Plant growth – A thermodynamicist's view

The synthesis of glucose requires an increase of enthalpy and a decrease of entropy such that the Gibbs free energy increases. This is impossible by the laws of thermodynamics unless there is an accompanying, compensating process that decreases the Gibbs free energy. Schr?dinger 1] has suggested that the accompanying process should be the absorption and reemission of radiation. This process supplies the heat of reaction and the entropy increase of radiation is more than enough to offset the chemical decrease of entropy. And yet we are not satisfied with Schr?dingers proposition, because we see no connection between the entropy increase of radiation and the physiology of the plant. Therefore we propose an alternative: The accompanying process consists of the transpiration of water and the mixing of water vapour with air; in this view radiation only furnishes the heat of reaction. Received February 14, 1997