During Z scheme, electrons excited by absorption of light if PS I are transferred to the primary acceptors, and tehrefore must bereplaced. The replacements come directly form

Options

A. NADP
B. ATP
C. PS II
D. Water.

Answer

To answer the question regarding the replacement of electrons in the Z scheme during photosynthesis, let's break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Z Scheme**: The Z scheme describes the flow of electrons during the light-dependent reactions of photosynthesis. It involves two photosystems: Photosystem II (PS II) and Photosystem I (PS I).

2. **Role of Photosystem I (PS I)**: When light is absorbed by PS I, it excites electrons, which are then transferred to primary electron acceptors. This process is crucial for the conversion of light energy into chemical energy.

3. **Need for Electron Replacement**: Once the electrons are transferred from PS I to the primary acceptors, they need to be replaced to maintain the continuity of the electron transport chain. If these electrons are not replaced, the process would halt.

4. **Source of Replacement Electrons**: The electrons that replace those lost from PS I come from the electron transport chain initiated by PS II. Specifically, the electrons that are excited and transferred from PS II ultimately flow to PS I.

5. **Conclusion**: Therefore, the correct answer to the question is that the replacements for the electrons excited by PS I come directly from **Photosystem II (PS II)**.

### Final Answer:
The replacements come directly from **Photosystem II (PS II)**.

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