To determine which statements regarding transpiration are correct, let's analyze each statement step by step.
### Step 1: Analyze Statement (i)
**Statement:** The rate of transpiration is directly proportional to the relative humidity.
**Analysis:** This statement is incorrect. The rate of transpiration is inversely proportional to relative humidity. When humidity is high, the air is already saturated with moisture, which reduces the rate of water vapor loss from the plant. Therefore, this statement is false.
### Step 2: Analyze Statement (ii)
**Statement:** It regulates plant temperature.
**Analysis:** This statement is correct. Transpiration helps in cooling the plant. When water evaporates from the stomata, it absorbs heat from the plant, thus regulating its temperature. Therefore, this statement is true.
### Step 3: Analyze Statement (iii)
**Statement:** Very low temperature closes stomata and hence decreases the rate of transpiration.
**Analysis:** This statement is also correct. At very low temperatures, plants tend to close their stomata to conserve water, which leads to a decrease in the rate of transpiration. Therefore, this statement is true.
### Step 4: Analyze Statement (iv)
**Statement:** It causes ascent of sap.
**Analysis:** This statement is correct as well. The process of transpiration creates a negative pressure (transpirational pull) in the leaves, which helps in the upward movement of water and nutrients (ascent of sap) from the roots to the leaves. Therefore, this statement is true.
### Conclusion
Based on the analysis:
- Statement (i) is incorrect.
- Statements (ii), (iii), and (iv) are correct.
Thus, the correct answer is that statements (ii), (iii), and (iv) are true.
### Final Answer
**The correct statements regarding transpiration are: (ii), (iii), and (iv).**
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