B6 Transpiration Flashcards
Describe how water is moved through a plant by cohesion tension theory
Water evaporated from the mesophyll cells
Reduces the water potential in cells
Water is drawn out of xylem vessels by osmosis
Creates tension between water molecules held together by hydrogen bonds
Water is pulled up the xylem vessels
The diameter of a tree is less during the day than it is at night. Explain how this supports cohesion tension theory
Water evaporates from surface of mesophyll cells and diffuses through stomata
Creates tension in the column of water in xylem vessels
Give 4 adaptations shown by xerophytes
Stomata in pits
Rolled leaves
Thick waxy cuticle
Hairs on surrounding stomata
Reduced number of stomata
Spines/fewer leaves
Why do some leaves have hairs on them?
Trap layer of water vapour around leaf (boundary layer)
Increases water potential around leaf
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of the leaf
Why do some leaves have stomata in pits?
Traps water vapour around the stomata
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of leaf
Why do some leaves have a thick waxy cuticle?
Hydrophobic waxy substances impede movement of polar water molecules
Increases diffusion distance
Decreases diffusion/transpiration of water molecules
Why do some leaves have rolled leaves?
Traps water vapour around the stomata
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of leaf
Why do some plants have spines or fewer leaves
Reduced surface area
Reduced water loss by diffusion/transpiration
Why might the rate of water uptake by a plant NOT be the same as the rate of transpiration?
Water used for turgidity
Water used in photosynthesis
Water used in hydrolysis
Water produced by condensation reactions
Water produced by respiration
Name the piece of apparatus that can be used to measure water uptake by a shoot
Potometer
List 4 environmental factors that increase the rate of transpiration
Increased temperature
Increased wind/air movement
Increased light intensity
Decreased humidity
Explain how an increase in temperature increases the rate of transpiration
Increased rate of evaporation
Increased rate of diffusion due to increased KE of water molecules out of leaf
Explain how an increase in wind increases the rate of transpiration
Air movement removes water molecules that have left the leaf
Maintains a steep diffusion gradient between internal and external surface of the leaf.
More water moves by diffusion through the stomata
Explain how an increase in light intensity increase the rate of transpiration
Stomata open to allow carbon dioxide to enter the leaf for photosynthesis
Increases number of water molecules moving through stomata and out of the leaf
Explain how an increase in humidity decreases the rate of transpiration
Increased number of water molecules in external atmosphere.
Reduces the water potential gradient between the internal and external environment
Decreases diffusion of water out of the leaf
