Transpiration cohesion theory explains that the upwards pull of
water is transmitted from top to bottom by cohesion of molecules caused by

Options

A. Hydrophilic cell walls
B. Hydrogen bons
C. Oxygen bonds
D. Surface tension

Answer

**Step-by-Step Solution:**

1. **Understanding the Transpiration Cohesion Theory**: The transpiration cohesion theory explains how water moves from the roots of a plant to its leaves. This process is driven by transpiration, which is the evaporation of water from the plant's surface, primarily through small openings called stomata.

2. **Role of Cohesion**: The upward movement of water is facilitated by the cohesive forces between water molecules. Cohesion refers to the attraction between molecules of the same substance. In this case, it is the attraction between water molecules that helps maintain a continuous column of water from the roots to the leaves.

3. **Formation of Hydrogen Bonds**: The cohesive force in water is primarily due to hydrogen bonds. Water molecules are polar, meaning they have a slight positive charge on one side and a slight negative charge on the other. This polarity allows water molecules to form hydrogen bonds with each other, creating a strong attraction that helps to keep the water column intact.

4. **Conclusion**: Therefore, the upward pull of water in the transpiration cohesion theory is transmitted from top to bottom by the cohesion of water molecules, which is caused by hydrogen bonds.

**Final Answer**: The correct answer is **hydrogen bond**.

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