First step of light phase of photosynthesis is :-

Options

A. Excitation of chlorophyll by light
B. Photolysis of water
C. Synthesis of ATP
D. Synthesis of NADPH

Answer

**Step-by-Step Solution:**

1. **Understanding Photosynthesis:**
- Photosynthesis is the process by which green plants convert light energy into chemical energy in the form of glucose. It occurs in two main phases: the light reactions and the dark reactions (Calvin cycle).

2. **Identifying the Light Phase:**
- The light phase of photosynthesis, also known as the light reaction, requires light to occur. This phase primarily takes place in the thylakoid membranes of chloroplasts.

3. **First Step of the Light Phase:**
- The first step of the light phase is the **excitation of chlorophyll by light**. When light (in the form of photons) hits the chlorophyll molecules, it excites the electrons in chlorophyll.

4. **Role of Accessory Pigments:**
- Accessory pigments absorb light and transfer the energy to chlorophyll a, which is the primary pigment involved in the light reactions. This energy transfer leads to the excitation of chlorophyll a.

5. **Electron Release:**
- Once chlorophyll a is excited, it releases an electron pair. This process is crucial as it initiates the series of reactions that lead to the production of ATP and NADPH, which are essential for the subsequent dark reactions.

6. **Conclusion:**
- Therefore, the first step of the light phase of photosynthesis is the excitation of chlorophyll by light.

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