APPENDIX 

 PHOTOSYNTHESIS 



The chemistry of photosynthesis is not completely known, 

 but some of the simpler aspects of it may prove valuable to 

 the student. The chemist's formula for water is H 2 O, in 

 which H stands for hydrogen and O for oxygen, and the 

 figure 2 indicates that two parts of hydrogen are united with 

 one part of oxygen. Similarly, CO 2 indicates that one part 

 of carbon is united with two parts of oxygen to form carbon 

 dioxide. When these compounds are broken up, there is, for 

 a very brief time at least, free C, H, and O. If one unit of 

 each compound (H O and CO 2 ) is thus broken up, there 

 will be two H, one O, one C, and two O or in all three O. 

 After photosynthesis has been going on for some time, starch 

 is usually formed. Starch consists of (C 6 H 10 O 5 ) W . This 

 means that six parts of carbon, ten parts of hydrogen, and five 

 parts of oxygen unite to form starch, and the n means that 

 the unit C 6 H JO O 5 does not appear singly, but that an unknown 

 number of them are united. Disregarding the fact that several 

 of the starch units are held together, and considering the single 

 unit C 6 H JO O 6 , we may be able to see what happens in the work 

 of photosynthesis. To secure the amount of carbon necessary 

 to form starch, six times the unit CO 2 must be taken, since 

 six units of carbon are to be used. To secure the needed 

 amount of hydrogen, five times the unit H 2 O must be used, 

 since there must be ten units of hydrogen, and two are secured 

 with each unit of water. We have therefore 6 (CO 2 ) and 

 5 (H 2 O). When the energy of the sun has broken these 

 things into their constituent parts, there are 6 (C), 12 (O), 

 10 (H), and 5 (O) or 17 (O) in all. But starch consists of 



343 



