In this investigation oxygen production was used to measure the light reaction. What are two additional products that could be measured? What purpose do they serve in the light-independent (dark) reaction?
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Answer:
It is fairly easy to show that plants produce oxygen and starch in photosynthesis. At age 14–16 students may have collected the gas given off by pond weed (for example Elodea) and tested leaves for starch.
It is not quite so easy to demonstrate the other reactions in photosynthesis. For the reduction of carbon dioxide to carbohydrate there must be a source of electrons. In the cell, NADP is the electron acceptor which is reduced in the light-dependent reactions, and which provides electrons and hydrogen for the light-independent reactions.
In this investigation, DCPIP (2,6-dichlorophenol-indophenol), a blue dye, acts as an electron acceptor and becomes colourless when reduced, allowing any reducing agent produced by the chloroplasts to be detected.