At constant temperature, the rate of transpiration will be higher at

Options

A. Sea level
B. 1 km below sea level
C. 1 km above sea level
D. 1.5 km above sea level

Answer

To solve the question regarding the rate of transpiration at constant temperature, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Factors Affecting Transpiration**:
- Transpiration is influenced by various environmental factors, including temperature, humidity, wind speed, and light intensity.
- At constant temperature, the primary factor we need to consider is humidity.

2. **Analyze the Role of Humidity**:
- Humidity refers to the amount of water vapor present in the air.
- Higher humidity levels mean that the air is already saturated with moisture, which reduces the rate of transpiration.
- Conversely, lower humidity levels increase the rate of transpiration because the gradient for water vapor to leave the plant is greater.

3. **Consider the Location Relative to Sea Level**:
- Locations closer to sea level typically have higher humidity due to the proximity to large bodies of water.
- As we move away from sea level (either higher or lower), the humidity tends to decrease.

4. **Evaluate the Given Options**:
- If the options include various altitudes, we need to determine which altitude would have the lowest humidity.
- Locations 1 km above sea level and 1 km below sea level will still have relatively high humidity.
- However, at 1.5 km above sea level, the humidity will be significantly lower.

5. **Conclusion**:
- Therefore, at constant temperature, the rate of transpiration will be higher at 1.5 km above sea level due to the lower humidity at this altitude.

### Final Answer:
The rate of transpiration will be higher at **1.5 km above sea level**.