Transpiration In Xylem Flashcards
How does air move through stomata to surrounding air
On the air spaces there is water vapour and low humidity creates concentration gradient causing water molecules to diffuse into the atmosphere
How does water move through cytoplasmically
The water move out of the mesophyll cells to the air spaces thr via evaporation this decreases the water potential
Water moves into the mesophyll cells via osomosis from neighbouring cells this decreases the water potential in neighbouring cells so these in turn also take water
How does water move up the stem
Water is cohesive nature
Water wveaporates from the mesophyll cells go the air spaces as water is cohesive when it evaporates it also pulls another water molecule behaving it this creates a long unbroken column of water in the xylem as the water evaporates more is pulled behind the transpiration pull transpiration puts the xylem under tension as less than atm pressure so pressure is negative
What evidence is there for transpiration pull
When a leaf is cut air is drawn up as water draws molecule up due to the pull and no more can no longer be drawn up as now column is broken
The diameter of a tree trunk shrinks in the day time when transpiration is highest as most negative pressure cause the walls to be pulled onwards
When a leaf is cut water doesn’t leak out as the water is under tension not pressure
