1. Water movement
in plants

2. 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

3. 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’

4. Transpiration through stomata
Water evaporates into the substomatal air space.
Air space almost saturated with water vapour.
Water diffuses out through the stoma.

5. 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

6. 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.

7. Factors affecting transpiration
1 Light intensity
increases with light intensity
due to opening of stomata
transpiration rate
light intensity

8. Factors affecting transpiration
2 Temperature
increases with temperature
due to an increase in evaporation from cell surface
transpiration rate
temperature (C)

9. Factors affecting transpiration
3 Relative humidity
decreases with relative humidity
due to a decrease in water potential gradient
transpiration rate
100
relative humidity of atmosphere (%)

10. Factors affecting transpiration
4 Air movement
increases with air movement
due to faster removal of water from leaf surface
transpiration rate
wind velocity
(air movement)

11. 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

12. Pathways of water movement in plants
1 Root hair takes in water from the soil.
water
root hair

13. Pathways of water movement in plants
2 Water moves to xylem vessels through cell walls and across cells.
xylem vessel
root cell

14. Pathways of water movement in plants
3 Water moves upwards through the xylem vessels to the stem and leaves.
leaf vein
xylem vessel

15. 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

16. 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