Transport in Plants - Xylem Flashcards
What do the vascular bundles in the leaf form
The midrib (main vein) and side veins of the leaf
What does the network of veins in the leaf allow
Branches network of veins spreading throughout the leaf helps support the leaf as well as transporting substances to and from the leaf cells
where is the xylem in each vein
above the phloem
Describe the palisade and spongy mesophyll cells in the leaf
- adapted for photosynthesis
- air spaces allow for diffusion
What cells does the xylem tissue contain
- Xylem vessels
- fibres
- xylem parenchyma
Describe the xylem vessels
Columns of fused, hollow (dead) cells which transport the water and mineral ions up the plant
Describe the fibres
Long dead cells with thick cell walls. Provide support
Describe the xylem parenchyma
Living cells. Firms packing tissue and stores food. May contain bitter tasting tannin to protect against insect attack
How do the xylem vessels begin
Starts as a column of live cells which lay down waterproof lignin inside the cell wall
How do the xylem vessels progress
- cell contents die and end cell walls break down
- without the end plates, long vessel elements are formed. Lignin increases as the cells age.
how is lignin arranged in the xylem
spirals, annular or reticulate patterns
what are pits
gaps in the lignin where there is only cellulose
how is the shape of the xylem vessel adapted it its function
- continuous column
- no contents or end walls to impede flow
what is the function of lignin in the xylem
- prevents walls from collapsing inwards due to tension
- allows for adhesion for water molecules
- arrangement of lignin allows for plant to grow, bend and branch without breaking
how is the diameter of the xylem vessel adapted for its function
diameter most effective for flow - small enough to maintain water column for capillary action
