Problems
20.1 Plants make chlorophyll whereas bacteria synthesize bacteriochlorophyll. What are
the differences between these molecules that give rise to the difference in the optical
spectra?
20.2 Based upon the optical spectra, how much light energy is absorbed by the primary electron
donor of reaction centers from purple bacteria compared to P680 of photosystem II?
20.3 Contrast the organization of the proteins and cofactors in the light-harvesting 2 complex
compared to the bacterial reaction center.
20.4 Why do the light-harvesting 1 and 2 complexes have different optical spectra?
20.5 Discuss the advantages and disadvantages of having two different light-harvesting com-
plexes in the cell.
20.6 Why is the EPR linewidth more narrow for a dimer than for a monomer?
20.7 Provide a possible reason why electron transfer proceeds down only one branch of cofactors
despite the symmetry of the structure.
20.8 How are the properties of the iron–sulfur clusters in photosystem I different from the
quinones in reaction centers?
20.9 Why does oxygen evolution show a cyclic pattern with a series of laser flashes?
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