A reduction in the quantity of oxygen evolution during photosynthesis may be observed at

Options

A. Light having wavelength more than 680 nm
B. Light having wavelength less than 680 nm
C. Light having wavelength 560 nm
D. Light having wavelength less than 360 nm

Answer

To solve the question "A reduction in the quantity of oxygen evolution during photosynthesis may be observed at," we need to analyze the relationship between light wavelengths and photosynthesis.

### Step-by-Step Solution:

1. **Understanding Photosynthesis**:
- Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, producing oxygen as a byproduct.
- The process primarily occurs in the chloroplasts of plant cells.

2. **Role of Light in Photosynthesis**:
- Light is essential for photosynthesis, and different wavelengths of light have varying effects on the process.
- The chlorophyll pigments in plants absorb specific wavelengths of light, primarily in the blue (around 430-450 nm) and red (around 640-680 nm) regions.

3. **Quantum Yield**:
- Quantum yield refers to the number of photons required to produce one molecule of oxygen (O2) during photosynthesis.
- It is noted that typically, 8 photons are needed to produce one molecule of O2, giving a quantum yield of 1/8 or 12.5%.

4. **Effect of Wavelength on Quantum Yield**:
- The efficiency of photosynthesis decreases in the far-red region of the light spectrum (wavelengths greater than 680 nm).
- This decrease is related to the Emerson effect, where the quantum yield drops when using light beyond the optimal absorption range of chlorophyll.

5. **Analyzing the Options**:
- **Option A**: Light having a wavelength more than 680 nanometers - This is in the far-red region where quantum yield decreases, leading to reduced oxygen evolution.
- **Option B**: Light having a wavelength less than 680 nanometers - This includes wavelengths that are still effective for photosynthesis.
- **Option C**: Light having a wavelength of 560 nanometers - This is in the green region, which is less effective but still contributes to photosynthesis.
- **Option D**: Light having a wavelength less than 360 nanometers - This is ultraviolet light, which can be harmful and not effective for photosynthesis.

6. **Conclusion**:
- Based on the analysis, a reduction in the quantity of oxygen evolution during photosynthesis is most likely observed at **Option A: light having a wavelength more than 680 nanometers**.

### Final Answer:
**A reduction in the quantity of oxygen evolution during photosynthesis may be observed at light having wavelength more than 680 nanometers (Option A).**