18 The Nature of Biological Diversity 



process. The bacteria can transform electromagnetic energy into 

 chemical energy, hut not with the evolution of oxygen. They use other 

 reducing agents than water in order to reduce the carbon and there- 

 fore they produce other oxidants than oxygen. But the bacteria are 

 able to capture electromagnetic energy from the sun and transform 

 it into chemical potential. 



These classifications of organisms really constitute the whole gamut 

 of biological diversity, as far as I am aware of it, which can do all, 

 or some, of this conversion (energy manipulation) process; they all 

 can do the crucial part of it — the quantum absorption and the quan- 

 tum conversion. 



Mechanism of the Photo synthetic Process 



A. The path of carbon in photosynthesis 



Let us see what we know about the mechanism of the process of 

 photosynthesis itself. Part of this knowledge is a result of the tracer 

 work which was mentioned earlier, 1,23 beginning before the war. 

 My colleague, Sam Ruben, began this work, using radioactive car- 

 bon-11. Right after the war in 1945 we took it up again, using carbon- 

 14 labeled carbon dioxide, to examine the sequence of events and 

 determine the sequence of compounds involved in the transformation 

 of C0 2 into carbohydrate. The answer to these questions is now avail- 

 able to us, and we can draw a rather complete road map of the re- 

 duction of carbon dioxide. (A simplified version of the carbon reduc- 

 tion cycle is shown in Fig. 1.) The first step in the photosynthetic 

 carbon cycle is the carboxylation of a sugar, ribulose diphosphate, 

 to give phosphoglyceric acid, and this, in turn, can now be reduced 

 to triose phosphate using some kind of reducing agent as well as some 

 pyrophosphate-containing compound. The triose phosphate then goes 

 through a series of rearrangements to produce ribulose diphosphate 

 again, and the carbon cycle can continue. 



The light is required to produce these two agents: a reducing agent, 

 here represented by [H] and a particular (pyrophosphate-containing) 

 phosphorus compound (which we shall mention in a moment) to 

 help the reducing agent in the reduction process. This particular 

 phosphorus compound seems to be adenosine triphosphate (ATP) 

 which contains a pyrophosphate linkage. This is of great importance 

 and will be discussed in detail later on. 



The major point that I want to introduce at this stage is the idea 

 that the reduction of carbon dioxide through the carbon cycle and 



