The major solute taken in by guard cells is `Na^(+)`

Options

A. `Na^(+)`
B. `Ca^(2+)`
C. `K^(+)`
D. `Mg^(2+)`

Answer

**Step-by-Step Solution:**

1. **Understanding Guard Cells:**
- Guard cells are specialized cells located on the epidermis of leaves and stems. They play a crucial role in regulating the opening and closing of stomata, which are small pores that allow gas exchange.

2. **Role of Solutes in Guard Cells:**
- The primary function of guard cells is to control the size of the stomatal pore. This is achieved through changes in turgor pressure within the guard cells, which is influenced by the uptake of solutes.

3. **Major Solute in Guard Cells:**
- The major solute that is taken up by guard cells is not `Na^(+)` (sodium ion), but rather `K^(+)` (potassium ion). When guard cells take up potassium ions, it leads to an increase in osmotic pressure, causing water to enter the cells and resulting in the swelling of guard cells. This swelling opens the stomata.

4. **Mechanism of Stomatal Opening:**
- As potassium ions accumulate in the guard cells, water follows by osmosis, increasing the turgor pressure. The guard cells become turgid and curve outward, which opens the stomatal pore. Conversely, when potassium ions are released, water exits the guard cells, leading to a decrease in turgor pressure and closure of the stomata.

5. **Conclusion:**
- Therefore, the statement that the major solute taken in by guard cells is `Na^(+)` is incorrect. The correct major solute is `K^(+)`.