Translocation & transpiration

• 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
• Uses of transported sugars

  • Directly for energy
  • Stored for later energy use
• Xylem tubes


  Columns of dead xylem cells with no ends, strengthened with lignin, to transport water and mineral ions from roots to leaves
• Transpiration


  Evaporation of water from leaves
• Transpiration stream


  Chain of water molecules pulled up plant as water evaporates from leaves
• Factors affecting rate of transpiration

  • Light intensity
  • Temperature
  • Air flow
  • Humidity
• High light intensity


  More photosynthesis, more stomata open, higher transpiration rate
• Nighttime (no photosynthesis)


  Stomata closed, very little transpiration
• High temperature


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


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


  Lower concentration gradient, lower transpiration rate