Transpiration and Translocation

• There aren't tiny trucks that transport substances around plants
• Food


  Mainly dissolved sugars
• Phloem Tubes Transport Food

  1. Made of columns of elongated living cells with small pores in the end walls to allow cell sap to flow through

  2. They transport food substances (mainly dissolved sugars) made in the leaves to the rest of the plant for immediate use (eg. in growing regions) or for storage

  3. The transport goes in both directions

  4. This process is called translocation
• Cell sap


  A liquid made up of the substances being transported and water
• Xylem Tubes Take Water Up

  1. Made of dead cells joined end to end with no end walls between them and a hole down the middle, strengthened with lignin

  2. They carry water and mineral ions from the roots to the stem and leaves

  3. The movement of water from the roots, through the xylem and out of the leaves is called the transpiration stream
• Transpiration


  1. Water evaporates from the leaves

  2. Water enters through the roots

  3. Transpiration is caused by the evaporation and diffusion of water from a plant's surface, mostly the leaves

  4. Evaporation creates a slight shortage of water in the leaf, so more water is drawn up from the rest of the plant through the xylem vessels to replace it

  5. 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
• Because there's more water inside the plant than in the air outside, the water escapes from the leaves through the stomata by diffusion