B8.3 - Transpiration Flashcards
Transpiration definition [3]
loss of water vapour from plant leaves (by evaporation of water at the surfaces of the mesophyll cells, followed by the diffusion of water vapour through the stomata)
Transpiration stream definition
movement of water through the plant from the root to the leaves
what is the journey of the water through the plant? [3]
1) Water is absorbed from the soil by the roots
2) Water travels up the stem, to the leaves, in the xylem
3) Water vapour is lost from the leaves to the air, out of the stomata in the leaves
4 factors affecting transpiration?
-light intensity
-wind speed
-humidity
-temperature
where does water evaporate to vapour?
from mesophyll cells into air spaces behind the stomata
how does water enter the roots
osmosis
how does water enter the mesophyll cells
osmosis
how does water leave the leaves [2]
-through the stomata
-by diffusion
how does water move from the mesopyll cells to the air spaces
evaporation
when the light intensity increases, what happens to the transpiration rate? [1]
why? [3]
increases
-more light makes more stomata open
-more water can evaporate + diffuse out of the stomatas
-stomata close in the dark to reduce water loss
when the temperature increases, what happens to the transpiration rate? [1]
why? [2]
increases
-water evaporates faster from the cells of the leaf
-diffusion of water vapour out of the leaf increases
when the wind speed increases, what happens to the transpiration rate? [1]
why? [3]
increases
-more water vapour molecules are blown away from the leaf
-steep concentration gradient (between leaf and surrounding air) is maintained
-water diffuses more quikcly out of the leaf
when the humidity increases, what happens to the transpiration rate? [1]
why? [3]
decreases
-more humid = more water vapour
-lower the concentration gradient between leaf and surrounding air
-water diffuses more slowly
