What is the difference between photosynthesis I and photosynthesis II?

Answer 1

Photosynthesis II or PS II (photosystem II) comes before PS I. PSII uses a pair of P680 chlorophyll a, while PSI uses a pair of P700 chlorophyll a. These systems populate the thylakoid membrane.

First, light hits PS II and excites its pigment molecules and the energy bounces off the pigment molecules until it gets to the P680 chlorophyll and excites its electrons which then causes it to give off an electron to the Primary electron acceptor.

Now the pair of P680 is deprived of an electron, this is where water comes nto play. An enzyme catalyzes the splitting of water to produce O2 and two electrons, these electrons supply the ones that the pair of P680 chlorophyll gave away, this enables the P680 to be able to get excited again and again without being deprived of electrons.

Back to the primary acceptor, the excited electron passes from PS II to PS I via the Electron Transport chain. This produces ATP.

The electron then is at the P700 pair of chlorophyll a's of PS I which excites it and it gives off that electron to another primary electron acceptor which transports its electrons via ETC as well, but the final electron acceptor is NADP+, which with the electron becomes: NADPH.

Answer 2

Photosynthesis I and II are named after photosystems I and II, respectively. Counterintuitively, photosystem II comes before photosystem I in the light-dependent reactions of photosynthesis. There are other differences:

1. PSII uses a pair of P680 chlorophyll a, while PSI uses a pair of P700 chlorophyll a.
2. PS II utilizes plastoquinone, which then passes the high-energy electron to cytochromes b6 and f. Photosystem I, on the other hand, passes the electron to ferredoxin.
3. In the non-cyclic version of photophosphorylation, PS II is responsible for the photolysis of water and subsequent synthesis of ATP. PS I, in this process, converts NADP+ to NADPH.