Dichlorphenolindophenol
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.