Mass Transport Systems of Plants

Introduction

• Overview of how plants transport sugars and water.
• Translocation: Transport of sugars.
• Transpiration: Transport of water.

Translocation

• Photosynthesis: Occurs in the leaves, produces sugars.
• Sugars need to be transported throughout the plant for energy.
• Phloem Cells: Responsible for translocation.
  • Arranged end to end, forming phloem tubes.
  • Contain small pores for movement of cell sap (water and sugar mixture).
• Functions of Sugars:
  • Used directly for energy.
  • Stored for future energy use.
• Phloem can transport substances in both directions (up or down the plant).

Xylem and Water Transport

• Xylem Tubes:
  • Made up of dead xylem cells, forming hollow tubes.
  • Strengthened by lignin.
• Function: Transport water and mineral ions from roots to leaves.
• Transpiration Process:
  • Driven by evaporation of water from leaves.
  • Water molecules in a chain, pulled up as water evaporates from stomata.
  • Continuous stream due to open stomata for carbon dioxide.

Factors Affecting Transpiration Rate

• Transpiration: Evaporation of water from leaves.
• Transpiration Stream: Chain of water molecules.
• Four main factors:
  1. Light Intensity:
     • More light increases photosynthesis, more stomata open, higher transpiration.
     • At night, less transpiration due to closed stomata.
  2. Temperature:
     • Higher temperature increases transpiration rate (more energy for evaporation).
  3. Air Flow:
     • High airflow blows away water molecules, maintaining a high concentration gradient, increasing transpiration.
  4. Humidity:
     • High humidity decreases transpiration (less concentration gradient).

Conclusion

• Summary of how translocation and transpiration function in plants.
• Importance of environmental factors on transpiration rate.