1958 – USA
‘The cycle of chemical reactions by which plants turn carbon dioxide and water into sugar during photosynthesis’
In the Calvin cycle, which takes place in most plants, the initial product of the dark reactions (in which carbon is converted to sugar) is a compound with three carbon atoms per molecule. These are known as C3 plants.
A small group of plants – including maize, sorghum and sugar cane – are formed by a different cycle, known as the Hatch and Slack pathway. In this cycle the initial product of the dark reactions is a compound with four carbon atoms per molecule. These are C4 plants and can assimilate carbon dioxide at about twice or more the rate of C3 plants, and hence grow faster.
Calvin used radioactive C14 to study the photosynthesis cycle.