Overview
This lecture covers the roles, structures, and arrangements of xylem and phloem, the main vascular tissues responsible for transport in plants.
Transport in Plants
- Plants need to transport water, minerals, and food between roots, leaves, and other tissues.
- Vascular tissue enables movement of essential substances throughout the plant.
Xylem
- Xylem transports water and minerals from roots to all parts of the plant.
- Consists of tracheids, vessels, fibers, and parenchyma cells.
- Tracheids connect roots and leaves with water passing through pitted walls.
- Vessels are long, hollow tubes for continuous water movement.
- Fibers provide structural support.
- Parenchyma stores food and are the only living xylem cells.
- Lignin strengthens xylem cell walls; patterns include ring, spiral, reticulate, and pitted.
Phloem
- Phloem moves manufactured food (e.g., sucrose, amino acids) from leaves to other parts (called translocation).
- Made up of sieve tubes, companion cells, fibers, and parenchyma.
- Sieve tubes are elongated cells with pores for food transfer, containing little cytoplasm.
- Companion cells support sieve tubes with cytoplasm and a nucleus.
- Fibers provide support and are the only dead cells in the phloem.
- Parenchyma stores food and other substances.
Arrangement of Vascular Tissue
- In dicot roots, xylem forms an X shape at the center, surrounded by phloem.
- In stems, xylem and phloem are in circular clusters near the stem's edge.
- In leaves, xylem is positioned above phloem within the vascular bundle.
Key Terms & Definitions
- Vascular tissue — specialized plant tissue for transporting water, minerals, and food.
- Xylem — tissue that transports water and minerals from roots upward.
- Phloem — tissue that carries food from leaves to the rest of the plant (translocation).
- Tracheids — elongated xylem cells with pitted walls for water movement.
- Vessels — wide, long tubes in xylem for continuous water flow.
- Sieve tubes — phloem cells with pores for food transport.
- Companion cells — phloem cells that assist sieve tubes.
- Lignin — substance strengthening xylem cell walls.
Action Items / Next Steps
- Review diagrams showing xylem and phloem arrangement in roots, stems, and leaves.
- Learn the differences between xylem and phloem cell types and their functions.