86 



PROBLEMS IN PHOTOSYNTHESIS 



Reaction 3 (dark) 



CO2 -^ CO2* - 70000 cal 



Over-all reaction: 



Vs CO2 + Nhv -^ 'U C + \l-i O, 



The light energy can be transferred without notable loss from the chlorophyll 

 molecule to the photolyte molecule. The light acts within the same molecule 

 that absorbs it. The light reaction of photosynthesis is thus nothing but the 

 photodissociation of a pigment. It is comparable to the photodissociation 

 of iron carbonyl compounds (§ 25) 



[FejCO + Nhv ^ [Fe] + CO 

 and the quantum requirement of 1 is almost self-evident. 



Numerical example (14): 



The one-quantum requirement of photosynthesis is studied by means of 

 the two- vessel method. Each vessel contains 49 ^ul cells which absorb 48% 

 of the incident green light (5460 A). The incident intensity is 44 /^l quanta/ 

 min. Photosynthesis is measured with alternate light and dark periods of 1 .5 

 min. 



h' = +23.0 mm h = +5.5 mm 



From the values of the vessel constants, it follows that 



A = 10.10 mm2 B = 15.10 mm^ C = -13.21 mm-' D = -22.81 mm^ 



According to equations 17 and 18, we find 



;co^ = h'A - hB = 23 X 10.10 - 5.5 X 15.10 = +149 m1 



