Molecular Equivalence of Carbohydrates to Carbon Dioxide in Photosynthesis.

The photosynthetic reaction is commonly summarized by the following equation: 6 C02+ 6 H20 = C6H1206+6 02 The organic material formed has been commonly assumed to be glucose or some other carbohydrate. This equation is based principally on three types of facts: (a), the preponderance of carbohydrate material in plants, and the observed rapid increase in carbohydrates on illumination of green plants; (b), the near quantitative agreement of the increase in weight of organic matter produced and the amount of carbon dioxide photosynthesized; and (c), the approximation to the value of unity of the ratio between oxygen evolved and carbon dioxide absorbed. The first of these facts, (a), is only qualitative and does not serve to establish the stoichiometric relations required by the equation. The investigations thus far reported, that have attempted to confirm the molecular equivalence between carbon dioxide assimilated and carbohydrate formed, have failed in their purpose as a brief review will show. Fifty years ago, SAPOSCHNIKOFF (12) determined, as glucose, the amount of carbohydrate formed during photosynthesis in relation to the amount of carbon dioxide absorbed. In three experiments with sunflower leaves, he found that 63.8, 67.7 and 87.1 per cent. of the theoretical amount of carbohydrate was formed from the carbon dioxide absorbed. Because he found so great a discrepancy between the observed and theoretical recovery of carbohydrate, he concluded that "Bei allen drei Versuchen erhielt ich ein Deficit der Kohlenhydrate im Vergleich zu der zersetzten Kohlensiiure. Auf diese Versuche hin muss man annehmen, dass ausser den Kohlenhydraten (Stiirke) sich noch ein anderer Stoff bildet, und vielleicht ist dies Eiweissstoff. " Later KRASCHENINNIKOV (8, 14b) examined five different plants and found the following ratios: (A), the increase in dry weight as compared to the carbon dioxide absorbed; (B), the increase in carbohydrate in relation to the carbon dioxide absorbed; and (C), the increase in carbohydrate as related to the increase in dry weight.