What keeps the force of gravity from pulling water molecules out of the leaves?

Options

A. Upward pressure from root
B. High water pressure in leaves
C. movement of water towards a sugar sink
D. Cohesion and adhesion of water molecules

Answer

To answer the question, "What keeps the force of gravity from pulling water molecules out of the leaves?" we can break down the explanation into several key points:

### Step-by-Step Solution:

1. **Understanding Water Transportation in Plants**:
- Water is primarily transported from the roots to the leaves through a tissue called xylem. This movement is unidirectional, meaning it typically goes in one direction—from the roots upwards to the leaves.

2. **Role of Transpiration**:
- The main driving force for the upward movement of water in plants is known as the "transpiration pull." Transpiration is the process where water evaporates from the surface of leaves, creating a negative pressure that pulls water upward from the roots through the xylem.

3. **Cohesion of Water Molecules**:
- Water molecules exhibit a property called cohesion, which means they are attracted to each other. This attraction helps to maintain a continuous column of water in the xylem, allowing it to resist the pull of gravity.

4. **Adhesion to Xylem Walls**:
- Water also exhibits adhesion, which is the attraction between water molecules and the hydrophilic (water-attracting) surfaces of the xylem vessels. This helps to keep the water column stable and assists in pulling water upward.

5. **Summary of Forces**:
- The combination of the transpiration pull (which creates negative pressure), the cohesive forces between water molecules, and the adhesive forces between water and the xylem walls work together to counteract the force of gravity. This allows water to move efficiently from the roots to the leaves, despite the downward pull of gravity.

### Conclusion:
The force of gravity is countered by the transpiration pull, along with the cohesive and adhesive properties of water molecules. This synergy allows water to be transported against gravity effectively.

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