Stomata open by

Options

A. Increasing solute concentration in guard cells
B. Weakening of cell walls of guard cell to allow them to stretch
C. Increasing water potential of guard cells
D. Decreasing the solute concentration of guard cells

Answer

**Step-by-Step Solution:**

1. **Understanding Stomata and Guard Cells**: Stomata are small openings on the surface of leaves that facilitate gas exchange and transpiration. They are surrounded by specialized cells known as guard cells, which control the opening and closing of these stomatal pores.

2. **Role of Guard Cells**: The guard cells regulate stomatal movement by changing their shape. When they become turgid (swollen with water), the stomata open; when they lose water and become flaccid, the stomata close.

3. **Process of Stomatal Opening**:
- During the daytime, the concentration of carbon dioxide inside the leaf decreases, and the pH level increases.
- The guard cells produce malic acid, which dissociates into malate ions and hydrogen ions (H⁺).
- The hydrogen ions are actively transported out of the guard cells, leading to a change in the ion concentration within the cells.

4. **Ion Exchange and Potassium Influx**: As hydrogen ions are transported out, potassium ions (K⁺) are taken into the guard cells. This influx of potassium ions increases the solute concentration inside the guard cells.

5. **Osmotic Pressure and Water Absorption**: The increase in solute concentration leads to a rise in osmotic pressure within the guard cells. Consequently, water moves into the guard cells from the surrounding epidermal cells through a process called endosmosis.

6. **Turgidity of Guard Cells**: As the guard cells absorb water and become turgid, they change shape, causing the stomatal pores to open.

7. **Conclusion**: The opening of stomata is primarily due to the increasing solute concentration in the guard cells, which leads to water absorption and turgidity. Therefore, the correct answer to the question "Stomata open by" is option 1: **increasing the solute concentration in guard cells**.

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