1. Xylem structure and function
26 April 2017
Xylem structure and function
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

2. Role of xylem
Absorbs
Water
Mineral salts
Oxygen
Resistance to forces

3. Vascular bundle Phloem Cambium Xylem Collenchyma Parenchyma
Arrangement of xylem in the stem
Collenchyma
Vascular bundle
Phloem
Cambium
Xylem
Parenchyma

4. How xylem and phloem are formed in the growing plant

5. 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

6. Provide support

7. Xylem are lignified
Impermeable to water and other solutes.
Form continual tubes.

8. 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

9. Stem
Ring around the edge gives resistance to bending

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

11. Resistance to tearing in the leaf

13. 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.