How many " down hill" movements of electrons is found in the Z-scheme ?

Options

A. 4
B. 5
C. 2
D. 1

Answer

To determine how many "downhill" movements of electrons are found in the Z-scheme of photosynthesis, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Z-scheme**: The Z-scheme is a model that describes the flow of electrons during the light reactions of photosynthesis. It involves two photosystems: Photosystem II (PSII) and Photosystem I (PSI).

2. **Identify Electron Movement**: In the Z-scheme, electrons are transferred from water molecules to NADP+ through a series of redox reactions. The movement of electrons from a higher energy state to a lower energy state is referred to as a "downhill" movement.

3. **First Downhill Movement**: The first downhill movement occurs when electrons are transferred from the primary electron acceptor of PSII to the electron transport chain (ETC). This movement is towards a lower redox potential.

4. **Second Downhill Movement**: The second downhill movement occurs when electrons are transferred from the ETC to the primary electron acceptor of PSI. This is also a movement towards a lower redox potential.

5. **Count the Downhill Movements**: In total, there are two distinct downhill movements of electrons in the Z-scheme: one from PSII to the ETC and another from the ETC to PSI.

6. **Conclusion**: Therefore, the total number of downhill movements of electrons in the Z-scheme is **two**.

### Final Answer:
The number of "downhill" movements of electrons found in the Z-scheme is **2**.

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