The force of attraction between water molecules and xylem walls is called?

• A. Adhesion
• B. Cohesion
• C. Surface tension
• D. Capillarity

Answer: (A)

This question tests how water interacts with surfaces versus with other water molecules. The force of attraction between water and the xylem walls is adhesion. Water bonds with the cellulose walls of the xylem, mainly through hydrogen bonding, so it sticks to the wall and can be drawn upward along it. This adhesion to the solid surface is different from cohesion, which is the attraction between water molecules themselves, helping water stay connected. Surface tension comes from cohesive forces at the water’s surface with air, not from attraction to a solid surface. Capillarity is the overall rise of liquid in narrow spaces due to both adhesion to the walls and cohesion within the liquid, resulting in water moving up in the xylem. So the specific attraction to the xylem walls is adhesion.