Topic 3 - Transpiration [14] Flashcards
What is Transpiration?
Transpiration is the passive process where water evaporates out of the leaf, through the stomata, causing more water to be drawn from the soil.
Temperature Affects Transpiration How?
Positive Correlation
More Heat = More Kinetic Energy
Faster Moving Molecules
More Evaporation
Humidity Affects Transpiration How?
Negative Correlation
More Water Vapour = More Positive WP In AIR means High WP outside of leaf. so the water potential gradient is reduced
water evaporate out less
Water Vapour Evaporates from stomata and an upwards pull on the water column from xylem occurs.
How does this affect Xylem?
Is this Negative Pressure or Positive Pressure?
Upwards Pull Creates Tension and pulls in the xylem walls making them narrower.
This increases the action of capillarity/adhesion
Negative Pressure - PULL
Root Pressure.
water moves in to roots by osmosis and increases pressure of roots when filled, forcing water above the roots to be pushed upwards (positive pressure).
Capillarity/Adhesion?
When water molecules stick to other molecules e.g. walls of Xylem
The narrower the Xylem, the more Adhesion
How does Water’s cohesion affect it in the Xylem
Water travels up Xylem as a continuous water column cuz stick together
Why does water have strong Cohesion?
Because it is Dipolar, this allows it to form H bonds between other waters and stick together
Whats Cohesion?
Cohesion is the attraction between the same type of molecule.
What does Water being Dipolar Allow it to do?
Enables them to form Hydrogen Bonds with each other, between the H and O of diff water molecules.
The water molecules stick together aka COHESION
Water is a Dipolar Molecule. What this mean?
slight negative oxygen
slight positive hydrogens.
Wind Affects Transpiration How?
Positive Correlation
More Wind, Humid Air Blown Away so Gradient maintained.
Light Intensity Affects Transpiration How?
Positive Correlation
More Light, More Stomata Open Resulting in Larger SA for water to evaporate out of
Light Intensity Affects Transpiration How?
Positive Correlation
More Light, More Stomata Open Resulting in Larger SA for water to evaporate out of
