Xylem Flashcards
What does xylem transport?
Water and mineral ions
What direction does xylem transport in?
Up to the leaves and other parts of the plant
What is the most obvious feature of xylem in dicotyledonous plants?
The xylem vessel, long cells and thick walls
What does xylem tissue consist of?
Tubes, for transport
Fibres, for support
Living parenchyma cells
What are xylem vesel walls impregnated with?
Lignin, as xylem develops lignin waterproofs the walls of the cells resulting in the cells dying and the end walls and content decaying, this leaves long columns of dead cells with no content- xylem vessels
Lignin strengthens walls which prevents what?
The cell walls collapsing inwards, keeping the vessel open even when there is a short supply of water
The lignin thickening forms patterns in the cell wall what are the three patterns?
Spiral
Angular- rings
Recticulate- network of broken ring
Why is the lignin thickening formed in these patterns?
To allow flexibility and stop rigidness in the stem or branch
Is ligninfication complete everywhere?
No it leaves pores in the walls of the vessel known as bordered pits
What is the function of bordered pits?
To allow water to leave one vessel and enter another or to enter a living part of the plant
How are the dead cells in xylem vessel structured?
They are aligned end to end to form a continuous uninterrupted column
Are the xylem tubes narrow or wide and why are they so?
They are narrow so that the water column does not break easily and so that capillary action(cohesion tension) can be effective
Does the lignin deposited in the walls of the xylem vessel allow xylem to stretch or not?
Yes, as the plant grows this enables the stem or branch to bend
Why is the flow of water not impended?
There are no end walls no content no nucleus or cytoplasm and the woody substance lignin prevents the columns from collapsing
