[Campbell Biology P.238] The text mentions the endosymbiont theory, stating that the origina... | Practice Question

The text mentions the endosymbiont theory, stating that the original chloroplast was a photosynthetic prokaryote that lived inside an ancestor of eukaryotic cells. Which of the following inferences is most strongly supported by this information, considering the general principles of evolution and cellular biology?

  • A: Photosynthesis in early Earth's environment was exclusively performed by free-living prokaryotes before the advent of eukaryotes.
  • B: The ability to perform photosynthesis within specialized, internalized membrane systems evolved in prokaryotes prior to their incorporation into eukaryotic cells.
  • C: Eukaryotic cells developed the capacity for photosynthesis only after acquiring chloroplasts from modern, fully evolved photosynthetic bacteria.
  • D: The endosymbiont theory implies that prokaryotes lost their photosynthetic capabilities after eukaryotic cells evolved to perform photosynthesis.

Explanation

The text states: 'The process of photosynthesis most likely originated in a group of bacteria that had infolded regions of the plasma membrane containing clusters of such molecules. In existing photosynthetic bacteria, infolded photosynthetic membranes function similarly to the internal membranes of the chloroplast.' This strongly suggests that prokaryotes had developed the complex system for photosynthesis within their own membranes before one was engulfed to become a chloroplast in eukaryotes.