pH of guard cells increases during day time due to

Options

A. Efflux of `H^(+)` ions
B. Influx of `K^(+)` ions
C. Influx of `Cl^(-)` ions
D. Influx of `H^(+)` ions

Answer

### Step-by-Step Solution:

1. **Understanding Guard Cells**: Guard cells are specialized cells that surround the stomata (tiny openings on the leaf surface) and control their opening and closing. This regulation is crucial for gas exchange and transpiration in plants.

2. **pH and Ion Movement**: The pH of a cell is influenced by the concentration of hydrogen ions (H⁺). A higher concentration of H⁺ ions results in a lower pH (more acidic), while a lower concentration results in a higher pH (more basic).

3. **Daytime Conditions**: During the daytime, plants undergo photosynthesis, which requires the uptake of carbon dioxide (CO₂). For stomata to open and allow CO₂ in, the pH of guard cells must increase.

4. **Ion Fluxes**: The increase in pH in guard cells during the day is primarily due to the efflux (outflow) of H⁺ ions. When H⁺ ions exit the guard cells, the concentration of H⁺ ions decreases, leading to an increase in pH.

5. **Role of Potassium Ions (K⁺)**: Concurrently, potassium ions (K⁺) enter the guard cells (influx), causing the cells to become turgid (swollen with water), which helps in the opening of the stomata.

6. **Conclusion**: Therefore, the correct answer to the question is that the pH of guard cells increases during the daytime due to the efflux of H⁺ ions, which leads to the opening of stomata.

### Final Answer:
The pH of guard cells increases during the daytime due to the efflux of H⁺ ions.

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