A controlled experiment was conducted to analyze the effects of darkness and boiling on the photosynthetic rate of incubated chloroplast suspensions. The dye reduction technique was used. Each chloroplast suspension was mixed with DCPIP, an electron acceptor that changes from blue to clear when it is reduced. Each sample was placed individually in a spectrophotometer and the percent transmittance was recorded. The three samples used were prepared as follows. Sample 1 - chloroplast suspension + DPIP
Sample 2- Chloroplast suspension surrounded by foil wrap to provide dark environment + DPIP
Sample 3- Chloroplast suspension that has been boiled + DPIP
Time Sample 1 Sample 2 Sample 3
(minutes) Transmittance % Transmittance % Transmittance %
0 28.8 29.2 28.8
5 48.7 30.1 29.2
10 57.8 31.2 29.4
15 62.5 37.4 28.7
20 66.7 31.8 28.5
A) On the graph paper provided, construct and label a graph showing results for the three samples.
B) Identify and explain the control or controls for this experiment.
C) The differences in the curves of the graphed data indicate that there were differences in the number of electrons produced in the three samples during the experiment. Discuss how electrons are generated in photosynthesis and why the three samples gave different transmittance results.