Which of the following is a true?

Options

A. The number of `O_(2)` molecules produced (in photosynthesis) per quantum of light absorbed, is called quantum requirement
B. The number of light quanta needed for the production of one molecule of oxygen during photosynthesis, is called quantum yield.
C. The quantum requirement of photosythesis is 8 quanta
D. Emerson's first effect is also called photosynthetic enhancement.

Answer

To determine which of the following statements is true regarding photosynthesis, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "The number of oxygen molecules produced per quantum of light absorbed is called quantum requirement."
- **Analysis**: This statement incorrectly defines quantum requirement. Quantum requirement refers to the minimum amount of light energy needed to produce a certain amount of oxygen, not the number of oxygen molecules produced per quantum of light absorbed. Therefore, this statement is **false**.

2. **Statement Analysis**:
- **Statement 2**: "The number of light quanta needed for the production of one molecule of oxygen during photosynthesis is called quantum yield."
- **Analysis**: This statement incorrectly defines quantum yield. Quantum yield is actually the number of oxygen molecules produced per quantum of light absorbed, while the statement describes quantum requirement. Thus, this statement is also **false**.

3. **Statement Analysis**:
- **Statement 3**: "The quantum requirement of photosynthesis is 8 quantum."
- **Analysis**: Research indicates that the quantum requirement for photosynthesis typically ranges from 8.8 to 12.4 quanta. Since 8 is within this range, this statement is **true**.

4. **Statement Analysis**:
- **Statement 4**: "Emerson's first effect is also called photosynthetic enhancement."
- **Analysis**: Emerson's first effect refers to the increase in the rate of photosynthesis when chloroplasts are exposed to light of specific wavelengths, while photosynthetic enhancement involves genetically engineered plants that exhibit more efficient photosynthetic traits. These are distinct concepts. Therefore, this statement is **false**.

### Conclusion:
The only true statement among the options provided is **Statement 3**: "The quantum requirement of photosynthesis is 8 quantum."