Xylem and Phloem - Transport in Plants

Introduction to Transport in Plants

• Every plant cell requires essential substances like water, minerals, and glucose.
• Plants rely on vascular tissues for the distribution of these substances.
• Two main vascular tissues: xylem and phloem.
• Xylem and phloem facilitate the movement of nutrients and water throughout the plant.

Xylem

• Function: Distributes water and minerals absorbed by roots.
• Components:
  • Tracheids: Conducting cells with pitted walls; water flows in series.
  • Vessels: Long, wide, hollow tubes for continuous water flow from roots to leaves.
  • Fiber Cells: Provide structural support.
  • Parenchyma: Living cells aiding in food storage.
• Strengthening: Lignin strengthens cell walls; patterns include ring, spiral, reticulate, or pitted.
• Unique Aspect: Some parts lack protoplasms or cell walls for easy passage of water and minerals.

Phloem

• Function: Transports manufactured food (sucrose, amino acids) from leaves to other parts.
• Process: Known as translocation.
• Components:
  • Sieve Tubes: Rows of elongated, thin-walled cells with perforated walls for passage.
  • Companion Cells: Support sieve tubes with cytoplasm and nucleus.
  • Fiber Cells: Provide structural support; the only dead cells in phloem.
  • Parenchyma: Stores food and other substances.

Arrangement of Vascular Tissue

• Root of herbaceous dicot plants: Xylem forms an x-like shape in the middle, surrounded by phloem.
• Stem: Xylem and phloem form circular clusters near the stem's edge.
• Leaf: Xylem is positioned above phloem within the vascular bundle.

Summary

• Vascular tissues are crucial for nutrient and water transport in plants.
• Xylem and phloem have distinct roles and structures that facilitate these processes.
• The arrangement of these tissues varies in roots, stems, and leaves, reflecting their function in plant physiology.