The Z-scheme of electron transport is

Options

A. cyclic photophosphorylation
B. Non-cyclic photophosphorylation
C. Both (1) and (2)
D. where only photosystem pigment-I is involved

Answer

### Step-by-Step Solution:

1. **Understanding the Z-Scheme**: The Z-scheme is a model that describes the light-dependent reactions of photosynthesis, specifically focusing on the flow of electrons through the photosystems.

2. **Non-Cyclic Photophosphorylation**: The Z-scheme is also referred to as non-cyclic photophosphorylation. This process involves the transfer of electrons in a linear manner rather than cycling back to the original photosystem.

3. **Initiation at Photosystem II**: The process begins at Photosystem II (PSII), where light energy is absorbed, exciting electrons. These high-energy electrons are then transferred to a primary electron acceptor.

4. **Electron Transport Chain**: After being accepted, the electrons travel through an electron transport chain (ETC). This chain consists of various proteins that facilitate the movement of electrons and help in the generation of ATP and NADPH.

5. **Transition to Photosystem I**: The electrons eventually reach Photosystem I (PSI), where they are again excited by light energy. This results in the production of another primary electron acceptor.

6. **Formation of a Z Pattern**: The movement of electrons from PSII to PSI and through the electron transport chain creates a 'Z' shape when plotted on a graph, hence the name "Z-scheme".

7. **Conclusion**: The Z-scheme illustrates the flow of electrons during non-cyclic photophosphorylation and is crucial for understanding how light energy is converted into chemical energy in the form of ATP and NADPH.