The rise of water in the xylem as an unbroken column depends mainly on

  • A. the low viscosity of water
  • B. the high density of water
  • C. cohesion between water molecules caused by hydrogen bonding
  • D. the fact that water is a poor solvent for gases

Explanation

Hydrogen bonds make water molecules stick to one another, so a column pulled by evaporation at the leaves does not break, and adhesion to the walls of the narrow xylem vessels supports the column as well. The same cohesion gives water its high surface tension, which lets small insects rest on a pond. Viscosity and density play no part in maintaining the transpiration stream.

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