Here we present a quantitative approach to study the effect of various factors on photosynthetic rates of aquatic plants using bromothymol blue. We can measure the absorbance by the dye at 615 nm as an indication of the acidity due to CO2 concentration in the solution, which relates to the rate of photosynthesis by the aquatic plant in the solution. We provide general instructions for using this dye to measure photosynthetic rates, as well as specific instructions for an experiment to study how photosynthetic rates are affected by the herbicide DCMU (3-(3,4-Dichlorophenyl)-1,1-dimethylurea), which blocks electron transport at the quinones in PSII. This example connects electron transport to CO2 fixation and the change in the chemistry of the solution as measured through light absorption by the dye. This system can be used to study the effects of various factors on photosynthesis, which can be treated as inquiry-based or as guided-inquiry.
Keywords: photosynthesis, herbicide, electron transport train, Inquiry-based learning, bromothymol blue
University of Victoria (2022)
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