CHAPTER VI 

 THE PHOTOSYNTHETIC PROCESS 



Such was the process. 

 — Othello 1:3. 



The Formaldehyde Hypothesis. — It has been previously shown 

 that the plant which contains chlorophyll is able to make car- 

 bohydrates out of the raw materials of carbon dioxide and water. 

 Also for every molecule of carbon dioxide taken in from the air 

 a molecule of oxygen is given off. The sum total of reactions can 

 then be expressed as follows, if we assume that a sugar like glucose 

 is the first product of photosynthetic activity: 



6C0 2 +6H 2 = C 6 H 12 6 +60 2 . 



Such an equation tells us only the alpha and the omega. It 

 states that water and carbon dioxide are used and that glucose is 

 formed. It also shows that for every molecule of carbon dioxide 

 used a molecule of oxygen is released. But all that such equations 

 state are simply the substances and the proportions; they tell 

 nothing whatever of the intermediary steps or of the numerous 

 reactions which may intervene between the beginning and the 

 end. 



In order to throw some light on these dark places von Baeyer 

 (1870) proposed that formaldehyde was an intervening product. 

 To explain what actually took place within the leaf the following 

 reactions were assumed: 



C0 2 -* CO+O 

 H 2 -> H 2 +0 

 CO+H 2 = CH 2 

 6CH 2 -> C 6 H 12 6 . 



These equations mean that the carbon dioxide is broken up into 

 carbon monoxide and oxygen, while the water is broken into 

 hydrogen and oxygen at the same time. The carbon monoxide 

 and hydrogen then unite to form formaldehyde, six molecules of 



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