Mass Transport Systems in Plants

Overview

• Plants transport their sugars and water through two processes: translocation and transpiration.
• Photosynthesis occurs in the leaves, producing sugars that need to be transported throughout the plant.

Translocation

• Definition: The process of transporting sugars produced in the leaves to other parts of the plant.
• Mechanism:
  • Utilizes phloem cells, arranged end-to-end forming long columns known as phloem tubes.
  • Phloem tubes have small pores/gaps allowing movement of sap (a liquid mixture of water and sugar).
  • Sugars can be used directly for energy or stored for later use.
  • Phloem can transport substances both upwards and downwards.

Transpiration

• Definition: The process of water movement from roots to leaves, driven by evaporation.
• Mechanism:
  • Utilizes xylem tubes, composed of dead cells forming a hollow tube, strengthened with lignin.
  • Water and mineral ions are transported from roots up the stem to the leaves.
  • Driven by evaporation of water from leaves, creating a "transpiration stream."

Factors Affecting Transpiration Rate

1. Light Intensity:
   • Higher intensity increases photosynthesis, opening more stomata, thus increasing transpiration.
   • Little to no transpiration at night.
2. Temperature:
   • Higher temperatures give water particles more energy, increasing evaporation and diffusion.
3. Air Flow:
   • High air flow blows away water molecules, maintaining a high concentration gradient and increasing transpiration.
4. Humidity:
   • High humidity lowers the concentration gradient, decreasing transpiration.

Additional Resources

• Cognito provides additional materials such as videos, questions, flashcards, and exam-style questions on their website.
• They offer tracking of progress to assist with study planning.