Most plants meet their water need by

Options

A. A.  transpiration pull
B. B. root pressure
C. C. both A and B
D. D. osmotic pressure

Answer

**Step-by-Step Solution:**

1. **Understanding Plant Water Needs**: Plants require water for various physiological processes, including photosynthesis, nutrient transport, and maintaining turgor pressure.

2. **Identifying Water Transport Mechanisms**: There are several mechanisms through which plants can transport water from the roots to the leaves. The primary mechanisms include transpiration pull, root pressure, and osmotic pressure.

3. **Transpiration Pull**: This is the main mechanism by which most plants meet their water needs. Transpiration occurs when water evaporates from the stomata (tiny pores) in the leaves. As water vapor exits, it creates a negative pressure (tension) that pulls more water upward from the roots through the xylem vessels.

4. **Root Pressure**: This is a less significant mechanism compared to transpiration pull. Root pressure occurs when water is absorbed by the roots and creates a pressure that pushes water upward. However, it is not the primary method for most plants, especially tall ones.

5. **Osmotic Pressure**: This refers to the pressure required to prevent the flow of water across a semipermeable membrane. While osmotic pressure plays a role in water uptake at the roots, it is not the main mechanism for meeting the water needs of plants.

6. **Conclusion**: Based on the above analysis, the correct answer to the question "Most plants meet their water needs by" is **transpiration pull**.

**Final Answer**: a. transpiration pull

---