Laboratory Review ❮ 253
Results
It is not important that you take away from this experiment that fruit flies enjoy the scent of
one type of substance over another. What is important is that you recognize how to set up an
experiment such as this one involving the choice chamber to measure chemotaxis in animals.
Key Skills
- Design a controlled experiment to determine environmental factors that either attract or
repel your fruit flies.
- Analyze your data to identify the effect of environmental factors on your flies’ behavior.
Investigation 13: Enzyme Activity
This experiment draws on information from Chapter 5, Chemistry. The experiment is
designed to practice the calculation of the rate of enzyme-catalyzed reactions through the
measurement of the products produced. In this particular experiment, the enzyme peroxi-
daseis used to convert hydrogen peroxide to water and oxygen, and the products are mea-
sured to assist in the determination of the rate of reaction. If you do not feel comfortable
with your knowledge of enzyme-substrate interactions, refer to Chapter 5 before continu-
ing this section.
The Nitty-Gritty About Experiment 2
The reaction of interest in this experiment is as follows:
2H 2 O 2 →2H 2 O+O 2
This reaction does indeed occur without the assistance of peroxidase, but it occurs at a slow
rate. When our friend peroxidase is added to the mix, the reaction occurs at a much faster
clip. Take a look at the enzymatic activity curve in Figure 19.4. Notice the constant rate of
reaction in the first six minutes of the experiment.
However, after the sixth minute, the rate slows, as if the enzyme has become tired. This
is because as the reaction proceeds, the number of substrate molecules remaining declines,
which means that fewer enzyme-substrate interactions can occur. When calculating the rate
of reaction, it is the constant linear portion of the curve that matters. That is the accepted
rate value for the enzyme. Do not attempt to factor in the slowing portion of the curve.
Basic Setup
In this particular experiment, turnip peroxidase is added to a beaker that holds H 2 O 2 and
is allowed to react for a certain period of time. After the reaction stops, the amount of O 2
BIG IDEA 4
Interactions
Figure 19.4 Enzyme-activity curve.
Moles of
product
1 2 3 4 5 6 7 8
Time
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