Transpiration

• Phloem tubes transport food substances ( mainly dissolved sugars) made in leaves to the rest of plant for immediate use or storage, the transport goes in both directions

  This process is called translocation
• Xylem tubes carry water and mineral ions from the roots to the stem and leaves

  The movement of water from the roots, through the xylem and out the leaves is called the transpiration stream
• Transpiration is the loss of water from the plant
• Transpiration is caused by the evaporation and diffusion of water from the plants surface. most transpiration happens at the leaves

  this evaporation 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

  This in turn means more water water is drawn up from the roots and so there’s a constant transpiration stream of water through the plant
• • Transpiration starts with the evaporation of water from cells inside the leaf
  • The water vapour diffuses through the air spaces in the spongy mesophyll and out the leaf, through the stomata
• The greater the light intensity, the greater the transpiration rate. stomata begins to close as it gets dark, photosynthesis can’t happen in the dark do they don’t need to be open to let CO2 in. when stomata are closed , very little water can escape
• the warmer it is, the faster transpiration happens

  when it’s warm the particles have more energy to evaporate and diffuse out the stomata
• The better the air flow around a leaf, the greater the transpiration rate as if air flow is pot, water Vapor surrounds leaf so there’s a high concentration of water particles outside the leaf and inside so diffusion doesn’t happen as quickly. if good air flow, water vapour is swept away so water outside is at a low concentration so diffusion can happen quickly
• The drier the area around the leaf, the faster transpiration happens

  If air is humid there’s a lot of water in it do there’s not much difference between the inside and outside so diffusion is slower