AP Syllabus focus:
‘Photosynthesis first evolved in prokaryotes; cyanobacterial photosynthesis oxygenated Earth’s atmosphere and underlies eukaryotic photosynthesis.’
Photosynthesis reshaped Earth by turning sunlight into chemical energy and transforming global chemistry. Understanding how it evolved—from early prokaryotes to chloroplast-bearing eukaryotes—explains major biological innovations and the rise of complex life.
Early Evolution: Photosynthesis Begins in Prokaryotes
Why prokaryotes were first
Practice Questions
FAQ
They look for converging signals: patterns in isotope ratios, minerals that form only under specific redox conditions, and sedimentary features that fit sustained, global oxygen production rather than local, abiotic events.
Early $O_2$ was rapidly consumed by “sinks” such as dissolved iron and reduced volcanic gases. Only after these sinks diminished could $O_2$ persist and build up in the atmosphere.
Yes. Oxygen is reactive and can damage cells. Many obligate anaerobes were pushed into anoxic refuges or went extinct, while oxygen-tolerant lineages diversified.
Commonly cited evidence includes chloroplast DNA, bacterial-like ribosomes, division resembling binary fission, and membrane traits consistent with an engulfment origin plus subsequent integration.
It drives most global primary production, supplying organic carbon and energy to food webs, and it maintains atmospheric $O_2$ levels that many organisms rely on for high-yield respiration.
