PHOTOSYNTHESIS 85 



plant growing in the light in an atmosphere free from 

 carbon dioxide cannot manufacture carbohydrates any 

 more than if it were in the dark. A plant lacking chloro- 

 plasts, e.g. the fungi, cannot manufacture carbohydrates 

 from carbon dioxide even if light be present (excepting cer- 

 tain bacteria, the so-called nitrite and nitrate bacteria). 

 The process takes place in the chloroplasts apparently. 

 The light rays most effective in photosynthesis seem to be 

 those in the red part of the spectrum while those at the 

 violet end also have some value. Those lying between 

 seem in the main to be useless. The green color represents 

 the portion of the white light that strikes the chlorophyll 

 and is reflected back or passes through it without being 

 absorbed. The raw materials are carbon dioxide and 

 water, the energy is derived from the absorbed rays of 

 light and the end products are carbohydrates and oxygen. 



125. The exact steps in photosynthesis are not 

 certainly known but the following seems to be the 

 probable course of events: 



C02-t-H20 = H2C03 (water, plus carbon dioxide, equals 

 carbonic acid). 



H2C03 = H2CO-f02 (carbonic acid acted on by the 

 energy derived from light by the cholorophyll is changed 

 into formaldehyde and oxygen) . 



6H2CO = C6H12O6 (formaldehyde, probably by the 

 aid of more energy derived from the light is polymerized 

 into glucose). 



It will thus be seen that for every molecule of carbon 

 dioxide used up one molecule of oxygen (O2) will be set 

 free. Glucose is the carbohydrate first formed in most 

 cases but as this accumulates in the chloroplasts and 

 cell sap it is often transformed rapidly into the insoluble 

 starch (CeHioOs)!! which becomes stored up in large 

 quantities in the chloroplasts. Sometimes instead of 



