Which pigment system is inactivated in red drop?

Options

A. PS-I and PS-II
B. PS-I
C. PS-II
D. None of the above

Explanation

**Step-by-Step Solution:**

1. **Understanding the Red Drop Effect**: The red drop effect, also known as the immersion effect, refers to a phenomenon observed during photosynthesis when light of specific wavelengths is used. It is characterized by a drop in the rate of photosynthesis when light shifts from the red spectrum to the far-red spectrum.

2. **Identifying Wavelengths**: In the context of the red drop effect, two important wavelengths are mentioned: 680 nanometers (nm) and 700 nm. The wavelength of 680 nm falls within the deep red spectrum, while 700 nm is in the far-red spectrum.

3. **Observing Photosynthesis Rates**: When light intensity is increased from 680 nm to 700 nm, the effectiveness of photosynthesis initially increases. However, once the light reaches 700 nm, there is a sudden drop in photosynthesis efficiency.

4. **Linking to Photosystems**: The drop in photosynthesis efficiency at 700 nm is linked to the inactivation of a specific photosystem. In higher plants, there are two main photosystems involved in photosynthesis: Photosystem I (PSI) and Photosystem II (PSII).

5. **Conclusion**: The inactivation that occurs at the red drop effect is specifically related to Photosystem II (PSII). Therefore, the correct answer to the question is that Photosystem II is inactivated in the red drop effect.

**Final Answer**: Photosystem II is inactivated in the red drop effect.

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