Lecture Notes: Transport in Plants

Introduction

• Topic: Transport in plants, focusing on xylem and phloem.
• Objective: Understand the functions, structure, and identification of xylem and phloem.

Xylem and Phloem

• Xylem:
  • Transports water and mineral ions.
  • Supports the plant.
  • Structure: Thick walls made of lignin, long hollow tubes, no cross walls.
• Phloem:
  • Transports sucrose and amino acids.
  • Structure: Sieve plates between cells.

Diagram Identification

• Root: Xylem in center, phloem on the outside.
• Stem: Xylem is typically colored red, phloem blue in diagrams.
• Leaf: Top part is phloem, bottom is xylem.
• Tip: Color code diagrams for easier identification.

Water Uptake and Transport

• Root Hair Cells:
  • Large surface area for maximum absorption.
  • No chloroplasts because they are underground.
• Water Pathway:
  • Enters root hair cells by osmosis.
  • Moves up via xylem to mesophyll cells in leaves.
  • Transpiration: Evaporation creates suction, aiding water movement.

Transpiration

• Definition: Loss of water vapor from leaves.
• Process:
  • Water evaporates into air spaces in leaf and exits through stomata.
  • Driven by a large internal surface area and the number of stomata.
• Factors Affecting Transpiration:
  • Temperature: Higher temperatures increase rate.
  • Humidity: Lower humidity increases rate.
  • Light Intensity: Higher light intensity increases rate.

Wilting

• Occurs when water loss exceeds water uptake.
• Cells become flaccid, plant loses support.
• Watering can reverse wilting.

Translocation

• Definition: Movement of sucrose and amino acids in phloem from sources to sinks.
• Sources and Sinks:
  • Sources: Parts of plant that release sucrose/amino acids.
  • Sinks: Parts that use/store sucrose/amino acids.
• Seasonal Changes:
  • Spring: Roots (source) to leaves (sink).
  • Summer/Autumn: Leaves (source) to roots (sink).

Exam Questions

• Transpiration: Keep other conditions constant when testing effect of temperature.
• Translocation Function: Primarily to transport starch.
• Transpiration Description: Loss of water vapor from leaves and stem.

Conclusion

• Review: Importance of understanding transport mechanisms in plants.
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