Photosynthesis Lab

Purpose: in this lab we were trying to test the rate if absorb acne and transmitance of light in chloroplasts.  Chloroplasts only absorbs certain amounts of light and we tried to test the amount absorbed over time.  Our dependent variable was time and our independent variable

of our experiment was the rate of absorbance for each of our cuvettes

Introduction: Photosynthesis requires light and co2 to work and the biproducts of photosynthesis is o2 and glucose. If there is deprivation of co2 the rate of photosynthesis will drop.  This would only occur in a closed system.

Methods: First we took five cuvettes, one was filled with just water, two with unboiled chloroplasts, one with boiled chloroplasts, and one with no chloroplasts.  All of these had DPIP in it except for the first cuvettes which had just water. One of the cuvettes with unboiled chloroplast had aluminum rapped around it. We used the cuvette filled with water to calibrate the spectrometer, then we took initial readings of all the other cuvettes.  We then exposed the cuvettes to light for five minutes and took the readings, we repeated this two more times. We also used a large water sink bath to prevent heat from being a factor.

Graph and Charts: 

Discussion: The cuvette with just water, dpip, and the phosphate saw no increase in photosynthetic productivity due to the fact that there was no chloroplast to process the light. The cuvettes with chloroplast that was on ice saw a slow decrease in photosynthetic productivity. This was expected because chloroplasts use the light to create O2 through the light reactions of photosynthesis. While it was not natural light, some of the UV rays are still able to be used by the chloroplast for photosynthesis. The cuvette that was wrapped in aluminum foil, still put in front of the light, and still had chloroplasts and dpip saw a sharp decrease in photosynthetic production because there was really no light going in and so all the light was used up. While it was expected that the light from the lamp would provide enough UV for photosynthesis to occur (which it did) it was surprising that the rate of photosynthetic production declined in all of our cuvettes except for the one with no chloroplast, which saw no decrease or increase in photosynthetic productivity. This was because since there are no chloroplasts, nothing could be photo synthesized. The dpip would turn from blue to colorless if it was used by the chloroplast, which it was. It did not turn from blue to colorless in the cuvette with the boiled chloroplast becasue since the chloroplasts were denatured the dpip couldn't be reduced and used. 

Conclusion: How is it possible that there was no increase in absorbance? The chloroplasts need CO2 to restart the cycle. Over time in a closed container there was no CO2 being made. Only a lot of oxygen. The oxygen could not keep the rate of photosynthesis going so there was a decrease in light absorbance.

Sources: http://www.answers.com/Q/What_is_the_effect_of_boiling_chloroplasts_on_the_subsequent_reduction_of_DPIP

Charles Filipek