Some photosynthetic bacteria (e.g., purple sulfur bacteria) have only photosystem I, whereas others (e.g., cyanobacteria) have both photosystem I and photosystem II. Which of the following might this observation imply?
A) Photosystem II was selected against in some species.
B) Photosynthesis with only photosystem I is more ancestral.
C) Photosystem II may have evolved to be more photoprotective.
D) Linear electron flow is more primitive than cyclic flow of electrons.
E) Cyclic flow is more necessary than linear electron flow.
E. coli bacteria cell
Some of the bacteria that can fix atmospheric nitrogen, converting it into a form usable by plants.
Photosynthetic Organisms Changed Earth's Atmosphere
Enhanced photomicrograph showing a macrophage (purple) attack- ing bacillus Escherichia coli (green)
bacteria
Pathways of nitrogen metabolism (purple) in the general pattern of intermediary metabolism