The main driving force behind the upward movement of water through xylem is _____

Options

A. guttation
B. transpiration
C. pressure flow
D. None of these

Answer

**Step-by-Step Solution:**

1. **Understanding Xylem Function**: Xylem is a type of tissue in plants responsible for the transport of water and nutrients from the roots to the leaves. It primarily conducts water in one direction, which is upward.

2. **Identifying the Driving Force**: The question asks for the main driving force behind the upward movement of water through xylem. We need to consider the options provided: guttation, transpiration, pressure flow, and none of these.

3. **Explaining Transpiration**: Transpiration is the process where water evaporates from the surface of leaves. This evaporation creates a negative pressure in the leaf, which pulls water upward from the roots through the xylem.

4. **Cohesion Theory**: According to the cohesion theory, water molecules are attracted to each other (cohesion) and to the walls of the xylem vessels (adhesion). This helps maintain a continuous column of water from the roots to the leaves.

5. **Conclusion**: Since transpiration creates the necessary force to pull water upward through the xylem, the correct answer to the question is **transpiration**.

**Final Answer**: The main driving force behind the upward movement of water through xylem is **transpiration**.

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