Results and Methods for Measurement of Photosynthetic Rate of the Leaves of Bean and Corn Plants

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Methods

To determine the rates of photosynthesis for the 5-week-old bean plant and the 5-week-old corn plant, the QUBIT Systems, Inc. apparatus was employed. A diagram of this apparatus is presented in page 4-5 of the biology lab manual (Bio, 2002). The computer connected to this apparatus was adjusted to present two graphs which measure the percentage of Oxygen in the air over time and photon flux (micromole quanta/m^2/s). Next, a leaf was retrieved from the top of a bean plant and sealed from the air in the laboratory via thumbscrews inside the leaf chamber of the apparatus. Caution was used to ensure that the leaf was not placed directly beneath the oxygen sensor of the apparatus, since doing so would result in improper amount of surface area of the leaf being exposed to sunlight. To ensure that the leaf was not over heated by the lamp's light, a petri dish was filled with water and placed directly over the leaf. Next, the mouse of the computer with the Logger Pro software was used to start the plot of the two graphs: %Oxygen / Time (s) and photon flux (micromole quanta/m^2/s) / Time (s) (maximum time for plot was 30 minutes). The students then filled a bag with their breath and connected it to the leaf chamber to flush out the laboratory air. The chamber was resealed, the lamp was adjusted to maximum luminance, and the graph was observed until the amount of oxygen being produced reached equilibrium, at which point the plot was stopped and printed off. The graph of %oxygen over time was analyzed for its slope (Beta sub-1) by the logger pro software in the stage at the beginning where oxygen production was slow, the stage where it was linear, and the stage where it was decreasing to equilibrium. The leaf was then removed from the chamber and the surface area of the leaf within the chamber was determined using a transparent grid. This procedure was then repeated in the exact same steps with a 5 week old corn plant leaf. The photosynthetic rate for each of the three stages and each leaf was then determined using the following formulas.

Rate of Oxygen Production (Bio,2002):

(Micromoles of Oxygen/L/min (T=Temperature=25C))

Rate of Oxygen Production as a function of leaf surface area (Bio, 2002):

Photosynthetic Rate=(Micromoles of Oxygen/m^2/min)

Results

The collection of data of the slope of each leave+s' oxygen production yielded two charts below, one entitled Bean and one Corn.

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