Lecture 6 - Atmosphere-Plant-Soil Continuum Flashcards
water movement in xylem
moves root to shoot
are mature xylem cells alive or dead?
dead
are immature xylem cells alive or dead
alive
2 cell types that are involved in water flow through the xylem
tracheids and vessels
tracheids
primitive water-conducting elements that are present in both gymnosperms and angiosperms
what do tracheids look like
long, thin cells with tapered ends and walls reinforced with lignin
what allows movement between tracheids
pit-pair
pit-pair
2 pits occurring opposite one another in the walls of adjacent tracheid or vessel elements
vessels
advanced water-conducting elements that are present only in the angiosperms
what are vessel cell sizes dependent on
species and environment dependent
what is a special feature of vessels
development of perforation plate
are large vessels always better
no
wider conduits are ______ (more/less) conductive
more
cavitation
a condition wherein an air bubble moves into a vessel
embolism
the blocking of a xylem vessel or tracheid by an air bubble or cavity
what does disruption to H-bonding lead to
leads to localized break in water column
embolized xylem vessel
can no longer hold water and decreases xylem hydraulic conductance
what do pit membranes do
they permit water flow and limit embolism spread
why does angiosperm have both vessel and tracheid in xylem
as vessels are more vulnerable to embolism, compared to tracheids
they also may evolve their xylem system to maintain water flow under drought conditions
cohesion tension theory
water forms a string of water molecules during tis movement through the xylem. the tensile strength of water is high enough to allow water to be pulled through the tracheary elements
experimental evidence for tension in xylem sap
high transpiration results in big tension in xylem sap that causes the the xylem walls pulled in towards lumen
