Some photosynthetic bacteria have photosystem I but not II, while others have both PSI and PSII. Which of the following might this observation imply?
A. Photosystem II must have been selected against in some species
B. Photosystem I must be ancestral
C. Photosystem II may have evolved to be more photoprotective
D. Cyclic flow must be more primitive than linear flow electrons
E. cyclic flow must be the most necessary of the two processes
Answer: B