CBL Interfacing

Experiments

Introduction

Which organism uses more oxygen, a germinating pea or an earthworm? Both need oxygen to metabolize their nutrients and form ATP for doing biological work. The germinating pea is growing rapidly using its stored reserves to pierce through the ground to reach light it can use for photosynthesis. The earthworm is an active and growing organism. Using a respirometer, we will make a comparison of the breathing rates of the two organisms.

The basis of today's experiment is straight-forward. As the organisms respire they consume oxygen and give off carbon dioxide. Volume wise, the amount of oxygen used is roughly equal to the amount of carbon dioxide given off. Therefore, if we placed the organisms in a sealed container, we would expect no pressure change. But, the carbon dioxide emitted will be "consumed" by potassium hydroxide according to the following reaction:

CO2 + 2KOH ¾¾> 2 KCO₃ + H₂O

Carbon Dioxide + Potassium Hydroxide Potassium Carbonate + Water

Since the potassium carbonate takes up virtually no volume, any carbon dioxide given off by the organism will not affect the pressure. Thus, the only pressure change caused by the living material will be due to the use of oxygen by the organisms being tested.

Perhaps fluctuations in temperature or other environmental factors will cause pressure changes within the respirometer vials. This will be taken into account by setting up a control with no organisms. We will subtract any pressure changes in the control from any pressure changes in the experimental.

We are comparing two organisms, a plant and an animal. In order to make a meaningful comparison we will determine the respiration rate per gram of tissue.

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