Photosynthetic enhancement with flashing light was first observed by

Options

A. Benson and Calvin
B. Hill and Calvin
C. Hatch and Slack
D. Emerson and Arnold.

Answer

To answer the question "Photosynthetic enhancement with flashing light was first observed by," we need to identify the correct scientists associated with this discovery.

### Step-by-Step Solution:

1. **Understanding the Enhancement Effect**:
- The enhancement effect refers to the increase in the rate of photosynthesis when chloroplasts are exposed to certain wavelengths of light, specifically red and far-red light.

2. **Identifying the Key Scientists**:
- The question provides four options: Vincent and Calvin, Hill and Calvin, H and Slack, and Emerson and Arnold. We need to determine which pair was responsible for the discovery of the enhancement effect.

3. **Reviewing Each Option**:
- **Vincent and Calvin**: They are known for their work related to the Calvin cycle, not specifically the enhancement effect.
- **Hill and Calvin**: Similar to the first option, they are associated with the Calvin cycle and not the enhancement effect.
- **H and Slack**: They are known for their contributions to the understanding of C4 photosynthesis, which is not related to the enhancement effect.
- **Emerson and Arnold**: They are credited with the discovery of the enhancement effect in photosynthesis when chloroplasts are exposed to red and far-red light.

4. **Conclusion**:
- Based on the analysis, the correct answer is **Emerson and Arnold**.

### Final Answer:
The correct answer is **Emerson and Arnold**.

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