Structure and Functions of Xylem

https://www.youtube.com/watch?v=U7EUUNiX0vA&feature=youtu.be

What 2 main types of tissue does xylem consist of

Xylem vessels and Xylem fibres.

What are xylem vessels

They start as a series of plant cells running up the stem from the roots to the leaves.

At a certain point, the carbohydrate wall lignin forms within the cell walls, lignin is impermeable

Living contents of cell wall dies, and end walls between cells break down

Pits are regions of the cell well free of lignin.

So final xylem consist of non living hollow tubes.

What do pits do

They allow water and dissolved substances to pass between vessels.

What does lignin do

Helps to support the structure of the xylem vessel.

When water is pulled up xylem vessels, causes pressure in vessels to fall slightly, lignin in vessel wall helps to prevent vessels from collapsing

What are xylem fibres formed from

Long narrow cells, very large amount of lignin form in these cells. The interior contents of the cells die.

Xylem fibres provide mechanical support for the plant.

Xylem fibres and vessels are non living tissue.

What do parenchyma cells do in the xylem

They can act as a store of starch,

They can also contain tannins which are bitter compounds that deter herbivores from eating the plant