RQ value for Opuntia at night is

Options

A. 1.3
B. 1
C. 7
D. 0

Answer

### Step-by-Step Solution:

1. **Understanding RQ (Respiratory Quotient)**:
- RQ is defined as the ratio of the volume of carbon dioxide (CO2) released to the volume of oxygen (O2) absorbed during respiration.
- The formula for RQ is:
\[ RQ = \frac{\text{Volume of CO2 released}}{\text{Volume of O2 absorbed}} \]

2. **Identifying the Plant Type**:
- The question refers to the Opuntia plant, which is a type of succulent.
- Succulent plants have unique adaptations for water conservation and gas exchange.

3. **Stomatal Behavior at Night**:
- In Opuntia and other succulents, the stomata (small openings on the leaf surface) are open at night and closed during the day.
- This adaptation allows the plant to take in CO2 at night while minimizing water loss.

4. **CO2 Fixation at Night**:
- At night, Opuntia fixes atmospheric CO2 into organic acids (such as oxaloacetate and malate) instead of releasing it.
- Since the stomata are open, CO2 is absorbed, but there is no net release of CO2 during this time.

5. **Net Evolution of CO2**:
- During the night, because there is no net evolution of CO2 (the plant is not respiring in the traditional sense), the volume of CO2 released is effectively zero.
- Therefore, the numerator in the RQ formula becomes zero.

6. **Calculating RQ**:
- Since there is no net evolution of CO2, the RQ value can be calculated as:
\[ RQ = \frac{0}{\text{Volume of O2 absorbed}} = 0 \]

7. **Conclusion**:
- The RQ value for Opuntia at night is 0.

### Final Answer:
The RQ value for Opuntia at night is **0**.

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