reduction reactions. The over-all reaction of photosynthesis may be 

 represented as follows: 



6 COo + 12 H.O — > C,,H,,A; + 6 Oo + 6 H.O 



The light energy absorbed by the chloroplast is converted to chemical 

 energy by this same organelle and is used to bring about the photolysis 

 or breakdown of water in the photosynthetic process (Figure 3-17). 



Photolysis 

 of water 



Glucose 



Reversal 

 of 



■• Embden-Meyerhof 

 cycle of 

 glycolysis 



Figure 3-17. Schematic Representation of the Photosynthetic Reaction. 



The electron released during photolysis reduces triphosphopyridine nu- 

 cleotide (TPN) with the concomitant release of molecular oxygen. The 

 reduced pyridine nucleotide (TPN.H) is oxidized by an electron trans- 

 port system consisting of flavins, ascorbic acid, and possibly vitamin K 

 and a cytochrome. The energy derived from this oxidation is utilized to 



STRUCTURE AND FUNCTION OF CYTOPLASMIC ORGANELLES / 43 



