Transpiration Flashcards
What are the 9 layers of a leaf from top to bottom?
-Waxy cuticle
-Upper epidermis
-Palisade layer
-Xylem/phloem vessels
-mesophyll layer
-lower epidermis
-waxy cuticle
-guard cells
-stomata
What is the role of the xylem?
-Transports water and minerals from the roots to the stem and the leaves of a plant.
-Provides mechanical support as walls are made from lignin.
How is the xylem adapted for transpiration?
-Unidirectional
-Made up of hollow, non-living cells (continues lumen).
What does cohesion mean?
Attraction between dipolar water molecules.
What does adhesion mean?
Attraction between dipolar water molecules and other polar molecules.
How is water moved up the xylem?
In a continuous stream by tension.
How is water vapour transported and how is water transported?
Water vapour-diffusion
Water-osmosis
How is transpiration controlled by opening and closing the stomata?
-guard cells curve apart when turgid.
-when flaccid they lie close together.
-Slows down transpiration rate as CO2 cannot enter the leaf so no photosynthesis will happen.
What evidence can support the cohesion tension theory?
-Change in diameter of tree trunks.
-If a bubble enters the xylem transpiration will stop.
-If the vessel is broken air enters but doesn’t leak due to tension.
What is the process of transpiration?
-Sun provides kinetic energy.
-Water molecules evaporate from leaf away from the stomata.
-There is a higher water potential in mesophyll layer.
-Water vapour diffuses out of the leaf down a water potential gradient.
-Lower water potential in roots.
-Water moves into roots by osmosis.
-Creates tension in the xylem due to the water potential gradient.
-Water moves out of the xylem by osmosis.
How does humidity effect transpiration?
-If high more water vapour outside so water potential outside of leaf will increases so rate decreases.
-If low less water vapour outside so lower water potential gradient and rate will increases.
How does temperature effect the rate of transpiration?
Increases rate of evaporation as it increases as the molecules have more kinetic energy which increases rate of diffusion from the leaf.
How does the stomata opening effect the rate of transpiration?
When open- more water can diffuse out so rate increases.
When closed-less water diffuses out so rate decreases (e.g at night).
How does wind speed effect the rate of transpiration?
-Wind carries away the water vapour which has diffused out so increases diffusion gradient so the higher the wind speed, the faster the rate.
