Photosynthesis dark stage/reactions

The essence of natural photosynthesis is the use of photochemical energy to split water and reduce CO2. Molecular oxygen is evolved in the reaction, although it appears at an earlier stage in the sequence of reactions than the reduction of carbon dioxide. Photochemical processes produce compounds of high chemical potential, which can drive a multistep synthetic sequence from CO2 to carbohydrate in a cyclic way. Reaction (16) is quite endoergic and thus thermodynamically very improbable in the dark (AG° = 522 kJ per mole of CO2 converted). Production of one molecule of oxygen and concomitant conversion of one molecule of carbon dioxide require the transfer of four electrons ... 

In land plants and green algae (chlorophytes), photosynthesis has two distinct stages, the light reactions, which convert light energy to ATP and NADPH and the dark reactions, which convert CO2 to carbohydrate using ATP and NADPH. Both occur in the chloroplasts (Fig. 13.4). 

Leaves, needles, algae and chloroplasts can be frozen to 77K. In this stage the fluorescence kinetics can be measured one or several times according to the dark time given between two excitations. The dynamic behaviour appears to be hyperbolic which confirms the h3 othesis of Strasser et al.(1,2,3). Reversibility of variable fluorescence has been observed earlier (4,5,6) and interpreted in a different manner. The following experiments can be considered as a powerful tool to describe the energetics of primary reactions of photosynthesis in a new way. 

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