Transpiration

• Transpiration is the loss of water from the plant
• 1. Transpiration is caused by the evaporation and diffusion of water from a plant's surface - most transpiration occurs at the leaves
• 2. The evaporation and diffusion creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it
• 3. When more water is drawn up through the rest of the plant through the xylem vessels, to replace the lack of water in the leaf, this in turn means more water is drawn up from the roots, and so there's a constant transpiration stream of water through the plant
• Transpiration is just a side effect of the way leaves are adapted for photosynthesis.
• Leaves must have stomata in them so that gases can be exchanged easily. Since there's more water inside the plant than in the outside air, the water escapes from the leaves through the stomata by diffusion
• Plants need to balance water loss with water uptake
• Plants have adaptations to help reduce water loss from their leaves


  Leaves usually have a waxy cuticle covering the upper epidermis; this helps make the upper surface of the leaf waterproof
• Plants have adaptations to help reduce water loss from their leaves

  Most stomata are found on the lower surface of a leaf where it's darker and cooler; this helps slow down diffusion of water out of the leaf
• Plants have adaptations to help reduce water loss from their leaves

  The bigger the stomata and the stomata a leaf has, the more water the plant will lose.
• Plants in hot climates really need to conserve water, so they have fewer and smaller stomata on the underside of the leaf and no stomata on the upper epidermis