Transport in the Xylem (Needs root transport added) Flashcards
What is Transpiration
Evaporation of water from a plant leaf
What evidence is there for the cohesion-tension theory?
If air enters a xylem, tree can no longer draw up water as continuous column broken
Water doesn’t leak out broken vessel due to negative pressure
How does Water move in the xylem and up the stem (big question)
Water evaporates from mesophyll cells via transpiration
Water molecules from H bonds and stick via cohesion
Continuous unbroken column formed across mesophyll cells and down the xylem
As water evaporates from mesophyll into air spaces beneath stoma, water is drawn up behind it due to cohesion
Column of water pulled up xylem as a result- transpiration pull
How does water move across cells of leaf
Mesophyll cells lose water via transpiration
Cell now have low water potential, draws in water from surrounding cells
Surrounding cells water potential decreases
Water taken in by other cells via osmosis
Drawbacks of potometer
Some of water could be used in photosynthesis or metabolism
Use of potometer
Measure rate of volume of water taken up by plant
Measures rate of transpiration
Control Measures of Potometer
Temperature
Light intensity
Humidity
Wind
Why is the diameter of a tree smaller in daytime than night?
During the day when transpiration is at its highest, there is more negative pressure in the xylem that pulls the xylem walls inwards.
At night, less negative pressure means the xylem walls are not pulled inwards, increasing tree diameter.
