Radioactive carbon and a flask of algae mapped how plants build sugar from air
In the early 1950s, Melvin Calvin's team fed radioactive carbon-14 dioxide to the algae Chlorella in a glass 'lollipop' vessel, then killed samples at split-second intervals and tracked which molecules lit up first on photographic film. Piecing together that sequence revealed the full cycle of reactions that fixes carbon dioxide into sugar in every photosynthesizing plant on Earth. Calvin won the 1961 Nobel Prize in Chemistry for mapping it.