Final answer:
In photosystem II, the electron removed from the reaction center is replaced by an electron from the splitting of water. In photosystem I, the electron removed from the reaction center is replaced by an electron from the chloroplast electron transport chain.
Step-by-step explanation:
In photosystem II (PSII), the electron removed from the reaction center is replaced by an electron donated by the splitting of water. This process releases oxygen as a waste product. On the other hand, in photosystem I (PSI), the electron removed from the reaction center is replaced by an electron from the chloroplast electron transport chain.