Stomata open when guard cells show

Options

A. Increase in both osmotic and turgor pressures
B. Decrease in both osmotic pressure and turgor pressure
C. Increase in osmotic pressure but decrease in turgor pressure
D. Decreases in osmotic pressure increase in turgor pressure

Answer

**Step-by-Step Solution:**

1. **Understanding Stomata and Guard Cells**:
- Stomata are small openings on the surfaces of leaves that facilitate gas exchange and transpiration (the loss of water vapor).
- Guard cells are specialized cells that surround each stoma and control its opening and closing.

2. **Role of Guard Cells in Stomata Function**:
- The opening and closing of stomata are primarily controlled by the turgidity (firmness due to water pressure) of the guard cells.
- When guard cells take up water, they become turgid (swollen with water), causing the stomata to open.

3. **Osmotic Pressure and Turgor Pressure**:
- Osmotic pressure refers to the pressure required to prevent the flow of water across a semipermeable membrane due to solute concentration.
- Turgor pressure is the pressure exerted by the fluid inside the cell against the cell wall, which is a result of osmotic pressure.

4. **Conditions for Stomata Opening**:
- Stomata open when there is an increase in both osmotic pressure and turgor pressure in the guard cells. This occurs when water enters the guard cells, making them turgid.

5. **Evaluating the Options**:
- The question provides four options regarding the conditions of osmotic and turgor pressure when stomata open:
- Increase in both osmotic and turgor pressure
- Decrease in both osmotic and turgor pressure
- Increase in osmotic pressure but decrease in turgor pressure
- Decrease in osmotic pressure and increase in turgor pressure
- The correct answer is the first option: **Increase in both osmotic and turgor pressure**.

6. **Conclusion**:
- Therefore, stomata open when guard cells show an increase in both osmotic and turgor pressure.

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