SC 3.4

• • Transpiration is the loss of water vapor from a plant through the stoma
  • Occurs through the stomata on the leaf surface
  • Importance
  • Remove excess water
  • Help to transport water and dissolved mineral salts from the roots to all parts of the plants
  • Helps to cool the plant when water evaporates
• Rate of transpiration

  • Control by the changes of the size of stomata
  • The size of stomata become small during hot day to reduce the loss of water
• Factors that affect transpiration rates

  • Surrounding temperature
  • The higher the surrounding temperature, the higher the rate of water evaporation (transpiration)
  • Light intensity
  • The higher the light intensity, the higher the rate of transpiration (open stoma)
  • Air movement (wind)
  • The stronger the air movement, the higher the rate of transpiration (blowing water vapor from the stoma)
  • Air humidity
  • The lower the humidity, the higher the transpiration rate (less water vapor)
• Cross section of leaf

  • Both upper and lower surface of the leaf, that is upper epidermis and lower epidermis, is covered by a layer of single epidermis cell
  • Epidermis secrets waxy cuticle that covers the upper epidermis and lower epidermis to reduce loss of water through transpiration
• Stomata

  • The size of stomata is controlled by the guard cells. The guard cells are kidney shaped surrounding the stoma

  Importance

  • The exchange of gases like oxygen and carbon dioxide in photosynthesis and respiration
  • Their size controls the rate of transpiration
• Exudation (Guttation)

  • Guttation is loss of water from plants in the form of liquid known as xylem sap through hydathodes which are always open on the edge of leaves
  • Guttation usually occurs at night or when air humiditiy is high
• The transport system through xylem and phloem

  • The transport system of flowering plants are made up of specialised tissues that is xylem and the phloem tissue
  • Xylem and phloem which are vascular bundles are found in the roots, stem and leaf
• Xylem

  Woody tissue that made up of long tubes to transport water and dissolved mineral salts from the roots to the stem and leaves

  Do not have cytoplasm
• Phloem

  • Found in the roots and stems outside the xylem
  • Function: Transport food like glucose from leaves to the stem and roots