Xylem Flashcards
(25 cards)
Characteristics of xylem 3
Carries water and mineral salts
Dead cells
One way
Characteristics of phloem
Carries sugar and amino acids
Live cells
Bidirectional
Packing off xylem and phloem in root
Centralised to anchor plant
Components of a root crossection
Vascular bundle (stele)
Endodermis
Cortex
Epidermis
2 types of tubes in the xylem
Tracheids
Vessels
Characteristics of tracheids 3
Narrower
Cells have perforated end walls
These cells provide support
Characteristics of xylem vessels 4
Wider cells
Reduced or absent end walls= continuous tube
Main conducting tubes
Only in flowering plants
What is the advantage of the xylem being made of dead cells
No cytoplasm, Easier for upflow of water
Function of lignin
Provide mechanical strength
Prevent collapse
Support plant
Allow adhesion of water molecules
Pits in xylem walls and function?
Areas of thinner lignin, allowing sideways movement of water through vessels
Components of xylem
Vessels
Tracheids
Fibres
Parenchyma
Structure and function of parenchyma
Living packing tissue, keeps all xylem/ phleom elements in place
Function of xylem/ phloem fibres
ONLY provide support, no transport
What causes the death of xylem cells
Deposition of lignin on cellulose cell walls makes them impermeable
In what structure is lignin deposited
Rings or spirals
Comparison points between xylem and phloem 4
Direction of flow
Product carried
Presence of end walls
Presence of lignin
What must occur to allow the continuous movement of the transpiration stream
Column of water in xylem must be intact, no breaks or bubbles
How is the affect of bubbles mitigated in the transpiration stream
Pits between adjacent vessels allow lateral movement of water, sk the column can bypass the bubbles
4 cell types in phloem
Seive tubes
Companion cells
Phloem fibres
Phloem parenchyma
Describe the organelles in seive tube elements 3
No nucleus
Few organelles
Only strands of cytoplasm
What do the cell walls of the seive elements in phloem form
Seive plates
Function of companion cells
Keep seive tube elements alive acting as their life support unit on their behalf
How are the cytoplasm of seive tube elements and that of companion cells joined
By plasmodesmata
Characteristics of companion cells 3
Dense cytoplasm
Several mitochondria and ribosomes
Very metabolically active
