Transpiration & Translocation

• Translocation - movement of food substances through the phloem
• Transpiration - loss of water from a plant, through evaporation
• Factors affecting rate of transpiration:

  • Temperature
  • Light intensity
  • Air flow
  • Humidity
• How does temperature effect rate of transpiration?

  • increase in temperature increases rate of transpiration
  • because it increases the evaporation of water from leaves
• How does humidity effect rate of transpiration?

  • increasing humidity decreases transpiration
  • because it decreases the water potential gradient (between inside and outside of leaf)
• How does air flow effect rate of transpiration?

  • increasing air movement increases rate of transpiration
  • because it removes water vapour around the leaf
  • and air flow maintains a high water potential gradient
• How does light intensity effect rate of transpiration?

  • increasing light intensity increases rate of transpiration
  • because it causes the stomata to open
  • open stomata allows more carbon dioxide in for photosynthesis
• Difference between xylem and phloem (structure and function);

  • Xylem is made of dead cells, phloem is made of living cells.
  • Xylem has no end walls, while phloem has holes (sieve plates) in its end walls.
  • Xylem is hallow.
  • Xylem contains lignin, whereas phloem doesn't.
  • Xylem transports water and mineral ions, while phloem transports dissolved sugars.
  • Xylem is involved in transpiration, whereas phloem is involved in translocation.
  • Xylem only transports up the plant, while phloem transports up and down the plant.
• What does the xylem transport?

  Water and mineral ions.
• What does the phloem transport?

  Dissolved sugars.