Transpiration + translocation

• Phloem Tubes


  Columns of elongated living cells with small pores in the end walls to allow cell sap to flow through
• Phloem Tubes Transport Food


  1. Transport food substances (mainly dissolved sugars) made in the leaves to the rest of the plant for immediate use or for storage

  2. The transport goes in both directions

  3. This process is called translocation
• Cell sap


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


  Made of dead cells joined end to end with no end walls between them and a hole down the middle, strengthened with lignin
• Xylem Tubes Take Water Up

  1. Carry water and mineral ions from the roots to the stem and leaves

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


  The loss of water from the plant, caused by the evaporation and diffusion of water from the plant's surface, mostly the leaves
• Transpiration creates a slight shortage of water in the leaf


  More water is drawn up from the rest of the plant through the xylem vessels to replace it
• More water is drawn up from the roots


  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, as they need stomata to exchange gases</b>
• Factors affecting transpiration rate

  • Light intensity
  • Temperature
  • Air flow
  • Humidity
• Measuring transpiration rate


  1. Set up a potometer apparatus

  2. Record the distance moved by the air bubble per unit time

  3. Keep conditions constant
• Guard Cells


  • Have a kidney shape to open and close stomata
  • Fill with water to open stomata, lose water to close stomata
  • Have thin outer walls and thickened inner walls to enable opening and closing
  • Are sensitive to light and close at night
  • Are more numerous on the underside of leaves
• Guard cells are adapted for gas exchange and controlling water loss within a leaf