Xylem Vessels Elements (Cambridge International AS Biology)

Exam board Cambridge International · ASUpdated 2025-09-26

Xylem Vessel Elements: Structure & Function

Spec point — 7.1.3 · draw and label xylem vessel elements, phloem sieve tube elements and companion cells from microscope slides, photomicrographs and electron micrographs

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:
- Tracheids(long, narrow tapered cells with pits)
- Vessel elements(large with thickened cell walls and no end plates when mature)
- Xylem parenchyma
- 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

Illustration of plant stem cross-section highlighting xylem vessels with lignin walls and lumen; magnified views show cell structure.

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

Diagram showing xylem vessel elements and lignin in cell walls. Section A highlights lignin; Section B highlights xylem vessel and vascular bundle.

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

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

Exam Hint 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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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