Inexpensive Apparatus for Measuring Respiration and Photosynthesis Based on CO₂

 

Paul Willing

Tested Studies in Laboratory Teaching, 2006, Volume 27

Abstract

This workshop presents a modification of a previous ABLE workshop (Winnett-Murray et al. 2000) that involved a comparison of the metabolic rates of an ectotherm (lizard) and an endotherm (mouse) at various temperatures. They sampled gases over time from closed containers containing the organisms. In our modification of this lab exercise, students monitor respiration continuously in a closed, circulating system, using a CO2 sensor, an analog to digital interface (Lab Pro**), and a laptop computer running Logger Pro software**. Students are able to work in groups of 3 because each setup is relatively inexpensive. CO2 sensors are usually based on infrared light absorption, and tend to be expensive, ranging from $1000 on up. However, Vernier** has a CO2 sensor for about $250 that has a sensitivity of + 20 ppm, which is quite adequate for educational use. With some modifications, this sensor can be built into a closed, circulating system to accurately monitor respiration of a single cricket in as little as 5-10 minutes. By simply switching chambers, the same apparatus and software can be used to monitor photosynthesis in a subsequent lab exercise.

Keywords:  photosynthesis, respiration

Virginia Tech (2005)