FIG. 8.6

How is CO₂ used to synthesize carbohydrates?

BACKGROUND In the 1940s, radioactive ¹⁴CO₂ became available in quantities that allowed experiments. Melvin Calvin and Andrew Benson used ¹⁴CO₂ to follow the incorporation of CO₂ into carbohydrates.

EXPERIMENTS AND RESULTS

CONCLUSION The initial step in the Calvin cycle unites the 5-carbon RuBP with CO₂, resulting in the production of two molecules of 3-PGA.

FOLLOW-UP WORK In the 1950s, Marshall Hatch and colleagues showed that some plants, including corn and sugarcane, accumulate a 4-carbon compound as the first product in photosynthesis. In Chapter 29, we explore how C₄ photosynthesis allows plants to avoid the oxygenase reaction of rubisco.

SOURCE Calvin, M., and H. Benson. 1949. “The Path of Carbon in Photosynthesis IV: The Identity and Sequence of the Intermediates in Sucrose Synthesis.” Science 109:140–142.