Assertion: Stomata open when guard cells have more `K^+`.
Reason: Increased `K^+` concentration results endosmosis in guard cells.

Options

A. if both Assertion and Reason are true, Reason is the correct explanation of Assertion.
B. if both Assertion and Reason are true but Reason is not the 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 Text Solution:**

1. **Understanding Stomata and Guard Cells**: Stomata are small openings found on the surfaces of leaves, which are surrounded by guard cells. These guard cells regulate the opening and closing of the stomata.

2. **Role of Potassium Ions (K⁺)**: When potassium ions (K⁺) accumulate in the guard cells, the concentration of solutes within these cells increases. This process is crucial for the functioning of the stomata.

3. **Osmosis in Guard Cells**: The increase in potassium ion concentration causes water to move into the guard cells through osmosis. Osmosis is the movement of water from an area of lower solute concentration to an area of higher solute concentration.

4. **Effect of Endosmosis**: As water enters the guard cells due to the osmotic gradient created by the increased concentration of K⁺, the guard cells swell. This swelling causes the stomata to open.

5. **Assertion and Reason Evaluation**:
- **Assertion**: "Stomata open when guard cells have more K⁺." This statement is true because the influx of K⁺ leads to the opening of the stomata.
- **Reason**: "Increased K⁺ concentration results in endosmosis in guard cells." This statement is also true, as the increase in K⁺ concentration leads to water entering the guard cells, causing them to swell and open the stomata.

6. **Conclusion**: Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.