water movement up a plant

• the movement of water from the roots to the leaves is called the transpiration stream. the mechanisms that move the water include tension, cohesion, and adhesion
• cohesion and tension - help water move up leaves against the force of gravity

  1. water evaporates from the leaves at the top of xylem ( transpiration)
  2. creates a tension (suction) pulling more water into the leaf
  3. water molecules are cohesive so stick together so when one is pulled into a leaf the others follow
  4. water enters the stem through the root cortex
• air bubbles form in the xylem which block the column of water which prevents water from reaching the cells and without enough water they can become flaccid and the plant wilts
• water movement up a plant increases as transpiration rate increases
• cohesion and tension allow for mass flow of water over long distances up the stem
• adhesion

  • partly responsible for the movement of water as it means water molecules are attracted to the walls of the xylem vessel which helps water to rise up the vessel
• cohesion and tension

  A) water evaporates

  B) tension

  C) cohesion