Syllabus Edition

First teaching 2023

First exams 2025

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Xylem Vessels Elements (CIE AS Biology)

Revision Note

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Cara Head

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Cara Head

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Xylem Vessel Elements: Structure & Function

  • The functions of xylem tissue in a plant are:
    • Vascular tissue that transports dissolved minerals and water around the plant
    • Structural support
    • Food storage
  • Xylem tissue is made up of four cell types that function together:
    1. Tracheids (long, narrow tapered cells with pits)
    2. Vessel elements (large with thickened cell walls and no end plates when mature)
    3. Xylem parenchyma
    4. Sclerenchyma cells (fibres and sclereids)
  • Most of the xylem tissue is made up of tracheids and vessel elements, which are both types of water-conducting cell

Xylem tissue micrographs

xylem-vessels-elements

Micrographs of xylem vessels allow structural lignin to be seen in both longitudinal section (A) and transverse section (B)

Drawing Xylem Tissue Diagramxylem-vessels-elements-showing-lignin

Biological drawing conventions can be applied to the drawing of xylem vessels from micrographs

Relating structure to function in xylem vessel elements table

Structure Function
Lignified cell walls Adds strength to withstand hydrostatic pressure so vessels do not collapse. Impermeable to water
No end plates Allows for mass flow of water and dissolved solutes as cohesive (between water molecules) and adhesive (between water molecules and xylem wall) forces are not impeded
No protoplasm (cells are dead when mature) Does not impede the mass flow of water and dissolved solutes
Pits in walls (in non-lignified sections) Lateral movement of water allows for continuous flow in case of air bubbles forming in the vessel
Small diameter of vessels (although larger than tracheids) Helps prevent the water column from breaking

Examiner Tip

You must be able to recognise the xylem vessel elements in images, so look for a thicker cell wall and a larger diameter.

You should be able to draw xylem vessel elements from micrograph images. For more detail on how to make biological drawings see our revision notes here.

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding