Determining Rates of Photosynthesis Through Chloroplasts
2) Purpose= measure the rate of photosynthesis in chloroplasts.
3) The chloroplast will be subjected to two experimental conditions- light, and the absence of light, using a spectrophotometer to determine the amount of DPIP reduced at specific time intervals under each condition.
4) I predict the amount of DPIP reduced will vary for each condition and increase over the time intervals. I hypothesize under the light condition the amount of DPIP will drastically be reduced within each five minute time interval. However, under the dark condition the DPIP will not be reduced due to the fact that light is required for photosynthesis.
5) The rates of photosynthesis in each of these reactions will be measured by the amount of light reaching the photocell in the spectrophotometer. This data will be a percentage that represents the amount of DPIP reduced.
DPIP will be used to determine the rate at which the cholorplasts are being reduced. The spectrophotometer will establish the wavelength of light that penitrats the chloroplast solution in turn determining the amount of electrons reduced. In the dark reactions, the spectrophotometer will measure the amount of light passing through a darker solution of DPIP and chloroplasts. In the light reactions, the lighter solution, caused by reduction of the chloroplasts, will allow a larger amount of light to pass through to the photocell of the spectrophotometer. Thus, the spectrophotometer will prove wheter the light or dark reactions affect the rate of photosynthesis in chloroplasts. We will also be using a reference solution made of water, phosphate buffer, and active chloroplasts. The purpose of this solution will be used to set the transmittance level for the experiment. The control solution, which is different than the reference solution, is comprised of water, phosphate buffer, and DPIP. It will be used to prove that the three element of the solution do affect the results- it is strictly the chloroplasts that are subjected to the light/dark conditions.
Requirements for Test Tube Set Up
Data Collected During Time Intervals
Photosynthetic Rate for Light Reactions
Photosynthetic Rate for Dark Reactions
The results for the various conditions differed dramatically. As seen in the table, Data Collected During Time Interval the reference test tube remained at a trasmittance level of 100% for all five experimental tests. The control solution remained fairly constant for all five tests, but did vary slightly after the five minute time interval. In the green test tube, which contained chlorolplasts, DPIP, water, and phosphate buffer, the rate of change increased considerably with each five minute time interval (this can been noted observed in the graph labeled Photosynthetic Rate of Light Reactions.) In the final solution labeled Dark, the rate of change was minimal. Note that in the graph labeled Photosynthetic Rate for Dark Reactions the level of increase is significantly less than the increase noted in the graph for Light Reactions.