Transpiration Flashcards
what are the 3 processes in transpiration
osmosis - xylem to mesophyll cells
evaporation - surface of the spongy mesophyll cells to intercellular spaces
diffusion - water vapour from intercellular spaces out through the stomata
what is the transpiration stream
continuous movement of column water from root to leaves via xylem
a result of evaporation at leaves and cohesive properties water
general process of transpiration
heat causes evaporation water
water is drawn from xylem replacing lost
detail transpiration process
heat from sun causes water to evaporate off walls of mesophyll
creates high water potential in stomata
water vapour diffuses out stomata down water potential gradient
air movements carry water vapour away and maintain diffusion gradient
(water drawn from xylem to replace lost causing transpiration stream)
advantages transpiration
cooling effect via evaporation due to high latent heat of water
transpiration stream helps uptake ions
turgor pressure supports leaves so large surface area for photosynthesis and for structure
how do stomata open
guard cells use transporter proteins to pump h+ ions out (atp provided by chloroplast)
activates k+ channels so k+ ions enter
decrease wp in cell so water enters by osmosis
difference in thickness wall means guard cell bends - opening stoma
stomata adaptions
thin outer wall
thick inner wall
guard cell
lots chloroplasts
opens in day time only so not unnecessary water loss at night
what controls rate transpiration
open/close stomata
number leaves
number stoma
diffusion gradient leaf air spaces and surrounding air
4 factors affect rate
conc gradient between inside leaf and outside
air movement
temp
light intensity
humidity
how does air movement impact
Air currents sweep water away from the surface, maintaining conc gradient and increasing the rate of transpiration
when air is still water molecules accumulate near surface. creates a local area of high humidity which lowers the concentration gradient and the rate of transpiration
temp impact on transpiration
increase temp
increase KE
molecules move faster
rate increase
too high stoma close due to flaccid guard cells to preserve water
light intensity impact
close in dark
light sufficient stoma open so rate increases
humidity impact
if high then there is a large concentration of water in the air surrounding the leaf surface so
low conc gradient
so rate decreases
