The respiration rate of organisms can be determined by measuring the CO2 content of the air they exhale. CO2 concentrations can be determined with an infra-red gas analyzer (IRGA) that detects changes in CO2 levels of a few parts per million (ppm). To measure respiration using an IRGA, air from a chamber containing an insect or other small organism is first dried of any moisture it contains (because water vapor interferes with the measurements) by passing it through column containing a desiccant (a material that will absorb water). The air then passes through the IRGA where the CO2 concentration in ppm is measured. A small gas pump is used to move air through the entire system. The rate of air flow can be controlled by placing a flow restrictor between the pump and the next component in the system. Before you begin measuring respiration rates, you need to set a base line of the CO2 content of the air you will be using (supplied from a gas bag) without the addition of any respiratory CO2. To do this the air is pumped directly into the desiccant column and then through the IRGA, by-passing the insect chamber. When you are ready to measure the CO2 output of the insect, the chamber is then placed in the gas-flow path, between the gas pump and the desiccant column. To test your understanding of the two gas flow paths described above, complete the quiz that follows. It will first ask you to order the components in the system for base line measurements and then again for measurements of the gas flowing through the insect chamber. If you wish to review the components of the system or see the compete apparatus, click here.
To assess your understanding of the two gas flow paths described above, complete the exercises that follow.
Exercise for Baseline measurement (instrument calibration)
Exercise for experimental setup
| Support and funding provided by: |
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Andrew W. Mellon Foundation |
Instrumentation manufactured by: |
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