Relationship between water loss & the structure of the leaf

• Structural adaptation of leaves to limit transpiration?

  Leaf size

  • small leaf = small surface area of evaporation

  Thorns

  • Leaves reduce to thorns, which have less stomata and therefore have less transpiration.

  Leaf position

  • some leaves are straight up = expose less area for evaporation
  • leaves at the top cover the leaves at the bottom

  Stomata position

  • stomata occur at the lower parts of the leaf and therefore are not as exposed to sunlight.

  Leaf hairs

  • water is trapped between epidermal hairs

  Cuticle size

  • Thicker cuticle = less transpiration
• External factors influencing transpiration?

  Temperature

  • the intercellular air spaces increase, the movement of water increases and the rate of diffusion increase, increasing the rate of transpiration.

  Light intensity

  • stomata open in the light and close in the dark
  • high light intensity increases the leaf’s temperature, water molecules moves faster and lead to more transpiration.

  Wilting

  • occurs when plants transpire more than what the roots can absorb.
  • turgor pressure decreases and the plant appears soft and flaccid.
  • can be reversed when the plant absorbs enough water.
• Guttation?

  • when humidity is high, the diffusion gradient is low & transpiration occurs slowly.
  • the plant absorbs more water than what is transpired
  • water is then forced out through small openings on the edges of leaves.
  • root pressure plays a role in guttation.
  • high root pressure + low transpiration = guttation.
• Flaccid: (of part of the body) soft and hanging loosely or limply, especially so as to look or feel unpleasant.
• Turgid: swollen and distended or congested