CHLOROPHYLL AND ENERGY 



175 



COOH 



CHa 



I 

 HC-COOH 



I 

 CO 



I 



COOH 



COOH 



I 

 CH2 



I 

 CH2 



I 

 CO 



COOH 



I 

 CH2 



CH2 



I 



I 

 COOH 



COOH 



4. Oxalosuccinic 5. Octoglutaric 6. Succinic 



acid 



acid 

 COOH 



CH2 



I 

 CHOH 



acid 

 COOH 



COOH 



I 

 CH 



CH 



I 

 COOH 



7. Fumaric 

 acid 



COOH 



CH2 



I 

 CO 



COOH 



8. Malic acid 



COOH 



9. Oxaloacetic 

 acid 



CO 



I 

 CH3 



10. Pyruvic 

 acid 



Formulae of acids taking part in the citric acid cycle 



A third valency is seized by a new atom of oxygen and we 

 have a carboxyl, an organic acid - COOH. The end of the 

 evolution is reached when the fourth valency is also saturated 

 by the oxygen and we have carbon dioxide, CO 2. 



H 



C-OH^ -C=0^ -C=0-> C=0 



H H OH O 



One can expect that reduction will proceed in the opposite 

 direction to oxidation; the carbon dioxide will liberate its 

 first valency from oxygen in becoming organic acid, and so on. 

 The research is thus set on a definite course. 



Oxidation-reduction 



Oxidation has, of course, its necessary counterpart, 

 reduction, for, if any substance is oxidized, the oxygen that it 

 acquires must come from another substance or at least from 



