the American biochemist who first described the photosynthetic process, whose steps are now known as the Calvin cycle, by tracking radioactive carbon dioxide as it is transformed into carbohydrates. He allowed carbon-14 to be absorbed by plants, then mashed up the cells and separated the contents using paper chromatography. He discovered intermediate reaction products of photosynthesis and worked out the reaction scheme. He also discovered that photosynthesis proceeds in the absence of light. He later confirmed the primary elements that formed the atmosphere from which primitive life developed. For these achievements he received the 1961 Nobel Prize in chemistry.