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DCPIP (its full name is 2,6-dichlorophenolindophenol) is a blue chemical used as a dye because when it is oxidized it is blue. Once DCPIP is reduced (by addition of electrons) it does not have a color anymore. This reaction can be reversed, and the colourless DCPIP will turn blue again, when it is oxidized.
DCPIP is often used to measure the electron transport chain in plants. It has a higher redox potential (electron affinity) than the Fe-S complex in cytochrome b and will therefore "steal" electrons from it. This means that cytochrome c does not receive them. The process cuts off the electron supply of photosystem I. A common way to illustrate this change is by the addition of vitamin C solution. This reduces the 'jelly' by transforming it to a colourless mass. This experiment can be carried out to illustrate the effect of changing cell sizes on SA/V (surface area:volume ratio). This is known as Titration.
- Mathews, Ahern, Van Holde, Biochemistry, Addison Wesley Longman Inc., 2000 pp534–5