A controlled experiment is conducted to analyze the effects of darkness and boiling on the rate of photosynthesis. The experimenter incubated chloroplast suspensions mixed with DPIP, an electron acceptor that changes from blue to colorless when it is reduced (gains electrons). Each sample was placed individually into a spectrophotometer to determine the percent transmittance (the amount of light that passes all the way through the sample). The three samples were prepared as follows: Sample 1: chloroplast suspension +DPIP +
Sample 2: chloroplast suspension surrounded by foil wrap to provide a 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 32.4 28.7
20 66.7 31.5 28.5
1. On the graph paper provided, construct and label a graph showing results for the three samples.
2. Identify and explain the control or controls for this experiment.
3. 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.