Vernier Probe Difficulties Power point (Sample Data) Power point to accompany Carbon Teaching Experiment Written by: Jonathon SchrammA, Eric KeelingB, Dijanna FigueroaC, Lindsay MohanA, Michele JohnsonC, and Charles W. AndersonA Culturally relevant ecology, learning progressions and environmental literacy Long Term Ecological Research Math Science Partnership 2012 Disclaimer: This research is supported by a grant from the National Science Foundation: Targeted Partnership: Culturally relevant ecology, learning progressions and environmental literacy (NSF-0832173). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

In the light What is happening in this chamber? It looks like “bad” results, because there is no net uptake of CO2 – superficially, one might say “the plant is not doing any photosynthesis”. However, we should inspect the results of the dark treatment before we jump to any conclusions. Go to next slide. Gross photosynthesis, but no net photosynthesis – see next slide MSP Carbon Teaching Experiment

In the dark The plant is respiring. We see this clearly in the dark. But it is safe to assume that at least this level of respiration is occurring in the light also. (The plant obviously doesn’t stop respiring in the light). So think back to the previous slide. In the light there was no net change in CO2 level in the chamber. But with this level respiration happening, that means there must be uptake of CO2 to just balance the release of CO2 from respiration. So there IS photosynthesis happening, but at a relatively low level. We would call that gross photosynthesis, but no net photosynthesis. Follow-up question for extended discussion: Could the plant grow if there is no net photosynthesis? Answer: No. The plant must “make more money than it spends”. Normally, in the light a healthy, thriving plant will take in much more carbon than it loses from respiration. The surplus carbon can then go into storage for future respiration, or into making biomass that allows the plant to grow larger or reproduce. MSP Carbon Teaching Experiment

In the light What is going on here? Looks kind of weird. Actually this is an empty chamber. Notice the vertical axes and how little those changes actually are. There is background “noise” in all instruments, Vernier probes are no exception. MSP Carbon Teaching Experiment

In the light Again, changes are very small. Drift of 20 ppm CO2 may be totally meaningless. Signal is not above noise. Temp may not be stable, also – the probes are affected by changing temperature to some extent. MSP Carbon Teaching Experiment