Transpiration

• what is the transpiration stream?

  the continual flow of water in at the roots, up the stem to the leaves, and out to the atmosphere
• what do plants have to balance water uptake with?

  with water loss
• how much water absorbed by the plant is lost by continual evaporation from the leaves, in the process of transpiration?

  about 99%
• what happens if a plant loses more water than it absorbs?

  it wilts
• what happens if a small volume of water is lost by a plant?

  a plant recovers when water is available
• what happens if an excessive volume of water is lost by a plant?

  the plant cant regain its turgor after wilting and it dies
• in the transpiration stream, what is water drawn upwards by?

  • the cohesive forces between water molecules
  • the adhesive forces between the water molecules and the hydrophilic lining of the xylem vessels
• what is transpiration?

  the evaporation of water vapour from the leaves and other above-ground parts of the plant, out through stomata into the atmosphere
• why must the stomata be open during the day?

  to allow gas exchange between the leaf tissues and the atmosphere
• what happens if stomata are open during the day?

  plants lose valuable water
• what is an adaptation of the stomata that reduces water loss?

  the stomata are open long enough for adequate gas exchange, but not so long that the plant dehydrates