Xylem structure and function

21 April 2023

WILF

Describe the structure of xylem tissue to include: Vessels; Tracheids; fibres and xylem parenchyma

Explain why xylem is dead tissue

Explain the role of xylem in support in the plant

Role of xylem

• Absorbs– Water– Mineral salts– Oxygen

• Resistance to forces

Vascular bundle

Xylem

Phloem

Cambium

Collenchyma

Parenchyma

Arrangement of xylem in the stem

How xylem and phloem are formed in the growing plant

Structure of xylem tissue

Elongated dead cells that form tubes.They are made up of •Tracheids

– Tapered cells with sloping end walls

•Xylem vessels•Shorter and fatter than tracheids.•Each are perforated by pits to allow sideways movement of water and minerals•Fibres and xylem parenchyma

Provide support

•Xylem are lignified

•Impermeable to water and other solutes.

•Form continual tubes.

Location of xylem tissue

• This differs in the stem, leaf and root.

• Stem: – Vascular bundles near the edge of the stem

• Root: – Vascular system in a central position

• Leaf: – Vascular bundles in the midrib and other leaf

veins

Stem

• Ring around the edge gives resistance to bending

In the root, resistance to the pulling force of the wind

Resistance to tearing in the leaf

Notes from the Student Guide

The vascular tissues are made up of:xylem tissue, which transports water and mineral salts from the roots to the leaves.• vessels - the main conducting cells• tracheids - also conduct water but are not as well adapted as vessels for this function• fibres – they have no role in water transport but function in support• xylem parenchyma - this acts as packing tissue.Vessels and tracheids are dead cells and they form a system of tubes through which water can travel.The cells are dead because lignin has been deposited on the cellulose cell walls rendering them impermeable to water and solutes. These cells also provide mechanical strength and support to the plant.The distribution of xylem tissue differs in primary stems, leaves and roots.• In stems it occurs as part of the peripheral vascular bundles. This organisation gives flexible support but also resistance to bending strain.• In leaves the arrangement of vascular tissues in the midrib and network of veins also gives flexible strength and resistance to tearing strains.• In roots the central arrangement is ideal for resistance to vertical stresses (pull) and so helps the anchorage of the plant.