Water movement in plants

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 increases with light intensity due to opening of stomata transpiration rate light intensity

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

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 (%)

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)

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