Xylem vessels

• Xylem is the water-conducting tissue.
• Tracheids are elongated cells with tapered ends that join end to end to form continuous tubes.
• Vessel elements are long tubes formed by end-to-end fusion of adjacent tracheid or parenchyma cell walls.
• Vessel elements are long, hollow cells joined together by pits at their ends.
• The primary function of xylem is to transport water from roots to leaves through transpiration pull.
• The lumen (cavity) of xylem vessels contains air, which provides support against negative pressure during transpiration.
• Lignin reinforces vessel walls and prevents collapse under tension.
• The lignin content of xylem varies among species.
• Water moves upwards due to cohesion between molecules and adhesion to the vessel wall.
• Water moves up the plant due to evaporation from leaf surfaces, creating a negative pressure gradient.
• Xylem vessels have thickened secondary walls made up of lignified middle lamellae and primary wall layers.
• Xylem vessels have thickened secondary walls with perforations called pit membranes that allow the passage of water but not air.
• Water moves upwards along the xylem vessels due to cohesion and adhesion forces.
• Pit membrane thickness can vary between species.
• Transpiration pulls water upwards through the xylem.
• Xylem vessels have no end walls or perforations, allowing continuous flow of water.
• Xylem vessels are dead cells with no nucleus or cytoplasm.
• Xylem vessels have thickened secondary cell walls made of lignin.