Transpiration Extra Flashcards
Which flow, apoplastic or symplastic, has more resistance?
Symplastic
What is the xylem?
Hollow, narrow, dead vessel that is a central tube that transports water up a plant
What is meant by the cohesion tension theory?
Cohesion is water molecules ‘sticking together’ due to H bonds
As water is pulled up through the xylem the xylem is put under tension
What evidence supports cohesion tension theory?
‘Hug a tree’ - diameter of tree changes
When transpiration rate is high there is more tension and diameter shrinks
When there is less transpiration there is less tension so diameter increases
What is transpiration?
The evaporation of water from the surface of leaves via the stomata
How does light effect transpiration?
More light more transpiration
Photosynthesis only occurs in the light - Stomata are open when light for gas exchange
When stomata are open water can evaporate
What is the effect of temperature on transpiration?
Increased temperature more transpiration
Kinetic energy of water molecules increases - more evaporation
Also decreases amount of water air can hold - steeper gradient
What is the effect of wind on transpiration?
More wind more transpiration
Water vapour naturally accumulates around the stomata on outside of the leaf - increases water potential outside leaf
More air movement disperses this layer more quickly maintains gradient between leaf and air
What is the effect of humidity on transpiration?
More humid less transpiration
More water in atmosphere so reduced gradient between leaf and atmosphere so less diffusion
What is an xerophyte?
A plant that has adapted to survive in an environment with very little water
How does a thick waxy cuticle help a plant conserve water?
Waxy - waterproof layer
Thick - less water can escape through
How does rolling up leaves help a plant conserve water?
Helps to trap a layer of still air within the leaf
This area becomes saturated with water vapour
No gradient between inside and outside of leaf
How do hairy leaves help a plant conserve water?
A thick layer of hair traps moist air next to the leaf surface
Reduces water potential gradient between inside and outside of leaf
How do sunken stomata help a plant conserve water?
Stomata in pits or grooves trap a layer of water vapour outside leaf so reduce gradient
Also reduces wind movement
