Respiration, Intramolecular

anaerobic respiration, the generation of gaseous carbon dioxide by a plant without the absorption of free oxygen.

Intramolecular respiration invariably accompanies ordinary respiration, as first shown by the Russian biologist S.P. Kosty-chev in 1907–11; however, under normal conditions, the proportion of intramolecular respiration is limited. Intramolecular respiration is characteristic of certain tissues (the meristem, the fleshy parts of fruits, tubers). Chemically, the intramolecular respiration of green plants is closely related to alcoholic fermentation. Intramolecular respiration intensifies sharply when the partial pressure of oxygen in the atmosphere falls below 5 percent. Most green plants will die if intramolecular respiration is prolonged, because of the sharp decrease in energy yield, the great expenditure of plastic substances (20–30 times higher than in ordinary respiration), and the poisoning of the plants by the toxic products of the process. Because of intramolecular respiration certain plants, such as rice, are capable of developing normally even with a constant deficiency of oxygen in the atmosphere.