Mass Transport Systems in Plants

Overview

• Plants transport sugars and water through systems known as translocation and transpiration.
• Translocation: Movement of sugars produced in photosynthesis from leaves to other parts of the plant.
• Transpiration: Movement of water from roots to leaves, involving evaporation from leaves.

Translocation

• Photosynthesis occurs in leaves, producing sugars.
• Phloem Cells:
  • Arranged end-to-end, forming phloem tubes.
  • Contain small pores for movement of cell sap (water and sugar mix).
  • Transport sugars from leaves to other parts of the plant.
  • Sugars are used for energy directly or stored for later use.
  • Phloem can transport substances in both directions, up and down the plant.

Transpiration

• Xylem Tubes:
  • Composed of dead cells with no end walls, forming hollow tubes.
  • Strengthened by lignin.
  • Transport water and mineral ions from roots to leaves.
• Driven by the evaporation of water from leaves.
• Water molecules act like a chain; evaporation pulls water upwards.
• Continuous evaporation ensures a steady stream of water flow.
• Evaporation from leaves is called transpiration.
• The flow of water molecules is known as the transpiration stream.

Factors Affecting Transpiration Rate

1. Light Intensity:
   • Higher light increases photosynthesis, requiring open stomata, leading to increased evaporation and transpiration.
   • No photosynthesis at night reduces transpiration as stomata close.
2. Temperature:
   • Higher temperatures increase rate as water molecules have more energy to evaporate.
3. Air Flow:
   • High air flow (wind) blows away water vapor, maintaining a high concentration gradient and increasing transpiration rate.
4. Humidity:
   • Higher humidity reduces transpiration rate as it decreases the concentration gradient between inside and outside of the leaf.

Conclusion

• Understanding these systems and factors is essential for grasping plant physiology and their environmental interactions.