transpiration and translocation

• Translocation


  Plants transport sugars made through photosynthesis in leaves to rest of plant
• Phloem cells


  Arranged end to end to form long columns called phloem tubes to transport cell sap (water and sugar)
• Phloem tubes


  • Have small pores/gaps between adjacent cells to enable movement of cell sap
  • Can transport substances in either direction (up or down the plant)
• Transpiration


  Movement of water from roots to leaves driven by evaporation of water from leaves
• Transpiration stream


  Chain of water molecules pulled up the plant as water evaporates from leaves
• Factors influencing rate of transpiration
• High light intensity


  More photosynthesis, more stomata open, higher rate of transpiration
• No photosynthesis at night

  Stomata closed, very little transpiration
• Higher temperature


  Water particles have more energy, higher rate of transpiration
• High airflow


  Water molecules blown away quickly, higher concentration gradient, higher rate of transpiration
• High humidity


  Lower concentration gradient, lower rate of transpiration
• Xylem tubes are made of dead xylem cells with no ends, strengthened with lignin, to transport water and mineral ions from roots to leaves