Overview
This lecture introduces the structure of xylem tissue in plants, focusing on its composition, location, and physical features, as a foundation for understanding its transport function.
Xylem as Vascular Tissue
- Xylem is classified as a vascular tissue, meaning it helps transport substances within a plant.
- Xylem mainly transports water and minerals.
- Xylem tissues are located in the root, stem, and leaf of plants.
- In cross-sections of plant organs, xylem tissue appears in specific positions, distinct from other vascular tissues.
Structure of Xylem Tissue
- Xylem tissue is made up of tube-like structures visible under a microscope.
- The majority of functional xylem consists of xylem vessels, large hexagonal tubes.
- Xylem vessels are formed from dead plant cells called xylem vessel elements.
- Each xylem vessel element loses its end walls, creating a continuous hollow tube.
- The walls of xylem vessels become thick and rigid due to the deposition of lignin.
Formation & Features of Xylem Vessels
- Lignin is a rigid, waterproof substance that surrounds the cells during development.
- As lignification proceeds, the cells die and become hollow, forming xylem vessel elements.
- Xylem vessel elements connect end-to-end, forming long xylem vessels.
- There are small unlignified regions in the cell wall called pits, which allow for lateral movement of substances.
- Xylem vessels, as seen in cross-section, have thick walls due to the lignin deposits.
Key Terms & Definitions
- Vascular tissue — tissue specialized for substance transport in plants.
- Xylem — vascular tissue that transports water and minerals.
- Xylem vessel — long, hollow tubes formed by joining dead cells called vessel elements.
- Xylem vessel element — a single dead cell that forms part of a xylem vessel.
- Lignin — a rigid, waterproof substance in xylem walls.
- Pit — an unlignified, thin area in the xylem wall permitting sideways movement of water.
Action Items / Next Steps
- Review diagrams of xylem location in roots, stems, and leaves.
- Prepare for a future lesson on how xylem structure enables its transport function.