MOLECULAR EQUIVALENCE OF CARBOHYDRATES TO CARBON DIOXIDE IN PHOTOSYNTHESIS

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Abstract
Methods are described whereby the amt. of CO2 taken up during photosynthesis by a sunflower leaf can be correlated with the increase in dry wt. and the increase in carbohydrate. The amt. of CO2 absorbed by the leaf during photosynthesis was detd. by measuring the changes in pH of a NaHCO3 soln. in equilibrium with the air being circulated within the apparatus. The pH was measured by means of a glass electrode. The increase in carbohydrate[long dash]monosaccharide, sucrose, "sugar not identified," "polysaccharide not identified," and starch[long dash]was detd. by Somogyi''s method either before or after hydrolysis, depending on the type of carbohydrate detd. The increase in the residue which remained after extraction of the carbohydrates enumerated was detd. by weighing. The expts. showed that the % of C in the photosynthate was 41.4%, which approximates the % of C in a disaccharide, 42.1%. This was much lower than the C content of all the organic matter in the leaf, which was about 51-52%. In the expts. at 20[degree] C, the carbohydrates enumerated contained 91.9% of the C absorbed as CO2, and the residue 6.5%[long dash]a total recovery of C of 98.4%. At 10[degree] C the recovery values were respectively: 98.7, 7.9, and 106.6%. It was concluded that the equivalence demanded by the commonly accepted phto-synthesis equation, 6 CO2 + 6H2O=C6H12O6 + 6O2, for the formation of carbohydrates from CO2 has been demonstrated to be valid for sunflower leaves. Expts. on respiration and transformation of the organic matter, newly formed by photosynthesis, indicated that the individual leaves utilized this material differently. The principal material respired, however, appeared to be carbohydrate,.

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