Botany lab twelve photosynthesis

This term the early preparation of plants was overlooked. Spring break preceded to the laboratory. Test plants were not set up until Easter Sunday. This also did not leave open the opportunity to dry run the set ups at the house. This failure to use well established plants and to have trial run the plants would haunt the laboratory.

Plants wound up in paper cups, and the plants were not yet stable with intact root hairs. The plants were still stressed by the following Tuesday, only 40 hours after being transplanted.

The tongs were to lower the paper cups into the photosynthesis chambers. The Vabira unit was measuring Centella asiatica.

The Vabira requires a rather lengthy calibration period to the current atmospheric carbon dioxide levels which are roughly 433 ppm at present.

The issue of the oxidation of RuBisCo, typically around 30°C, would also be a potential issue.

The Neulog unit was measuring Alternanthera sessifolia.

This term the Vabira unit would bottom out at 400 ppm and would not drop below 400 ppm. The carbon dioxide in the chamber would drop in a matter of minutes to 400 ppm where the value would remain pegged for at least 30 minutes.

On a first run, the Vabira/Centella photosynthesis chamber rapidly heated to 30°C. This was thought to contribute to the flatline CO2 values. 

For a second run the sensors were tucked up higher in the chamber. Not that this would troubleshoot the temperature issue, but this pulled the sensors up out of the leaves.

The Neulog team also saw CO2 flatline at 400 over a period of twenty minutes. The oxygen sensor, recorded a drop on oxygen, rather than the expected gain in oxygen. That the carbon dioxide levels fell suggests the Calvin cycle was operational, so photosynthesis was likely to have been occurring and oxygen should have been generated. But the plant was apparently respiring and burning more oxygen than it produced.

As done last year, the Neulog sensors were put on the sink top.

The graph wasn't graphing and the touch screen was balky. Eventually the screen accepted the Run input which seemed to necessary to starting up the graph. 

Writing the values manually once again proved the best approach. With CO2 falling by the minute, data should be recorded every minute.

This arrangement may have left the cable exposed to lateral forces from students crowding around the sensor readout panels.

The USB make plug disintegrated. Fortunately there were two cables, one for the WiFi and one for the USB module. The downside is the the module female is a USB mini, not a USB micro or USB C which are more ubiquitous.

The problems with the oxygen sensor and the dependence on a single power cord suggest a need to replace the sensors. 

Data was reflected onto the whiteboard.

Data must be recorded every minute. The above data, however, is somewhat cherry picked. The reality was more complex.

Upon closing the lid, the CO2 levels rose and then fell. There appears to be on the order of a two to three minute lag between a value and a reading by the meter. The first three values probably represent the cardon dioxide readings in open air. Why the chamber would have more CO2 is not entirely clear. Piror to the second run the air was circulated, perhaps incompletely, in the chamber. 

The laboratory ran to two hours and took another 45 minutes to clean up. Most of the set up was done in class, but equipment was pre-positioned the day before in A101 to ensure everything was at ambient temperature. 

Vernier produces some expensive but interesting bluetooth connected oxygen sensor in their Go Direct O2 Gas Sensor and related series of device. That is an option to be explored prior to 2027.