this reading every 5 minutes for 20 minutes.