Emerson's enhancement effect and red drop have been instrumental in the discovery of

Options

A. Photophosphorylation and non-cyclic electrotransport
B. Two photosystems operating simulateneously
C. Photophosphorylation and cyclic electron transport
D. oxidative phosphorylation

Answer

To answer the question regarding Emerson's enhancement effect and red drop, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Emerson's Enhancement Effect**:
- Emerson's enhancement effect refers to the phenomenon where the rate of photosynthesis is significantly increased when chloroplasts are exposed to two specific wavelengths of light: red light (around 670 nm) and far-red light (around 700 nm). When both wavelengths are present simultaneously, the efficiency of photosynthesis is much higher than when either wavelength is used alone.

2. **Understanding the Red Drop Effect**:
- The red drop effect describes a sharp decrease in the efficiency of photosynthesis when the light wavelength exceeds 700 nm. This means that beyond this point, the quantum yield of photosynthesis drops significantly, indicating that chlorophyll absorbs light less effectively in this range.

3. **Connecting the Effects to Photosynthesis**:
- Both the enhancement effect and the red drop effect were crucial in understanding the role of different wavelengths of light in photosynthesis. They helped scientists realize that there are two distinct photosystems (PS1 and PS2) that operate simultaneously during the light-dependent reactions of photosynthesis.

4. **Identifying the Correct Option**:
- Given the options provided:
- Photophosphorylation and non-cyclic electron transport
- Two photosystems operating simultaneously
- Photophosphorylation and cyclic electron transport
- Oxidative phosphorylation
- The correct answer is "Two photosystems operating simultaneously," as both the enhancement effect and red drop effect provided evidence for the existence of PS1 and PS2.

### Final Answer:
The correct answer is **"Two photosystems operating simultaneously."**

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