Water Balance of Plants - 3 Flashcards
Where does water leave in plants and how does water reenter the plant
water leaves through the leaves which allows water to enter from the roots and soil and move up the xylem conduits through bulk flow
Water content and rate of movement in soils depend on what two factors and why
soil type and structure
because they influence pressure gradient and hydraulic conductivity
water absorption increases due to increases surface area of what
root hairs
what defines soil texture
the diameter
ex. sand is 1mm or larger
clay is 2um or less
What is the difference between clay and sand soil
clay has greater surface area because of smaller particles and therefore have smaller channels in between them and cause water to be retained longer
Explain the difference in pressure potential for wet and dry soils
pressure potential is higher in dry soils because they are fighting harder to get water from plant because they have less of it
what causes gravitational potential to increase in soil
increase in elevation
How does water move through soil
by bulk flow, from regions of higher soil water content to lower
rate of water flow in soils depending on what two factors
- size of the pressure gradient
- hydraulic conductivity of the soil = measure of ease which water movies through (which once again varies with water content and soil type)
does clay or sand have higher hydraulic conductivity
sand because easier because bigger particles so less turns in the pathway
Define root hairs
filamentous extensions of root epidermal cells that greatly increase SA of root and soil water contact
Explain the variability of permeability of root hairs
the older/mature roots are less permeable because they develop a modified layer of cells with hydrophobic material to enable water uptake (dont lose water in all parts of roots)
What pathways does water move through in roots
apoplast, symplast, and transmembrane pathways
Define apoplast pathway
water moves through cell walls and intercellular airspaces of non-living cells. this pathway is obstructed by the casparian strip which forces the water to move into symplast pathway in order to enter xylem
Define casparian strip
obstructs apoplast pathway and its function is to insulate water from exiting the xylem
symplast pathway
water moves through network of cell cytoplasm that is interconnected by plasmodesmatea (gates) that is a facilitated movement
transmembrane pathway
water moves through cell membrane of each cell, twice, and need solute potential. facilitated by aquaporins and requires energy from respiration
Root pressure is most likely to occur when soil water potentials are ____ and transpiration rates are ____
high
low
Define guttation
occurs when plants develop root pressure frequently and produce liquid droplets on the edges of leaves.
this pressure can reduce effects of cavitation
what consists of the longest part of the pathway of water transport in plants
xylem
define tracheids
elongated spindle shaped cells that overlap vertical to one another and water flows through pits. pits of tracheids will line up and form pit pairs that dont include secondary cell wall to provide lower resistance
Define vessel elements
shorter segments than tracheids that allows water to move through pits and perforation plates
What are the two types of xylem conduits
- tracheids
- vessel elements
What allows water to move throughout the plant starting from the soil
prsesure-driven bulk flow moves water throughout the xylem and the decrease of water potential at evaporation sites in leaves allows for the ascent of water from the soil throughout the plant
