Question

DCPIP ( dichlorophenolindophenol) is
a. Inhibitor of electron transport
b. Herbicide
c. Inhibitor of photosynthesis
d. Blue coloured hill oxidant which becomes colourless on being reduced

Answer 1

DCPIP (dichlorophenolindophenol) is a compound that is often used as a redox dye. It is used in measurements of the electron transport chain in plants for its higher affinity for electrons than ferredoxin.

Complete answer:
DCPIP (dichlorophenolindophenol) is a redox dye which is used commercially as an acid-base indicator. In an oxidized state, it is blue while in a reduced state, it becomes colourless. It is commonly used in Hill reaction as a hill oxidant. DCPIP is used as a substitute for NADP+. The rate of light-dependent reaction (Hill reaction) can be measured with this property of DCPIP, as one of the stages of the light reaction is an electron transport chain that usually ends with the reduction of NADP+. If DCPIP is present in the reaction, it also gets reduced to DCPIPH2.
The rate of photosynthesis can be measured by measuring the rate at which this dye changes colour (is reduced) when exposed to light in a photosynthetic system. The rate of DCPIP colour change over time is directly proportional to the rate of oxygen evolution from the chloroplasts. Thus, it is a good measure of photosynthesis. This reaction is reversible, as colourless DCPIP can be re-oxidized to blue.

Thus, the correct answer is option D.

Note: DCPIP, an artificial electron acceptor, is a useful tool for measuring oxygen evolution rates, because it mimics NADP. The dye is blue in oxidized state with a maximal absorption at 600 nm whereas in reduced, DCPIP is colourless. It is also commonly used as an artificial electron acceptor for enzyme assays.