Evolution of Photos) nthetic Mechanisms 17 



synthesis from this point on than in the previous hundred years. This 

 was the stage that was available to us roughly one hundred years ago. 

 Only slow progress was made in increasing the chemical knowledge 

 of photosynthesis until just prior to World War II — beginning in the 

 middle thirties and then going on after the war at an increasinglv 

 rapid rate. 



What do we know today about the process of photosynthesis? 

 Rather than try to give you a history of how the knowledge has 

 evolved, I am going to ( 1 ) put down some of the established things 

 that we know about photosynthesis, represented by the overall reac- 

 tion, (2) then see which organisms perform this process, (3) then 

 determine what the biological apparatus is within some of the organ- 

 isms (as far as we can do it), and (4) finally go further on down to 

 the molecular level. You see, the question of the evolution of a process 

 of this sort also raises others: What level shall we deal with? Shall 

 we deal with photosynthesis at the level of the whole organism, the 

 level of the cell, the level of subcellular particles, the level of the 

 macromolecules, or the level of the small substrate molecules that 

 are involved? We should, in fact, deal with all of these, if possible, 

 but this is another complication which makes the organization of 

 such a discussion as this extremely difficult. I am going to try to pick 

 up two aspects of it, the mechanism itself on the substrate, and 

 possibly submolecular level, and the apparatus on the subcellular, or 

 macromolecular level. 



Nature of the organisms 



I hardly need review for you the nature of the organisms which are 

 capable of performing the process of photosynthesis. Quite obviously, 

 the higher green plants, such as a wheat field or a forest, do this on 

 a grand scale. There is, however, a whole set of other organisms be- 

 sides the higher green plants which are able to do this, or parts of it, 

 and they represent an important part of the biological scheme of 

 things in the course of our study. These are the marine algae; both 

 the green and the red ones are important in terms of the amount of 

 carbon which is turned over on the surface of the earth per year, as 

 the algae represent the largest single plant family involved in this 

 turnover. Then, there is another group, the blue-green algae, which 

 appear to be more primitive organisms which are capable of doing 

 the entire process of photosynthesis, that is, reducing carbon and 

 evolving oxygen. And, finally, we come to the bacteria, both the green 

 and the red, which are capable of performing part of this conversion 



