Connor Sallee

Lab Abstract


This experiment was derived to find if temperature affects a C-3 or C-4 plantÕs rate of photosynthesis. C-3 plants generally accumulate in damp, low-light habitats, and C-4 plants live in dry, arid habitats. The C-4 plants have introduced an extra cycle into the Calvin cycle, an early reaction that fixes CO2 into 4-carbon sugars called oxaloacetate (hence the names C-3 and C-4 for the number of carbon sugars) by putting CO2 onto a different receptor molecule (PEP) from the enzyme, PEP carboxylase. Because the C-4 plants have this cycle, they can close their stomata to retain moisture under hot, dry conditions, but still keep photosynthesis running at good efficiency. Therefore, temperature must affect the rate of photosynthesis; cold temperatures will least affect a C-3 plant, and hot temperatures will least affect a C-4 plant. We tested both C-3 and C-4 plants in a closed chamber with a CO2 sensor, in room temperature, cold temperature, and hot temperature for ten minutes each. Data was collected using the program Logger Pro. After all the data was collected, we created a graph, showing the increased and decreased rates of photosynthesis. A statistical test was run, and we found our data to be insignificant, the P-value was . The results of the experiment were the opposite of the proposed hypothesis. The data graph showed that temperature did not affect photosynthesis, and made it look as if photosynthesis was solely based upon the amount of light being shown upon a plant. There were several potential problems with the experiment that would explain the faulty outcome. The experimentÕs data was created using only five grams of each plant. It could be possible that more grams were necessary in order to show the true rate of photosynthesis in any given situation. The chambers that held the plants could have not been adequately aired out between each experiment. Also, the plants were only submersed in the different temperatures for ten minutes each. This could have been too short a time for the plants to adequately adjust to the alternate temperature. The CO2 interface also could have been not functioning properly – in the cold temperature test for the C-4 plant, the data showed that it had over 1500 ppm CO2 almost the entirety of the ten minutes. There was no initial fluctuation of the data like there was for the other trials, for the CO2 interface to adjust to proper temperature. The hypothesis of the experiment was mirrored by two alternate studies found on the CABLE website. When in hot conditions, C-4 plants benefit by having high rates of photosynthesis, and C-3 plants cannot handle the heat. In cold conditions, C-3 plants benefit, and C-4 plants cannot handle the cold. The C-4 plant, when in cold temperatures, cannot utilize the benefit it receives from its extra cycle. Thus, the plant cannot photosynthesize to its potential, and is rendered useless in a cold environment. C-3 plants have more chlorophyll, to utilize their generic low-light environment. In a hot environment, the plants take in too much sunlight and die. A plantÕs rate of photosynthesis is almost entirely based upon temperature. This is a common hypothesis on which these two studies both agreed. Studies similar to this experiment should have a proper amount of time and materials in order to collect proper data. Our experimentÕs data showed that we lacked the proper amount of time and materials, but our hypothesis was correct."Low temperature effects on leaf physiology and survivorship in the C-3 and C-4 subspecies of Alloteropsis semialata" by Osborne CP, Wythe EJ, Ibrahim DG, et al. "The temperature response of C-3 and C-4 photosynthesis" by Sage RF, Kubien DS