The energy available from the protonmotive force across the thylakoid membrane is about 20 kJ/mol of protons. How much energy per mole of photons absorbed by the two photosystems does this equal?

Question

Quizplus · Accepted Answer

The energy per mole of photons absorbed by the two photosystems equals the energy available from the protonmotive force divided by the number of photons required to generate one mole of protons. 
The number of photons required depends on the type of photosystem, but on average, it takes about 8 photons to generate one mole of protons. 
Therefore, the energy per mole of photons absorbed by the two photosystems is:
20 kJ/mol / 8 photons/mol = 2.5 kJ/photon 
To get the answer in kJ/mol, we need to multiply by the number of photons absorbed per mole, which is about 12 for PSII and 6 for PSI. 
So, (2.5 kJ/photon) x (12 + 6) = 30 kJ/mol. 
Therefore, the correct answer is B.

The Energy Available from the Protonmotive Force Across the Thylakoid