Transport in Plants Flashcards
(49 cards)
What is transpiration?
the evaporation of water from a plants surface.
this happens through the stomata
What is the function of the stomata?
they open to allow the entry of CO2 for photosynthesis
How is the rate of transpiration affected by light?
- during daylight the stomata open to let CO2 enter
- increases rate if transpiration as water evaporates from the mesophyll cells and diffuse out
How does temperature affect the rate of transpiration?
- increase in temp increases rate of transpiration
- water molecules are provided with more kinetic energy so the evaporate more rapidly m
How does humidity affect the rate of transpiration?
- increase in humidity increases water potential in air
- this decreases rate of transpiration
- water potential gradient for diffusion of water decreases
Hoe does air movement affect the rate of transpiration?
- Air movement removes water vapour from the leaf surface
- This increases the water potential gradient and rate of transpiration
How does still air affect rate of transpiration?
- in still water vapour will build up around the leaf
- this decreases the water potential gradient thus rate if transpiration
What is a Xerophyte?
a plant that possesses a range of adaptations that limit water loss via transpiration
What is the purpose of the thick cuticle on a Xerphyte?
- provides a long diffusion pathway
this reduces the rate if transpiration
What is the function of the Hairs in Xerophyte leaves?
- hairs on leaf surface trap layer of still air
- this becomes saturated with water vapour which reduces the water potential gradient for water loss
What is the purpose of the rolling up if leaves in Xerophytes?
- traps layer if still air which becomes saturated with water vapour
- reduces water potential gradient for water loss
- thus reducing transpiration rate
How does the position of stomata reduce water loss in Xerophytes?
- they’re positioned in epidermal pits/grooves beneath leaf’s surface
- this reduces exposure to air
- this trapped air becomes saturated with water vapour
- reduces water potential gradient for evaporation
Describe the structure of the Xylem
- no cell contents
- hollow tubes
- cell wall strengthened by lignin which makes cell rigid and provides support
Describe the Cohesion-Tension theory.
- water moves across leaf down water potential gradient
- water is drawn from xylem, this creates tension in xylem
How is the water column in the xylem maintained?
by cohesive and adhesive forces
What is cohesion?
attention of water molecules to each other by hydrogen bonds
What is adhesion?
attraction of the water molecules to the xylem walls
How is water taken from the soil?
- upward movement of water from the xylem in the roots maintain water potential gradient across root cells
- water is taken from soil via osmosis
Describe the evidence for Cohesion-Tension theory.
as rate if transpiration increases the diameter of a tree trunk decreases
- evaporation from leaves draws water from xylem by osmosis
- so water is pulled up xylem creating tension
- the tension pulls in the walls of xylem vessels
What is a potometer?
measures rate of transpiration
Why is the rate of water uptake not the same as rate of transpiration?
some of the water taken up by plants is often used to maintain turgidity and a small % is used in photosynthesis
What measurements do you need when calculating rate if transpiration in a potometer?
- distance travelled by air buble
- radius of lumen of the capillary tubing
- time taken for air bubble to move
What is the calculation for the volume of water taken up in a potometer?
π x r^2 x d
pi x radius squared x distance moved
What is needed for the potometer to work?
- no air bubbles
- rubber bung must have air tight seal
