Laboratory Review ❮ 245
The CO 2 problem can be handled by adding potassium hydroxide, which reacts with
CO 2 to produce K 2 CO 3. This reaction allows us to limit the number of variables that could
be affecting the volume around our beloved peas to
- Change in the volume of oxygen
- Change in the temperature (PV =nRT )
- Change in the pressure of the surrounding atmosphere
Aerobic respiration requires and uses oxygen. So, one would expect the volume of oxygen
around the pea to decline as respiration occurs. The reactions of interest for this experiment
occur in a tubelike device known as a respirometer. To calculate the change in volume that
occurs with these peas, one first has to measure the initial volume around the peas. A con-
trol group must then be set up that consists of peas that are not currently germinating and
will have a rate of respiration lower than that of germinating seeds. This will give the exper-
imenter a baseline with which to compare the respiration rate of the germinating seeds.
Since temperature and pressure are also able to affect the volume around the peas, it is
important to set up another control group that can calculate the change in volume that is
due to temperature and pressure as opposed to respiration. Any changes in this control
group should be subtracted from the changes found in the germinating seeds to determine
how much of the volume change is actually due to oxygen consumption and respiration.
Just a side thought: Can you imagine how awkward it could have been if one of
Mendel’s lab partners had decided to run this experiment? I can see it now: Mendel walks
into the lab and asks, “Has anyone seen my peas? After seven long years, I’ve nearly com-
pleted my research. Just need to tally up that last generation of peas.... Very exciting....
Hmm.... I thought my peas were sitting here on this desk by my respirometer.”
Results
- Germinating seeds consume moreoxygen than do nongerminating seeds. This makes
sense, because they have more reactions going on.
- Seeds germinating at a lower temperature consume lessoxygen than do seeds germinat-
ing at a higher temperature.
- You can determine how much oxygen is consumed by watching how much water is
drawn into the pipettes as the experiment proceeds. (Refer to your classroom lab manual
if you are confused by the pipette portion of this lab.) This water is drawn in as a result
of the drop in pressure caused by the consumption of oxygen during respiration.
Key Concepts
- A respirometer measures respiration rates by tracking the amount of oxygen being used
in cellular respiration.
- Warm conditions usually speed up cellular respiration; cold slows it down.
Investigation 7: Cell Division: Mitosis and Meiosis
This experiment draws on information found in Chapter 9, Cell Division.
Part 1: Onion Roots Treated with a Mitosis-Inducing Chemical
Basic Setup for Part 1
Your goal is to see if there is a greater number of cells undergoing mitosis in root cells
treated with lectin, a chemical that induces mitosis. Either you or your teacher will prepare
KEY IDEA
BIG IDEA 3
Genetics and
Information
Transfer
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