20.10 Based upon the S cycle, what is the maximum rate of oxygen production possible in
plants?
20.11 Why does P680 have a high oxidation/reduction midpoint potential? What type of reac-
tions can P680 perform that P865 cannot?
20.12 Suggest a possible reason as to how P680 can achieve a significantly higher midpoint
potential than that observed for chlorophyll in solution.
20.13 What role does tyrosine play in the water-oxidation process?
20.14 What gives rise to the many hyperfine lines observed for photosystem II?
20.15 Why do the S states have different EPR spectra?
20.16 How many EXAFS lines are expected for a Mn 4 cluster? Given the observed spectrum,
estimate the number of possible configurations of the Mn 4 cluster that are consistent with
the EXAFS data.
20.17What does the hydrogen-abstraction model predict about the number of protons transferred
during each step of the S cycle?
20.18 Propose a chemical model of the water-oxidation process that predicts the changes in the
oxidation states of each Mn in the Mn 4 cluster during the S cycle.
20.19 In 1957, Barry Commoner reported the presence of an EPR signal from a plant leaf.
What signal do you think that he saw?
singke
(singke)
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