Transpiration

• Transpiration


  Loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers)
• Transpiration


  1. Evaporation of water at the surfaces of the spongy mesophyll cells

  2. Diffusion of water vapour through the stomata
• Transpiration


  • Many interconnecting air spaces between the mesophyll cells and the stomata creates a large surface area
  • Evaporation can happen rapidly when the stomata are open
• Transpiration in plants


  Water moves through the xylem vessels in a continuous transpiration stream from the roots to the leaves via the stem to replace the water that has been lost due to transpiration
• Cohesion


  The effect of transpiration
• Transpiration


  The loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers)
• Transpiration


  1. Loss of water occurs through evaporation of water at the surfaces of the spongy mesophyll cells

  2. Followed by diffusion of water vapour through the stomata
• Transpiration


  • The many interconnecting air spaces between the mesophyll cells and the stomata creates a large surface area
  • This means evaporation can happen rapidly when the stomata are open
• Cohesion


  The water in the xylem creates a continuous unbroken column (each individual molecule 'pulls' on the one below it)
• Transpiration produces tension or 'pulls' on the water in the xylem vessels


  If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker
• Functions of transpiration


  • Transporting mineral ions
  • Providing water to keep cells turgid in order to support the structure of the plant
  • Providing water to leaf cells for photosynthesis
  • Keeping the leaves cool, the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy