Plant Respiration

Another lab that I have not yet tried, it comes from The American Biology Teacher (Lisa Weise, The American Biology Teacher, Volume 68 No. 5, May 2006) I've written an introduction and added my usual lab formatting, keeping the basic experimental design from the original article. It looks like a very clever way to measure relative CO2 production in radish seedlings in a modified pipette.

Plant Respiration Lab

A cotton swab soaked in an NaOH solution is loaded into the bulb of several pipettes, followed by several seedlings. The tips of the pipettes are then placed (using a home-made, cardboard holder) in a petri dish containing water. As CO2 is produced by the seedlings, it reacts with the NaOH to form baking soda, essentially removing the gaseous CO2, causing a decrease in the pressure inside the pipette. Voila, water rises in the pipette proportional to the amount of CO2 produced. Remember that the initial production of CO2 simply replaces a molecule of O2 with a molecule of CO2 so the pressure differential only comes about when the CO2 is removed.

In a related story, I'm trying to get my school to invest in Vernier's new LabQuest probeware. If that happens, I may or may not use this particular set-up. In some ways it is better for bringing in the chemistry, but on the other hand chemistry is such a big mystery to 8-10th graders, it may actually distract from the lesson. I could always do both...