Root pressure is caused by:

Options

A. transpiration of water out of the xylem
B. osmotic flow of water into the xylem
C. cchesion of water molecules to one another
D. adhesion of water molecules to wals of the xylem

Answer

**Step-by-Step Text Solution:**

1. **Understanding Root Pressure**: Root pressure is a phenomenon that occurs in plants, particularly when there is a lack of transpiration. It is important to understand that root pressure is not caused by the upward movement of water but rather by the accumulation of water in the roots.

2. **Role of Transpiration**: Transpiration is the process by which water is lost from the plant, primarily through small openings in the leaves called stomata. When transpiration occurs, it creates a pull that helps to draw water up from the roots through the xylem. However, when transpiration is minimal or absent, this pull is reduced.

3. **Osmosis in Roots**: In the absence of transpiration, water is still absorbed from the soil into the roots through a process called osmosis. Osmosis is the movement of water from an area of lower solute concentration (in the soil) to an area of higher solute concentration (inside the root cells).

4. **Accumulation of Water**: As water is absorbed into the root cells, it accumulates in the xylem vessels of the roots. This accumulation of water increases the pressure within the xylem, which is referred to as root pressure.

5. **Analyzing Options**:
- **Option 1**: Transpiration of water out of the xylem - This is incorrect as transpiration reduces root pressure.
- **Option 2**: Osmotic flow of water into the xylem - This is correct as it explains how water accumulates and increases root pressure.
- **Option 3**: Cohesion of water molecules to one another - This does not cause root pressure directly.
- **Option 4**: Adhesion of water molecules to the walls of the xylem - This also does not cause root pressure.

6. **Conclusion**: Based on the analysis, the correct answer is that root pressure is caused by the osmotic flow of water into the xylem.

**Final Answer**: Root pressure is caused by osmotic flow of water into the xylem.

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