Farmers want to use the most dilute concentration of herbicide that will still s
ID: 64735 • Letter: F
Question
Farmers want to use the most dilute concentration of herbicide that will still stop the rate of photosynthesis of weed plants. A photosynthesis experiment was conducted that was similar to the experiment that we conducted in Investigation 2. Three different concentrations of herbicide were added to tubes containing chloroplasts and DCPIP, and the change in absorbancy was measured over a 4.5 minute interval. A fourth treatment was also run in which no herbicide was added to the chloroplasts and DCPIP, but the tubes were kept in the dark. According to the results of the photosynthesis experiment shown below, which concentration of herbicide was the most dilute concentration that was able to stop photosynthesis? The three Moruron herbicide treatments were 1 X 10-10 M Moruron, 1X 10-8 M Moruron and 1X10-7 M Moruron.
in 0.0s 1X10-7 0.1 -1 x 10-10 1 X 10-8 1 x 10-8 -0.15 _ Dark -0.2 ·0.25 TimeExplanation / Answer
Option C seems to be correct since, DCPIP absorbance (might be blue) is not altered with 1 x 10-8 dilution of herbicide indicating complete inhibition of photosynthesis at different time intervals. If we look at 1 x 10-10 dilution, the photosynthesis is very active, where the absorbance is decreased from 0 (blue) to -0.2 (colorless) after 4.5 min i.e. DCPIP is reduced from blue to colorless with active photosynthesis results in decreased absorbance at 600 nm in the spectrophotometer. In case of dark without herbicide and 1 x 10-7 dilution also have a slight change in absorbance due to a very low (narrow range) rate of photosynthesis that in contrast to 1 x 10-8 dilution where it is completely abrogated.
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