Xylem and Phloem - Transport in Plants | Biology | FreeAnimatedEducation

Key Concepts:

• Xylem: Vascular tissue transporting water and minerals from roots to other plant parts.
• Phloem: Vascular tissue transporting manufactured food (e.g., sucrose, amino acids) from photosynthetic areas to other plant parts (translocation).
• Tracheids: Conducting cells in xylem with pitted walls, allowing water flow between cells.
• Xylem Vessels: Long, continuous tubes in xylem for efficient water transport.
• Sieve Tubes: Elongated cells in phloem with perforated walls (sieve plates) for food transport.
• Companion Cells: Cells associated with sieve tubes, providing metabolic support.
• Lignin: Substance strengthening xylem cell walls, with varying patterns (ring, spiral, reticulate, pitted).
• Vascular Bundle: Cluster of xylem and phloem tissues.
• Translocation: The process of transporting manufactured food through the phloem.

Xylem

• Function: Distributes water and minerals absorbed by the roots throughout the plant.
• Composition:
  • Tracheids: Conducting cells connected via pitted walls, allowing water to flow between them. Water flow is not continuous.
  • Xylem Vessels: Long, wide, hollow tubes stretching continuously from roots to leaves for efficient water transport.
  • Fiber: Provides structural support.
  • Parenchyma: Living cells involved in food storage.
• Cellular Characteristics: Some xylem parts lack protoplasm or cell walls for easier water passage.
• Lignin: Strengthens xylem cell walls. Lignin patterns vary (ring, spiral, reticulate, pitted) depending on location.
• Example: The heartwood and sapwood of a fallen tree are primarily xylem tissues.

Phloem

• Function: Transports manufactured food (e.g., sucrose, amino acids) from photosynthetic areas (leaves) to other plant parts (translocation).
• Composition:
  • Sieve Tubes: Elongated, thin-walled cells arranged in a row, with sieve plates (perforated walls) for food passage. Mature sieve cells have a thin cytoplasm layer.
  • Companion Cells: Provide metabolic support to sieve tubes, containing abundant cytoplasm and a nucleus. They have thin, flexible cell walls.
  • Fiber: Provides structural support.
  • Parenchyma: Stores food and other substances.
• Cellular Characteristics: Sieve tube cells have degenerated protoplasm, requiring companion cells for vital processes.
• Cellular Characteristics: Fiber cells are the only dead cells in phloem.
• Example: Translocation moves sucrose from leaves to roots for storage.

Arrangement of Vascular Tissue

• Roots (Herbaceous Dicot Plants): Xylem forms an X-shape in the center, with phloem filling the spaces around the xylem.
• Stems: Xylem and phloem are clustered into circular shapes located near the edge of the stem.
• Leaves: Xylem and phloem are located in the vascular bundle, with xylem positioned above the phloem.

Synthesis/Conclusion

Xylem and phloem are the two primary vascular tissues in plants, responsible for transporting essential substances. Xylem transports water and minerals from the roots, while phloem transports manufactured food from photosynthetic areas. Their distinct cellular structures and arrangements in different plant parts (roots, stems, leaves) are optimized for their respective functions. The presence of supporting cells like fibers and parenchyma, along with specialized features like lignin in xylem and companion cells in phloem, contribute to the overall efficiency and structural integrity of the vascular system.