The following diagram summarizes the light reactions of photosynthesis.
The diagram shows light-dependent reactions of photosynthesis, including the reaction centers, electron transport chains, and the overall reactions within each of these. The free energy per electron is shown for the oxidation-reduction reactions. The free change of the captured radiant energy is shown.
2NADP+ + 2H
+ + 2H2 O + 3ADP + 3Pi ?
O2 + 4H
+ + 2NADPH + 3ATP
A. In the overall mass balance equation for the light reactions shown above, identify the source of electrons for the synthesis of NADPH.
B. Calculate the number of electrons transferred in this reaction.
C. Using the free energies per electron displayed, calculate the free energy change of the lightdependent reactions.
D. Given that the free energy change for the hydrolysis of ATP is -31.5 kJ/mole and the free
energy change for the formation of NADPH from NADP+ is 18 kJ/mole, calculate the total
production of free energy for the light reactions.
E. Using this definition of energy efficiency, calculate the efficiency of the light reaction of
photosynthesis: energy efficiency = free energy produced/energy input