SUMMARY: This article looks at the still-not-yet-fully-known evolution and history of photosynthesis. There were various types of photosynthesis, the main difference being the type of electron donor. Some organisms used water as an electron donor, while others used things like hydrogen and manganese. The origins are difficult to pinpoint because the genes have changed so much. There are seven types of bacteria that can photosynthesize, but only one species that uses two photosystems (cyanobacteria, related to chloroplast). More primitive versions of photosynthesis include using rhodopsin as a way to power ion pumps. Section 6 of this article goes in-depth comparing the different enzymes in the light-dependent step of photosynthesis in the various types of photosynthetic bacteria. Differences in these enzymes give clues to the evolution and the relationship between these organisms. Finally, the last few sections look at the different ways some bacteria fix carbon and how the energy produced by photosynthesis is used by bacteria to fix nitrogen (turning atmospheric nitrogen into ammonia requires lots of energy).
LESSON COMMENTS: After students have learned the basics of photosynthesis as described by biology texts, this article can be used to further explore the process and purpose of photosynthesis. Other topics that can be covered include: redox reactions, electrons, hydrogen ions and ion pumps, light energy and electron excitability, wavelength of light (Why are plants green? What type of light do plants absorb/reflect?) evolution, endosymbiosis, and energy use/glucose production by autotrophs.
Nowicka, B., & Kruk, J. (2016). Powered by light: Phototrophy and photosynthesis in prokaryotes and its evolution. Microbiological Research,186-187, 99-118. doi:10.1016/j.micres.2016.04.001