BIOLOGICAL CHEMISTRY 



formed by treating chlorophyll with ethyl alcohol so that the 

 phytol is replaced by an ethyl group. 



Chlorophyll contains magnesium and by treating it with 

 acid magnesium is split off, leaving a phytol ester called 

 phaeophytin. Phaeophytin is an acid substance, and by 

 combining it with metals, such as zinc, iron, copper, etc., the 

 green colour and fluorescence of chlorophyll are restored. 



Further decomposition of chlorophyll with alkali at 

 increasing temperatures leads to the production of a series of 

 products ending in porphyrins, which are allied to the 

 derivative of haemoglobin, called hsematoporphyrin, in that 

 they contain pyrrol groups. 



STAGES IN THE DECOMPOSITION OF CHLOROPHYLL a 



Mg + phaeophytin 



By acid 



"Chlorophyll a 



Phytol + phytochlorin*" > isochlorophyllin a chlorophyllin a + 

 ByMgO 1 + phytol phytol. 



A seri 



es of changes by 



alkali at increasi ng temperatures. 



By acid | By acid 



Phylloporphyrin*^~phyllophyllin Pyrrophyllin^" ~jpyrroporphyrin 

 By MgO By MgO 



Decomposition of chlorophyll b follows very much the same series 

 of changes to give the same final end products. 



(Abbreviated from Willstatter and Stohl.) 



THE ENERGY SUPPLY FOR PHOTOSYNTHESIS 

 The supply of energy for the photosynthesis of carbo- 

 hydrates comes from the sun, and in order that the energy 

 can be used the light must be absorbed. 



By absorbing all the light heat is produced, thus the total 

 energy of the light can be measured. The distribution of 

 energy in the various regions of the spectrum of sunlight is 

 known, and by measuring the amount of the various coloured 

 lights absorbed the energy of the absorbed light can be 

 calculated. The chlorophyll absorbs most energy from the 

 portion of the spectrum corresponding to the absorption 

 band in the red, and this is the region of the spectrum which 



