How many carbon dioxide molecules are needed to make one glucose molecule through photosynthesis?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — Photosynthesis Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

To produce one molecule of glucose ( $C_{6} H_{12} O_{6}$ ) through photosynthesis, six molecules of carbon dioxide ( $C O_{2}$ ) are required.123

This process occurs during the "dark reactions," or the Calvin-Benson cycle, which takes place in the stroma of the chloroplast. During this cycle, the enzyme RuBisCO attaches carbon dioxide to a five-carbon compound, eventually leading to the formation of three-carbon compounds that are converted into glucose using chemical energy generated during the light reactions. Specifically, six revolutions of the cycle are necessary to fix six carbon dioxide molecules, which ultimately yield the carbon atoms needed to synthesize one six-carbon glucose molecule.43