Download Water movement in Plants

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Loss of water in plants
Transpiration through stomata
Replacement of water loss
Transpiration pull
Factors affecting transpiration
Uptake of water by plant
Pathways of water movement in plants
Loss of water in plants
Water is lost through
• stomata on the surface of leaves and
green stems (>90%)
• lenticels in woody stems (<10%)
• cuticle of stems and leaves
• The loss of water vapour from the surfaces
of plants due to evaporation is called
‘transpiration’
Transpiration through stomata
Water evaporates into
the substomatal air
space.
Air space almost
saturated with water
vapour.
Water diffuses out
through the stoma.
Replacement of water loss
Water loss from
stomata is replaced by
pulling water from
neighbouring cells
1 through the cell wall
2 through the cells
Transpiration pull
• A water potential gradient is set up
between mesophyll cells and xylem
vessels.
• This creates a force pulling water up the
xylem vessels, this pull is called
transpiration pull.
Factors affecting transpiration
1 Light intensity
transpiration
rate
light intensity
• increases with
light intensity
• due to opening
of stomata
Factors affecting transpiration
2 Temperature
transpiration
rate
temperature (C)
• increases with
temperature
• due to an increase
in evaporation from
cell surface
Factors affecting transpiration
3 Relative humidity
• decreases with
relative humidity
• due to a decrease
in water potential
gradient
transpiration
rate
0
100
relative humidity of
atmosphere (%)
Factors affecting transpiration
4 Air movement
transpiration
rate
wind velocity
(air movement)
• increases with
air movement
• due to faster
removal of water
from leaf
surface
Uptake of water by plants
• Mainly through roots from the soil
• Absorbed by root hair cells by
1 transpiration pull
2 osmosis
• Water then moves from the root, through
xylem vessels to the stem and leaves, and
evaporates to the atmosphere
Pathways of water movement in plants
1 Root hair takes in water from the soil.
water
root hair
Pathways of water movement in plants
2 Water moves to xylem vessels through
cell walls and across cells.
xylem vessel
root cell
Pathways of water movement in plants
3 Water moves upwards through the xylem
vessels to the stem and leaves.
leaf vein
xylem vessel
Pathways of water movement in plants
4 Water moves into leaves and out to
the atmosphere through the stomata.
upper epidermis of the leaf
stoma
Summary
• Plants lose water mainly through stomata by
transpiration
• Transpiration pull is resulted from
transpiration
• Transpiration is affected by light intensity,
temperature, relative humidity and air
movement
• Water is replaced by absorption by root
hairs as a result of transpiration pull