Transport Vessels
Xylem Vessels
Transports water and dissolved mineral ions from roots to leaves
Flow of water is not impeded because:
o Nos cross-walls
o No cell contents
o Lignin prevents collapse
Living parenchyma cells act as packaging to separate and support vessels
Xylem Vessel Elements
Dead cells aligned end-to-end to form continuous columns
No contents (empty lumen) so doesn’t impede the flow of water
Allows for rapid, low resistance conduction of water
Xylem Adaptations
Narrow tubes so water column doesn’t break easily
Bordered pits (non-lignified parts of cellulose wall) allow water to move between
vessels
End wall is lost to allow free passage of water to next cell
Dead cells are waterproof and have no contents
Thickening of lignin provides support and prevents collapse
Phloem Vessels
Transports assimilates (mainly sucrose and amino acids)
Sucrose is dissolved in water to form sap
Sieve tubes are made up of sieve tube elements
End plates act as filters between sieve tube elements
Parenchyma cells are used for storage
Companion cells between and outside sieve tubes carry out metabolic processes to load
and unload assimilates
Xylem Vessels
Transports water and dissolved mineral ions from roots to leaves
Flow of water is not impeded because:
o Nos cross-walls
o No cell contents
o Lignin prevents collapse
Living parenchyma cells act as packaging to separate and support vessels
Xylem Vessel Elements
Dead cells aligned end-to-end to form continuous columns
No contents (empty lumen) so doesn’t impede the flow of water
Allows for rapid, low resistance conduction of water
Xylem Adaptations
Narrow tubes so water column doesn’t break easily
Bordered pits (non-lignified parts of cellulose wall) allow water to move between
vessels
End wall is lost to allow free passage of water to next cell
Dead cells are waterproof and have no contents
Thickening of lignin provides support and prevents collapse
Phloem Vessels
Transports assimilates (mainly sucrose and amino acids)
Sucrose is dissolved in water to form sap
Sieve tubes are made up of sieve tube elements
End plates act as filters between sieve tube elements
Parenchyma cells are used for storage
Companion cells between and outside sieve tubes carry out metabolic processes to load
and unload assimilates
