Which photosystem-1 or 2-most likely evolved first?
To determine which photosystem likely evolved first, we can look at the general sequence of events in the evolution of photosynthesis. Please note that this explanation is based on scientific theories and may be subject to ongoing research and debate.
Photosynthesis is a process used by plants, algae, and some bacteria to convert sunlight into chemical energy. It involves two photosystems: Photosystem I (PSI) and Photosystem II (PSII). PSII functions before PSI in the light-dependent reactions of photosynthesis.
Scientists believe that PSII likely evolved before PSI for several reasons. One important factor is that PSII is involved in the oxidation of water molecules. This process, called water-splitting, releases oxygen as a byproduct. Oxygenic photosynthesis, the type of photosynthesis most familiar to us, releases oxygen as a result of water oxidation. It is believed that early phototrophic organisms first evolved the ability to perform this water-splitting process, which eventually led to the accumulation of oxygen in the atmosphere.
On the other hand, PSI does not directly participate in water-splitting and does not produce oxygen. It functions in the next step of the photosynthetic process, utilizing electrons from PSII to produce energy-rich molecules like ATP (adenosine triphosphate).
In summary, the general consensus among scientists is that PSII likely evolved before PSI. By analyzing the overall sequence of events and the role of these photosystems in photosynthesis, researchers have developed this understanding. However, it's essential to keep in mind that scientific theories evolve as new evidence emerges, so our understanding may be refined in the future.