The first step in photosynthesis is photolysis of water by

Options

A. Excitation of chlorophyll by light
B. Ionization
C. ATP synthesis
D. Production of assimilatory power

Answer

**Step-by-Step Solution:**

1. **Understanding Photosynthesis**: Photosynthesis occurs in two main stages: the light reactions and the dark reactions (Calvin cycle). The light reactions take place in the thylakoid membranes of the chloroplasts, while the dark reactions occur in the stroma.

2. **Role of Chlorophyll**: Chlorophyll is the green pigment in plants that absorbs light energy. It is primarily located in the thylakoid membranes of the chloroplasts.

3. **Light Absorption**: When light is absorbed by chlorophyll, it excites electrons within the chlorophyll molecules. This is a crucial step in the light reactions of photosynthesis.

4. **Excitation of Electrons**: The absorbed light energy causes the electrons in chlorophyll to move to a higher energy state (excitation). This is essential for the subsequent steps in the light reaction.

5. **Photolysis of Water**: The excited electrons from chlorophyll are transferred to an electron acceptor. To compensate for the loss of these electrons, water molecules (H2O) undergo photolysis, which is the splitting of water using light energy.

6. **Products of Photolysis**: The photolysis of water results in the production of oxygen (O2), protons (H+), and electrons (e-). The reaction can be summarized as:
\[ 2H_2O \rightarrow 4H^+ + 4e^- + O_2 \]

7. **Conclusion**: Therefore, the first step in photosynthesis is the photolysis of water, which is driven by the light energy absorbed by chlorophyll.