Plant transport - leaf structure

• 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 happens at the leaves.
• 1. This 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.
• 1. 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. They have to have stomata in them so that gases can be exchanged easily (see next page). Because there's more water inside the plant than in the air outside, the water escapes from the leaves through the stomata by diffusion.
• The transpiration stream does have some benefits for the plants, however:

  1. The constant stream of water from the ground helps to keep the plant cool.
  2. It provides the plant with a constant supply of water for photosynthesis.
  3. The water creates turgor pressure in the plant cells, which helps support the plant and stops it wilting.
  4. Minerals needed by the plant can be brought in from the soil along with the water.