Which cell's turgidity causes opening or closing of stomata.

Answer

**Step-by-Step Solution:**

1. **Understanding Stomata**: Stomata are small openings on the surfaces of leaves and stems that allow for gas exchange. They play a crucial role in the process of transpiration, which is the loss of water vapor from plant surfaces.

2. **Identifying the Cells Involved**: The cells that control the opening and closing of stomata are known as guard cells. These cells are located on either side of the stomatal pore.

3. **Shape and Structure of Guard Cells**: Guard cells are typically kidney or bean-shaped. They have a unique structure with a thicker inner wall (concave wall) and a thinner outer wall (convex wall).

4. **Turgidity of Guard Cells**: The turgidity (swelling due to water uptake) of guard cells is essential for their function. When guard cells take up water, they become turgid.

5. **Mechanism of Opening and Closing**:
- **Opening of Stomata**: When guard cells are turgid, they swell and curve away from each other, causing the stomatal pore to open.
- **Closing of Stomata**: Conversely, when guard cells lose water and become flaccid, they lose their turgidity, which causes them to close the stomatal pore.

6. **Conclusion**: The turgidity of guard cells directly influences the opening and closing of stomata, making them the key cells responsible for this process.

**Final Answer**: The cells whose turgidity causes the opening or closing of stomata are the **guard cells**.

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