Assertion : According to Scarth, opening and closure of stomata is controlled by pH value.
Reason : Low pH value favours opening of stomata and higher pH value closure of stomata.

Options

A. If both Assertion and Reason are true and Reason is correct explanation of Assertions.
B. If both Assertion and Reason are true but Reason is not correct explanation of Assertion.
C. If Assertion is true but Reason is false.
D. If both Assertion and Reason are false.

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that according to Scarth, the opening and closing of stomata is controlled by pH value. This means that the pH of the surrounding environment affects the behavior of stomata.

**Hint**: Consider what stomata are and their role in plants.

2. **Understanding the Reason**: The reason provided explains that a low pH value favors the opening of stomata, while a higher pH value leads to their closure. This implies that the acidity or alkalinity of the environment influences stomatal behavior.

**Hint**: Think about how pH levels can affect cellular processes in plants.

3. **Function of Stomata**: Stomata are small openings on the surface of leaves that allow for gas exchange (CO2 in, O2 out) and transpiration (loss of water vapor). The opening and closing of these stomata are regulated by guard cells.

**Hint**: Recall the structure and function of guard cells surrounding the stomata.

4. **Role of pH in Stomatal Movement**: According to the information, during the day, photosynthesis occurs, which reduces CO2 levels and keeps the pH low (alkaline), leading to the opening of stomata. Conversely, at night, the lack of photosynthesis causes CO2 to accumulate, forming carbonic acid, which increases pH (acidic), resulting in the closure of stomata.

**Hint**: Consider how day and night cycles affect photosynthesis and gas exchange.

5. **Evaluating the Assertion and Reason**: Both the assertion and the reason are correct. The assertion correctly states that pH controls stomatal movement, and the reason accurately describes the relationship between pH levels and stomatal behavior.

**Hint**: Think about how both statements relate to each other and whether one supports the other.

6. **Conclusion**: The correct option is that both the assertion and reason are correct, but the reason does not fully explain the assertion. The reason provides a correct relationship but lacks detail on how pH influences the guard cells' turgidity.

**Hint**: Reflect on the completeness of the explanation provided in the reason.

**Final Answer**: Both the assertion and the reason are correct, but the reason does not adequately explain the assertion.