Mark the incorrect one with reference to stomatal opening according to Levitt :-

Options

A. Low pH in guard cell during day
B. Efflux of `H^(+)` ions
C. Influx of `K^(+)` ions
D. Production of OAA & malic acid

Answer

### Step-by-Step Solution

1. **Understanding Stomatal Opening**: Stomata are small openings on the surface of leaves that allow for gas exchange. The opening and closing of stomata are regulated by guard cells.

2. **Role of Guard Cells**: During the day, guard cells take in potassium ions (K+) and water, causing them to swell and open the stomata. This process is influenced by the concentration of hydrogen ions (H+) and the pH level within the guard cells.

3. **Potassium Ion Pump Theory**: According to Levitt's potassium ion pump theory, during daylight:
- Starch produced in epidermal cells is converted to phosphoenolpyruvate (PEP).
- PEP is then converted to malic acid.
- Malic acid dissociates into hydrogen ions (H+) and malate ions (negatively charged).

4. **Effects of Increased H+ Concentration**: The increase in H+ concentration leads to a decrease in pH (making it more acidic) in the guard cells. This triggers the efflux (outward movement) of H+ ions from the guard cells to the epidermal cells.

5. **Influx of K+ Ions**: The efflux of H+ ions activates a potassium hydrogen ion pump, which facilitates the influx (inward movement) of K+ ions into the guard cells. This is an active process that requires ATP.

6. **Water Movement and Turgor Pressure**: The increase in K+ concentration in the guard cells raises the solute concentration, causing water to enter the guard cells from the neighboring epidermal cells. This influx of water increases turgor pressure, leading to the opening of the stomata.

7. **Nighttime Changes**: At night, the process reverses. The plant stops producing starch, leading to an increase in carbon dioxide concentration, which activates abscisic acid (ABA). ABA prevents the influx of K+ ions, causing water to leave the guard cells, making them flaccid and closing the stomata.

8. **Identifying the Incorrect Statement**: The question asks to mark the incorrect statement regarding stomatal opening according to Levitt. The statements provided include:
- Low pH in guard cells during the day (Correct)
- Efflux of H+ ions (Correct)
- Influx of K+ ions (Correct)
- Production of oxaloacetic acid and malic acid (Incorrect, as only malic acid is produced).

9. **Conclusion**: The incorrect statement is the production of oxaloacetic acid, as it is not produced in this process.

### Final Answer
The incorrect statement with reference to stomatal opening according to Levitt is: **Production of oxaloacetic acid and malic acid.**

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