Anoxygenic phototrophs harvest the energy of sunlight, but do not generate O2 because they do not use water as a source of electrons when making reducing power in the form of NADPH. The purple sulfur bacteria and the green sulfur bacteria use hydrogen sulfide as a source of electrons; the purple non-sulfur and green non-sulfur bacteria preferentially use organic compounds.
■ Describe a structural characteristic that distinguishes the purple sulfur bacteria from the green sulfur bacteria.
■ What is the function of gas vesicles?
■ Why is it beneficial to the anoxygenic phototrophs to have light-harvesting pigments that absorb wavelengths of light that penetrate to greater depths?
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