Things you should be able to explain to someone else after this lab:

• Aerobic respiration
• Anaerobic respiration
• Fermentation

Slideshow

Introduction

All living things require energy. The energy carrying molecule of the cell is ATP, or adenosine tri-phosphate. ATP is a nucleic acid. ATP releases energy when one of the three phosphates is removed forming the molecule ADP. Through the process of aerobic respiration, living things break down glucose to create ATP. The equation for aerobic respiration is shown below. Notice that along with glucose oxygen is a substrate of aerobic respiration.

C₆H₁₂O₆ + 6O₂ → 6H₂O + 6CO₂ + ATP

Aerobic respiration is the most efficient way to create energy in cells but it is not the only option. Anaerobic respiration is a simpler process that does not require oxygen. However, anaerobic respiration does not produce as many ATP. Fermentation is one type of anaerobic respiration. Lactic acid fermentation is used by some bacterial species for ATP production. Alcoholic fermentation is a process that takes place in yeast cells. You might be familiar with some of the products created through alcoholic fermentation such as beer, wine, and bread.

Today you will investigate aerobic respiration in insects comparing pill bugs and bean beetles. As animals, insects undergo aerobic respiration to create the ATP needed for processes such as metabolism, reproduction, growth, and movement. You will track aerobic respiration using a carbon dioxide sensor.

If aerobic respiration is occurring will there be an increase or a decrease in carbon dioxide concentration?

Procedure

1. Observe the pill bugs and bean beetles available for the experiment. Do they differ in size? Which one is larger and which one is smaller?
2. Do you think size of the insect will influence aerobic respiration? With your group, create a hypothesis about how the size of the insect will affect aerobic respiration as measured through carbon dioxide concentration. Make sure that your hypothesis is a testable statement.
3. Plug the lab quest computer in using the electrical cord. Turn on the computer.
4. Attach the carbon dioxide sensor to the lab quest. Make sure the switch on the sensor is set to “low.”
5. Make sure that the computer is set to record data for 600 seconds (upper right corner). If you need to change the time tap on “length” on the computer screen.
6. Obtain 5 bean beetles and place them into your respiration chamber.
7. Insert the carbon dioxide sensor into the opening of the respiration chamber. Make sure it is a tight fit but do not force it.
8. Wait 2 minutes (to allow the chamber to equilibrate) and click on the green arrow button on the bottom left corner of the computer screen to begin recording data. The data will continuously record and automatically stop after 10 minutes.
9. During the data collection, make observations regarding the behavior of the insect. Record any important observations on the next page.
10. Once data collection is complete, a graph of carbon dioxide concentration verses time will be visible on the computer screen. The slope of this line indicates the rate of respiration
11. To determine the slope of this line:
    1. Click on the analyze menu (top of the screen) and select “curve fit”
    2. On the next screen scroll down fit equation and choose “linear.”
    3. The equation of the line will be displayed on the screen. Record the m value (slope) in your data table.
    4. Select OK
12. Repeat the experiment two more times with the bean beetles. At the end of each 10 minute trial record the m value in the data table.
13. Remove the bean beetles from the respiration chamber and put them back in their original container.
14. Repeat steps 6-13 using pill bugs and record your results in the data table and your observations below. Make sure you conduct three replicate trials with the pill bugs.
15. Once you have completed the experiment please rinse out the respiration chamber, unplug the equipment and return it to the case.

Results

Record your observations of the bean beetles.

Record your observations of the pill bugs.

Conclusions

1. Do your results support your hypothesis? Explain why or why not.
2. How does the size of the insect impact aerobic respiration?
3. What evidence do you have that cellular respiration occurred?
4. Identify one potential source of error in your experiment.
5. Describe a possible follow up experiment you could conduct based on your findings.