The important role of PS-II in photosynthesis is

Options

A. To cause photolysis of water
B. To release energy
C. To trap & assimilate `CO_(2)`
D. To reduce NAD to `NADH_(2)`

Answer

**Step-by-Step Solution:**

1. **Understanding Photosystem II (PS-II)**:
- Photosystem II is a crucial component of the photosynthetic process in plants. It is a protein-pigment complex located in the thylakoid membranes of chloroplasts.

2. **Role in Light Absorption**:
- PS-II absorbs light energy, primarily in the blue and red wavelengths, using chlorophyll pigments. This light energy excites electrons within the chlorophyll molecules.

3. **Excitation of Electrons**:
- When light is absorbed, the energy excites electrons in PS-II, causing them to move to a higher energy state. This is essential for the photosynthetic process.

4. **Electron Transport Chain (ETS)**:
- The excited electrons are transferred to an electron transport chain (ETS), which is a series of proteins embedded in the thylakoid membrane. As electrons move through this chain, they release energy.

5. **Photolysis of Water**:
- To replace the electrons lost by PS-II, water molecules are split in a process known as photolysis. This reaction occurs in the presence of light and produces oxygen, protons (H+), and electrons.
- The equation for photolysis can be summarized as:
\[ 2H_2O \rightarrow 4H^+ + 4e^- + O_2 \]

6. **Release of Oxygen**:
- The oxygen produced during photolysis is released as a byproduct into the atmosphere, which is essential for aerobic life on Earth.

7. **Energy Capture and Carbon Fixation**:
- The energy released during the electron transport process is used to create a proton gradient across the thylakoid membrane, which drives ATP synthesis. This ATP, along with NADPH (produced from the reduction of NADP+), is then used in the Calvin cycle to assimilate carbon dioxide and produce glucose.

8. **Summary of PS-II Function**:
- In summary, the important role of PS-II in photosynthesis includes:
- Absorbing light energy.
- Exciting electrons and transferring them through the ETS.
- Splitting water molecules to release oxygen and replenish electrons.
- Contributing to the formation of ATP and NADPH for the Calvin cycle.

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