Sir J.C. Bose proposed in theory of ascent of sap known as

Options

A. Pulsation theory
B. Transpiration pull theory
C. Relay pump theory
D. Capillary force theory

Answer

**Step-by-Step Solution:**

1. **Identify the Theory**: The theory proposed by Sir J.C. Bose regarding the ascent of sap in plants is known as the **Transpirational Pull Theory**.

2. **Understand Transpirational Pull**: This theory explains that there is a negative pressure (or pull) created due to the process of transpiration, which is the loss of water vapor from the aerial parts of the plant, primarily through small openings called stomata.

3. **Role of Transpiration**: Transpiration leads to the evaporation of water from the leaves, which creates a vacuum or negative pressure in the leaf's air spaces. This negative pressure pulls water upward from the roots through the xylem vessels.

4. **Cohesion and Adhesion**: The movement of water in plants is facilitated by two key properties:
- **Cohesion**: This is the attraction between water molecules, which allows them to stick together and form a continuous column of water in the xylem.
- **Adhesion**: This is the attraction between water molecules and the walls of the xylem vessels. It helps water to cling to the walls, assisting in the upward movement of water.

5. **Capillary Action**: The combination of cohesion and adhesion results in capillary action, which is the ability of water to flow in narrow spaces without the assistance of external forces. This is crucial for the ascent of sap in tall trees.

6. **Summary of the Process**: In summary, the transpirational pull theory describes how water is pulled from the roots to the leaves of tall plants through a combination of transpiration, cohesion, adhesion, and capillary action.

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