TOPIC 9.1 Xylem transport Flashcards
What is Transpiration
Loss of Water vapour from the stems and leaves of plants
How does Transpiration occur
Light energy converts water in leaves to vapour which evaporates out the leaf via the stomata
New water is absorbed by the roots creating pressure difference.
Water flows through the xylem along pressure gradient to the leaves where water was lost
How is water loss within plants regulated
Regulated by the opening and closing of the stomata
Transpiration rates higher when stomata open than closed
When plants lacks water absidic acid released which triggers the release of Potassium decreasing water pressure
A loss of pressure makes pores close as guard cells become flacid and block the opening
What is the transpiration stream
The flow of water through the xylem from the roots to the leaves against gravity
Two crucial properties of water for the transpiration stream
Cohesion and adhesion
What is cohesion
The force of attraction between two particles of the same substance
Water molecules form hydrogen bonds allowing them to be dragged up the xylem towards the leaves
What is adhesion
The force of attraction between two particles of different substances
Xylem wall also polar allowing water to bond to it. Water sticks to the xylem wall generating more tension as it moves up
STRUCTURE OF THE XYLEM
is a tube composed of dead cells that are hollow (no protoplasm) to allow for the free movement of water
Because the cells are dead, the movement of water is an entirely passive process and occurs in one direction only
The cell wall contains numerous pores (called pits), which enables water to be transferred between cells
Walls have thickened cellulose and are reinforced by lignin, so as to provide strength as water is transported under tension
What is an Xerophyte and what are its properties
Plants that tolerate dry conditions
Properties include- Reduced leaves, Thick waxy cuticle and low levels of growth
What are halophytes and what are its properties
Plants that tolerate salty conditions
Properties include- Salt excretion, Root level exclusion and Altered flowering schedule
Factors which impact transpiration rates
Temperature, Humidity, Light intensity and Wind exposure
ROOT UPTAKE REVISE SEPERATLY
