Red drop is due to

Options

A. Decline in quantum yield in separate beams of red light
B. Non functioning of PS II in free red light
C. Inhibiting effect of Red light on PS I
D. Oxidation of chlorophyll

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Concept of Quantum Yield**:
- Quantum yield refers to the efficiency of photosynthesis, specifically the number of oxygen molecules produced per unit of light absorbed (light quanta). It is a measure of how effectively light energy is converted into chemical energy during photosynthesis.

2. **Identifying the Red Drop Effect**:
- The red drop effect is observed when there is a significant decline in the efficiency of photosynthesis when light wavelengths exceed 680 nanometers. This phenomenon indicates that certain wavelengths of light are less effective for photosynthesis.

3. **Role of Photosystems**:
- In photosynthesis, there are two photosystems: Photosystem I (PS1) and Photosystem II (PS2). PS2 is primarily active at wavelengths around 680 nanometers, while PS1 operates optimally at around 700 nanometers.

4. **Analyzing the Options**:
- Option 1: Decline in quantum yield in separated beams of red light - This is related but not the direct cause of the red drop.
- Option 2: Non-functional activity or non-functioning of PS2 in free red light - This directly relates to the red drop effect, as PS2 is not active in red light, leading to decreased efficiency.
- Option 3: Inhibiting effect of the red light on PS1 - This is incorrect as PS1 is still functional in red light.
- Option 4: Oxidation of chlorophyll - While chlorophyll is involved in photosynthesis, this is not the cause of the red drop effect.

5. **Conclusion**:
- The correct answer is Option 2: the non-functioning of PS2 in free red light. This explains the significant drop in photosynthetic efficiency when light wavelengths exceed 680 nanometers.

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