The electrons, that are removed from photosystem-II and photosystem-I during z-scheme, must be replaced. This is achieved by electrons released

Options

A. By photosystem-I `NADP^+`
B. By splitting of water and NADPH
C. By ATP and photosystem-II
D. By splitting of water and photosystem-II

Answer

To solve the question regarding how the electrons removed from photosystem II and photosystem I during the Z-scheme are replaced, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Z-Scheme**: The Z-scheme is part of the light-dependent reactions of photosynthesis, where two photosystems (Photosystem II and Photosystem I) are involved in the transfer of electrons.

2. **Electrons in Photosystem II**: When light is absorbed by Photosystem II, it excites electrons in the chlorophyll molecule. These electrons are then transferred to a primary electron acceptor and subsequently passed through an electron transport chain.

3. **Replacement of Electrons in Photosystem II**: The electrons that leave Photosystem II create a deficiency (or "hole") in the chlorophyll molecule. This deficiency is filled by electrons derived from the photolysis (splitting) of water. The reaction can be summarized as:
- 2 H₂O → 4 H⁺ + 4 e⁻ + O₂
This means that the electrons released from the splitting of water replace the electrons lost from Photosystem II.

4. **Electrons in Photosystem I**: Similarly, when electrons are excited in Photosystem I, they also leave the chlorophyll molecule, creating another deficiency. The electrons that fill this gap come from plastocyanin, which is part of the electron transport chain that connects Photosystem II to Photosystem I.

5. **Conclusion**: Therefore, the electrons removed from Photosystem II are replaced by electrons from the photolysis of water, and the electrons removed from Photosystem I are replaced by plastocyanin.

### Final Answer:
The correct option is: **by splitting of water and photosystem II**.