Question

In light reactions of photosynthesis why photosystem II occurs before photosystem I?​

Answer 1

Answer:

Photosystems I and II are named such because Photosystem I was actually discovered (and named) before Photosystem II, even though Photosystem II comes before Photosystem I during photosynthesis (i.e., Photosystem II precedes Photosystem I in the electron flow of photophosphorylation).

Answer 2

In light reactions of photosynthesis, photosystem II occurs before photosystem I because the process of photosystem II is the very first process in the chain to perform photosynthesis.

• Even the process of photosystem I comes after the process of photosystem II but still it is named as I because it was discovered first and photosystem II afterwards and hence, they are named accordingly.
• Photosystem II uses the energy by capturing the energy to obtain electrons from the molecules of the water.
• In Photosystem I, the transfer of electrons across the thylakoid membrane to ferredoxin from plastocyanin is catalyzed by using the light energy.

Hence, the process of photosynthesis starts with the photosystem II but Photosystem I was discovered first and hence it is named accordingly.