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 The transportation of water and minerals involves three distinct and interconnected
processes –

1.Absorption of water and minerals

2.Ascent of sap or upward movement of water and minerals

3.Transpiration, i.e., loss of water in the form of sap

1.Absorption of water and minerals

 ROOT PRESSURE THEORY
 Vessels, tracheids of the roots, stems and leaves are connected to form a
continuous system in xylem cells to transport water to all the parts of the
plants.

 Cells in the roots which are in contact with the soil take up ions which creates
a difference of concentration between the roots and the soil and therefore
water moves to the roots to eliminate the difference.

 Water is moved into xylem of roots and from where it is pushed upward.

2. Ascent of sap or upward movement of water and minerals

 TRANSPIRATION PULL
 COHESION TENSION THEORY
 These two theories explain the upward movement of water in tall trees

 TRANSPIRATION PULL
 According to this theory, the main force responsible for upward movement of
water is transpiration pull generated in the leaves which pulls the water
column filled in the xylem tracheids and vessels
 The force for ascent of sap lies in the aerial parts.
 Here, Mesophyll and other cells lose water to outside air through transpiration
which produces a negative pressure.
 COHESION TENSION THEORY

Water column does not break due to two forces –
1. Cohesion force among the water molecules
2. Adhesion force between water molecules and the wall of the xylem
channels.

 Plants use different mechanisms to pull water upwards through xylem like-

 Water which is lost through stomata is replaced by water absorbed by the roots.
 Evaporation of water from leaf creates a suction force which pulls water.
 The loss of water in the form of water vapor is called transpiration.

Importance of transpiration-

 Regulates temperature.