Table of Contents
Photosynthesis is converting light energy to chemical energy that is stored in sugars or other organic compounds that occurs in plants, algae, and certain prokaryotes (Campbell Biology). Chloroplast is the organelle that leads two sets of reactions of photosynthesis. That light energy that photosynthesis renovates, is used to decrease NADP+ into NADPH and to also produce ATP, through the light dependent reactions of photosynthesis. Carbon dioxide is used to produce glucose, by using chemical bond energy that is stored in that reducing command of NADPH and in ATP while, the independent reactions of photosynthesis occur (Lab Handout for Photosynthesis Leaf Disk Assay.)
There are many experiments that can examine photosynthesis, and the rate at which photosynthesis can occur, which could depend on environmental variables like light intensity and color or brightness, the Sodium Bicarbonate solution (the carbon source for photosynthesis- ranging from 0.2% – 0.5%), pH level, their temperatures, or the plant variables, like the plant type, leaf color, or leaf size.
An example could be experimentally designing the study light color, comparing photosynthetic rate with red light (experimental group), to photosynthetic rate with white light (control group). The independent variable, light color (red), would be tested, with all other variable constant, to see if it has an effect on the photosynthetic rate using an assay for example the one used in the Photosynthesis Leaf Disk Assay lab experiment.
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Materials and Methods
In preparing the Photosynthesis Leaf Disk Assay experiment, two students hole punched spinach leaves, avoiding large veins, until there was totaling 24 disks, 12 for sodium bicarbonate and 12 for the water solution and then were placed immediately into those two petri dishes. The plungers to two syringes were then removed by the two students, and the 12 leaf disks, from both the one-half filled sodium bicarbonate (0.2%) and water petri dishes, were gently transferred all the way down to the tip of the syringes by spatula/forceps.
The plungers were then placed and pushed back down to about the 2mL mark of the syringe, carefully without the leaf disks being damaged. Five mL of the water and then also five mL of the sodium bicarbonate were sucked up by the syringes, and after the two students held them upright and pushed as much air out as possible ensuring all the leaf disks were submerged. Next, the two students placed their thumbs over the tip of each syringe and pulled back slowly on the plunger to about the ten mL mark on the syringe.
The two students pulled back the plunger a little when ensuring not to damage the discs, while vacuuming and pulling the air out of the leaf disks, which was creating a vacuum and pulling out the air of the leaf. This was repeated a few times until the leaf disks dropped to the bottom of the solutions in the syringes, a few were still floating which was okay, because the two students did not want to over vacuum infiltrate, that would have damaged the leaf tissue. The students emptied the disks and solution, from the syringe, back into the correct petri dish filled with each solution.
Finally, the two students placed both cups under the standard light conditions at thirty cm and recorded the number of floating disks and any disk that was no longer touching the bottom of the dish every two minutes, stirring the solutions gently and periodically, until they reach thirty minutes. The two students conducted the same experiment only changing the light source variable to the color red, to determine which light produced a faster rate of photosynthesis, their experimental design. (Lab Handout for Photosynthesis Leaf Disk Assay.)
Results
Overall, the standard white lighting showed a faster rate of photosynthesis, then the red lighting. The rate at 50% gives the best approximation of the overall rate of photosynthesis. The white light produced a photosynthetic rate of 0.45/min. while red light produced a rate of 0.24/min. Figure 1 represents this with the percent of leaf disks floating in minutes in the sodium bicarbonate under white light and figure 2 is showing that also only with the leaf’s under red light. Despite this, the rate at which it took the red lights disks floating to reach 100% was quicker than the white lights.
The red lighting took estimated six minutes to reach 100%, where it took the white light disks eight minutes to reach 100% of floating disks. However, the white lighting rate of floating disks was still faster than the red lighting, according to our rate at 50% calculated. Figure 3 represents the percent of leaf disks floating in minutes in the sodium bicarbonate under white versus red light.
Annotated Bibliography
- Bie, Z., Ito, T., Shinohara, Y. 2004. Effects of sodium sulfate and sodium bicarbonate on the growth, gas exchange and mineral composition of lettuce. Scientia Horticulturae 215-224.
“Effects of sodium sulfate and sodium bicarbonate on the growth, gas exchange and mineral composition of lettuce,” is an experiment written by Bie, Ito, and Shinohara that tested the effects of sodium sulfate and sodium bicarbonate on lettuce by testing the growth, gas exchange and mineral composition on the lettuce. It showed that the two plants tested were affected differently by the sodium sulfate and sodium bicarbonate in comparison to water, and unlike structures of the lettuce were adjusted due to the salinity treatments A nutrient solution that contained 0, 20, 40 and 60 mm Na2SO4 or 0, 2.5, 5 and 7.5 mm NaHCO3, was what the treatments were pertained through. Under the NaHCO3(Sodium bicarbonate) salinity, the water uptake was not disturbed but it did affect lettuce leaf growths negatively, proving that plants can be affected by toxic treatments.
- Harris, G., Cheesbrough, J., Walker, D. 1982. Measurement of CO2 and H2O Vapor Exchange in Spinach Leaf Discs’. Plant Physiol 102-107.
Harris, Cheesbrough and Walker wrote “Measurement of CO2 and H2O Vapor Exchange in Spinach Leaf Discs’” which was done to measure CO2 and H20 vapor exchange and the levels in spinach leaf disks. This was conducted to give additional awareness to photosynthesis and all the factors which can affect plants and their mechanisms. What caused the plants to break down and not allow photosynthesis to occur at the higher levels of CO2 is what this experiment proved.
When conducting the experiment, they used a leaf chamber, which measured the levels that they were in search for and to also pump into the closed chamber, the water and any other metabolites. The leak disks had a moderately low resistance to H2O water vapor, therefore in the normal atmosphere it could also maintain many hours of photosynthesis. However, in the abaxial surface, the results show that the leaf disks had a higher resistance to water vapor and while the CO2 levels were nurtured, the photosynthesis was not saturated including during the daylight. This experiment gave even more understanding and awareness on the way that plants do produce oxygen. Also, how the environment, the normal or abaxial atmosphere, can cause a plant to stop working.
- Terashima, I., Evans, J. 1988. Effects of Light and Nitrogen Nutrition on the Organization of the Photosynthetic Apparatus in Spinach. Plant and Cell Physiology. 29(1): 143-155.
“Effects of Light and Nitrogen Nutrition on the Organization of the Photosynthetic Apparatus in Spinach” was written by Ichiro Terashima and John R. Evan. It discussed an experiment that they conducted to determine if photosynthesis was disturbed if Nitrogen budgets of totally prolonged young leaves of spinach were gown under three growth irradiances at four nitrate concentrations.
- Yorio, N., Goins, G., Kagie, H., Wheeler, R., Sager, J. 2001. Improving Spinach, Radish, and Lettuce Growth under Red Light-emitting Diodes (LEDs) with Blue Light Supplementation. Hort Science. 36(2):380–383.
Neil C. Yorio1, Gregory D. Goins, and Hollie R. Kagie, Raymond M. Wheeler and John wrote an article about an experiment they conducted called, “Improving Spinach, Radish, and Lettuce Growth under Red Light-emitting Diodes with Blue Light Supplementation.” In this experiment, they took and grew radish, lettuce, and spinach under 660-nm red light-emitting diodes, and they also grew some under cool-white fluorescent lamps or red light-emitting Diodes enhanced with 10% blue light from blue fluorescent lamps.
The results were that they found that the adding of blue light to the red light-emitting Diodes was unsatisfactory for accomplishing the greatest growth for these plants. This was because the total dry weight for the radish and spinach were considerably lower when they were growing under the red light-emitting Diodes + 10% blue fluorescent light than when grew under cool-white fluorescent light.
