All of Melvin’s previous experiments guided him toward his eventual discovery of how photosynthesis is accomplished. Melvin, through his many previous experiments, and using some experiments used by other chemists, was able to track the carbon molecule through the whole process, which he called “the path of carbon in photosynthesis.” The radiocarbon isotope, 14C , was crucial in Melvin’s work, because the radioactive emissions made it possible to track where that carbon was in the cycle of reactions involving photosynthesis.
Calvin first showed that the radioactive carbon of carbon dioxide got trapped in compounds that already existed inside the organelle, called a chloroplast because it has chlorophyll in it. Then he found that this fixed carbon was transferred into carbohydrates by a transfer of electrons that were energized by light (remember his earlier work on activated electrons with platinum-hydrogen bond?). This notion came in handy here.
He showed that photosynthesis actually consisted of two interacting series of actions: a light phase and a dark phase. The light phase involves the production of activated electrons and release of energy, both of which are used in the dark phase (now called the Calvin cycle) where carbon dioxide gets made into sugars. Calvin showed that the series of reactions involving trapping of carbon from carbon dioxide in air and moving it into sugars all occurred in the dark. Light was needed by the plant to generate energy and the activated electrons. The dark cycle consists of carbon moving through five different compounds that are regenerated.
Between the Nobel Prize and his retirement, Melvin continued to do research and wrote a book about the chemical evolution of life, which was published in 1969. In all, he had over 500 scientific papers and a total of seven books. Even after retirement, Melvin continued to do research through the years. His discoveries lead to the U.S. Department of Energy’s interest in the source of power from solar energy. In addition to working with that department, Melvin also worked with the National Aeronautics and Space Administration (NASA) and the Executive office of the President.
Calvin, M. 1992. Following the Trail of Light. A Scientific Odyssey. American Chemical Society, Washington, D. C.