Which process exerts the pull on water molecules that is relayed from leaf to root via cohesion in plants?

• A. Osmosis
• B. Photosynthesis
• C. Transpiration
• D. Respiration

Answer: (C)

Verified step by step guidance

1. Understand the concept of transpiration: Transpiration is the process by which water evaporates from the surface of plant leaves, primarily through small openings called stomata. This creates a negative pressure (tension) in the leaf's air spaces.
2. Learn about cohesion and adhesion: Water molecules exhibit cohesion due to hydrogen bonding, which allows them to stick together. Adhesion helps water molecules stick to the walls of the xylem vessels, facilitating upward movement.
3. Explore the role of transpiration in water movement: As water evaporates from the leaves during transpiration, it creates a pull (tension) that is transmitted down the xylem vessels to the roots. This pull relies on the cohesive properties of water molecules.
4. Understand the connection between leaf and root: The cohesive forces between water molecules allow the pull generated by transpiration to be relayed from the leaves to the roots, enabling the continuous upward movement of water through the plant.
5. Differentiate transpiration from other processes: Osmosis involves the movement of water across a membrane, photosynthesis is the process of converting light energy into chemical energy, and respiration is the breakdown of glucose for energy. None of these processes directly create the pull on water molecules like transpiration does.